| |
| United States Patent
|
7,371,970 |
| Flammer , et al. |
May 13, 2008 |
Rigid-flex circuit board system
Abstract
A rigid-flex circuit board system that can be manufactured using
less expensive and more reliable rigid circuit board methods and
equipment, and can maintain rigidity and dimensional stability until
the time when it is first desired to flex.
| Inventors: |
Flammer; Jeffrey D.
(Scottsdale, AZ), Forcier; Robert (Mesa, AZ) |
| Appl. No.:
|
10/731,390 |
| Filed: |
December 8, 2003 |
Related U.S. Patent Documents
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Application Number |
Filing Date |
Patent Number |
Issue Date |
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60431239 |
Dec., 2002 |
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| Current U.S.
Class: |
174/255 ;
174/254 |
| Current
International Class: |
H05K
1/03 (20060101) |
| Field of
Search: |
361/749-751,780,781 174/254,255,261,259 |
References Cited
[Referenced By]
U.S. Patent
Documents
Foreign Patent Documents
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2001-036246 |
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Sep., 2001 |
|
JP |
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Primary Examiner: Patel; Ishwar (I. B.)
Attorney, Agent or Firm:
Stoneman Volk Patent Group Stoneman; Martin L. Volk, Jr.;
Michael D.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
The present application claims the benefit of provisional
application Ser. No. 60/431,239, filed Dec. 6, 2002, entitled
"FLEXIBLE PRINTED CIRCUIT BOARD AND METHOD FOR THE FABRICATION
THEREOF", the contents of which are incorporated herein by this
reference and is not admitted to be prior art with respect to the
present invention by the mention in this cross-reference section.
Claims
What is claimed is:
1. A rigid-flex printed circuit board system comprising, in
combination: a) at least one rigid layer: b) wherein said at least
one rigid layer comprises i) at least one top side, and ii) at least
one bottom side; c) at least one first flexible layer bonded to at
least one first portion of said at least one top side; d) at least
one second flexible layer bonded to at least one second portion of
said at least one bottom side; e) wherein said at least one rigid
layer comprises at least one first structural weakness at least one
first selected location; f) wherein said at least one first
structural weakness is structured and arranged to facilitate
breaking said at least one rigid layer at such at least one first
selected location into at least two rigid pieces to provide at least
one first flexible connection formed by said at least one first
flexible layer between such rigid pieces; g) wherein said at least
one rigid layer comprises at least one second structural weakness at
at least one second selected location; and h) wherein said at least
one second structural weakness is adapted to facilitate breaking
said at least one rigid layer at such at least one second selected
location into at least two second rigid pieces to provide at least
one second flexible connection formed by said at least one second
flexible layer between such second rigid pieces.
2. The rigid-flex printed circuit board system according to claim 1
wherein such first structural weakness comprises at least one score
that partially penetrates said at least one rigid layer.
3. The rigid-flex printed circuit board system according to claim 2
wherein said at least one score penetrates about two-thirds of the
total thickness of said at least one rigid layer.
4. The rigid-flex printed circuit board system according to claim 1
wherein: a) said structural weakness comprises i) at least one top
score on said at least one top side at such at least one first
selected location, and ii) at least one bottom score on said at
least one bottom side at such at least one first elected location.
5. The rigid-flex printed circuit board system according to claim 1
further comprising: a) at least one adhesive to bond at least one
flexible layer portion of said at least one first flexible layer to
at least one rigid layer portion of said at least one rigid layer;
b) wherein said structural weakness comprises selective absence of
adhesive at such selected location between said at least one rigid
layer and said at least one flexible layer.
6. The rigid-flex printed circuit board system according to claim 1
wherein said at least one first structural weakness comprises at
least one laser score.
7. The rigid-flex printed circuit board system according to claim 1
wherein said at least one first structural weakness comprises at
least one mechanical score.
8. The rigid-flex printed circuit board system according to claim 1
wherein said at least one rigid layer comprises fiberglass.
9. The rigid-flex printed circuit board system according to claim 1
wherein said at least one first flexible layer comprises polyimide.
10. The rigid-flex printed circuit board system according to claim 1
wherein: a) said at least one first flexible layer comprises i) at
least one substantially flexible insulating layer, and ii) at least
one substantially flexible conductive layer; and b) said at least
one rigid layer comprises i) at least one substantially rigid
insulating layer, and ii) at least one conductive layer.
11. The rigid-flex printed circuit board system according to claim 1
wherein said at least one first structural weakness comprises at
least one groove.
12. The rigid-flex printed circuit hoard system according to claim 1
wherein said at least one first structural weakness comprises at
least one chemically milled groove.
13. The rigid-flex printed circuit hoard system according to claim 1
wherein a) said at least one first flexible layer comprises at least
one top outermost layer; and b) said at least one second flexible
layer comprises at least one bottom outermost layer.
14. The rigid-flex printed circuit board system according to claim 1
further comprising at least one breakaway portion.
15. The rigid-flex printed circuit board system according to claim 1
wherein a) said at least one first flexible connection is structured
and arranged to provide upwardly concave flexure at said at least
one first selected location; and b) said at least one second
flexible connection is structured and arranged to provide downwardly
concave flexure at said at least one second selected location.
Description
BACKGROUND
This invention relates to providing a rigid-flex circuit board
system which can be produced more efficiently and has greater
functionality than prior art rigid-flex circuit boards. In the past,
manufacturing rigid flex circuit boards has been problematic. Many
factors, difficult to control given current manufacturing
techniques, result in high scrap rates (circuit boards that do not
work). For example, in the past, it has been troublesome to align
flexible printed circuit layers with rigid printed circuit layers
since the flexible printed circuit layers are not dimensionally
stable (the flexible portions stretch, warp, shrink, etc.). This
dimensional instability introduces a significant degree of
variability in the manufacturing process. On a rigid printed circuit
board, the location of the traces, and the pads for drilling and
mounting components, etc. can be located with great reliability.
Rigid board manufacturing processes can typically rely on
determining the locations of the traces and pads etc. from
registering just a couple points on the rigid board. With flexible
printed circuit boards, locations of traces and pads cannot be as
reliably mapped and registered since the flexibility results in the
traces and pads etc., shifting by variable amounts. As a result,
when flexible printed circuit layers are laminated to rigid circuit
boards the connections between the two layers (at the interface) may
not be aligned properly throughout due to the inconsistencies caused
by dimensional instability of the flexible layer (with the result
that the circuit board will not work properly, and must be scrapped,
which is wasteful and expensive). In order to increase reliability
(and reduce scrap) in manufacturing rigid-flex circuit boards, more
expensive machinery and more complicated processes are used (than
for manufacturing standard rigid boards). In the past, those
attempting to reduce scrap, utilizing available manufacturing
techniques, have also sacrificed the number and density of
connections between the rigid and flexible layers, since these
connections have been problematic (for the above reasons). However,
as is well known in the industry, achieving higher densities can
have many benefits (such as, for example, reduced size, reduced
energy consumption, increased speed, etc.).
Further, even if the flexible layers are successfully connected to
the rigid layers, later manufacturing steps are often still
troublesome (and more expensive than standard rigid board
manufacturing) as a result of the dimensional instability (variable
stretching) introduced by the flexible portions. For example,
reliability in soldering components to a rigid-flex board may be
reduced due dimensional instability. Any fabrication and component
assembly process involving handling the rigid-flex boards may be
complicated due to portions of the board "flopping around" etc.
In the past (since mechanical support is needed during the assembly
process of placing components, reflow of the solder process, and for
installation in the housing, etc.) stiffeners (without conductive
layers and without electrical connections/function) have been added
to flex layers to provide such mechanical support. Also, in the
past, manufacturing flexible circuits has been complicated by the
need to use stabilization frames and/or rigid leaders and/or
specialty plating racks in order to provide support for flexible
portions of circuit boards during the manufacturing process. These
methods add complexity, cost and increased scrap rates, to the
manufacturing process.
These are just a few of the many complications that make
manufacturing and manipulating flexible and rigid-flex circuit
boards more difficult and expensive than standard rigid boards.
OBJECTS AND FEATURES OF THE INVENTION
A primary object and feature of the present invention is to provide
a rigid-flex circuit board system that is efficient to manufacture.
It is a further object and feature of the present invention to
provide such a rigid-flex circuit board system that can be
manufactured using standard rigid circuit board methods and
equipment.
It is a further object and feature of the present invention to
provide such a rigid-flex circuit board system that can maintain
rigidity and dimensional stability until the time when it is first
desired to flex.
It is a further object and feature of the present invention to
provide such a rigid-flex circuit board system that have dimensional
stability and mechanical support throughout the manufacturing
process (provided by the continuity of the rigid layer until the
structurally weakened rigid layer is bent/broken) thereby
eliminating the need for additional stiffeners, stabilization
frames, rigid leaders, plating racks, etc.
A further primary object and feature of the present invention is to
provide such a system that is efficient, inexpensive, and handy.
Other objects and features of this invention will become apparent
with reference to the following descriptions.
SUMMARY OF THE INVENTION
A rigid-flex printed circuit board system comprising, in
combination: at least one rigid layer; at least one flexible layer
bonded to at least one portion of such at least one rigid layer;
wherein such at least one rigid layer comprises at least one
structural weakness at at least one selected location; wherein such
at least one structural weakness is adapted to facilitate breaking
such at least one rigid layer at such at least one selected location
into at least two pieces to provide a flexible connection formed by
such at least one flexible layer between such pieces. Moreover, it
provides such a rigid-flex printed circuit board system wherein such
structural weakness comprises at least one score. Additionally, it
provides such a rigid-flex printed circuit board system wherein:
such at least one rigid layer comprises at least one top side, and
at least one bottom side; such structural weakness comprises at
least one score on such at least one top side at such at least one
selected location, and at least one score on such at least one
bottom side at such at least one selected location. Also, it
provides such a rigid-flex printed circuit board system wherein such
structural weakness comprises at least one gap at such selected
location between such at least one rigid layer and such at least one
flexible layer. In addition, it provides such a rigid-flex printed
circuit board system further comprising: at least one adhesive to
bond at least one portion of such at least one flexible layer to at
least one portion of such at least one rigid layer; wherein such
structural weakness comprises selective absence of adhesive at such
selected location between such at least one rigid layer and such at
least one flexible layer. And, it provides such a rigid-flex printed
circuit board system wherein such structural weakness comprises at
least one laser score. Further, it provides such a rigid-flex
printed circuit board system wherein such structural weakness
comprises at least one mechanical score. Even further, it provides
such a rigid-flex printed circuit board system wherein such at least
one rigid layer comprises epoxy. Moreover, it provides such a
rigid-flex printed circuit board system wherein such at least one
rigid layer comprises metal. Additionally, it provides such a
rigid-flex printed circuit board system wherein such at least one
rigid layer comprises epoxy reinforced fiberglass. Also, it provides
such a rigid-flex printed circuit board system wherein such at least
one flexible layer comprises polyimide. In addition, it provides
such a rigid-flex printed circuit board system wherein: such at
least one flexible layer comprises at least one substantially
flexible insulating layer, and at least one substantially flexible
conductive layer; and such at least one rigid layer comprises at
least one substantially rigid insulating layer, and at least one
conductive layer.
In accordance with another preferred embodiment hereof, this
invention provides a rigid-flex printed circuit board system
comprising, in combination: at least one substantially rigid layer;
at least one substantially flexible layer bonded to at least one
portion of such at least one substantially rigid layer; wherein such
at least one substantially rigid layer comprises at least one
structural weakness at at least one selected location to facilitate
bending such at least one rigid layer at such at least one selected
location to provide at least one flexible connection. And, it
provides such a rigid-flex printed circuit board system wherein such
at least one substantially rigid layer comprises metal. Further, it
provides such a rigid-flex printed circuit board system wherein such
at least one substantially rigid layer comprises aluminum. Even
further, it provides such a rigid-flex printed circuit board system
wherein such at least one structural weakness comprises at least one
groove. Moreover, it provides such a rigid-flex printed circuit
board system wherein such at least one structural weakness comprises
at least one chemically milled groove.
In accordance with another preferred embodiment hereof, this
invention provides a process of fabricating a rigid-flex printed
circuit board system comprising the steps of: bonding at least one
portion of at least one flexible layer to at least one portion of at
least one rigid layer; peeling at least one portion of such at least
one flexible layer away from such at least one rigid layer, at at
least one selected location, to provide at least one flexible
circuit portion. Additionally, it provides such a process of
fabricating a rigid-flex printed circuit board system further
comprising the step of structurally weakening at least a portion of
such flexible layer to assist in such peeling. Also, it provides
such a process of fabricating a rigid-flex printed circuit board
system further comprising the step of cutting at least one portion
of such flexible layer to assist in such peeling. In addition, it
provides such a process of fabricating a rigid-flex printed circuit
board system wherein: such bonding comprises selectively applied
adhesive; such adhesive is selectively applied to substantially omit
adhesive from being applied, at such at least one selected location,
between such at least one flexible layer and such at least one rigid
layer to assist in such peeling. And, it provides such a process of
fabricating a rigid-flex printed circuit board system further
comprising the steps of: applying an adhesive to form such bonding;
selectively removing at least one portion of such adhesive, at such
at least one selected location, between such at least one flexible
layer and such at least one rigid layer to assist in such peeling.
In accordance with another preferred embodiment hereof, this
invention provides a process of fabricating a rigid-flex printed
circuit board system comprising the steps of: bonding at least one
portion of at least one flexible layer to at least one portion of at
least one rigid layer; breaking at least one portion of such at
least one rigid layer, at at least one selected location, into at
least two pieces; wherein such at least one flexible layer provides
a flexible connection, at such at least one selected location,
between such at least two pieces. Further, it provides such a
process of fabricating a rigid-flex printed circuit board system
further comprising the step of structurally weakening, at such at
least one selected location, at least one portion of such at least
one rigid layer to assist in such breaking. Even further, it
provides such a process of fabricating a circuit board system
further comprising the step of scoring such at least one rigid
layer, at such at least one selected location, to assist in such
breaking. Moreover, it provides such a process of fabricating a
rigid-flex printed circuit board system wherein such scoring
comprises a process selected from the group consisting of laser
scoring mechanically scoring mechanically punching. Additionally, it
provides such a process of fabricating a rigid-flex printed circuit
board system further comprising the steps of: applying an adhesive
to form such bonding; selectively removing at least a portion of
such adhesive, at such at least one selected location, between such
flexible layer and such rigid layer to assist in such breaking.
Also, it provides such a process of fabricating a rigid-flex printed
circuit board system wherein: such bonding comprises selectively
applied adhesive; such adhesive is selectively applied to
substantially omit adhesive from being applied, at such at least one
selected location, between such flexible layer and such rigid layer
to assist in such breaking.
In accordance with another preferred embodiment hereof, this
invention provides a process of fabricating a rigid-flex printed
circuit board system comprising to steps of: bonding at least one
flexible layer to at least one rigid layer; wherein such flexible
layer comprises a conductive layer; etching such flexible layer
after such flexible layer has been bonded to such outer surface of
such rigid layer; breaking, at a selected location, at least one
portion of such rigid layer into at least two rigid pieces after
such flexible layer has been bonded to such outer surface of such
rigid layer; wherein such flexible layer provides a flexible
connection, at the location of the break, between such pieces of
such rigid layer. In addition, it provides such a process of
fabricating a rigid-flex printed circuit board system further
comprising the step of selective removal of at least a portion of
such rigid layer to assist in such breaking. And, it provides such a
process of fabricating a rigid-flex printed circuit board system
wherein at least one laser is used to accomplish at least a portion
of such selective removal. Further, it provides such a process of
fabricating a rigid-flex printed circuit board system wherein
mechanical abrasion is used to accomplish at least a portion of such
selective removal. Even further, it provides such a process of
fabricating a circuit board system wherein mechanical impact is used
to accomplish at least a portion of such selective removal.
Moreover, it provides such a process of fabricating a rigid-flex
printed circuit board system further comprising the step of
selectively removing at least a portion of such rigid layer, before
bonding such at least one flexible layer to at least one outer
surface of such rigid layer, to assist in such breaking.
Additionally, it provides such a process of fabricating a rigid-flex
printed circuit board system further comprising the step of
selectively removing at least a portion of adhesive between such
flexible layer and such rigid layer to assist in such breaking.
Also, it provides such a process of fabricating a rigid-flex printed
circuit board system wherein: such flexible layer is bonded to such
rigid layer with an adhesive layer; such adhesive layer is
selectively applied to avoid placing adhesive at such selected
location. In addition, it provides such a process of fabricating a
rigid-flex printed circuit board system wherein: such rigid layer
comprises material selected from the group consisting essentially of
tri-functional and multifunctional epoxy resins, systems reinforced
(such as, for example, by fiber glass fabric, etc.) cast coated
epoxy and polyimide non-reinforced materials. And, it provides such
a process of fabricating a rigid-flex printed circuit board system
wherein: such flexible layer comprises material selected from the
group consisting essentially of polyimide, mylar, polyester,
polyethylene napthalate, with adhesive films such as acrylics,
polyesters, phenolic butyral adhesives, and polyimides made up of
polyamic acids or esters, In accordance with another preferred
embodiment hereof, this invention provides a process of fabricating
a rigid-flex printed circuit board system comprising the steps of:
laminating at least one portion of at least one flexible layer to at
least one portion of at least one rigid layer; imaging and etching
at least one portion of such at least one flexible layer to form
conductor patterns after such at least one portion of at least one
flexible layer has been laminated to such at least one portion of at
least one rigid layer; breaking at least one portion of such at
least one rigid layer, at at least one selected location, into at
least two pieces; wherein such at least one flexible layer provides
a flexible conductive connection, at such at least one selected
location, between such at least two pieces.
In accordance with another preferred embodiment hereof, this
invention provides a rigid-flex printed circuit board system
comprising, in combination: insulating means for electrically
insulating conductive portions of the rigid-flex printed circuit
board; conducting means for conducting electricity through portions
of the rigid-flex printed circuit board; rigidity means for
providing rigidity to all portions of such conducting means;
conversion means for converting portions of rigidity means into a
flexible means for flexing portions of such conductor means.
Further, it provides such a rigid-flex printed circuit board system
according to claim 40 wherein such conversion means comprises
structural weakness means for structurally weakening selected
portions of such rigidity means.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a top view of a rigid-flex circuit board according to a
preferred embodiment of the present invention.
FIG. 2 shows an exploded side view through section 2-2 of FIG. 1 of
a rigid core portion of a rigid-flex circuit board.
FIG. 3 shows a cross-section side view of the rigid core portion of
FIG. 2 after it has been laminated (bonded) together, drilled,
plated, printed and etched.
FIG. 4 shows a cross-section side view of the rigid core portion of
FIG. 3 after it has been structurally weakened at selected
locations.
FIG. 5 shows a cross-section side view of the rigid core portion of
FIG. 4 with flexible layers about to be attached.
FIG. 6 shows a cross-section side view of the rigid core portion of
FIG. 5 after flexible layers have been attached (called rigid flex
now that flexible layers have been attached).
FIG. 7 shows a cross-section side view of the rigid flex of FIG. 6
after it has been drilled.
FIG. 7a shows a cross-section side view of the rigid flex of FIG. 7
after conductive material has been applied.
FIG. 7b shows a cross-section side view of the rigid flex of FIG. 7a
after portions of conductive material have been etched away.
FIG. 8 shows a cross-section side view of the rigid flex of FIG. 7b
after solder mask has been applied.
FIG. 9 shows a cross-section side view of the rigid flex of FIG. 8
which has been further structurally weakened at selected locations.
FIG. 10 shows a cross-section side view of the rigid flex of FIG. 9
after electrical components and hardware items have been attached.
FIG. 11a shows a cross-section side view of the rigid flex of FIG.
10 that is ready to be broken and flexed.
FIG. 11b shows a cross-section side view of the rigid flex of FIG.
11a that has been broken and is being flexed.
FIG. 12a shows a cross-section side view of rigid flex that is being
laser drilled to create a 3-dimensional flexible circuit, according
to an alternate preferred embodiment of the present invention.
FIG. 12b shows a perspective view of rigid flex showing a
3-dimensional flexible circuit that has been peeled away from the
rigid core portion, according to an alternate preferred embodiment
of the present invention.
FIG. 13 shows a cross-section side view of the rigid flex of FIG.
12b with a 3-dimensional flex circuit peeled away from rigid core
portion.
FIG. 14 shows a cross-section side view of rigid flex being laser
drilled according to an alternate preferred embodiment.
FIG. 15 shows a cross-section side view of the rigid flex of FIG. 14
being flexed.
FIG. 16a shows a top view of a small panel used to manufacture rigid
flex circuit boards.
FIG. 16b shows a top view of a large panel used to manufacture
multiple rigid flex boards, according to a preferred embodiment of
the present invention.
FIG. 17a shows a side view of a rigid core portion of a rigid-flex
circuit board according to a preferred embodiment of the present
invention.
FIG. 17b shows a side view of the rigid core portion of FIG. 17a
after it has been structurally weakened.
FIG. 17c shows a side view of the rigid core portion of FIG. 17b
after embedded electrical components have been added.
FIG. 17d shows a side view of the rigid core portion of FIG. 17c
with flexible layers about to be attached (called rigid flex now
that flexible layers have been attached).
FIG. 17e shows a side view of the rigid flex of FIG. 17d after
flexible layers have been attached.
FIG. 17f shows a side view of the rigid flex of FIG. 17e after holes
have been drilled through flexible layers.
FIG. 17g shows a side view of the rigid flex of FIG. 17f after
conductive material is applied.
FIG. 17h shows a side view of the rigid flex of FIG. 17g after
portions of conductive material are etched away.
FIG. 17i shows a side view of the rigid flex of FIG. 17h after an
insulating layer is applied.
FIG. 17j shows a side view of the rigid flex of FIG. 17i after
electrical components are added.
FIG. 17k shows a side view of the rigid flex of FIG. 17j after rigid
flex has been bent.
FIG. 18a shows a side view of a rigid-flex circuit board according
to an alternate preferred embodiment of the present invention.
FIG. 18b shows a side view of the circuit board of FIG. 18a after
portions of the rigid carrier have been removed.
FIG. 18c shows a side view of the circuit board of FIG. 18b after a
flexible solder mask has been applied.
FIG. 18d shows a side view of the circuit board of FIG. 18b after
solder balls and electrical components have been added.
FIG. 18e shows a side view of the circuit board of FIG. 18b after
the circuit board has been flexed and folded.
FIG. 19a is a flow diagram showing a preferred process for
manufacturing rigid-flex according to a preferred embodiment of the
present invention.
FIG. 19b is a flow diagram (a continuation of FIG. 19a) showing the
remaining steps in a preferred process for manufacturing rigid-flex
according to a preferred embodiment of the present invention.
FIG. 20a shows a side view of rigid flex semiconductor according to
a preferred embodiment of the present invention.
FIG. 20b shows a side view of the rigid flex semiconductor of FIG.
20a after conductive material has been applied.
FIG. 20c shows a side view of the rigid flex semiconductor of FIG.
20b after it has been printed and etched and solder balls have been
applied.
FIG. 20d shows a side view of the rigid flex semiconductor of FIG.
20c being cut by lasers so that it can be flexed and bent.
FIG. 20e shows a side view of the rigid flex semiconductor of FIG.
20d after it has been flexed and bent.
DETAILED DESCRIPTION OF THE BEST MODE AND PREFERRED EMBODIMENTS OF
THE INVENTION
FIG. 1 shows a top view of rigid core portion 100 with electrical
pads 105 and traces 111, according to a preferred embodiment of the
present invention.
FIG. 2 shows an exploded side view of rigid core portion 100 of
rigid-flex circuit board system 200 according to a preferred
embodiment of the present invention. Preferably rigid-flex circuit
board system 200 comprises rigid core portion 100, as shown.
Preferably, rigid core portion 100 comprises at least one inner
layer 101. Preferably inner layer 101 comprises at least one
substantially rigid insulating layer 102. Preferably, rigid
insulating layer 102 comprises epoxy reinforced with fiberglass.
Upon reading the teachings of this specification, those with
ordinary skill in the art will now understand that, under
appropriate circumstances, considering issues such as production
cost, intended use, advances in materials and technology, etc.,
other rigid insulating layer arrangements may suffice, such as, for
example, other types of resins, tri-functional and multifunctional
epoxy resins, systems reinforced (such as, for example, by fiber
glass fabric, etc.) or non-reinforced materials, aramid fibers, cast
coated epoxy or cast polyimide resin systems on copper foil carriers
and also thermo-set and thermoplastic film adhesives on release film
carriers, polyimides made up of polyamic acids or esters, reinforced
by fiberglass fabric or non-reinforced cast film adhesives. Mixed
Epoxy resins with cyanate ester and polyolefin adders, and Teflon or
FEP (fluorinated ethylene propylene) mixed with glass fiber
materials or ceramic filled for high speed circuits, also materials
such as ceramic circuit materials used as LTCC (low temperature
co-fired ceramic) or HTCC (high temperature co-fired ceramic), metal
core base materials or mixed metal alloys cores with CTE
(coefficient of thermal expansion) controlling materials embedded in
such metals such as nickel, invar and molybdenum, etc. Thermo-set
adhesives are thermally cured with cross-linking between polymer
chains and will not re-melt with repeated heating. Thermoplastic
adhesives are long chain linear polymers that become fluid above
their glass transition temperature (Tg) and can be remelted again
repeatedly.
Preferably, inner layer 101 comprises at least one conductive layer
104, preferably one conductive layer 104 on top of rigid insulating
layer 102 and another conductive layer 104 on bottom of rigid
insulating layer 102, as shown. Preferably, conductive layer 104
comprises at least one copper layer bonded to rigid insulating layer
102, as shown. Upon reading the teachings of this specification,
those with ordinary skill in the art will now understand that, under
appropriate circumstances, considering issues such as advances in
materials and technology, production cost, intended use, etc., other
conductive layer arrangements may suffice, such as, for example,
using copper alloys, conductive materials other than copper,
conductive ceramics, superconductive materials, semiconductor
silicon wafer materials, piezoelectric compounds as ceramic circuit
boards, a single conductive layer instead of multiple conductive
layers, etc.
Preferably, conductive layer 104 is processed (such as, for example,
by printing and etching, etc.) to form traces 111 and pads 105 and
any other circuit board elements formed from the conductive layers
of circuit boards known currently (or in the future) to those
familiar in the art. Preferably rigid core portion 100 is processed
as described herein.
Preferably, rigid core portion 100 is processed according to the
flow diagram in FIG. 19a and continued in FIG. 19b.
FIG. 2 through FIG. 11 show a preferred method for manufacturing a
rigid flex printed circuit board according to a preferred embodiment
of the present invention.
Preferably conductive layer 104 is bonded to rigid insulating layer
102.
Preferably, conductive layer 104 is cleaned with an alkaline
solution (to remove oils, dirt, fingerprints, etc.) Preferably,
conductive layer 104 is enhanced with a micro-etch solution (to
enlarge the surface area thereby assisting in bonding of the
resist).
Preferably, a photosensitive negative or positive acting resist, Dry
film or liquid resist is then applied to conductive layer 104.
Preferably, conductive layer 104 is exposed to an image (of the
desired conductor patterns of traces 111 and pads 105, etc.) using
prepared tooled artwork, which allows polymerized portions of the
resist (forming a protective coating over the portions of conductive
layer 104 that are to remain as traces 111 and pads 105, etc.).
Preferably, the undeveloped (unpolymerized portions) of the resist
(and unprotected portions of conductive layer 104) are etched away,
leaving behind conductive patterns of traces 111 and pads 105, etc.
Preferably, the polymerized resist is then stripped away.
Preferably, inner layer 101 is electrically tested and inspected.
Preferably, if inner layer 101 passes electrical testing and
inspection, inner layer 101 may be laminated together with
additional inner layers 101. Rigid core portion 100 may comprise one
inner layer 101 or multiple inner layers 101, as shown.
Preferably, when laminating multiple inner layers 101 together,
intermediary non-conductive layers 106 are interleaved between
conductive layers 104, as shown. Preferably intermediary
non-conductive layers 106 comprise b-staged uncured glass reinforced
epoxy (also called "pre-preg").
Preferably at least one non-conductive layer 106 and conductive
layer 110 are laminated to at least one inner layer 101 of rigid
core portion 100, as shown. Preferably conductive layer 110
comprises copper foil.
Preferably pins and or rivets are used to maintain registration of
all inner layers 101 for the duration of the lamination process
(including during any applied heat, pressure and curing stages).
Upon reading the teachings of this specification, those with
ordinary skill in the art will now understand that, under
appropriate circumstances, considering issues such as advances in
materials and technology, intended use, available machinery,
production cost, etc., other rigid core portion assembly
arrangements may suffice, such as, for example, omitting steps,
adding additional steps, using alternate cleaning methods, using
alternate enhancing methods, using alternate printing methods, like
laser direct imaging, using alternate plating methods and etching
methods, using alternate layer arrangements, using alternate
materials, using alternate registration and lamination methods, etc.
FIG. 3 shows a side view of a rigid core portion 100 which has been
laminated (bonded) together, drilled, plated, printed and etched.
Preferably, inner layers 101 are interconnected (forming electrical
connections) at locations by drilling holes 112 through portions of
rigid core portion 100, as shown. Preferably, holes 112 are drilled
to between pads 105 on different conductive layers 104 of inner
layers 101. Preferably holes 112 are mechanically drilled, laser
drilled and or plasma drilled. Holes 112 may be drilled completely
through rigid core portion 100, as shown, or may only extend
partially through rigid core portion 100. Preferably, conductive
material 114 is applied to holes 112 and conductive layer 110 to
form electrical connections between pads 115 on different conductive
layers, as shown. Preferably, conductive material is applied by
plating electroless copper as a seed layer for the subsequent
plating operations. Upon reading the teachings of this
specification, those with ordinary skill in the art will now
understand that, under appropriate circumstances, considering issues
such as materials used, production cost, quality control, etc.,
other conductive material arrangements may suffice, such as, for
example, plated conductive carbon polymers, conductive paste
coatings, chemical vapor deposition, ion target sputtering methods,
etc.
Preferably, conductive material 114 and conductive layer 110 are
processed (such as, for example, printed, plated and etched, etc.,
preferably using the steps outlined above) to form traces 111 and
pads 105, etc., on the outer surface of rigid core portion 100, as
shown.
FIG. 4 shows a side view of a rigid core portion 100 which has been
structurally weakened at selected locations. Preferably, rigid core
portion 100 is structurally weakened at at least one selected
location, creating rigid core weakness 116, as shown. Preferably,
rigid core weakness 116 allows rigid core portion 100 to be broken
in a substantially reliable and predictable way at the selected
location of rigid core weakness 116 (embodying herein conversion
means for converting portions of rigidity means into a flexible
means for flexing portions of said conductor means; and embodying
herein structural weakness means for structurally weakening selected
portions of said rigidity means). Preferably rigid core weakness 116
is created by removing rigid core material, preferably by
mechanically scoring rigid core portion 100, preferably "v-scoring,"
as shown. Preferably, rigid core weakness 116 is created on the side
of rigid flex 130 that will be concave when the rigid core portion
is broken and flexed at the selected location. For example, in FIG.
4, if rigid core portion 100 will eventually be flexed so that it is
concave upward at a location, a top rigid core weakness 116a should
be created (over which a flexible layer will later be added as a
flexible connection bridging the gap created when the rigid core
portion 100 is broken at that location). Preferably, rigid core
weakness 116 is of sufficient depth and width to allow efficient
location of rigid core weakness 116 and to provide efficient
breaking of rigid core portion 100 at the location when it is time
to do so.
Preferably, standard tooling methods are employed (such as, for
example, locating a tooling drilled hole) for the placement location
of the structural weakening process or method. A mechanical process
can maintain a location tolerance of about +/-100 um (0.004''), and
laser drilling a fiducial location can be of a tolerance, such as,
for example, about +/-50 um (0.002'').
FIG. 5 shows a side view of a rigid core portion 100 to which
flexible layers 122 are in the process of being attached. Preferably
flexible layers 122 are bonded to rigid core portion 100 with
adhesive 120. Preferably, adhesive 120 is selectively applied to
rigid core portion 100 leaving gaps 132, preferably where rigid core
weakness 116 (and remaining weakened portions 155) are located, as
shown. Upon reading the teachings of this specification, those with
ordinary skill in the art will now understand that, under
appropriate circumstances, considering issues such as material
composition of rigid core portion and flexible layer, production
cost, quality control, etc., other adhesive arrangements may
suffice, such as, for example, using alternative kinds of adhesives
such as, for example, pre-preg, different kinds of epoxy, other
types of adhesive, selectively applying adhesive 120 to flexible
layer 122 (prior to bonding to rigid core portion 100), bonding
flexible layer 122 directly to rigid core portion 100 without
adhesive, etc. Adhesive 120 may be applied to flexible layer 122
first, or to rigid core portion 100 first, as shown. Upon reading
the teachings of this specification, those with ordinary skill in
the art will now understand that, under appropriate circumstances,
instead of, or in addition to, selectively applying adhesive 120,
portions of adhesive 120 may be selectively removed from flexible
layer 122 and/or rigid core portion 100 to form gaps 132, preferably
where rigid core weakness 116 and weakened portions 155 are located,
as shown. Preferably, gaps 132 help preserve structural weakening
effect of rigid core weaknesses 116 (otherwise, for example, if
adhesive were allowed to cover rigid core weakness 116, the desired
structural weakening provided by rigid core weakness 116 could be
nullified to an extent by strengthening provided by the adhesive).
Preferably adhesive 120 comprise chemical flow restrictors designed
to limit the squeeze out (infiltration) of adhesive into gaps 132.
Preferably, adhesive 120 is selectively applied with cut out relief
by known methods, such as, for example, applying a liquid adhesive
by a screen printing method or by liquid spin coating method. Upon
reading the teachings of this specification, those with ordinary
skill in the art will now understand that, under appropriate
circumstances, considering issues such as flexible layer 122
material, production cost, etc., other adhesive application
arrangements may suffice, such as, for example, applying adhesive as
a cast film, selectively removing adhesive with a laser, punch die,
mechanical abrasion, or other selective adhesive removal methods can
be employed such as photo-imageable adhesives that can be applied
dried, imaged, and developed away for the gaps areas, etc.
Preferably gaps 132 in adhesive 120 are formed before flexible layer
122 is bonded to rigid core portion 100.
Preferably, adhesive 120 comprise b-staged (uncured) material
similar to that used in the rigid insulating layer, such as, for
example, glass reinforced epoxy materials. Upon reading the
teachings of this specification, those with ordinary skill in the
art will now understand that, under appropriate circumstances,
considering issues such as flexible layer 122 material, production
cost, etc., other adhesive arrangements may suffice, such as, for
example, tri-functional and multifunctional epoxy resin systems,
reinforced (such as, for example, with fiber glass fabric) or non
reinforced materials, aramid fibers, cast coated epoxy, polyimide
resin systems, thermo set and thermoplastic film adhesives (for
example, on release film carriers), acrylics, polyesters, phenolic
butyral adhesives, and polyimides made up of polyamic acids or
esters, epoxy mixed resins with cyanate ester and or polyolefin
adders, etc. Preferably, adhesive performs as "no-flow" to avoid
filling in gaps 132. Upon reading the teachings of this
specification, those with ordinary skill in the art will now
understand that, under appropriate circumstances, considering issues
such as flexible layer 122 material, whether gaps 132 are created by
selective application and/or selective removal of adhesive, etc.,
other adhesive arrangements may suffice, such as, for example,
adhesive that is "restricted flow" or "normal flow".
FIG. 6 shows a side view of a rigid core portion 100 to which
flexible layers 122 have been bonded, comprising rigid flex 130.
Preferably, flexible layers 122 are laminated to rigid core portion
100 in a flat platen lamination press under heat and pressure for a
duration of time to cure adhesive 120. Preferably, some of adhesive
120 penetrates hole 134 during the lamination process resulting in
adhesive filled hole 126, as shown. Upon reading the teachings of
this specification, those with ordinary skill in the art will now
understand that, under appropriate circumstances, considering issues
such as flexible layer 122 material, rigid core portion 100
material, type of adhesive, etc., other lamination arrangements may
suffice, such as, for example, curing without increased levels of
heat and/or pressure, chemical curing, other methods of curing
adhesive, roller presses instead of flat platen presses, etc.
Preferably, flexible layers 122 comprise at least one conductive
layer 124, as shown. Preferably, at least one conductive layer 124
is the outermost layer, as shown. Preferably, flexible layers 122
comprise polyimide. Upon reading the teachings of this
specification, those with ordinary skill in the art will now
understand that, under appropriate circumstances, considering issues
such as rigid core portion 100 material, type of adhesive, amount of
flexibility required, anticipated number of flex cycles (i.e. flex
to install versus continuous flex), etc., other flexible layer
arrangements may suffice, such as, for example, using epoxy films,
mylar or polyester films, poly-ethylene naphtalate (PEN) films,
liquid crystal polymer (LCP) films, some thin aramid fiber woven and
non-woven and thin Teflon or FEP (fluorinated ethylene propylene)
copper clad films, (to achieve lower cost for limited flexibility
applications with fewer than 50 flexing cycles thin epoxy glass
reinforced copper clad material may suffice), etc.
Preferably, rigid flex 130 at the stage of manufacture shown in FIG.
6 is still completely rigid (structurally weakened locations have
not been broken). Thus, rigid flex 130 at this stage of manufacture
has the dimensional stability advantages of normal rigid printed
circuit boards.
FIG. 7 shows a side view of rigid flex 130 that has been drilled.
Preferably, conductive layers 104 and conductive layers 110 from
rigid core portion 100 and conductive layers 124 from flexible
layers 122 are interconnected (forming electrical connections) at
locations by drilling holes 134 (and holes 138) through portions of
rigid flex 130, as shown. Preferably, holes 134 (and holes 138) are
drilled to between pads 105 on different conductive layers
(conductive layers 104, conductive layers 110, and conductive layers
124) of rigid flex 130. Preferably holes 134 (and holes 138) are
mechanically drilled, laser drilled, plasma or chemically drilled.
Holes 134 may be drilled completely through rigid flex 130, as
shown, or may only extend partially through rigid flex 130. Holes
138 may be drilled completely through rigid flex 130, or may only
extend partially through rigid flex 130, as shown.
FIG. 7a shows a side view of rigid flex 130 after conductive
material 140 has been applied. Preferably, holes 134, holes 138, and
conductive layer 124 are cleaned and prepared before conductive
material 140 is applied. Preferably, conductive material 140 is
applied to holes 134, holes 138, and conductive layer 124 to form
electrical connections between pads 105 on different conductive
layers (preferably using the same materials and processes described
above in applying conductive material 114).
FIG. 7b shows a side view of rigid flex 130 after portions of
conductive material 140 have been removed. Preferably, conductive
material 140 and conductive layer 124 are processed (such as, for
example, plated, printed and etched, or printed, plated and etched,
etc., preferably using the methods described above in processing
conductive layer 104) to form traces 111, pads 105, and gaps 144,
etc., on the outer surface of rigid flex 130, as shown. Additional
flexible layers can be added by repeating this process of laminating
flexible materials, drilling, plating, printing and etching of
conductive patterns of pads and traces.
FIG. 8 shows a side view of rigid flex 130 after solder mask has
been applied. Preferably, flexible solder mask 146 is applied in
locations where flexure will occur, as shown. Preferably, cover
sheet 148 comprises flexible dielectric and adhesive layer bonded to
rigid flex 130, as shown. Preferably, cover sheet 148 comprises a
flexible dielectric layer and a flexible adhesive layer. Preferably,
portions of cover sheet 148 and flexible solder mask 146 comprise
openings 152 to allow electrical components and hardware items to be
attached, as shown (see FIG. 10). Upon reading the teachings of this
specification, those with ordinary skill in the art will now
understand that, under appropriate circumstances, considering issues
such as production cost, material properties of solder mask, etc.,
other solder mask arrangements may suffice, such as, for example,
applying non-flexible solder mask in areas where flexure will not
occur, using other materials for solder mask, etc.
FIG. 9 shows a side view of rigid flex 130 which has been further
structurally weakened at selected locations. Preferably, portions of
flexible layers 122, cover sheet 148 and flexible solder mask 146
are selectively removed to form final structural weaknesses 154,
preferably coinciding with the locations of rigid core weaknesses
116, as shown. Preferably, top rigid core weaknesses 116a are
created opposite where bottom rigid core weaknesses 116b are located
(and vice-versa), as shown. Preferably, final structural weaknesses
154 are located on the side of rigid flex 130 that will be convex
when the rigid flex 130 is broken and flexed at the structurally
weakened portion 155, as shown. Preferably, at least one flexible
layer 122 bridges the structurally weakened portion 155 on the side
of rigid flex 130 that will be concave when the rigid flex 130 is
broken and flexed at the structurally weakened portion 155, as
shown. Preferably, final structural weaknesses 154, top rigid core
weaknesses 116a, and bottom rigid core weaknesses 116b are created
by removing material (including flex and rigid material), preferably
using the methods described above for creating rigid core weaknesses
116 (for example, by mechanically scoring), as shown.
Score depth control is important in creating rigid core weaknesses
116 and final structural weaknesses 154. Preferably, the total depth
of rigid core weaknesses 116 (top rigid core weaknesses 116a plus
bottom rigid core weaknesses 116b) at a location should be about two
thirds of the total thickness of rigid core portion 100, preferably
one top rigid core weakness 116a with a depth about one third of the
total thickness of rigid core portion 100, and one bottom rigid core
weaknesses 116b with a depth about one third, as shown. Preferably,
the thickness of remaining weakened portion 155 should be about one
third of the total thickness of rigid core portion 100 (preferably
remaining weakened portion 155 is of sufficient thickness to prevent
or minimize accidental breakage of rigid core portion 100 before the
intended time, and yet still allow for controlled and efficient
breakage of rigid core portion 100 at the intended time).
Preferably, final structural weaknesses 154 are created after
flexible layers are laminated to the rigid core portion 100
(preferably, as the last step, such as, for example, after assembly
of electric components). Upon reading the teachings of this
specification, those with ordinary skill in the art will now
understand that, under appropriate circumstances, considering issues
such as dimensions and materials of rigid core portion, available
machinery, production cost, quality control, etc., other structural
weakening arrangements may suffice, such as, for example, laser
routing and/or mechanical machining and/or plasma machining and/or
mechanically impacting, structurally weakening without removing
material, using different ratios for depth of material removal and
remaining weakened portion 155, structurally weakening (and/or
removing material from) only one side of rigid core portion 100
instead of both sides, and or structurally weakening (and/or
removing material from) only one side of rigid flex 130 instead of
both sides, etc.
Laser scoring may be used to provide very accurate depth control for
structural weakening (especially useful for thinner boards). For
example, for a 0.008 inch thick rigid core portion 100 a laser may
be used to make the top rigid core weakness 116a about 0.002 inches,
and a laser may be used to make the bottom rigid core weakness 116b
about 0.002 inches, leaving the remaining weakened portion 155 to be
about 0.004 inches. Laser stop pads 168 may be used to assist in
controlling the depth of the cut 167 (see FIG. 14.). Preferably,
laser stop pads 168 comprise metal.
FIG. 10 shows a side view of rigid flex 130 after electrical
components 156 and hardware items 158 have been attached. Preferably
rigid flex 130 comprises electrical components 156 and hardware
items 158, as shown. Preferably, flexible solder mask 146 and cover
sheet mask 148 comprise openings at selected locations to allow
access to pads 105 and traces 111, etc. (for mounting electrical
components 156 and hardware items 158, etc., such as, for example,
computer chips, resistors, capacitors, wires, etc.), as shown.
FIG. 11a shows a side view of rigid flex 130 that is ready to be
broken and flexed. FIG. 11a shows a side view of rigid flex 130 that
has been broken and is being flexed. When rigid core portion 100 is
broken at a location of a rigid core weakness 116 a breakaway
portion 160 may detach, as shown. Rigid core portion 100 may also be
broken without detaching a breakaway portion 160. Preferably, rigid
core portion 100 is broken by flexing rigid core portion 100 so that
the side on which flexible layers 122 will form a flexible
connection 128 is concave, as shown. For example, if the flexible
connection 128 will be on top, the rigid core portion is flexed (so
that the rigid core portion is concave in the upward direction)
until the rigid core portion is broken at the location of rigid core
weakness 116, as shown. After rigid core portion 100 is broken at
the location of rigid core weakness 116, flexible layers 122 form a
flexible electrical connection, bridging the pieces of the rigid
core portion 100 on either side of such location, as shown.
FIG. 12 shows a side view of rigid flex 130 that is being laser
drilled, according to an alternate preferred embodiment of the
present invention. Preferably gap 132 is created in adhesive 120
underneath a portion of flexible layers 122 (preferably over a
portion of rigid core portion 100 that has not been structurally
weakened), as shown. Preferably partial perimeter 166 is cut from
flexible layers 122, as shown. Preferably flexible layers are cut
with a laser beam 164 from a laser drill 162, as shown. Upon reading
the teachings of this specification, those with ordinary skill in
the art will now understand that, under appropriate circumstances,
considering issues such as material composition of flexible layers
122, flexible solder mask 146 and cover sheet masks 148, etc.,
available machinery, production cost, quality control, etc., other
cutting arrangements may suffice, such as, for example, mechanical
cutting means, routing, mechanical machining, punching, impacting,
mechanical abrasion, etc.
FIG. 13 shows a side view of rigid flex 130 with 3-dimensional flex
circuit 165 peeled away from rigid core portion 100. Preferably,
after partial perimeter 166 is cut, 3-dimensional flex circuit 165
is peeled away from rigid core portion, as shown in FIG. 13.
3-dimensional flex circuit 165 can be cut and peeled away from rigid
core portion 100 before or after final component assembly.
FIG. 14 shows a side view of rigid flex 130 according to an
alternate preferred embodiment. Preferably, laser stop pads 168 are
embedded within rigid flex 130. Preferably, laser stop pads 168 are
embedded on the same side of rigid core portion 100 as the flexible
layers 122 which will form the flexible connection, as shown.
Preferably, laser beam 164 from laser drill 162 cuts through rigid
flex 130 (from the opposite side from which laser stop pad 168 is
located) to laser stop pad 168, resulting in cut 167, as shown.
Preferably, cut 167 extends completely through rigid core portion
100, as shown. Cut 167 may also extend only partially through rigid
core portion 100 thus comprising a structural weakness in rigid core
portion 100 so that rigid core portion 100 may be efficiently broken
later (to create a flexible connection at such location). Depending
on the number of (preferably parallel) cuts 167 (two cuts are shown
at each of the two locations shown in FIG. 14), rigid flex 130 can
be flexed with different radiuses. Increasing the number of cuts 167
may increase the bend radius and may also increase the flexibility
of the connection.
FIG. 15 shows rigid flex 130 of FIG. 14 in a flexed position.
Preferably, rigid flex 130 as shown in FIG. 14 and 15 is suitable
for "static flex" or "flex for installation only."
FIG. 16a shows a top view of a rigid flex unit 300 comprised of
rigid portions 301 and flexible portions 302. In the past,
production of rigid flex units 300 has been limited to small
manufacturing panels 304 since traditional flex portions 302 (which
can bend, flex, and stretch etc., during the manufacturing process)
limit the ability to efficiently and effectively manufacture rigid
flex units 300 on larger panels. For example, the greater the number
of flexible portions 302 per unit the more difficult it is to
manipulate and control the rigid flex unit 300. Increased difficulty
in handling and manipulation (such as from bending, flexing and
stretching etc., during the manufacturing processes) result in
higher cost and higher scrap rates, etc. Thus, in the past the
ability to manufacture and process multiple units on larger panels
has not been effective. Further, the size and complexity (for
example, the number of flexible portions) has had to be minimized in
order to reduce the undesirable effects of the flexible portions.
Preferably the flexible layers are located on the outer layers of
the rigid support circuit board, which allows a build-up method of
manufacturing the rigid flex. Preferably, the flexible layers are
attached and processed on the outer layer rigid support mechanism.
Processing the flexible layers (printing, plating and etching, etc.)
and then sandwiching them in the middle of other layers would cause
manufacturing complications due to the need to register connections
between layers during lamination (dimensional instability before and
after each lamination step would negatively impact process yields).
Processing the flexible material on the outer layers allows
utilization of the flexible outer layer as a high density
interconnect layer thus using the latest laser drill technology to
produce smaller holes and finer conductive features. This method
also allows the manufacturer to use various materials that are
significantly thinner overall. This method of laminating the
thinnest dielectrics and the thinnest metalization flex layers on
the outside support rigid circuit board allow for newer and more
advanced electronic applications such as continuous flexing
applications as seen in printer heads, flip cell phones, DVD
players, disk drives, cameras, high-density applications for flip
chip, and direct chip attachment methods for microelectronic
assemblies etc.
FIG. 16b shows a top view of multiple rigid flex units 300a, each
comprised of rigid portions 301a and flexible portions 302a, being
manufactured on a large manufacturing panel 304a. Since, flexible
portions 302a are rigid throughout the manufacturing process (until
it is desired for them to become flexible, such as by breaking the
rigid core at selected structurally weakened locations) the
undesirable effects of bending, flexing and stretching etc., are
avoided during the manufacturing process. As a result, the number of
flexible portions 302a is not a limiting factor, neither is the size
of rigid flex unit 300a. In fact, whereas in the past, manufacturing
a rigid flex unit 300 has been limited to smaller sized panels, now,
given the teachings herein, a rigid flex unit 300a can be
manufactured in any size as if it were a completely rigid board
(since it is a completely rigid board until the structurally
weakened portions are broken). Preferably, multiple rigid flex units
300a are produced on larger manufacturing panels 304a (and then cut
apart) in order to take advantage of increased efficiencies from
larger scale manufacturing.
FIG. 17a shows a side view of a rigid core portion 180' of a
rigid-flex circuit board according to a preferred embodiment of the
present invention. Preferably rigid core portion 180' comprises a
metal core, preferably copper or aluminum, as shown. Upon reading
the teachings of this specification, those with ordinary skill in
the art will now understand that, under appropriate circumstances,
considering issues such as intended use, production cost, etc.,
other rigid core material arrangements may suffice, such as, for
example, other metals, copper, copper alloys, aluminum alloys,
stainless alloys, etc.
FIG. 17b shows a side view of the rigid core portion 180' of FIG.
17a after it has been structurally weakened. Preferably,
structurally weakened locations 182' are created by removing
material from rigid core portion 180' at selected locations, as
shown. Preferably, structurally weakened areas have a weaker cross
sectional strength than non-weakened areas. Preferably, structurally
weakened locations 182' comprise grooves, as shown. Preferably, the
chemical etching process comprises applying a suitable photo resist
and projecting an image, developing the photo resist away and
chemically etching a pattern using a system of FeCl (Ferric
chloride) etching solution, or other means to remove a pattern of
material from the metal plate to form structurally weakened
locations 182'. Chemical etching may be suitable for fast and
accurate relief patterning and also may provide a pre-etched pattern
for the final outer layer circuitry, allowing for finer pattern
etching from the backside of the circuit pattern. Preferably,
locations for embedded components 183' are created by removing
material from rigid core portion 180' at selected locations, as
shown. Preferably, structurally weakened locations 182' and
locations for embedded components 183' are created by etching away
selected portions of rigid core portion 180', as shown. Upon reading
the teachings of this specification, those with ordinary skill in
the art will now understand that, under appropriate circumstances,
considering issues such as dimensions and materials of rigid core
portion, available machinery, production cost, quality control,
etc., other structural weakening arrangements may suffice, such as,
for example, laser routing, laser drilling, mechanical machining,
plasma machining, structurally weakening without removing material,
other etching methods, using mechanical routing, mechanically
impacting, die punching, other abrading or impact means, etc.
FIG. 17c shows a side view of rigid core portion 180' of after
embedded electrical components have been added. Preferably, embedded
electrical components such as screen or stencil printed embedded
resistor material 184' and screen or stencil printed embedded
capacitor material 186' are placed on rigid core portion 180',
preferably at locations for embedded components 183', as shown.
Locations for embedded components 183' assist in providing for a
more predictable or more precise amount of screen/stencil printed
embedded resistor material 184' and screen/stencil printed embedded
capacitor material 186' to be placed. Preferably, screen/stencil
printed embedded resistor material 184' and screen/stencil printed
embedded capacitor material 186' are screen printed or lift off
stencil printed and cured with standard thick film semi-conductive
resistive materials and or standard thick film capacitive materials.
Preferably screen/stencil printed embedded resistor material 184'
and screen/stencil printed embedded capacitor material 186' are
polymer based or ceramic based as used in (LTCC) process "Low
temperature co-fired ceramic" processing. Copper and stainless foils
and their alloys are suited for the high temperature baking or
firing process for both polymer and ceramic base materials. Aluminum
metal cores and their alloys are typically suited for polymer base
materials that cure by baking at or below four hundred degrees F.
FIG. 17d shows a side view of rigid core portion 180' with flexible
layers about to be attached. Preferably, flexible layers 122'
comprise at least one conductive layer 124', as shown. Preferably,
at least one conductive layer 124' is the outermost layer, as shown.
Preferably, flexible layers 122' comprise polyimide. Preferably
flexible layers 122' are bonded to rigid core portion 180' with
adhesive 120'. Preferably, adhesive 120' comprises polyimide.
Preferably, adhesive 120' is selectively applied to rigid core
portion 180' leaving gaps 132' at structurally weakened locations
182', as shown. Under appropriate circumstances, other arrangements
may suffice, such as, for example, the arrangements described above
for adhesive 120, flexible layers 122, conductive layer 124, gaps
132, etc.
FIG. 17e shows a side view of rigid core portion 180' after adhesive
120' (with adhesive gaps 132'), flexible insulating layers 122' and
flexible conductive layer 124', have been attached.
FIG. 17f shows a side view of rigid core portion 180' after holes
138' have been drilled. Preferably holes 13' are drilled as
described above for holes 138'. Preferably holes 138' are used to
make interconnects between conductive layers, as shown. Preferably,
holes 138' and make by the same processes as holes 138.
FIG. 17g shows a side view of rigid core portion 180' after
conductive material 140' is applied. Preferably conductive material
140' is applied as described above for conductive material 140.
FIG. 17h shows a side view of rigid core portion 180' after portions
of conductive material 140' are etched away. Preferably conductive
material 140' is etched away as described above for conductive
material 140.
FIG. 17i shows a side view of rigid core portion 180' after flexible
solder mask 146' is applied. Preferably, flexible solder mask 146'
comprises openings 152' at selected locations to allow access for
mounting electrical components 156' and hardware items 158' (see
FIG. 17j), etc., (such as, for example, computer chips, resistors,
capacitors, wires, etc.) as shown.
FIG. 17j shows a side view of rigid core portion 180' after
electrical components 156' and hardware items 158' have been
attached. Preferably rigid core portion 180' comprises electrical
components 156' and hardware items 158', as shown.
FIG. 17k shows a side view of rigid core portion 180' after rigid
core portion 180' has been bent (such as, for example, for final
installation). Rigid core portion 180' may, for example, be bent for
installation into a box or self contained metal enclosure or used
for many new electronic devices such as self contained and EMI
shielded devices. Preferably, rigid core portion 180' is malleable,
so that it bends rather than breaks at structurally weakened
location 182', as shown. Preferably, gaps 132' and structurally
weakened locations 182' (which preferably comprise removed material)
allow flexible layers 122' to bend without breaking. Preferably gaps
132' provide the flexible layers 122' a deformation relief area in
which to expand. Preferably, during the bending or folding of the
rigid core portion 180' the flexible layers 122' will be put into
compression, and the relief area created by gaps 132' allow for the
compressed forces to bend the flexible layers 122' into the bend
relief area, thus relieving the stresses and avoiding any breakage
issues, as shown.
FIG. 18a shows a side view of rigid-flex circuit board 198 according
to an alternate preferred embodiment of the present invention.
Preferably, circuit board 198 comprises metal support carrier 190,
adhesive 120, flexible layers 122, conductive layer 124, pads 105,
traces 111, conductive material 114, gaps 144, etc., (as described
above), as shown.
FIG. 18b shows a side view of circuit board 198 after portions of
metal support carrier 190 have been removed. Preferably, portions of
metal support carrier 190 are selectively removed, preferably
selectively etched away, as shown, creating gaps 192, providing
conductive pads 105, and removing rigidity from circuit board 198.
FIG. 18c shows a side view of circuit board 198 after flexible
solder mask 146 (with openings 152) has been applied (as described
above), as shown.
FIG. 18d shows a side view of circuit board 198 after solder balls
188, electrical components 156' and hardware items 158' have been
added (as described above), as shown.
FIG. 18e shows a side view of circuit board 198 after the circuit
board has been flexed and folded, such as for example for
installation on circuit board 199, as shown. For example circuit
board 198 may be used for high density high flexural use (called
dynamic flex) or used as one-time fold to provide 3-dimensional
Z-axis build-up system packaging used in what is called system in a
package (SIP) in microelectronic devices. Preferably, the processes
are similar to the above described methods except that preferably
adhesive 120 is applied to the entire metal support carrier 190.
Preferably, for circuit board 198, there no need for adhesive gap or
pre-etched grooves for bending metal support carrier 190 since the
majority of metal support carrier 190 is removed to provide
flexibility . Preferably, metal support carrier 190 provides support
for the manufacture and processing and buildup of the flexible
layers 122, etc.
FIG. 19a and FIG. 19b (which is a continuation of FIG. 19a) show a
preferred process for manufacturing rigid-flex according to a
preferred embodiment of the present invention.
FIGS. 20a-20e show that rigid core portion may comprise
semiconductor material, and that the methods taught herein can be
used to produce semiconductors which can be bent and/or flexed (such
as, for example, for installation).
FIG. 20a shows a side view of rigid flex semiconductor 210 according
to a preferred embodiment of the present invention. Preferably rigid
flex semiconductor, 210 comprises semiconductor substrate.
Preferably, semiconductor substrate is a solid chemical element or
compound that conducts electricity under certain conditions, such
as, for example, Gallium Arsenide (GaAs), Silicon Germanium (SiGe),
Indium phosphide (InP), Gallium Nitride (GaN), Aluminum Nitride
(AiN), Indium Gallium Arsenide Nitride (InGaAsN), etc. Silicon
semiconductor wafer materials with build up layers and conductive
patterns and semi-conductive materials may be used as integrated
circuits for cell phones, pagers, memory chips and many more
devices. This flexible material build up process allows a conductive
pattern layer on the outside of the semiconductor wafer which now
can be a flexible circuit, after removal of material in selective
areas by laser cut or mechanical wafer sawing. This process can be
single sided or on both sides and can be repeated for multilayers.
Preferably the methods of manufacture and buildup are as described
above. Preferably, rigid flex semiconductor 210 comprises bonding
pads 212, as shown.
FIG. 20b shows a side view of the rigid flex semiconductor 210 after
conductive material 140a has been applied.
FIG. 20c shows a side view of the rigid flex semiconductor 210 after
it has been plated, printed, etched and solder mask applied 146a and
solder balls 188a have been applied.
FIG. 20d shows a side view of the rigid flex semiconductor 210 being
cut by laser drill 162 to create cuts 167 so that it can be flexed
and bent.
FIG. 20e shows a side view of the rigid flex semiconductor 210 after
it has been flexed and bent at the location of cuts 167 with
flexible connections 128 formed by flexible layers such as, for
example, adhesive and solder mask 146a, as shown.
Although applicant has described applicant's preferred embodiments
of this invention, it will be understood that the broadest scope of
this invention includes such modifications as diverse shapes and
sizes and materials. Such scope is limited only by the below claims
as read in connection with the above specification.
Further, many other advantages of applicant's invention will be
apparent to those skilled in the art from the above descriptions and
the below claims.
* * * * *
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