U.S. patent application number 09/755082 was filed with the patent office on 2001-12-13 for base webs for printed circuit board production using the foam process and acrylic fibers.
This patent application is currently assigned to Ahlstrom Glassfibre Oy.. Invention is credited to Komlenic, Rod, Rennels, Kelly, Rokman, Kay, Sabel, Hakan.
Application Number | 20010050130 09/755082 |
Document ID | / |
Family ID | 23580915 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010050130 |
Kind Code |
A1 |
Rokman, Kay ; et
al. |
December 13, 2001 |
Base webs for printed circuit board production using the foam
process and acrylic fibers
Abstract
A printed circuit board is made from at least one non-woven
sheet or web layer comprising at least 50% by weight acrylic
fibers, with any balance substantially electrically non-conductive
fibers, filler, and binder. The sheet or web is preferably made by
the foam process, and may contain 60-80% straight polyacrylonitrile
fibers and 40-20% fibrillated (pulp) ones. The web or sheet is
preferably compressed by thermal calendering so that it has a
density of about 0.1-1 grams per cubic centimeter; and the web or
sheet may have a basis weight of between about 20-120 grams per
square meter. The web or sheet may also have a 1-40% of
substantially electrically non-conductive organic or inorganic
binder, or may be substantially binder free. A printed circuit
board made using the layers of these non-woven webs or sheets is
otherwise conventional, including a pre-preg material, electrically
conductive circuit elements, and electronics, and has improved
properties compared to woven glass and non-woven aramid products,
including improved fiber consolidation, easy board construction,
and improved MD/CD ratio and stability.
Inventors: |
Rokman, Kay; (Karhula,
FI) ; Komlenic, Rod; (Mt. Holly Springs, PA) ;
Rennels, Kelly; (Mt. Holly Springs, PA) ; Sabel,
Hakan; (Karhula, FI) |
Correspondence
Address: |
Nixon & Vanderhye P.C.
8th Floor
1100 N. Glebe Rd.
Arlington
VA
22201
US
|
Assignee: |
Ahlstrom Glassfibre Oy.
|
Family ID: |
23580915 |
Appl. No.: |
09/755082 |
Filed: |
January 8, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09755082 |
Jan 8, 2001 |
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09399775 |
Sep 21, 1999 |
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6258203 |
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Current U.S.
Class: |
156/64 ;
428/343 |
Current CPC
Class: |
D21H 13/18 20130101;
B32B 5/28 20130101; Y10T 442/608 20150401; Y10S 428/901 20130101;
H05K 1/0366 20130101; Y10T 442/632 20150401; C08J 5/046 20130101;
H05K 2201/0278 20130101; Y10T 428/28 20150115; Y10T 428/24917
20150115; D21F 11/002 20130101; D21H 25/005 20130101; Y10T 442/637
20150401; D21H 13/40 20130101; D21H 25/06 20130101; C08J 5/24
20130101; H05K 2201/0293 20130101; D21H 25/04 20130101; H05K
2201/0145 20130101; Y10T 442/2008 20150401; D21H 13/24 20130101;
H05K 2201/0251 20130101; D21H 13/22 20130101; Y10T 442/2738
20150401; D21H 13/26 20130101 |
Class at
Publication: |
156/64 ;
428/343 |
International
Class: |
B32B 031/00; B32B
031/00 |
Claims
What is claimed is:
1. A printed circuit board comprising: a plurality of substantially
electrically non-conductive substrate layers; at least one of said
layers comprising, prior to pre-preg, a non-woven layer including
fibers, and at least 50% by weight of said fibers comprising
acrylic fibers; and electrically conductive circuit elements
provided on or between at least one of said substrate layers.
2. A printed circuit board as recited in claim 1 wherein said
acrylic fibers comprise at least about 50% high tenacity acrylic
fibers from about 3-12 mm long and from about 6-15 microns in
diameter.
3. A printed circuit board as recited in claim 2 wherein said
fibers comprise at least about 90% polyacrylonitrile fibers.
4. A printed circuit board as recited in claim 2 wherein the fibers
of said non-woven layer consist essentially of acrylic fibers.
5. A printed circuit board as recited in claim 1 wherein said
non-woven layer is substantially binder-free.
6. A printed circuit board as recited in claim 1 wherein said
non-woven layer includes an organic or inorganic binder comprising
between about 1-40% by weight of said non-woven layer.
7. A printed circuit board as recited in claim 1 wherein said
non-woven layer comprises a mixture of straight and fibrillated
acrylic fibers.
8. A printed circuit board as recited in claim 1 wherein said
non-woven layer includes at least 10% by weight other fibers
besides acrylic fibers.
9. A printed circuit board as recited in claim 1 wherein said
non-woven layer includes at least 10% by weight material comprising
one or more of liquid crystalline polymers, aramid fibers, aramid
pulp fibers, micro fiberglass, polyester fibers, DuPont fibrids,
PEN fibers, PPS fibers, MF fibers, and phenolic fibers.
10. A printed circuit board as recited in claim 1 wherein said
non-woven layer is produced by the foam process.
11. A printed circuit board as recited in claim 10 wherein said
non-woven layer is densified by thermal calendering at a
temperature over 200.degree. C. and a pressure of greater than 500
psi.
12. A printed circuit board as recited in claim 7 wherein said
non-woven layer comprises about 60-80% straight fibers and 40-20%
refined fibrillated fibers.
13. A printed circuit board as recited in claim 2 further
comprising a plurality of electronic components mounted on or
between at least one of said substrate layers and electrically
connected to said circuit elements.
14. A method of producing a printed circuit board comprising: (a)
producing a non-woven sheet or web comprising at least 50% by
weight acrylic fibers and the balance at least one of substantially
electrically non-conductive fibers, filler, and binder; (b)
densifying the sheet or web from (a); (c) forming a printed circuit
board layer using the sheet or web from (b); (d) combining the
layer from (c) with other substantially electrically non-conductive
layers; and (e) providing electrically conductive circuit elements
on or between at least one of the layers from (c).
15. A method as recited in claim 14 wherein (a) is practiced by
using a mixture of both fibrillated and straight acrylic
fibers.
16. A method as recited in claim 15 wherein (a) is practiced by
using a mixture of about 60-80% straight fibers, and about 40-20%
fibrillated fibers that may have been refined.
17. A method as recited in claim 14 wherein (b) is practiced by
thermal calendering at a temperature of greater than 200.degree. C.
and a pressure of greater than 500 psi.
18. A method as recited in claim 14 further comprising (f), between
(c) and (d), forming a pre-preg from the layer of (c) by
impregnating the layer with resin; and (g), after (e), of curing
the pre-preg to produce a printed circuit board.
19. A method as recited in claim 14 wherein (a) is practiced using
polyacrylonitrile fibers from about 3-12 mm long and from about
6-15 microns in diameter.
20. A method as recited in claim 19 wherein (a) is practiced
substantially without binder.
21. A method as recited in claim 19 wherein (a) is practiced using
1-40% by weight organic or inorganic binder.
22. A method as recited in claim 14 wherein (a) and (b) are
practiced to produce a sheet or web having a density of 0.1-1
g/cm.sup.3, and wherein (a) is practiced by the foam process using
a slurry having a solids consistency of at least about 5%
23. A method as recited in claim 14 wherein (a) is practiced by the
foam process.
24. A non-woven sheet or web comprising at least 50% by weight
acrylic fibers, and any balance substantially electrically
non-conductive fibers or filler or binder, or combinations
thereof.
25. A non-woven sheet or web as recited in claim 24 comprising
about 60-80% straight acrylic fibers and about 40-20% fibrillated
acrylic fibers.
26. A non-woven sheet or web as recited in claim 24 wherein said
web or sheet is substantially devoid of binder.
27. A non-woven sheet or web as recited in claim 24 wherein said
web or sheet has been compressed so that it has a density of about
0.1-1 g/cm.sup.3.
28. A non-woven sheet or web as recited in claim 24 further
comprising about 1%-40% by weight of a substantially electrically
non-conductive organic or inorganic binder.
29. A non-woven sheet or web as recited in claim 25 comprising at
least about 90% acrylic fibers.
30. A non-woven web or sheet as recited in claim 25 wherein the
fibrillated fibers are refined.
31. A non-woven web or sheet as recited in claim 24 wherein the web
or sheet is made by the non-woven process.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
[0001] Printed circuit boards (also called printed wire boards or
PWBs) are conventionally made of primarily fiberglass fibers, with
electrically non-conductive fillers. However there has been
increasing interest in making printed circuit boards from aramid
fibers since aramid fibers have a number of advantages over glass,
or mixtures of aramid and glass fibers are used. For example,
duPont Chemical Company uses its own brand of aramid fiber
("THERMOUNT") in the production of printed circuit boards.
[0002] The duPont aramid PCBs are made using the conventional
liquid laid process for non-woven web production using a foraminous
element, such as a wire. In order to effectively make non-woven
webs using aramid fibers by the liquid laid process, duPont uses a
blend of different length and diameter aramid fibers, some of which
may be fibrillated, in an attempt to produce versatile and entirely
commercially acceptable printed circuit boards. However there are
numerous problems associated with the water laid process of
production of aramid non-woven sheets or webs using conventional
para aramid fibers (which are "straight").
[0003] Conventional aramid printed circuit boards, and layers
formed of non-woven webs making up such boards, have a significant
number of problems including the inability to randomly disperse the
aramid fibers as uniformly as customers would like, and typically
the aramid sheets are directional. This directionality creates
different coefficients of thermal expansion in the machine
direction and the cross-machine direction in the finished product,
and in tear characteristics relating to saturating the sheet. Also
such boards are difficult to handle and require a significant
amount of handling experience by customers, and they have an
affinity to absorb moisture so that some customers must bake each
roll in an oven to drive off humidity before it can be used. Also
great care must be exercised during manufacturing to avoid chain
wrinkles, lay flat, and other undesirable features which can be
introduced during the forming, calendering, and rewinding
processes. Also there is a recognized problem with electrically
conductive particulate contamination, which reduces the electrical
properties of the web produced.
[0004] According to the present invention a printed circuit board
layer, the printed circuit board per se, and a method of producing
printed circuit boards, are provided which are advantageous
compared with conventional aramid-based and glass-based printed
circuit boards. According to the invention it is preferred to use
the foam process, such as described in U.S. Pat. No. 5,904,809 (the
disclosure of which is hereby incorporated by reference herein).
and the primary fiber used in the construction of PWBs according to
the invention is acrylic fiber, more particularly a high tenacity
acrylic fiber such as polyacrylonitrile. According to the invention
it has been found that acrylic fibers are highly advantageous in
the production of PWBs.
[0005] According to another aspect of the present invention, the
non-woven web or sheet may be made utilizing the foam process. The
foam process is highly efficient in handling fibers like acrylic
fibers, allowing the formation of a much more uniform web, and
allowing fiber blending to a much better extent than webs produced
by the water laid process. Fiber blending may be particularly
important in the production of printed circuit board layers
containing acrylic fibers. Conventional non-conductive fillers
(such as plastic or glass particles) can be incorporated in the
foam and are uniformly distributed in the final web produced. Also
by using the foam process the density of the fiber-containing webs
or sheets produced may be much more closely regulated than when the
water laid process is utilized, other fibers such as aramid and
glass may be readily incorporated, and the entire formation process
is less expensive and more energy efficient.
[0006] Utilizing the invention, printed circuit boards, and layers
for printed circuit boards, may be produced containing at least 50%
acrylic fiber, and preferably about 60-80% straight high tenacity
acrylic fiber about 3-12 mm long with a diameter of about 6-15
microns, and about 40-20% fibrillated acrylic fibers (i.e. pulp
fibers). Substantially 100% acrylic fiber boards and layers may be
produced according to the invention, but there typically will be at
least some other non-conductive fibers, like glass fibers, or
aramid fibers, or non-conductive fillers, and 0-40% non-conductive
organic or inorganic binder.
[0007] The web or sheet produced according to the invention is
typically densified or compressed (as by using conventional thermal
calendering rolls) preferably so that it has a density of between
about 0.1-1 grams per cubic centimeter, and a basis weight of
between 20-120 grams per square meter. The web or sheet may be
binder free, or may comprise about 1%-40% (preferably less than
20%) by weight of a substantially electrically nonconductive
organic or inorganic binder.
[0008] According to another aspect of the present invention a
printed circuit board is provided comprising the following
components: A plurality of substantially electrically
non-conductive substrate layers. At least one of the layers
comprising, prior to pre-preg, a non-woven layer comprising at
least 50% by weight acrylic fibers. [Preferably a pre-preg
material, impregnates at least some of the layers.] And,
electrically conductive circuit elements provided on or between at
least one of the substrate layers. Most printed circuit boards are
made with between three to six layers, although a significant
number of boards are also made using seven to eight layers, and
there are also many boards made using nine or more layers. The
pre-preg material when used is entirely conventional, and typically
is epoxy resin, and the electrically conductive circuit elements
are also completely conventional (as is their positioning),
typically comprising copper strips, wires, or deposits, or like
physical structures of other conductive materials such as silver.
Typically the at least one layer containing the acrylic fibers is
produced by the foam process (although it may be produced by the
water laid process), and may have at least about 90% by weight
acrylic fibers prior to pre-preg. Each of the substrate layers may
have a density of about 0.1-1 grams per cubic centimeter prior to
pre-preg, and the board typically further comprises a plurality of
electronic components (such as computer chips, diodes, resistors,
etc.) connected to the board substrate, and to the electrically
conductive circuit elements, using entirely conventional
techniques.
[0009] According to another aspect of the present invention, a
method of producing a printed circuit board is provided comprising
the following: (a) Producing a non-woven sheet or web comprising at
least 50% by weight (up to substantially 100%) acrylic fibers, and
the balance at least one of substantially electrically
non-conductive fibers, filler, and binder. (b) Densifying (e.g.
thermal calendering) the sheet or web from (a). (c) Forming a
printed circuit board layer using the sheet or web from (b). (d)
Combining the layer from (c) with other substantially electrically
non-conductive layers, and (e) Providing electrically conductive
circuit elements on or between at least one of the layers from (c).
There may also be, between (c) and (d), (f) forming a pre-preg from
the layer of (c) by impregnating the layer with resin or the like.
And, (g) curing the pre-preg of (d)-(f) to produce a printed
circuit board.
[0010] Procedure (b) is conventional, and typically is accomplished
utilizing calendering rollers, and a temperature over 200.degree.
C. and a pressure of at least 500 psi. The layering of the sheets
or webs to produce the printed circuit board, of (c), and the
pre-preg formation of (f), and combining a layer from (c) with
other substantially electrically non-conductive layers as in (d),
and providing the electrically conductive circuit elements as
recited in (e), as well as the securing of (g), are also all
conventional. Also there preferably are the further conventional
procedures of (h) mechanically acting on the board from (g); and
(i) electrically and physically connecting electronic components to
the board from (h), and to the circuit elements.
[0011] In the implementation of the invention (a) is preferably
practiced by the foam process. Also, (a) and (b) are typically
practiced to produce a sheet or web having a density of about 0.1-1
grams per cubic centimeter, and (a) is typically practiced using
about 40-20% fibrillated acrylic fibers (e.g. about 30%), and about
60-80% straight high tenacity acrylic fibers. Either substantially
no binder, or about 1-40% by weight organic or inorganic
non-conductive binder, may be used.
[0012] The substrates according to the invention, and produced
according to the method of the invention, are advantageous compared
to the prior art. They have or are:
[0013] Far superior resin wet out than aramid papers or woven
glass.
[0014] Improved fiber consolidation creating less fiber fuzz during
resin impregnation.
[0015] Easier to cut both in the substrate form, and in the
impregnated pre-preg or laminate form.
[0016] Easier to laser cut and drill holes because glass absorbs
laser energy more than the non-wovens of the invention.
[0017] Lower moisture pick up than aramid papers.
[0018] Improved dimensional stability.
[0019] Improved MD/CD ratio and stability.
[0020] Lower weight than glass fiber; and
[0021] Good adhesion to impregnating resins typically used in
laminate production.
[0022] It is the primary object of the present invention to produce
acrylic fiber-containing layers, and printed circuit boards formed
from one or more of such layers, which have enhanced utility and/or
enhanced ease and reduced cost of production, compared to
conventional glass and aramid fiber-containing layers or boards.
This and other objects of the invention will become clear from an
inspection of the detailed description of the invention, and from
the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a schematic view illustrating an exemplary method
according to the present invention, resulting in the production of
a printed circuit board;
[0024] FIG. 2 is an exploded schematic view of a circuit board
according to the present invention without electronic components
mounted thereon; and
[0025] FIG. 3 is a schematic representation of the practice of the
foam process utilizing the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 schematically illustrates a preferred method 10 of
producing printed circuit boards, which have at least one layer
containing acrylic fibers. The first procedure according to the
invention is the production of a web or a sheet preferably using
the foam process, although the wet laid process may be used
instead, as illustrated schematically at 11 in FIG. 1. Acrylic
fibers from source 12, other fibers or fillers from source 112,
surfactant and water from source 14, and the like are provided, and
the foam process is practiced preferably as described in U.S. Pat.
No. 5,904,809, or the prior art mentioned therein. Typically the
slurry has a consistency of at least about 5%, e.g. about 5-50%.
Typically some binder will be added to the web, either prior to
formation, as indicated schematically at 15 in FIG. 1, and/or after
formation, as indicated schematically at 16 in FIG. 1. The binder
may comprise about 1%-40% (preferably less than 20%) by weight of a
substantially electrically non-conductive organic binder. Examples
of known binders for that purpose are: epoxy, acrylic, melamine
formaldehyde, polyvinyl alcohol, phenolics, or urethanes, and
combinations thereof. Alternatively about 1-40% inorganic binder,
such as silica, may be used.
[0027] After web or sheet formation, the web or sheet is dried as
indicated schematically at 17 in FIG. 1 using conventional drying
equipment (such as a drying oven), and the web is densified as
indicated schematically at 18, e.g. using conventional calendering
rolls in a thermal calendering operation at a temperature greater
than 200.degree. C. and a pressure greater than 500 psi. Typically
steps 11, 15 and 16, 17 and 18 will take place at one location, and
then the final web or sheet produced (if a web is produced it is
wound using conventional techniques, and if sheets are produced
they are typically stacked for transport) is transported to another
location where the other conventional steps for printed circuit
board production take place.
[0028] The webs or sheets produced by the steps 11 and 15 through
18 typically have a density of between about 0.1-1 grams per cubic
centimeter, and a basis weight of between about 20-120 grams per
square meter.
[0029] The step schematically illustrated at 20 in FIG. 1 is a
pre-preg step, where the web or sheets from 18 are impregnated with
epoxy resin from source 21 or the like, the impregnating resin
being substantially electrically non-conductive. After pre-preg
formation, the board is layered--that is various layers are
utilized (either the layers from procedure 18, or other layers
produced by conventional techniques and of more conventional
materials, such as glass or aramid fibers or the like, blends with
liquid crystalline polymers (e.g. Vectran), fibrillated acrylic
fibers (normally >90% polyacrylonitrile), acrylic pulp, DuPont
Fibrids, micro fiberglass (normally <5 micron diameter),
polyester fiber, PEN fibers, PPS fibers, MF fibers, and
phenolic)--are assembled together and circuit elements added, as
schematically illustrated at 22. Circuit elements may be added in
any conventional manner (e.g. screen printing, cladding, mechanical
laydown and attachment, etc.) Then the layered intermediate board,
with circuit elements, is cured in a conventional manner as in a
curing oven, as illustrated schematically at 23 in FIG. 1.
[0030] After curing at 23, the intermediate board is acted on
mechanically--as illustrated schematically at 24 in FIG. 1--as is
conventional, e.g. various holes being formed therein, shaping,
shaving, texturing, enhancing exposure of circuit elements, or the
like.
[0031] Then the electronic components are added--as schematically
illustrated at 25 in FIG. 1--to produce the final circuit board
illustrated schematically at 26 in FIG. 1. The electronic component
addition step 25 is also conventional, various electronic elements
that are to be utilized on the final board 26 being mechanically
connected to the board and electrically connected to each other
and/or circuit elements.
[0032] The board 26, being only very schematically illustrated in
FIG. 1, comprises the substrate 27 formed of multiple (typically
between three and nine, but most typically between three and six)
layers, illustrated schematically at 28 in FIG. 1. According to the
invention each of the layers 28 may comprise at least 50% by weight
(prior to pre-preg) acrylic fibers (preferably a mixture of
straight and pulp) fibers. However the layers 28 may have different
percentages and types of acrylic fibers therein, or some of the
layers 28 may be conventional glass or aramid layers, or have other
conventional constructions. However about 90% (by weight) or more
acrylic pulp fibers may be used.
[0033] The final circuit board 26 illustrated in FIG. 1 also has
electrically conductive circuit elements 29, which are strips,
wires, or deposits of electrically conductive material, such as
copper, silver, or other conventional conductive materials or
blends thereof. The elements 29 connect electronic components
together, and connect the board 26 to a power source, other boards,
or other external components. FIG. 1 schematically illustrates
conventional chips 30 as electronic components, as well as diodes
or resistors or capacitors 31, or the like. Any conventional
electronic components can be utilized in the construction of the
board 26 according to the invention.
[0034] The board 26 according to the invention will have better
dimensional stability in moisture than conventional aramid and
glass boards, therefore can have higher circuit density and is less
susceptible to high frequency energy corruption. Also because of a
better co-efficient of thermal expansion, the board 26 can be
expected to have longer life than an otherwise conventional board,
and is otherwise advantageous as described above.
[0035] In the web formation step 11, the appropriate type and
percentage of fibers will be added to get the desired results, as
described more fully with respect to FIG. 3. The fibers added at 12
are at least 50% by weight acrylic fibers. Conventional straight
and fibrillated (pulp) high tenacity acrylic fibers may be
added--conventional fillers may also be utilized, as long as they
are substantially electrically non-conductive, such as known glass
and plastic particulate fillers--and other fibers may be
added..
[0036] FIG. 2 schematically illustrates the board 26 before the
mechanical activity at 24 and the electrical component addition at
25 from FIG. 1, showing the components in an exploded view. Each of
the layers 28 are preferably produced by the steps 1 1 and 15
through 18 (as well as by pre-preg at 20) and can have varying
fiber compositions, but preferably each have at least 50% acrylic
fibers. The electrically conductive circuit elements are shown
disposed between the layers 28, and may overlap the edges of the
layers 28 for connection to external components, or to facilitate
connection to components that will ultimately be mounted on the
substrate 27. As is conventional, one or more of the layers 28 may
be etched, mechanically sanded or handled, or otherwise acted upon
to expose circuit elements 29 where necessary or desirable.
[0037] FIG. 3 schematically shows a procedure for producing
non-woven webs according to the invention. Acrylic fibers are added
to a pulper 33 along with surfactant and water, and possibly other
types of fibers, binder, or fillers. The acrylic fibers added to
pulper 33 are preferably high tenacity straight acrylic fibers such
as polyacrylonitrile fiber preferably from 3-12 mm in length and
6-15 microns in diameter.
[0038] The foam slurry discharged from 33 is pumped by pump 34 to a
line 35 leading to conventional mixer 36. From mixer 36 the slurry
proceeds to conventional web formation at 37. As is conventional,
foam and liquid removed from 37 goes to wire pit 38 and is
recirculated by pump 39 to the mixer 36, the recirculated slurry
from wire pit 38 being mixed with the fiber slurry from pulper 33
in mixer 36.
[0039] Preferably the straight acrylic fibers from 33 are also
mixed with acrylic pulp (fibrillated) fibers too. This may be
accomplished in several ways, such as the two alternative (or
complementary) ways shown in FIG. 3.
[0040] Acrylic pulp fibers are added to pulper 41 with water, and
preferably water and surfactant, and then the slurry so formed is
pumped by pump 42 to be refined in a conventional refiner or
deflaker 43, or another device capable of applying high shear to
the acrylic pulp in the slurry.
[0041] From the high shear device 43 the slurry of fibrillated
acrylic fibers may be added directly to line 35 prior to mixer 36,
so that the straight and fibrillated acrylic fibers are uniformly
dispersed prior to web formation. In addition, or alternatively,
some of the fibrillated acrylic fiber slurry may be fed from high
shear device 43 to the pulp 33.
[0042] In the preferred embodiment at least some fibrillated
acrylic fibers are added to the straight acrylic fibers to comprise
the at least 50% acrylic fiber product produced. The desired mix of
acrylic fibers is about 20-80% (preferably about 70%) straight
fibers, and about 40-20% (preferably about 30%) fibrillated
fibers.
[0043] As one example 30% refined fibrillated acrylic fibers and
70% straight acrylic fibers, which collectively make up about 85%
by weight of the final non-woven sheet or web to be produced are
mixed with about 10% by weight glass or polyester or aramid fibers
and about 5% by weight organic binder [all prior to pre-preg
percentages]. The non-woven web or sheet produced is made by the
wet laid or foam process, preferably the foam process.
[0044] In the description provided above all ranges include all
narrower ranges within a broad range. For example, about 1-40% by
weight binder means 2-5%, 3-20%, 25-15%, and all other narrower
ranges within the broad range.
[0045] It will thus be seen that according to the present invention
a highly advantageous non-woven sheet or web for use in a printed
circuit board construction, a printed circuit board, and a method
of producing a printed circuit board, have been provided. While the
invention has been herein shown and described in what is presently
conceived to be the most practical and preferred embodiment
thereof, it will be apparent to those of ordinary skill in the art
that many modifications may be made thereof within the scope of the
invention, which scope is to be accorded the broadest
interpretation of the appended claims so as to encompass all
equivalent structures and methods.
* * * * *