U.S. patent application number 10/989614 was filed with the patent office on 2005-03-31 for low signal loss bonding ply for multilayer circuit boards.
This patent application is currently assigned to Tonoga, Inc.. Invention is credited to McCarthy, Thomas F., Wynants, David L. SR..
Application Number | 20050069722 10/989614 |
Document ID | / |
Family ID | 25492956 |
Filed Date | 2005-03-31 |
United States Patent
Application |
20050069722 |
Kind Code |
A1 |
McCarthy, Thomas F. ; et
al. |
March 31, 2005 |
Low signal loss bonding ply for multilayer circuit boards
Abstract
A low loss circuit board sheet includes a first layer disposed
on a second layer. The first layer includes a thermosetting
adhesive composition and the second layer is selected from a woven
fabric substrate impregnated with at least one rubber, a nonwoven
fabric substrate impregnated with at least one rubber and a
polymeric film having at least one rubber disposed thereon.
Inventors: |
McCarthy, Thomas F.;
(Bennington, VT) ; Wynants, David L. SR.;
(Cambridge, NY) |
Correspondence
Address: |
HESLIN ROTHENBERG FARLEY & MESITI PC
5 COLUMBIA CIRCLE
ALBANY
NY
12203
US
|
Assignee: |
Tonoga, Inc.
Petersburgh
NY
12138
|
Family ID: |
25492956 |
Appl. No.: |
10/989614 |
Filed: |
November 16, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10989614 |
Nov 16, 2004 |
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10289984 |
Nov 7, 2002 |
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10289984 |
Nov 7, 2002 |
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09952486 |
Sep 14, 2001 |
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6500529 |
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Current U.S.
Class: |
428/494 ;
428/325; 428/413; 428/458 |
Current CPC
Class: |
H05K 2201/0209 20130101;
H05K 2201/0195 20130101; Y10T 428/24917 20150115; Y10T 428/31681
20150401; H05K 3/4626 20130101; H05K 1/0366 20130101; Y10T 428/252
20150115; H05K 2201/0278 20130101; Y10T 428/2804 20150115; Y10T
428/31833 20150401; H05K 1/034 20130101; Y10T 428/24994 20150401;
Y10T 428/31511 20150401; H05K 3/386 20130101; Y10T 428/25 20150115;
H05K 2201/029 20130101; H05K 2201/015 20130101; H05K 1/036
20130101 |
Class at
Publication: |
428/494 ;
428/325; 428/413; 428/458 |
International
Class: |
B32B 027/38; B32B
025/12; B32B 015/08 |
Claims
1. A low loss circuit board sheet comprising a first layer disposed
on a second layer, said first layer comprising a thermosetting
adhesive composition and said second layer selected from a woven
fabric substrate impregnated with at least one rubber, a nonwoven
fabric substrate impregnated with at least one rubber and a
polymeric film having at least one rubber disposed thereon.
2. A low loss circuit board sheet according to claim 1, wherein the
second layer is a woven fabric substrate impregnated with at least
one rubber.
3. A low loss circuit board sheet according to claim 1, wherein the
second layer is a nonwoven fabric substrate impregnated with at
least one rubber.
4. A low loss circuit board sheet according to claim 1, wherein the
second layer is a polymeric film having at least one rubber
disposed thereon.
5. A low loss circuit board sheet according to claim 1,
additionally comprising at least one metallization layer.
6. A low loss circuit board sheet according to claim 1, wherein
said thermosetting adhesive composition comprises an epoxy
resin.
7. A low loss circuit board sheet according to claim 1, wherein
said thermosetting adhesive composition comprises a rubber.
8. A low loss circuit board sheet according to claim 1, wherein the
first layer or the second layer additionally comprises a ceramic
filler.
9. A low loss laminate comprising a plurality of low loss circuit
board sheets laminated together by means of a thermosetting
adhesive composition, wherein each of said low loss circuit board
sheets comprises a first layer disposed on a second layer, said
first layer comprising said thermosetting adhesive composition and
said second layer selected from a woven fabric substrate
impregnated with at least one rubber, a nonwoven fabric substrate
impregnated with at least one rubber and a polymeric film having at
least one rubber disposed thereon.
10. A low loss laminate according to claim 9 wherein the second
layer is a woven fabric substrate impregnated with at least one
rubber.
11. A low loss laminate according to claim 9, wherein the second
layer is a nonwoven fabric substrate impregnated with at least one
rubber.
12. A low loss laminate according to claim 9, wherein the second
layer is a polymeric film having at least one rubber disposed
thereon.
13. A low loss laminate according to claim 9, additionally
comprising at least one metallization layer.
14. A low loss laminate according to claim 9, wherein said
thermosetting adhesive composition comprises an epoxy resin.
15. A low loss laminate according to claim 9, wherein said
thermosetting adhesive composition comprises a rubber.
16. A low loss laminate according to claim 9, wherein the first
layer or the second layer of the low loss circuit board sheets
additionally comprises a ceramic filler.
17. A low loss laminate according to claim 9, additionally
comprising a layer selected from a woven fabric substrate
impregnated with a thermosetting resin, a nonwoven fabric substrate
impregnated with a thermosetting resin, a polymeric film coated
with a thermosetting resin, a woven fabric substrate impregnated
with a rubber, a nonwoven fabric substrate impregnated with a
rubber and a polymeric film coated with a rubber.
18. A low loss laminate according to claim 17, wherein the
additional layer is sandwiched between at least two of said low
loss circuit board sheets.
19. A low loss laminate according to claim 17, wherein the
additional layer comprises a thermoset impregnated fiberglass.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of copending U.S. patent
application Ser. No. 10/289,984, filed on Nov. 7, 2002, which is a
Divisional of U.S. patent application Ser. No. 09/952,486, filed
Sep. 14, 2001, now U.S. Pat. No. 6,500,529, the priority of which
is claimed herein. The entire disclosure of both applications is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to a multilayer bonding prepreg
comprising a fluoropolymer, a substrate typically consisting of
fiberglass to reinforce the low signal loss fluoropolymer, a
surface coated thermosetting resin and optionally a ceramic filler
to control the coefficient of thermal expansion. Ceramic filler is
used in either the fluoropolymer coated glass component, the
thermosetting resin surface component, or in both components. The
composite is used as a low signal loss bonding ply which can be
pressed at low temperatures to manufacture a multilayer circuit
board for high frequency applications
BACKGROUND OF THE INVENTION
[0003] In the electronics industry multilayer circuit boards are
prepared by bonding a layer of incompletely cured thermosetting
resin reinforced with fiberglass between layers of a fully cured
print and etched laminate. For a four-layer epoxy based circuit
board, first an epoxy coated fiberglass composite is laminated with
thin copper foil on both sides. On one side of the laminate, the
copper is patterned using conventional printed circuit board
manufacturing processes. The side containing the patterned copper
layer is referred to as the inner layer. Two laminates having the
inner layers facing each other are then bonded together typically
using an FR-4 prepreg (a flame retarded partially cured sheet of
epoxy coated fiberglass that has no copper foil cladding). The
inner layers are then bonded together using the partially cured
epoxy as an adhesive layer by pressing the construction together in
a press at temperatures such as 360.degree. F. (182.degree. C.) for
two hours at 200 psi, thereby fully curing the epoxy FR-4 adhesive
layer. A composite is thereby created having non-pattered copper
layers at the surfaces and patterned inner layers being separated
by the adhesive layer. The top and bottom non-patterned copper
layers (the outer layers) can then be print and etched yielding a
four-layer circuit board.
[0004] One drawback of using many conventional thermosetting resins
as the adhesive layer is the poor electrical properties of the
bonding adhesive layer. Epoxy based thermosetting resin, for
example, has poor electrical loss characteristics in the 1-100
gigahertz range. For very long trace lengths, signal degradation
forces the use of lower loss dielectrics. This is increasingly
becoming the case for high speed digital applications (routers,
backplanes, motherboards and daughter boards). For the RF and mm
wave frequencies, polytetrafluoroethylene (PTFE) based materials
are traditionally used to prevent signal loss. PTFE based materials
have been available for a long time for the most demanding low
signal loss applications but have been avoided for cost
considerations. Conventional thermosetting resins have too high a
loss tangent at the high frequencies and are nearing their ultimate
limits at 2.5 GHz. As frequencies extend to the 5 and 10 GHz range,
it is likely that epoxy resins will be replaced by higher
performing materials. Suppliers of epoxy laminate have been
reducing the loss tangent of their products by switching to lower
loss polyphenylene oxide based polymers and ceramic fillers.
Typical PTFE products have 0.002-0.004 loss tangents versus
0.007-0.014 for epoxies and related materials (10 GHz). As signal
integrity drives the use of higher performing materials, epoxy
based solutions will eventually fall short even with high loadings
of ceramics.
[0005] An alternative solution is the use of expanded PTFE that has
been filled with epoxy and ceramic, thereby diluting the
concentration of the higher loss epoxy component. This combination
of epoxy, ceramic, and PTFE results in a sufficiently low loss
product to be acceptable for high speed digital applications. The
downside is that the expanded PTFE based solution is quite
expensive and there are issues of dimensional movement that becomes
significant with increasing layer count. U.S. Pat. Nos. 4,985,296;
4,996,097; 5,538,756; and 5,512,360 awarded to W. L. Gore describe
the use of a thermosetting resin impregnated into an expanded PTFE
web. These patents teach the use of incorporating ceramic in the
PTFE expanded web manufacture and/or part of the non-fluorinated
adhesive resin system to obtain low loss materials.
[0006] Ceramic filled resin systems based on polybutadiene-woven
fiberglass based prepregs, both filled and unfilled with flame
retardant additives, are known to be relatively low loss materials
(U.S. Pat. No. 5,571,609). These materials suffer from the
inconsistent quality of the peroxy cured rubber system and the poor
bond strengths of the cured rubber to copper foil. A related
material, crosslinked polyesters filled with kaolin, have
attractive dielectric properties but unattractive peel strengths
and other fabrication problems.
[0007] Polyphenyleneoxide (PPO, APPE, PPE) based resin systems that
are cured systems of low molecular weight PPO and epoxy resins have
some process limitations (U.S. Pat. No. 5,043,367; 5,001,010;
5,162,450) for high speed digital or high frequency applications.
Their loss tangents in the gigahertz frequency range are reported
to be in the 0.006-0.008 range. This is an incremental improvement
over standard epoxy. Secondly, their lack of flow is a serious
constraint.
[0008] Very low loss solutions include PTFE based materials and
optical interconnects. Solutions containing pure PTFE based
adhesive layers have the disadvantage that these materials need to
be processed at temperatures exceeding 700.degree. F. (fusion
bonding, 371.degree. C.). There are fabricators today building
multilayer structures based on fluorinated resin systems. Most
fabricators do not have equipment capable of pressing at these
temperatures, nor are the extended heating and cooling cycles
attractive to fabricators. High temperature pressing on a 34 layer
count stackup could result in decreased reliability of plated
through holes, PCB warping, and copper pad distortion. In high
speed digital applications, via holes are a real source of signal
loss. The alternative is very high layer count boards. The number
one obstacle for high speed digital applications is the high layer
count stack-up that encourages OEMs to source board materials that
are process friendly. For high speed digital applications, the high
frequency materials will be separated from the standard FR4 lower
frequency layers. This leads to multiple lamination cycles.
Fabricators prefer to press laminates relatively quickly at
conventional epoxy pressing temperatures below 350.degree. F.
(177.degree. C.) and have scaled their pressing capacity so that it
is not a bottleneck in the entire printed circuit board fabrication
process. Thus FR-4 is a material of choice. However, increasing
operating frequencies demand materials having lower loss
characteristics. Therefore, a composite that enables multilayer
lamination at epoxy processing temperatures that has a minimum
component of a hydrocarbon resin is especially desirable.
[0009] Disclosed in this invention is a fluoropolymer coated
fiberglass composite that is used as the component to deliver low
signal loss properties. The fluoropolymer coated fiberglass
composite is then surface treated to enable it to bond to other
surfaces. Surface treatment is conducted on the nanometer scale in
order to maintain the desirable bulk properties of the
fluoropolymer. A thin layer of a thermosetting resin which may or
may not contain a ceramic filler (refer to FIG. 1) is then applied
to the surfaces of the chemically modified sheet of fluoropolymer
coated glass. Although the thermosetting resin represents a
compromise to the otherwise good electric properties of the PTFE
coated fiberglass, the thermoset enables the manufacture of a
multilayer laminate at conventional epoxy processing temperatures.
The thermosetting resin is partially cured (B-staged) during the
application of the thermoset onto a fluoropolymer composite
comprising a substrate selected from woven fabric, non-woven or a
polymeric film. The electrical properties of the resulting prepreg
is then determined by the ratio of the coated thermosetting resin
to the fluoropolymer coated fiberglass starting material. It is
preferred to limit the amount of thermosetting resin to just enough
to fill the spaces between the copper traces of the inner layers
and still obtain a good bond.
SUMMARY OF THE INVENTION
[0010] In one aspect, the present invention relates to a process
for fabricating a low loss multilayer printed circuit board using a
bonding ply comprising a fluoropolymer substrate and a
thermosetting adhesive composition. The fluoropolymer composite
comprises at least one fluoropolymer and a substrate selected from
woven fabrics, nonwoven fabrics and polymeric films.
[0011] In another aspect, the invention relates to a multilayer
printed circuit board comprising a plurality of printed circuit
board layers bonded together by means of the same bonding ply.
[0012] In yet another aspect, the invention relates to a
composition comprising a fluoropolymer composite comprising at
least one fluoropolymer and a substrate selected from woven
fabrics, nonwoven fabrics and polymeric films; and a thermosetting
adhesive composition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG.1 shows a schematic of the bond ply comprising
fiberglass, PTFE, and a thermosetting resin adhesive layer.
[0014] FIG.2 is a microsection showing the gap filling ability of a
bond ply (prepreg or bonding ply) comprised of 7628 style
fiberglass, ceramic, PTFE, and an thermosetting adhesive layer, to
fill signal traces in a hybrid multilayer.
[0015] FIG.3 is a microsection showing the gap filling ability of a
bond ply comprised of 7628 style fiberglass, ceramic, PTFE, and an
thermosetting adhesive layer, to fill signal traces in a hybrid
multilayer.
[0016] FIG.4 is a microsection showing the gap filling ability of a
bond ply comprised of 106 style fiberglass, ceramic, PTFE, and an
thermosetting adhesive layer, to fill signal traces in a hybrid
multilayer.
[0017] FIG.5 shows a schematic of a laminate core material
comprising fiberglass, PTFE, a thermosetting resin adhesive layer,
and copper cladding.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The present invention relates to a process for fabricating a
low loss multilayer printed circuit board. The process comprises
laminating together a plurality of printed circuit board layers by
means of at least one thermosetting adhesive-coated fluoropolymer
composite bonding ply. The bonding ply comprises a fluoropolymer
composite and a thermosetting adhesive composition; the
fluoropolymer composite comprises at least one fluoropolymer and a
substrate selected from woven fabrics, nonwoven fabrics and
films.
[0019] PTFE copper clad laminate suppliers currently sell
composites consisting of PTFE and either fiberglass or chopped
fiber. Woven fiberglass is preferably coated with PTFE at
700.degree. F. (371.degree. C.) to a desired thickness. Generally,
multiple coating passes are necessary to sequentially build layers
of PTFE such that a composite is obtained having the desired
thickness. The coated fiberglass is then sandwiched between copper
to form a composite consisting of a component that is electrically
conductive (the copper) and a component that is not
(PTFE/fiberglass).
[0020] Disclosed herein is a process that enables circuit board
fabricators to connect multiple layers of fluoropolymer-based
substrates together at reasonable fabrication temperatures
(.congruent.350.degree. F./177.degree. C.). The invention disclosed
herein is a hybrid composite that has the advantages of PTFE but
can be processed like a low temperature thermoset. FIG. 1 shows a
low signal loss microwave circuit bonding ply that can be used to
connect two double sided circuit boards (PTFE/fiberglass double
sided circuits). The thermosetting resin (adhesive) can be thought
of as the adhesive that holds the printed circuit boards together.
During epoxy lamination, for example, the printed circuit boards
can be withdrawn from a press rapidly after holding at their curing
temperature and placed in a cooling press.
[0021] The reinforced first phase (fluoropolymer composite) can be
prepared by impregnating, for example, woven fiberglass in a roll
to roll fashion using a dip-coating process or a dual reverse roll
coating process. Sequential buildup facilitates the manufacturing
of the overall composite. Woven glass fabric is conveniently
impregnated with PTFE dispersion or a common fluoropolymer aqueous
dispersion in a multi-pass process to a desired thickness or build
weight. Coating is continued until a homogenous sheet is formed
where the glass fabric may or may not be completely coated. Coating
could be a single pass or a multiple pass process.
[0022] It is a preferred embodiment of this invention that the
particulate filled resin be cast onto a substrate. The substrate
may or may not be a reinforcement. Suitable substrates include:
woven or non-woven fabrics; crossplies of unidirectional tape; a
polymeric film; or a metallic film. Metallic films include copper,
aluminum, and the various grades of steel. Polymeric films include
Kapton.RTM. (available from Dupont), and Upilex.RTM. (available
from UBE industries), a polyimide based on biphenyltetracarboxylic
dianhydride and either of p-phenylenediamine or
4,4'diaminodiphenylether. Woven fabrics can be prepared from glass
filaments or filaments based on various polymers. Suitable organic
polymeric fibers consist of the following: PTFE or other
fluoropolymer fibers; polyaramides such as Teijin's Technora based
on p-phenylenediamine and 3,4'-diaminodiphenylether, meta aramids
such as Nomex.RTM. based on poly(m-phenyleneisophthalamide); liquid
crystalline polyesters such as those based on hydroxynapthoic acid
and hydroxybenzoic acid; polyetheretherketones (PEEK.RTM.,
available from Victrex USA); polybenzoxazole (PBO, available from
Toyobo); and polyimides. These polymeric fibers can be used to make
woven fabrics or they can be chopped or pulped and used to make
non-woven fabrics. In the preparation of non-woven fabrics, blends
of different fibers might be used, or blends containing chopped
glass fiber can be used. Non-woven fabric has the advantage that
very thin laminates can be prepared. Because the fibers are random,
improved drilled holes can be obtained, regardless of the drilling
technique, laser or mechanical. Low in-plane CTE results in
exceptional layer to layer registration. The non-woven fabric can
be coated roll to roll in a typical dipcoating process or
alternatively staple-pulped fiber can be added to an aqueous PTFE
dispersion and coated onto a release substrate. In another
embodiment, a fluoropolymer coating can be applied to the fabric by
hot roll laminating a fluoropolymer film or a fluoropolymer skived
material into the fabric thus eliminating the need for multiple
coating passes. The film may or may not contain a ceramic
filler.
[0023] Woven glass reinforced composites could be prepared from the
following glass styles (E, D, S, NE), or mixtures thereof. Newly
developed NE glass styles available from Nittobo (Japan) have lower
loss characteristics but have a cost disadvantage. Glass fabric
based on 4-6 micron filaments are preferred from a drilling
perspective. Typical glass styles that are preferred include: 106,
1080, 2112, 2113, 2116, and 7628. For laser drilling applications
the smaller diameter based glass fabrics are preferred.
[0024] Woven glass fabrics are particularly suitable as substrates
for the fluoropolymer composite. Examples of such woven glass
include 7628, 1080, or 106 style glasses with a 508 heat cleaned
finish produced by Hexcel Schwebel.
[0025] Various fluoropolymers can be used to prepare the reinforced
first phase. Polytetrafluoroethylene (PTFE) or modified
polytetrafluoroethylene are well known to those skilled in the art.
Modified PTFE contains from 0.01% to 15% of a comonomer which
enable the particles to fuse better into a continuous film. PTFE is
typically modified with a small quantity of a fluorinated alkyl
vinyl ether, vinylidene fluoride, hexafluoropropylene,
chlorotrifluoroethylene, and the like. High level of modification
leads to polymers such as PFA poly(perfluorinatedalkylvinyle-
ther-tetrafluoroethylene) or FEP
poly(perfluorinatedtetrafluoroethylene-he- xafluoropropylene).
Other fluoropolymers which may serve as a dielectric include:
polychlorotrifluoroethylene; copolymers of chlorotrifluoroethylene
with vinylidene fluoride, ethylene, tetrafluoroethylene, and the
like; polyvinylfluoride; polyvinylidenefluoride; and copolymers or
terpolymers of vinylidene fluoride with TFE, HFP, and the like; and
copolymers containing fluorinated alkylvinylethers. Other
fluorinated, non-fluorinated, or partially fluorinated monomers
that might be used to manufacture a copolymer or terpolymer with
the previously described monomers might include: perfluorinated
dioxozoles or alkyl substituted dioxozoles; perfluorinated or
partially fluorinated butadienes; vinylesters; alkylvinyl ethers;
and the like. Hydrogenated fluorocarbons from C2-C8 are also
envisioned. These would include trifluroethylene,
hexafluoroisobutene, and the like. Fluoroelastomers including the
following are also envisioned: HFP with VDF; HFP, VDF, TFE
copolymers; TFE-perfluorinated alkylvinylether copolymers; TFE
copolymers with hydrocarbon comonomers such as propylene; and TFE,
propylene, and vinylidene fluoride terpolymers. Fluoroelastomers
can be cured using the following crosslinking agents: diamines
(hexamethylenediamine); a bisphenol cure system
(hexafluroorisopropylidenediphenol); peroxide
(2,5-dimethyl-2,5-di-t-butyl-peroxyhexane); any base that can act
as a dinucleophile.
[0026] Fluoropolymer dispersions that (1) readily rewet (2) are
available at low cost and (3) have low dielectric loss
characteristics are preferred. Aqueous dispersions of
fluoropolymers can contain a particle size from 1 nanometer to 1000
nanometers. The particle size of the fluoropolymer dispersion is
not important as long as the substrate can be well impregnated.
Microemulsions or blends of conventional fluoropolymer dispersions
with aqueous microemulsions are also suitable. The fluoropolymer
component could also be coated from a solvent vehicle onto the
reinforcement.
[0027] Although it is embodied that the reinforced core first
component comprise a fluoropolymer, the first component could be
comprised of a hydrocarbon polymer that could benefit from an
adhesive layer that could improve the performance of the
hydrocarbon resin alone. Cured elastomers such as polybutadiene,
for example, are known to have poor adhesive properties and would
benefit from a second layer of an adhesive phase. The rubber may be
any natural or synthetic rubber or a combination thereof.
Generally, the rubber may be any saturated or unsaturated
polyalkylene rubber made up of ethylene, one or more alkenes with
3-8 carbon atoms, for instance, propylene and/or 1-butene, and, if
desired, one or more polyethylenically unsaturated compounds with
non-conjugated double bonds, for instance, 1,4-hexadiene,
dicyclopentadiene, 5-methylene-2-norbomene,
5-ethylidene-2-norbornene and 5-isopropylidene-2-norbornene. The
rubber can therefore be any suitable natural rubber, synthetic
polyisoprene, any of the neoprenes,(polychloroprene),
styrene-butadiene rubbers (SBR), acrylonitrile-butadiene rubbers
(NBR), acrylonitrile-butadiene-styrene polymers (ABS) high
molecular weight olefin polymers with or without other monomers or
polymers such as butyl rubber and cis- and trans-polybutadienes,
bromobutyl rubber, chlorobutyl rubber, ethylene propylene rubbers,
nitrile elastomers, polyacrylic rubber, polysulfide polymers,
silicone elastomers, poly- and copolyesters, ethylene acrylic
elastomers, vinylacetate ethylene copolymers, or chlorinated or
chlorosulfonated polyethylenes, or a mixtures thereof. The rubber
may also contain a ceramic filler.
[0028] It is envisioned that such a first phase could comprise a
ceramic, fused silica for example, a reinforcement, woven
fiberglass for example, and a cured elastomer resin system,
containing high and low molecule weight polymers comprised of
butadiene, isoprene, neoprene, or styrene. The second adhesive
component then might comprise a polymeric resin system known to
have better adhesive properties or better flow properties. This
second adhesive component might include an epoxy, a cyanate ester,
or any number of the various thermosetting resin systems known to
those skilled in the art.
[0029] The surface of the fluoropolymer composite or the first
phase composite can then be treated before applying the
thermosetting adhesive composition to facilitate bonding
therebetween. Etching techniques for modifying the surface of a
fluoropolymer are known in the art. These include etching by:
sodium ammonia etch, radiation, electron beam, sodium naphthalene
etch, plasma using hydrogen, argon, nitrogen, carbon tetrafluoride
gases, and the like. Once the surface of the first phase is
treated, a thermosetting resin can be applied by conventional
coating methods. Depending on the amount of filler incorporated
into the reinforced first phase, surface treatment may not be
necessary to obtain good adhesion to the adhesive layer. It is
known to those skilled in the art that laminates having high
ceramic loadings that have drilled holes may not need surface
treatment before plating. The second phase is typically coated
simultaneously onto both sides of the fluoropolymer composite using
two reverse roll treaters, one per side. The second phase is
typically prepared by driving off the solvents used to dissolve the
thermosetting resin. The thermosetting resin is applied as a flat
continuous film on the surface of the fluoropolymer impregnated
reinforced sheet. Although it is preferred that the second
component be a thermosetting resin processible at low temperatures,
deposition of a thermoplastic layer onto the first component is
also envisioned.
[0030] The thermosetting component is preferably a
non-fluoropolymer but a thermosetting fluoropolymer is also
envisioned. The thermosetting adhesive component should have a
glass transition of at least 100.degree. C. or a glass transition
that is very difficult to detect by common techniques such as DMA
or TMA, or a CTE that results in a total (x, y, and z) coefficient
of thermal expansion in the unreinforced state of around 50-100 ppm
over the temperature range 50-300.degree. C., although less than 50
ppm would be preferred.
[0031] Typical thermosetting resin systems that could be used
include: epoxies (phenol epoxy novolacs; cyclopentadiene based
epoxies; brominated epoxies; diamine cured epoxy resin systems
(diaminodiphenylsulfone); trisepoxies; multifunctional epoxies;
styrene-maleic anhydride copolymers cured with epoxies or
polyamines; norbomene-maleic anhydride copolymers cured with
epoxies or polyamines; bicyclic alkane compounds of the general
structure bicyclo[x.y.z.]alkane-anhydride copolymers cured with
epoxies; cyanate ester resins such as those based on bisphenol A or
novolac resins; cyanate ester resins cured with epoxies;
polynorbomene cured with a free radical generator; polynorbomene
blends containing, for example, any combination of polybutadiene or
polyisoprene; free radically cured polybutadiene of varying
molecular weights with optionally polyisoprene; acetylene
functionalized polyimide; functionalized polyphenylene oxide and
blends of functionalized PPO with epoxies; bis-triazine resin
systems with the optional addition of epoxies; multifunctional
aziridines; poly(bismaleimides), specifically bismaleimides based
on diaminodiphenylmethane; and bismaleimides cured with
diallylbisphenol A or other bisallylphenyl compounds; norbornene
terminated polyimides, poly(bis phenylcyclobutane); free radically
cured unsaturated polyesters; and the like. Other non fluorinated
adhesive layers could also include: polymethylvinylether;
polyvinylpyrrolidone; polybutadiene; copolymers of polybutadiene
and styrene; elastomers containing any combinations of butadiene,
isoprene, styrene, or neoprene, elastomers of ethylene and
propylene; elastomers of acrylonitrile and butadiene; and the like.
The thermosetting resin system does not include lightly crosslinked
pressure sensitive adhesives which have a low glass transition
temperature. The thermosetting resin can be applied immediately
following the preparation of the first substrate in a pseudo
one-step process or it can be applied at any time thereafter.
[0032] The adhesive layer could also include a fluorelastomer.
Fluoroelastomers include the following: copolymers of vinylidene
fluoride and hexafluoropropylene; copolymers of
hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene;
copolymers of vinylidene fluoride and perfluoroalkyl vinylethers
with or without tetrafluoroethylene; copolymers of
tetrafluoroethylene with propylene; copolymers of
tetrafluoroethylene with perfluoroalkylvinylethers; a terpolymer of
propylene, vinylidene fluoride, and tetrafluoroethylene.
Fluoroelastomers can be cured using the following crosslinking
agents: diamines (hexamethylenediamine); a bisphenol cure system
(hexafluroorisopropyliden- ediphenol); peroxide
(2,5-dimethyl-2,5-dit-butyl-peroxyhexane); any base that can act as
a dinucleophile. In some cases it might be preferred to incorporate
a cure site monomer into the polymer backbone to promote curing.
These might include halogen containing olefins such as
1-bromo-2,2-difluoroethylene or 4-bromo-3,3,4,4-tetrafluoro-butene.
Other cure site monomers might include nitrile containing
vinylethers and hydrogen containing olefins
[0033] The thermosetting resin may optionally contain a flame
retardant. Brominated aromatics can be readily used including:
brominated epxoy resins; glycidyl ethers of brominated bisphenol A;
ethylene bistertrabromophthalal imide; tetradecabromo diphenoxy
benzene; pentabromodiphenylether; brominated trimethylphenyl
indane; pentrabromobenzylacrylate; poly pentabromobenzylacrylate;
2,4,6-tris(tribromophenoxy)-1,3,5-triazine; oligomeric brominated
polycarbonate; antimony oxide; phosphate esters; brominated
phosphate ester compounds; and the like.
[0034] Either the thermosetting resin adhesive component or the
reinforced first phase or both may optionally contain any one or
combination of a number of fillers. Particulate fillers are
typically polymeric, inorganic, ceramic, or organometallic. Fillers
are used to modify the electrical, thermal, improve the dimensional
stability of the laminate, and reduce cost. It is well known that
the addition of various fillers will reduce the coefficient of
thermal expansion of the composite, a reduction in the z axis being
highly desirable for the reliability of plated through holes. X-Y
CTE reduction enables smaller copper pads to be used and less layer
to layer miss-registration.
[0035] In many cases, particulate fillers are added to tailor the
dielectric constant of the composite. Ceramic fillers typically
include any one of the following: quartz; alumina; titanium
dioxide; strontium titanate; barium titanate; alumina; colloidal,
or crystalline silica; chopped glass fiber; magnesia; aluminum
silicate (kaolin); steatite; zircon; quartz; boron nitride; silicon
nitride; aluminum nitride; silicon carbide; talc; beryllia; barium
titanate; mica; hollow or solid glass spheres. However, at times it
is advantageous to add polymeric fillers available as powders
including PTFE, polyetherketones, polyetheretherketones,
polyphenylenesulfide, polyethersufone, polyimide, polyester, liquid
crystalline polyester, polyamide, polyesteramide, polybutadiene
rubber, and other elastomeric materials which might include
butadiene, isoprene, neoprene, or dicyclopentadiene. Low loss
fillers that can be readily dispersed in a solvent born matrix are
preferred. For aqueous dispersions, small particle powders are
preferred.
[0036] The introduction of particulate fillers, particularly
inorganic fillers, into a printed circuit board laminate is not
without its drawbacks. The fillers introduce another interface into
the composite that can be a source of moisture absorption leading
to blistering and delamination upon exposure of the board to wet
chemistry steps (print and etch), followed by exposure to higher
temperatures during sweat soldering or hot air solder leveling. The
proximity of the filler to the glass or polymeric reinforcement may
lead to a weak boundary region between interfaces leading to a
laminate that is susceptible to delamination, blistering, or the
plating of unwanted metals. In addition, the ceramics generally do
more damage to a mechanical drill bit during the preparation of
plated through holes. This exposure of new ceramic surface area
during mechanical drilling might also be a source of failure. It
has been previously disclosed in the art to pre-coat the surface of
the particulate with a hydrophobic coating to improve the moisture
resistance of the resulting composite which is also claimed to
improve the adhesion of the particle to the matrix materials. (U.S.
Pat. Nos. 5,024,871, 4,849,284, and 5,149,590). The disclosed
examples specifically teach the use of hydrophobic coatings
consisting of either silanes, zirconates, or titanates, all well
known inorganic coupling compounds. According to prior art, in a
separate step, the particulate is precoated and then the precoated
particle can be further formulated, extruded, or further processed
in a separate step. Depending on whether the filler is added to a
water born system or a solvent born thermosetting system, there use
of a hydrophic surface coating may or may not be required. Other
technologies are available that eliminate the need for a
hydrophobic coating such as an organosilane.
[0037] The dielectric properties will consequently be a combination
of the thermosetting component and the thermoplastic component.
Therefore it is preferred to limit the thermosetting component to
just a sufficient quantity to accomplish bonding of the various
layers or encapsulation of copper or another substrate. Because an
epoxy, for example, has a substantially worse dielectric loss, it
is preferred to limit its use. The preferred embodiment includes
applying a 0.1 to a 0.7 mil dry layer of the thermosetting resin
onto the surface of the fluoropolymer coated glass composite.
Because the thermosetting layer is preferably thin, inorganic or
organic fillers should have a sufficiently low particle size to
yield a homogeneous film. The filler should be less than 50 microns
in size, preferably less than 25 microns, and most preferred, less
than 10 microns. The filler should be less than 80% by weight of
the combined filler and thermosetting resin total dry weight,
preferably from 10-60%, and most preferred from 30-50%. Too high a
filler content is difficult to coat and leads to poor adhesion
between the layers. Too low a filler content leads to less
dimensional stability, higher cost, and in some cases higher loss.
The same considerations are true for ceramics incorporated into the
fluoropolymer reinforced composite substrate. The preferred ceramic
loading is 10-70 wt %.
[0038] The thermosetting resin composition and the fluoropolymer
dispersion can be coated using a number of different methods. The
resin compositions can be applied to the carrier or substrate using
spray coating, dipcoating, reverse roll coating, gravure coating,
metering rod coating, pad coating, or any combination of the above.
In the case of the fluoropolymer component, the preferred method is
to dipcoat the reinforcement into a resin composition and using a
metering rod control the amount of pickup of the resin composition
onto the carrier or reinforcement. In the case of the thermosetting
resin system, it can be metered on by a Mayer rod after dipcoating
the fluorpolymer sheet into a resin bath or it can be transferred
coated using a dual reverse roll controlled gap setup.
[0039] The weight ratio of the surface coated thermosetting
hydrocarbon resin to the reinforced core is preferably 1:1 to 1 to
50. The core is defined as the first phase composite comprised of
the substrate and the polymeric resin system and optionally a
filler. It is more preferred that the surface coated thermosetting
resin have a weight ratio of 1:2 to 1:20 to the reinforced core. It
is most preferred that the surface coated thermosetting resin have
a weight ratio of 1:3 to 1:10. The most preferred ratio of
thermosetting resin surface coating to the reinforced core will
vary depending on the low loss characteristics of the epoxy, the
thickness of the copper, the degree to which the copper is etched
yielding a requirement for a volume of space that must be filled by
the flowing thermosetting component, and the amount and type of
ceramic that may or may not be added to the thermosetting resin
composition. The previously described weight ratios take into
consideration any ceramic filled that would be added to the
thermosetting resin composition. Although ceramic might also be
added to the core material, the weight ratios assume the total
weight of the core, regardless of the core is comprised of a resin,
a reinforcement, or a filler.
[0040] In an alternative embodiment of the invention, the bondply
can be laid up with copper and pressed in a conventional FR-4
copper clad lamination press. A single bond ply can be sandwiched
between coppers to make a single laminate core, as shown in FIG. 5.
The choice of copper styles could include rolled or
electrodeposited. The copper could be zinc free or zinc containing,
low profile, very low profile, or ultralow profile. Copper could
also be sputtered onto the faces of the adhesive layer to obtain
very thin layers of copper. Other copper styles could be high
temperature elongation or reverse treated. Alternatively, an omega
foil nickel resist could be applied.
[0041] In the preparation of a copper clad laminated using this
invention it is envisioned that appreciably less thermosetting
adhesive is necessary. As a bond ply, the thermoset needs to flow
and encapsulate 0.5, 1.0, and 2.0 ounce circuitry of varying
density. As a laminate core material, the thermoset need only fill
the dendritic surface area of electrodeposited copper, for example.
Depending on the topography of the metallization layer, very low
profile copper or rolled copper would need little thermosetting
adhesive to promote bonding between the layers.
[0042] This invention also enables the incorporation of UV dyes
into a fluoropolymer based printed circuit board. UV dyes are
typically incorporated into FR4 epoxy formulations to enable
automated optical inspection (AOI). Many of these dyes would not be
stable at the processing temperatures of many fluoropolymers.
However, the UV dye can be added as an additive to the lower
temperature thermosetting adhesive composition.
[0043] Essentially any printed circuit boards may be laminated
together using a bonding ply according to the present invention. In
particular, printed circuit boards composed of epoxy fiberglass
composites, such as FR-4; or laminates comprised of any of the
following: PTFE; cyanate ester; polyimide; styrene; maleic
anhydride; butadiene; bismaleimide; isoprene; neoprene; polyester,
and others known to those skilled in the art would be suitable.
EXAMPLES
Example 1
[0044] Preparation of a Fluoropolymer Coated Woven Glass Fabric
[0045] 7628 style woven fiberglass with a 508 heat cleaned finish
(available from Hexcel Schwebel) was further heat cleaned in a 3
zone vertical coating tower at 7.5 feet/min. The temperatures in
the 3 zones were as follows: 121.degree. C., 204.degree. C., and
418.degree. C. A 5% solution of 3-aminopropyltriethoxysilane in
water was then applied to the fabric using a smooth metering rod.
The fabric was fed into a dip basin and the pickup was controlled
by the smooth metering rod on each side of the fabric. Oven
temperatures were: 121.degree. C., 177.degree. C., and 260.degree.
C. Coating speed was 5 feet/min. The fabric was then dipcoated with
a 1.45 specific gravity aqueous dispersion of PTFE to which was
added 5% based on PTFE solids of 3-aminopropyltriethoxysilane. The
PTFE aqueous dispersion was coated using two sets of smooth bars to
apply the dispersion. Oven temperatures were as follows:
121.degree. C., 204.degree. C., and 391.degree. C. Coating speed
was 3 feet/min. The fabric was then coated repeatedly using a
multiple pass process with a ceramic filled aqueous PTFE
dispersion. The ceramic dispersion contained titanium dioxide,
PTFE, 3-aminopropyltriethoxysilane, a ceramic dispersing agent, a
non-ionic surfactant, a strong organic acid, and a perfluorinated
poly(tetrafluoroethylene-alkylvinylether) copolymer. Coating speed
varied from 4-8 feet/min. Oven temperatures were 93.degree. C.,
204.degree. C., and 399-407.degree. C. Coating speeds were from 3-8
feet/min. The 7628-508 style fiberglass was coated to a final
weight of 0.95 lbs/yd.sup.2 to yield a smooth sheet. The sheet was
obtained on a roll and was treated with a sodium ammonia etching
compound to activate the surfaces.
Example 2
[0046] Preparation of an Epoxy Coated Fluoropolymer Impregnated
Woven Glass Fabric
[0047] An epoxy formulation was prepared by blending a catalyst
composition with an epoxy resin formulation. The catalyst
composition was prepared by mixing 1.98 kg of methylether ketone
solvent, 0.184 kg of a non-ionic surfactant (Pluronic L92 available
from the BASF Corporation), and 0.0369 kg of manganese
2-ethylhexanoate (available from OMG Americas). The epoxy
formulation was prepared by blending the following: 40.147 kg of
Dow 538-A80 (a glycidyl ether of brominated bisphenol A available
from the Dow Chemical Company), 38.87 kg of BT2110 (a
bismaleimide/bisphenol A dicyanate oligomer available from the
Mitsubishi Gas Chemical), 13.9337 kg of DER560 (a brominated epoxy
resin available from the Dow Chemical Company), 5.379 kg of Shell
Epon 55-BH-30 (a bisphenol A based epoxy available from the Shell
Oil Company), 12.16 kg of dimethylformamide solvent, 9.0 kg of
methyletherketone, 9.0 kg of propyleneglycol methyl ether acetate,
and 5.7 kg of Phenoxy PKHS-40 (a poly(hydroxyether) available from
Inchem Corp). Prior to use, 136 kg of the epoxy formulation was
mixed with 2.20 kg of the catalyst solution.
[0048] The thermosetting resin solution was coated onto both sides
of the fluoropolymer coated 7628 fabric using a Litztler dual
reverse roll coater. The thermoset was applied using a 13 mil gap
between the two reverse rolls. The Litzler had two oven sections.
Zone 1 was 90.degree. C. while Zone 2 was 165.degree. C. The
Litzler is a vertical treater with one 7.5 meter length zone
extending vertically connected to another 7.5 meter zone that
returns to the base of the treater. The thermoset was coated at 2.5
meters/minutes resulting in a 3 minute dwell time in each of the
high and low temperature ovens. The dried prepreg had a final 10
mil thickness, 9 mil from the base fluoropolymer coated fabric, and
0.5 mil per side of the thermosetting resin.
[0049] 3 plies of the prepreg were stacked up and pressed at
176.6.degree. C. for 10 minutes at 300 psi. The prepreg was weighed
before and after pressing. The resin that squeezed out of the press
was collected and weighed. 3.5% resin flowout was obtained.
[0050] Two plies of the material were sandwiched between 2 pieces
of 1 oz. zinc free foil and pressed between skived PTFE sheets that
was used for release purposes. The press conditions were 176.6C for
2 hours at 300 psi. The copper cladding was etched off and the
samples were dried. The following electrical properties were
obtained: dielectric constant was 3.50 (IPC-TM 650 2.5.5, 1 MHz),
dielectric loss of 0.0047 (IPC-TM 650 2.5.5, 1 MHz), dielectric
constant at 10 GHz of 3.41 (EPC TM 650 2.5.5.5), dielectric loss at
10 GHz of 0.0055 (IPC TM 650 2.5.5.5). Peel strength was 13.6
lbs/linear inch (IPC-TM 650 2.4.8). Moisture absorption was 0.28%
after 24 hour immersion. Moisture absorption after 1 hour of
pressure cooker exposure was 0.84%. This example demonstrates that
very attractive electrical properties can be obtained even in the
absence of a ceramic filler that might be added to the
thermosetting resin to offset the less desirable loss tangent
properties of the thermosetting resin itself.
Example 3
[0051] Preparation of a Hybrid 4 Layer Mutlilayer Circuit Board
Using the Bond Ply from Example 2.
[0052] The inner layers of (1) a 21 mil PTFE coated fiberglass
laminate cladded on both sides with 0.5 oz copper and (2) a 48 mil
FR-4 epoxy laminate cladded on both sides with 0.5 oz copper were
patterned and etched according to the following (subtractive
process) standard printed circuit board procedures: punch, holes
drilled, hole deburr, scrub & coat inner layers with
photoimaging material, expose inner layers, develop inner layers,
and strip inner layers. The inner layers of the FR-4 and PTFE
fiberglass were then treated with metal oxide, baked, and laminated
together using the multilayer bond ply prepeg from Example 2. Press
conditions were 176.degree. C. for 2 hours at 300 psi. The 4 layer
multilayer was then treated with the following standard outerlayer
print and etch processes: drilled, deburred, baked, treated for
etchback, sodium napthalene etch, electroless plated, photomaterial
lamination, expose outer layers, develop outer layers, pattern
plate copper and then tin, resist strip, and etch outer layers. A
second imaging step was done as follows: bake dry film and apply,
coat outer layers, expose outer layers, develop outer layers,
tin/lead strip, strip resist, bake before reflow, solder reflow,
coat liquid photoimageable soldermask, expose solder mask, develop
soldermask, and UV cure solder mask.
[0053] Examples of the gap filling ability of the multilayer
prepreg bond ply from Example 2 can be found in FIGS. 2 and 3.
FIGS. 2 and 3 confirm the desired gap filling properties of the
bond ply. Microsectioning of the hybrid board did not reveal the
prescence of any voids between the copper circuitry. This example
demonstrates that multilayer hybrid boards can be prepared at
conventional thermosetting resin conditions using a
fluoropolymer-fiberglass-epoxy resin composite B-staged bond ply as
the adhesive layer.
Example 4
[0054] Preparation of a Hybrid 4 Layer Mutlilayer Circuit Board
Using a 106 Style Fiberglass Composite Bond Ply
[0055] Examples 1 and 2 were repeated with the exception that the
base PTFE composite was a PTFE coated 106 style woven fiberglass
that was coated in a multi pass process to a 60% PTFE content based
on the total composite (1.45 mil thickness). The material was then
etched using a sodium ammonia etching process. Thermosetting resin
was applied to both sides using the previously described
procedures. The gap between the reverse rolls was 10 mil that
yielded a product having a thickness of approximately 2.5 mils. A 4
layer multilayer was made using the procedure described in Example
3. The gap filling properties of the bond ply are shown in FIG. 4.
FIG. 4 confirms the desired gap filling of the bond ply. This
example also demonstrates that the invention disclosed herein is
applicable to very thin substrates.
Example 5
[0056] Preparation of a Fluoropolymer Impregnated Woven Fiberglass
Composite using a Talc filled Epoxy as the Bonding Layer
[0057] Example 2 was repeated except that 86.5 kg of talc (Benwood
talc available from Zemex Fabi Benwood, LLC) is dispersed into the
thermosetting resin formulation to reduce the impact of the
thermosetting resin on the dielectric loss properties of the final
laminate. The talc filled thermosetting resin solution is coated
onto the 7628 style fiberglass using the previously described
coating method. The talc filled bond ply is used as described in
Example 3 to make a 4 layer multilayer. The example demonstrates
that ceramics can be incorporated into the thermosetting resin
layer to reduce cost; x, y, and z coefficients of thermal
expansion; and dielectric loss properties.
Example 6
[0058] Preparation of a Fluoropolymer Coated Non-Woven Glass
Fabric
[0059] 1.5 mil non-woven polyaramide fabric (Thermount, available
from Dupont) made from pulped and/or staple Kevlar or Nomex fibers
is coated under low tension according to Example 1 to a 70% PTFE
resin content using a PTFE aqueous dispersion. The surface of the
composite is sodium naphthalene etched and coated with
thermosetting resin according to the process described in Example
2. A 4 layer multilayer is built using the procedure outlined in
Example 3. This examples demonstrates that a bond ply can be
prepared from a non-woven substrate that is suitable for high
density interconnect packages such as: multichip modules, ball grid
array packages, direct chip attach, and ultra fine lines and
spaces. This example further demonstrates that a substrate can be
produced that is well suited for laser drilling.
Example 7
[0060] Preparation of a Fluoropolymer Impregnated Non-Woven Glass
Fabric Surface Coated with a Talc filed Thermosetting Resin
[0061] Example 6 is repeated with the exception that the
thermosetting resin contains a ceramic filler, kaolin. This example
demonstrates that a ceramic filler can be used to reduce cost; x,
y, and z coefficients of thermal expansion; and dielectric loss
properties in high layer count multilayers and packages
incorporating fine lines and spaces (multichip modules, ball grid
array packages, and direct chip attach).
Example 8
[0062] Preparation of a Bond Ply using a Fiberglass Composite
Prepared using a Hot Roll Laminator
[0063] Example 4 is repeated with the exception that the 106 style
fiberglass is not fully impregnated with a PTFE dispersion. Two
separate 1.0 mil skived PTFE films are pressed onto the two sides
of a lightly PTFE coated 106 style fiberglass using a hot roll
laminator operating at 375C. A thermosetting resin is applied
according to the previously described procedures and a 4 layer
multilayer PWB is prepared. This example demonstrates that a more
cost effective method can be used to apply the PTFE component to
the reinforcing component of the bond ply.
Example 9
[0064] Preparation of a Ceramic Filled Bond Ply using a Fiberglass
Composite Prepared from a Hot Roll Laminator
[0065] Example 8 is repeated with the exception that the skived
PTFE contains a ceramic filler. This example demonstrates that a
ceramic filled PTFE film can be laminated onto a lightly coated
fiberglass to increase key properties in a cost efficient
manner.
Example 10
[0066] Preparation of a Bond Ply using a Non-woven Reinforcement
Prepared using a Hot Roll Laminator
[0067] Example 8 is repeated with the exception that a 1.5 mil film
of poly(perfluorinated alkylvinylether-tetrafluoroethylene
copolymer) is hot roll laminated into a non-woven polyaramide
fabric creating a flat substrate. The bond ply is manufactured by
sodium napthalene ething the sheet followed by application of the
thermosetting resin as previously described. The 4 layer multilayer
is prepared using the previously described procedures. This example
demonstrates that a non-woven reinforced fluoropolymer composite
can be prepared in a cost efficient manner by impregnating a
nonwoven fabric with a melt flowable fluorinated polymeric film
using a hot roll laminator.
Example 11
[0068] Preparation of a Bond Ply using a Non-Woven
Reinforcement
[0069] PBO staple and pulped fiber is added to a PTFE dispersion.
The filled dispersion is then dipcoated in a multipass process onto
a 5 mil polyimide carrier film using the temperature conditions
outlined in Example 1. The PTFE coated non-woven substrate is then
calendered to form a 2 mil flat sheet at 371.degree. C. using a
flame-heated hollow cylinder. The sheet is then consolidated from
the polyimide carrier film. The sheet is then surface treated using
a sodium naphthalene etching solution. The flat sheet is then
surface coated with the thermosetting resin composition from
Example 2. A 4 layer multilayer is built according to the procedure
of Example 3. This example demonstrates that a laser drillable
substrate containing PTFE can be prepared from a fiber filled PTFE
dispersion yielding a thin low loss composite having controlled x,
y, and z coefficient of thermal expansion values.
Example 12
[0070] Preparation of a Fluoropolymer Coated Non-Woven Fiber Glass
Fabric
[0071] Non-woven fiberglass, 0.007" and 0.015" thick respectively,
(available from Lydal Manning as Manninglas.RTM. styles 1201 and
1200 respectively) was coated under low tension according to
Example 1 to an 83 to 86% PTFE resin (available from I. E. DuPont)
content using a 1.400 specific gravity PTFE aqueous dispersion at 1
to 8 fpm using a smooth metering rod. A subsequent top coat of PFA
dispersion was coated onto the substrate using a 1.400 specific
gravity at 3-5 fpm to a finished resin content of 88-91%. The
surface of the composite is sodium naphthalene etched and coated
with thermosetting resin according to the process described in
Example 2. A 4 layer multilayer is prepared using the procedure
outlined in Example 3. This examples demonstrates that a bond ply
can be prepared from a non-woven substrate. That substrate has
ample "good" electrical resin added in much fewer manufacturing
steps. The non woven reinforecment is not a fiberglass matrix,
therefore no glass fiber window "voids" from the weaving process
exist which makes a woven product less homogeneous. This provides
for a more uniform product that is suitable for high density
interconnect packages such as: multichip modules, ball grid array
packages, direct chip attach, and ultra fine lines and spaces. This
example further demonstrates that a substrate can be produced that
is well suited for laser drilling.
Example 13
[0072] Preparation of a Fluoropolymer Impregnated Non-Woven Fiber
Glass Composite using a Talc Filled Epoxy as the Bonding Layer
[0073] Example 12 is repeated except that the thermosetting resin
of Example 5 is used to coat the non-woven substrate. The talc
filled bond ply is used as described in Example 3 to make a 4 layer
multilayer. The example demonstrates that ceramics can be
incorporated into the thermosetting resin layer to reduce cost; x,
y, and z coefficients of thermal expansion; and dielectric loss
properties. This example further demonstrates that a substrate can
be produced that is well suited for laser drilling.
Example 14
[0074] Preparation of a Ceramic Filled FluoropolyMer Coated
Non-Woven Fiber Glass Fabric
[0075] Non-woven fiberglass, 0.007" and 0.015" thick respectively,
(available from Lydal Manning as Manninglas.RTM. styles 1201 and
1200 respectively) was coated under low tension according to
Example 1. A 25 wt % loading of TiO.sub.2 (Available from SCM.
TIONA.RTM. RCS-9 rutile TiO.sub.2 slurry) and 25 wt % of SiO.sub.2
(available from ITC-SiO.sub.2 with 0.5% A-187 fluorosurfactant as a
surface treatment) was used by weight in a PFA (available from I.
E. DuPont) aqueous dispersion. The ceramic filled dispersion was
broken down with water to 1.400 specific gravity and coated from
0.5-2 fpm to achieve a total resin content of 80 to 90%. No top
coating and the abundance of ceramic obviates the need for the
etching process before the application of the thermosetting bonding
layer. A 4 layer multilayer is prepared using the procedure
outlined in Example 3. This examples demonstrates that a bond ply
can be prepared from a non-woven substrate that is suitable for
high density interconnect packages such as: multichip modules, ball
grid array packages, direct chip attach, and ultra fine lines and
spaces. This example further demonstrates that a substrate can be
produced that is well suited for laser drilling. This example
further demonstrates that with highly filled ceramic composites the
chemical etching process is not always required.
Example 15
[0076] Preparation of a Ceramic Filled Fluoropolymer Impregnated
Non-Woven Fiberglass Composite using a Talc filled Epoxy as the
Bonding Layer
[0077] Example 14 is repeated except that the thermosetting resin
of Example 5 is used to coat the non-woven base ply. The talc
filled bond ply is used as described in Example 3 to make a 4 layer
multilayer. The example demonstrates that ceramics can be
incorporated into the thermosetting resin layer to reduce cost; x,
y, and z coefficients of thermal expansion; and dielectric loss
properties. This example further demonstrates that a substrate can
be produced that is well suited for laser drilling.
* * * * *