U.S. patent application number 11/355715 was filed with the patent office on 2006-06-29 for circuit substrate material, circuits comprising the same, and method of manufacture thereof.
Invention is credited to Bruce G. Kosa, Vincent R. Landi, Murali Sethumadhavan.
Application Number | 20060141132 11/355715 |
Document ID | / |
Family ID | 32871727 |
Filed Date | 2006-06-29 |
United States Patent
Application |
20060141132 |
Kind Code |
A1 |
Sethumadhavan; Murali ; et
al. |
June 29, 2006 |
Circuit substrate material, circuits comprising the same, and
method of manufacture thereof
Abstract
An electrical circuit material having a conductive layer
disposed a substrate, wherein the substrate is formed from a
thermosetting composition comprising a polybutadiene or
polyisoprene resin; an optional, functionalized liquid
polybutadiene or polyisoprene resin; an optional butadiene- or
isoprene-containing copolymer; an optional low molecular weight
polymer; an optional curing agent; a cross-linking agent; a
particulate fluoropolymer; and about 20 to about 50 percent by
weight, based on the total weight of the thermosetting composition,
of a magnesium hydroxide having a low ionic content. Use of
magnesium hydroxide allows the composition to attain a high level
of flame retardancy without use of halogenated flame retardants,
while maintaining good moisture absorption and other physical
properties.
Inventors: |
Sethumadhavan; Murali;
(Shrewsbury, MA) ; Landi; Vincent R.; (Phoenix,
AZ) ; Kosa; Bruce G.; (Woodstock, CT) |
Correspondence
Address: |
CANTOR COLBURN LLP
55 Griffin Road South
Bloomfield
CT
06002
US
|
Family ID: |
32871727 |
Appl. No.: |
11/355715 |
Filed: |
February 16, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10700343 |
Nov 3, 2003 |
7022404 |
|
|
11355715 |
Feb 16, 2006 |
|
|
|
60423281 |
Nov 1, 2002 |
|
|
|
Current U.S.
Class: |
427/58 ;
428/209 |
Current CPC
Class: |
Y10T 428/249933
20150401; Y10T 428/31707 20150401; Y10T 428/24917 20150115; H05K
1/032 20130101; H05K 2201/0158 20130101; C08K 5/14 20130101; B32B
27/04 20130101; Y10T 428/25 20150115; H05K 2201/0212 20130101; Y10T
428/31605 20150401; Y10T 428/3154 20150401; C08L 27/12 20130101;
C08K 3/36 20130101; C08K 3/22 20130101; C08L 9/00 20130101; Y10T
428/31609 20150401; C08L 9/00 20130101; C08L 2666/04 20130101; H05K
2201/0209 20130101; H05K 2201/015 20130101; H05K 1/0373
20130101 |
Class at
Publication: |
427/058 ;
428/209 |
International
Class: |
B05D 5/12 20060101
B05D005/12 |
Claims
1. A method of making an electrical circuit substrate material, the
method comprising disposing onto a conductive layer a thermosetting
composition comprising a polybutadiene or polyisoprene resin; a
cross-linking agent; a particulate fluoropolymer; and about 20 to
about 50 percent by weight, based on the total weight of the
thermosetting composition, of a magnesium hydroxide having less
than about 1000 ppm of ionic contaminants; and curing the
thermosetting composition wherein the substrate has a UL-94 rating
of at least V-1.
2. The method of claim 1, wherein the thermosetting composition
further comprises a butadiene- or isoprene-containing
copolymer.
3. The method of claim 2, wherein the butadiene- or
isoprene-containing copolymer is an unsaturated butadiene- or
isoprene-containing copolymer.
4. The method of claim 3, wherein the volume to volume ratio of the
polybutadiene or polyisoprene resin to the unsaturated butadiene-
or isoprene-containing copolymer is between 1:9 and 9:1,
inclusive.
5. The method of claim 1, wherein the thermosetting composition
further comprises a curing agent.
6. The method of claim 5, wherein the curing agent is an organic
peroxide, a dicumyl peroxide, a di(2-tert-butylperoxyisopropyl)
benzene, a t-butylperbenzoate, a t-butylperoxy hexyne-3, or a
combination comprising one or more of the foregoing curing
agents.
7. The method of claim 1, wherein the thermosetting composition
further comprises a low molecular weight polymer.
8. The method of claim 1, wherein the thermosetting composition
further comprises a functionalized liquid polybutadiene or
polyisoprene resin.
9. The method of claim 1, wherein the cross-linking agent is
triallylisocyanurate, triallylcyanurate, diallyl phthalate, divinyl
benzene, a multifunctional acrylate monomer, or a combination
comprising one or more of the foregoing cross-linking agents.
10. The method of claim 1, wherein the particulate fluoropolymer is
a difluoroethylene polymer, a tetrafluoroethylene polymer, a
tetrafluoroethylene-hexafluoropropylene copolymer, a copolymer of
tetrafluoroethylene with fluorine-free ethylenic monomers, or a
combination comprising one or more of the foregoing particulate
fluoropolymers.
11. The method of claim 1, wherein the substrate has a moisture
absorption value less than about 0.2% and a UL-94 flammability
rating of V-0.
12. The method of claim 1, wherein the substrate has a dielectric
constant less than about 4.5 and a dielectric loss factor less than
about 0.01.
13. The method of claim 1, wherein the conductive layer is
copper.
14. The method of claim 1, wherein the thermosetting composition
further comprises a woven or non-woven glass web.
15. The electrical circuit material of claim 1, wherein the
magnesium hydroxide comprises less than about 500 ppm of metal.
16. The method of claim 1, wherein the thermosetting composition
further comprises a chlorine-containing flame retardant, a
bromine-containing flame retardant, or a combination comprising one
or more of the foregoing flame retardants.
17. The method of claim 1, wherein the magnesium hydroxide has an
average surface area of about 3 to about 12 meters squared per
gram.
18. The method of claim 1, wherein the magnesium hydroxide is
coated with an aminosilane.
19. The method of claim 1, further comprising a filler.
20. The method of claim 19, where the filler further comprises a
coupling agent.
21. The method of claim 19, where the coupling agent is a silane.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefits of U.S. Provisional
Patent Application Ser. No. 60/423,281 filed Nov. 1, 2002, which is
fully incorporated herein by reference.
BACKGROUND
[0002] This disclosure relates generally to a method of making
thermosetting compositions for use in electrical circuit materials
and the resulting products, and in particular to thermosetting
polybutadiene and polyisoprene circuit substrate materials.
[0003] As used herein, a circuit material is an article used in the
manufacture of circuits and multi-layer circuits, and includes
circuit laminates, bond plies, resin coated conductive layers, and
cover films. Circuit laminates, bond plies, resin coated conductive
layers, and cover films in turn are formed from dielectric
materials that can comprise a thermosetting or thermoplastic
polymer. The dielectric material in a bond ply, resin covered
conductive layer, or cover film may comprise a substantially
non-flowable dielectric material, i.e., one that softens or flows
during manufacture but not use of the circuit, whereas the
dielectric material in a circuit laminate (e.g., a dielectric
substrate) is designed to not soften or flow during manufacture or
use of the circuit or multi-layer circuit. Dielectric substrate
materials are further typically divided into two classes, flexible
and rigid. Flexible dielectric substrate materials generally tend
to be thinner and more bendable than the so-called rigid dielectric
materials, which typically comprise a fibrous web or other forms of
reinforcement, such as short or long fibers or fillers.
[0004] A circuit laminate as used herein refers to one or two
conductive layers fixedly attached to a dielectric substrate, which
is formed from a dielectric material. Patterning a conductive layer
of a laminate, e.g., by etching, provides a circuit. Multi-layer
circuits comprise a plurality of conductive layers, at least one of
which contains a conductive wiring pattern. Typically, multi-layer
circuits are formed by laminating one or more circuits together
using bond plies, and, in some cases, resin coated conductive
layers, in proper alignment using heat and/or pressure. The bond
plies are used to provide adhesion between circuits and/or between
a circuit and a conductive layer, or between two conductive layers.
In place of a conductive layer bonded to a circuit with a bond ply,
the multi-layer circuit may include a resin coated conductive layer
bonded directly to the outer layer of a circuit. In such
multi-layer structures, after lamination, known hole forming and
plating technologies may be used to produce useful electrical
pathways between conductive layers.
[0005] Polybutadiene and polyisoprene thermosetting materials have
been successfully employed as rigid electrical circuit substrates.
These materials have typically used halogenated, particularly
brominated, flame retardant additives to achieve the necessary
levels of flame retardancy. In recent years, brominated flame
retardants have come under scrutiny, such that certain of them will
be banned by January 2008. The remaining brominated flame
retardants will require special incineration/disposal procedures.
In light of the impending ban, manufacturers are placing additional
pressures upon suppliers to produce flame retardant additives that
are effective, yet that do not contain halogens.
[0006] The most commonly used alternative flame retardant additives
are phosphorous/nitrogen compounds. However, phosphorous/nitrogen
compounds possess high dielectric constants, loss factors, and
moisture absorption properties. These properties are adverse to
intended uses in applications such as the electronic industries,
automobile industries, and particularly in circuit boards and
related applications. Accordingly, there remains a need for
non-halogen containing flame retardant thermosetting compositions
that provide the desired flame retardant properties without
impairing physical properties such as electrical and moisture
absorption properties.
SUMMARY
[0007] The above discussed and other problems and deficiencies of
the prior art are overcome or alleviated by a substrate for an
electrical circuit material, wherein the substrate is formed from a
thermosetting composition comprising a polybutadiene or
polyisoprene resin; an optional, functionalized liquid
polybutadiene or polyisoprene resin; an optional butadiene- or
isoprene-containing copolymer; an optional low molecular weight
polymer; a cross-linking agent; a particulate fluoropolymer; and
about 20 to about 50 percent by weight, based on the total weight
of the thermosetting composition, of a magnesium hydroxide having
less than about 1000 ppm of ionic contaminants, and further wherein
the substrate has a UL-94 rating of at least V-1.
[0008] In another embodiment, an electrical circuit material
comprises a substrate and a layer of conductive metal disposed on
the substrate, wherein the substrate is formed from a thermosetting
composition comprising a polybutadiene or polyisoprene resin; an
optional, functionalized liquid polybutadiene or polyisoprene
resin; an optional butadiene- or isoprene-containing copolymer; an
optional low molecular weight polymer; a cross-linking agent; a
particulate fluoropolymer; and about 20 to about 50 percent by
weight, based on the total weight of the thermosetting composition,
of a magnesium hydroxide having a low ionic content, and further
wherein the substrate has a UL-94 rating of at least V-1.
[0009] Use of magnesium hydroxide in the thermosetting compositions
allows the substrate materials to achieve a desired flame
retardancy without use of brominated flame retardants, but does not
adversely affect properties such as dielectric constant or moisture
absorbance. The above-discussed and other features and advantages
will be appreciated and understood by those of ordinary skill in
the art from the following detailed description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Referring now to the drawings, wherein like elements are
numbered alike in the several FIGURES:
[0011] FIG. 1 is a schematic representation of a diclad circuit
material containing a woven web; and
[0012] FIG. 2 is a schematic representation of a circuit
material.
DETAILED DESCRIPTION
[0013] A thermosetting composition having particular utility as a
substrate for an electrical circuit material comprises a
thermosetting polybutadiene or polyisoprene resin system; about 20
to about 50 percent by weight, based on the total weight of the
composition, of magnesium hydroxide having a low ionic content; a
crosslinking agent; and a particulate fluoropolymer.
[0014] Use of magnesium hydroxide as a flame retardant agent allows
the circuit material to achieve the desired flame retardancy in the
absence of halogenated flame retardants, particularly brominated
flame retardants. Dielectric properties are also acceptable with
use of magnesium hydroxide. This result is particularly surprising
in view of the fact that magnesium hydroxide has a high dielectric
constant and the presence of such large amounts of magnesium
hydroxide would have been expected to greatly increase the
dielectric constant of the composition. However, the inventors
hereof have discovered that use of a particular polybutadiene or
polyisoprene thermosetting composition, together with about 20 to
about 50 percent by weight of a magnesium hydroxide having a low
ionic content, produces a thermosetting composition exhibiting
excellent flame retardancy, electrical and moisture resistance
properties.
[0015] A number of commercially available magnesium hydroxides are
suitable for use in the present thermosetting compositions, for
example those available under the trade name MAGNIFIN.RTM. from
Albemarle Corp. According to the product literature, MAGNIFIN.RTM.
H51V and MAGNIFIN.RTM. H10IV are magnesium hydroxides having a low
ionic content, and are treated (coated) with an aminosilane. Low
ionic content is herein defined as containing less than about 1,000
ppm, preferably less than about 500 ppm by weight of ionic
contaminants such as chloride ion. In addition, it is preferred
that the magnesium hydroxide has a low total metal content, herein
defined as less than about 500 ppm, preferably less than about 400
ppm, more preferably less than about 300 ppm by weight of metal
contaminants such as iron, aluminum, chromium, manganese, copper,
and the like. It is especially preferred that the amount of iron
oxide be limited to less than about 100 ppm, preferably less than
about 50 ppm. Other suitable magnesium hydroxides are commercially
available under the trade name MAGSHIELD from Martin Marietta
Corp., ZEROGEN from J. M. Huber Engineering materials, and FR20
from Dead Sea Bromine Group.
[0016] In addition, the particulate size of the magnesium hydroxide
can impact the electrical and flame retardant properties of the
substrate material. Preferably the magnesium hydroxide has an
average surface area (BET) of about 3 to about 12 square meters per
gram, preferably about 5 to about 10, and an average particle size
of about 0.1 to about 2 micrometers. The magnesium hydroxide
comprises about 20 to about 50 percent by weight of the total
thermosetting composition (i.e., resin system as described below,
curing agent, crosslinking agent, particulate fluoropolymer, and
magnesium hydroxide, but exclusive of any reinforcing glass web or
filler).
[0017] The magnesium hydroxide is used in combination with a
polybutadiene or polyisoprene thermosetting resin system comprising
(1) a polybutadiene or polyisoprene resin; (2) an optional,
functionalized liquid polybutadiene or polyisoprene resin; (3) an
optional butadiene- or isoprene-containing copolymer; and (4) an
optional low molecular weight polymer.
[0018] As a first component, the resin system comprises a
polybutadiene resin, a polyisoprene resin, or mixture thereof. The
polybutadiene or polyisoprene resins may be liquid or solid at room
temperature. Liquid resins may have a molecular weight greater than
about 5,000, but preferably have a molecular weight of less than
about 5,000 (most preferably between about 1,000 and about 3,000).
The preferably liquid (at room temperature) resin portion maintains
the viscosity of the composition at a manageable level during
processing to facilitate handling, and it also crosslinks during
cure. Polybutadiene and polyisoprene resins having at least 90%
1,2-addition by weight are preferred because they exhibit the
greatest crosslink density upon cure owing to the large number of
pendant vinyl groups available for crosslinking. High crosslink
densities are desirable because the products exhibit superior
performance in an electrochemical cell environment at elevated
temperatures. A preferred resin is B3000 resin, a low molecular
weight polybutadiene liquid resin having greater than 90 weight
percent (wt. %) 1,2-addition. B3000 resin is commercially available
from Nippon Soda Co., Ltd.
[0019] The resin system further optionally comprises a
functionalized liquid polybutadiene or polyisoprene resin. Examples
of appropriate functionalities for butadiene liquid resins include
but are not limited to epoxy, maleate, hydroxy, carboxyl and
methacrylate. Examples of useful liquid butadiene copolymers are
butadiene-co-styrene and butadiene-co-acrylonitrile. Possible
functionalized liquid polybutadiene resins include Nisso G-1000,
G-2000, G-3000; Nisso C-1000; Nisso BN-1010, BN-2010, BN-3010,
CN-1010; Nisso TE-2000; and Nisso BF-1000 commercially available
from Nippon Soda Co., Ltd. and Ricon 131/MA commercially available
from Colorado Chemical Specialties, Inc.
[0020] The optional, butadiene- or isoprene-containing copolymer is
preferably unsaturated and can be liquid or solid. It is preferably
a solid, thermoplastic elastomer comprising a linear or graft-type
block copolymer having a polybutadiene or polyisoprene block, and a
thermoplastic block that preferably is styrene or 1-methyl styrene.
Possible block copolymers, e.g., styrene-butadiene-styrene
tri-block copolymers, include Vector 8508M (commercially available
from Dexco Polymers, Houston, Tex.), Sol-T-6302 (commercially
available from Enichem Elastomers American, Houston, Tex.), and
Finaprene 401 (commercially available from Fina Oil and Chemical
Company, Dallas, Tex.). Preferably, the copolymer is a
styrene-butadiene di-block copolymer, such as Kraton D1118X
(commercially available from Shell Chemical Corporation). Kraton DI
118X is a di-block styrene-butadiene copolymer containing 30 vol %
styrene.
[0021] The butadiene- or isoprene-containing polymer may also
contain a second block copolymer similar to the first except that
the polybutadiene or polyisoprene block is hydrogenated, thereby
forming a polyethylene block (in the case of polybutadiene) or an
ethylene-propylene copolymer (in the case of polyisoprene). When
used in conjunction with the first copolymer, materials with
enhanced toughness can be produced. Where it is desired to use this
second block copolymer, a preferred material is Kraton GX1855
(commercially available from Shell Chemical Corp.), which is
believed to be a mixture of styrene-high 1,2-butadiene-styrene
block copolymer and styrene-(ethylene-propylene)-styrene block
copolymer.
[0022] Thus, in a preferred embodiment, the butadiene- or
isoprene-containing polymer comprises a solid thermoplastic
elastomer block copolymer having the formula X.sub.m(Y--X).sub.n
(linear copolymer) or ##STR1## (graft copolymer), where Y is a
polybutadiene or polyisoprene block, X is a thermoplastic block,
and m and n represent the average block numbers in the copolymer, m
is 0 or 1 and n is at least 1. The composition may further include
a second thermoplastic elastomer block copolymer having the formula
W.sub.p(Z-W).sub.q (linear copolymer) or ##STR2## (graft copolymer)
where Z is a polyethylene or ethylene-propylene copolymer block, W
is a thermoplastic block, and p and q represent the average block
numbers in the copolymer, p being 0 and 1 and q being at least
1.
[0023] The volume to volume ratio of the polybutadiene or
polyisoprene resin to butadiene- or isoprene-containing polymer
preferably is between 1:9 and 9:1, inclusive. The selection of the
butadiene- or isoprene-containing polymer depends on chemical and
hydrolysis resistance as well as the toughness conferred upon the
molded material.
[0024] The optional low molecular weight polymer resin is generally
employed to enhance toughness and other desired characteristics of
composition. By low molecular weight polymer, it is meant a polymer
having a molecular weight of less than about 50,000, preferably
less than about 5, 000. Examples of suitable low molecular weight
polymer resins include, but are not limited to, telechelic polymers
such as polystyrene, multifunctional acrylate monomers and ethylene
propylene diene monomer (EPDM) containing varying amounts of
pendant norbornene groups and/or unsaturated functional groups. The
optional low molecular weight polymer resin can be present in
amounts of zero to about 30 wt % of the resin system.
[0025] A curing agent may be used to accelerate the curing
reaction. When the composition is heated, the curing agent
decomposes to form free radicals, which then initiate cross linking
of the polymeric chains. Preferred curing agents are organic
peroxides such as Luperox, dicumyl peroxide, t-butyl perbenzoate,
2,5-dimethyl-2,5-di(t-butyl peroxy)hexane,
.alpha.,.alpha.-bis(t-butyl peroxy)diisopropylbenzene, and
2,5-dimethyl-2,5-di(t-butyl peroxy) hexyne-3, all of which are
commercially available. They may be used alone or in combination.
Typical amounts of curing agent are about 1.5 wt % to about 6 wt %
of the resin system.
[0026] Crosslinking agents may also be added to increase the
crosslink density of the resin(s). Examples of preferred
cross-linking agents include triallylisocyanurate,
triallylcyanurate, diallyl phthalate, divinyl benzene, and
multifunctional acrylate monomers (e.g., the Sartomer resins
available from Arco Specialty Chemicals Co.), and combinations
thereof, all of which are commercially available, with
triallylisocyanurate being generally preferred. The cross-linking
agent content of the thermosetting composition can be readily
determined by one of ordinary skill in the art, depending upon the
desired flame retardancy of the composition, the amount of the
other constituent components, and the other properties desired in
the final product. UL-94, an Underwriters Laboratories flammability
test, provides four possible ratings, HB, V-2, V-1, and V-0. V-0 is
the most difficult rating to obtain, requiring that five bars of
material self extinguish with an average flame out time of five
seconds or less without dripping. More particularly, the amount of
cross-linking agent depends upon the loading of magnesium hydroxide
and amount(s) of the other components in the thermosetting
composition, and attaining excellent flame retardancy, electrical
and moisture properties. In general, effective quantities are
greater than or equal to about 0.5 wt %, preferably greater than or
equal to about 1 wt %, and most preferably greater than or equal to
about 5 wt % based on the total weight of the thermosetting
composition. Effective quantities are typically less than about 15
wt %, preferably about 10 wt %, and most preferably about 8 wt %
based on the total weight of the resin system.
[0027] Suitable particulate fluoropolymers for inclusion in the
thermosetting composition include those known in the art for
circuit substrates, and include but are not limited to fluorinated
homopolymers, for example polytetrafluoroethylene (PTFE), and
fluorinated copolymers, e.g. copolymers of tetrafluoroethylene with
hexafluoropropylene or perfluoroalkylvinylethers such as
perfluorooctylvinyl ether, or copolymers of tetrafluoroethylene
with ethylene. Blends of fluorinated polymers, copolymers, and
terpolymers formed from the above listed monomers are also suitable
for use with the present invention. A particularly preferred
fluoropolymer is PTFE.
[0028] Useful forms of particulate fluoropolymer resin include fine
powder and granular fluoropolymer, both of which are widely
commercially available. As used herein, granular and dispersion are
terms of art commonly used in connection with the forms of
fluoropolymers, and refers to the physical characteristics of the
fluoropolymer, particularly particle size. Particle size in turn is
determined by the method of fluoropolymer manufacture.
[0029] Fine powder PTFE (or coagulated dispersion) is made by
coagulation and drying of dispersion-manufactured PTFE. Fine powder
PTFE is generally manufactured to exhibit a particle size of
approximately 400 microns to 500 microns. It is used in the
manufacture of paste extruded articles, such as wire insulation and
in paste extrusion and calendaring.
[0030] Granular PTFE is made by a suspension polymerization method.
Granular PTFE is generally used for compression molding of PTFE
articles. It is also widely used for the molding of billets that
are then skived on a lathe to produce PTFE sheet. Granular PTFE is
generally manufactured in two different particle size ranges. The
standard product is made with a median particle size of
approximately 30 microns to 40 microns. The high bulk density
product exhibits a median particle size of about 400 microns to 500
microns. In addition to these forms of PTFE, other fluoropolymer
compositions such as DuPont Teflon FEP and PFA are also available
in pellet form. The pellets can be cryogenically ground to exhibit
a median particle size of less than 100 microns (.mu.m). It is
expected that such materials, with the appropriate particle size
distribution would act to achieve the same end in the present
invention as granular PTFE. Accordingly, granular fluoropolymers as
used herein may refer to fluoropolymers manufactured by either
suspension polymerization or by cryogenic grinding of pellets to
the granular form. Particularly preferred for use is a granular
PTFE commercially available under the trade name Zonyl MP-1100,
available from DuPont, Wilmington, Del. having a particle size on
the order of 35 microns.
[0031] The optimal particulate fluoropolymer content of the
thermosetting composition can be readily determined by one of
ordinary skill in the art, depending upon the necessary flame
retardancy of the composition, for example, based on V-0, V-1 or
V-2 in UL-94, the amount of the other constituent components, and
the other properties desired in the final product. More
particularly, the amount of the fluoropolymer composition depends
upon the loading of magnesium hydroxide and amount(s) of other
synergists in the thermosetting composition, and attaining
excellent flame retardancy, electrical and moisture properties. In
general, effective quantities are greater than or equal to about 1
phr, preferably greater than or equal to about 5 phr, and most
preferably greater than or equal to about 10 phr (parts per hundred
parts by weight) of the total thermosetting resin composition.
Effective quantities are typically less than or equal to about 90
phr, preferably less than or equal to about 75 phr, and most
preferably less than or equal to about 50 phr of the total weight
of the thermosetting composition.
[0032] Use of magnesium hydroxide as disclosed herein can eliminate
the need for a halogenated flame retardant, and at the very least,
allows use of advantageously low levels of such flame retardants.
The thermosetting composition thus optionally comprises a
halogenated flame retardant. The halogenated flame retardant can
comprise less than or equal to about 900 parts per million (ppm) of
a chlorine-containing flame retardant and less than or equal to
about 900 ppm of a bromine-containing flame retardant, for a total
halogenated flame retardant concentration of 1800 ppm, based on the
resin system, preferably based on the total thermosetting
composition (resin system plus magnesium hydroxide), more
preferably based on the total dielectric material (resin system
plus magnesium hydroxide plus particulate inorganic filler plus
woven or non-woven web). A suitable bromine-containing flame
retardant is ethylenebistetrabromopthalimide available as Saytex
BT-93 from Albermarle Corp. A suitable chlorine-containing flame
retardant is 1,4:7,10-dimethanodibenzo (a,e) cyclooctane
1,2,3,4,7,8,9,10,13,13,14,14-dodecachloro-1,4,4a,5,6,6a,7,10,10a,11,12,12-
a-dodecahydro, which is available as Dechlorane Plus from
OxyChem.
[0033] The thermosetting composition optionally comprises a filler.
Preferably, the filler material and quantity thereof is selected so
as to provide the substrate with a coefficient of thermal expansion
that is equal or substantially equal to the coefficient of thermal
expansion of the metal layer. Suitable fillers include, for
example, rutile titanium dioxide and amorphous silica because these
fillers have a high and low dielectric constant, respectively,
thereby permitting a broad range of dielectric constants combined
with a low dissipation factor to be achieved in the final cured
product by adjusting the respective amounts of the two fillers in
the composition. To improve adhesion between the fillers and resin,
coupling agents, e.g., silanes, can be used.
[0034] The volume percent (vol %) of the filler (based upon the
combined volume of the resin system, and particulate filler) is
about 5% to about 60%, preferably about 30% to about 50%. Examples
of preferred fillers include titanium dioxide (rutile and anatase),
barium titanate, strontium titanate, silica (particles and hollow
spheres) including fused amorphous silica and fumed silica;
corundum, wollastonite, aramide fibers (e.g., Kevlar), fiberglass,
Ba.sub.2Ti.sub.9O.sub.20, glass spheres, quartz, boron nitride,
aluminum nitride, silicon carbide, beryllia, alumina or magnesia.
They may be used alone or in combination.
[0035] A very high surface area particulate filler such as fumed
silica may be additionally used to prevent tackiness and stickiness
in the prepreg. The preferred fumed silica is available from
Degussa under the trade name AEROSIL 200, and has a surface area of
about 200 m.sup.2/g, with a typical primary particle size of about
12 nanometers. The amount of fumed silica used may be about 0.2 to
about 5 vol %, and preferably about 0.5 to about 1.5 vol %.
[0036] The compositions optionally comprise woven, thermally stable
webs of a suitable fiber, preferably glass (E, S, and D glass) or
high temperature polyester fibers (e.g., KODEL from Eastman Kodak).
The web is present in an amount of about 10 to about 40 vol %, and
preferably about 15 to about 25 vol % with respect to the
thermosetting resin composition. Such thermally stable fiber
reinforcement provides the laminate with a means of controlling
shrinkage upon cure within the plane of the laminate. In addition,
the use of the woven web reinforcement renders a dielectric
substrate with a relatively high mechanical strength. In general,
the thermosetting composition is processed as follows. First, all
the components (resin, magnesium hydroxide, cross-linking agent,
particulate fluoropolymer and other desired additives) are
thoroughly mixed in conventional mixing equipment along, preferably
with a peroxide curing agent. The mixing temperature is regulated
to avoid substantial decomposition of the curing agent (and thus
premature cure). Mixing continues until the ingredients are
uniformly dispersed throughout the resin. For those applications
where the thermosetting composition is to impregnate a woven web
forming a prepreg, conventional prepreg manufacturing methods can
be employed. Typically the web is impregnated with the slurry,
metered to the correct thickness, and then the solvent removed to
form a prepreg.
[0037] The lamination process entails a stack-up of one or more
saturated woven webs (or a non-saturated woven web sandwiched
between two bond plies) between one or two sheets of conductive
foil (copper). The stack-up is then cured (via lamination) in a one
step or two step curing cycle.
[0038] The stack-up can be cured using a conventional peroxide cure
step at temperatures between about 150.degree. C. and about
200.degree. C. The peroxide-cured stack-up may then be subjected to
a high-energy electron beam irradiation cure (E-beam cure) or a
high temperature cure step under an inert atmosphere to impart an
unusually high degree of cross-linking to the resulting laminate.
The temperature is greater than about 250.degree. C. but less than
about 400.degree. C., or the decomposition temperature of the
resin. This high temperature cure is preferably carried out in an
oven but can also be performed in a press, namely as a continuation
of the initial lamination step.
[0039] In the alternative, the thermosetting composition can be
mixed with a solvent to form a casting composition. The casting
composition is applied to a substrate. Thereafter, the solvent is
removed and the cast resin system is subjected to the
aforementioned cure cycle.
[0040] In one preferred embodiment, the thermosetting composition
includes a plurality of woven webs (such as E-glass webs) embedded
in a mixture of the polybutadiene or polyisoprene based resin
system and inorganic filler (e.g., silica) laminated between one or
two sheets of conductive foils (e.g., copper) to produce a circuit
board material that is especially well suited for microwave
applications. Of course, if very thin (e.g., less than 5 mil
thickness) cross-sections are desired, then only a single saturated
web may be used for the dielectric layer. Referring now to FIG. 1,
a cross-sectional view of a circuit material comprising the
thermosetting composition is shown generally at 10. Circuit
substrate 10 has been laminated in accordance with one of the
processes described above wherein a woven web 12 is embedded in a
thermosetting composition as described herein 14 and laminated
between two conductive layers 16, 18, for example copper foils, to
produce a circuit material. As discussed above with reference to
the processing conditions, the thermosetting composition 14 may
either be cast onto woven web 12 using known casting equipment, or
woven web 12 may be saturated by thermosetting composition 14 by
sandwiching woven web 12 between a pair of bond plies formed from
thermosetting composition 14 and laminating the stack up together
with the conductive layers 16, 18. While FIG. 1 depicts a single
layer of woven web 12, it will be appreciated that typically a
plurality of layers of saturated woven web 12 will be used in
forming circuit laminates. However, a single layer as shown in FIG.
1 is desirable where very thin cross-sections, e.g., less than
about 5 mils, are required.
[0041] In FIG. 2 is shown a circuit material 20 formed from a
dielectric material 22 comprising a flame retardant thermosetting
polybutadiene or polyisoprene resin composition as described herein
disposed on a conductive layer 24, such as copper. Any one or more
of conductive layers 16, 18, or 24 may be etched by known methods
to provide a circuit layer.
[0042] The thermosetting composition described above has numerous
advantages. A UL-94 rating of V-1 or better may be obtained without
the use of halogenated flame retardants. In addition a dielectric
constant (Dk) less than about 4.5 and preferably less than about
4.0 may be obtained. The dissipation or dielectric loss factor (Df)
is less than about 0.01 and preferably less than about 0.006.
Finally the moisture absorption of the thermosetting composition is
less than about 0.2 and preferably less than about 0.15%.
[0043] The following non-limiting examples further describe the
thermosetting composition.
EXAMPLES
[0044] Compositions as described in U.S. Pat. No. 6,048,807,
comprising a polybutadiene resin (B3000 from Nisso) and a cure
agent, together with the additives as shown with Table 1, were
formulated and tested. In general, the compositions were processed
as follows. First, the polybutadiene resin, magnesium hydroxide,
and all other components were thoroughly mixed to form a slurry in
conventional mixing equipment. The mixing temperature was regulated
to avoid substantial decomposition of the curing agent (and thus
premature cure). Next, conventional prepreg manufacturing methods
were employed. Typically, if used, the web was impregnated with the
slurry, metered to the correct thickness, and then the solvent was
removed (evaporated) to form a prepreg. The lamination process
entailed a stack-up of one or more prepreg layers between one or
two sheets of conductive foil (copper). This stack-up was then
densified and cured via lamination or a combination of lamination
and oven baking. The stack-up was cured in a conventional peroxide
cure step; typical cure temperatures were between about 330 and
about 425.degree. F. (about 165 to about 218.degree. C.).
[0045] In the following examples, flame retardance was measured in
accordance with UL-94. The designation "fail" indicates that the
sample did not attain V-1.
[0046] Dielectric constant (Dk) values are the averages of the
measured dielectric constants from a 1-10 Ghz frequency sweep.
[0047] Dissipation Factor (Df) values are the lowest recorded value
of a given 1-10 Ghz frequency sweep.
[0048] Specific gravity ("Sp.g.") was determined in accordance with
ASTM D79291.
[0049] Water absorption was measured by IPCTM-650 2.6.2.1 (with 48
hr exposure). TABLE-US-00001 TABLE 1 Example No. 1* 2* 3* 4 5 6 7**
Component (wt %) Magnesium hydroxide 50 20 25 20 (Magnifin H10)
Magnesium hydroxide 38 35 50 (Zerogen) Magnesium hydroxide 30
(Magnifin H5A) Magnesium hydroxide 15 20 (Magnifin H5) Magnesium
hydroxide 10 10 (Magnifin H3) Silica 18 25 28 8 15 15 15
Triallylisocyanurate 5 5 5 5 5 Particulate PTFE 5 5 5 5 5 Flame
retardant (Saytex BT-93) 0.2 0.2 0.2 Flame retardant (Dechlorane
0.2 0.2 0.2 plus) Results UL-94 Fail Fail Fail V-1 V-0 V-0 V-0 Df
at 3 GHz 0.0047 0.0053 0.0054 0.0061 0.0047 0.0047 0.0047
Dielectric constant 3.93 3.93 4.06 4.01 3.83 3.94 Water absorbance
0.2 0.25 0.11 0.17 0.08 0.12 Specific gravity 1.88 1.88 1.88
*Denotes comparative examples **Post cured with Perkadox
[0050] Comparative Example 1 has magnesium hydroxide only,
Comparative Example 2 has a combination of magnesium hydroxide and
triallylisocyanurate cross-linker, and Comparative Example 3 has a
combination of magnesium hydroxide and polytetrafluoroethylene. All
of the comparative examples failed the UL-94 test. In addition, the
samples had dissipation factors less than about 0.006, dielectric
constants less than about 4.5, water absorption of less than about
0.2, and xylene absorption (data not shown) of less than about
1.1.
[0051] Example 4 with magnesium hydroxide, triallylisocyanurate
cross-linker, and polytetrafluoroethylene had a UL 94 rating of
V-1. Thus, the combination of three additives provides a V-1 rating
in the absence of additional flame retardants.
[0052] Examples 5-7 contain fire retardants in addition to the
magnesium hydroxide, triallylisocyanurate cross-linker, and
polytetrafluoroethylene. All three examples achieve a V-0 rating.
In addition, the samples had dissipation factors less than about
0.005, dielectric constants less than about 4.1, and water
absorption of less than about 0.2. Example 5 contains a combination
of uncoated (Magnifin H10) and coated (Magnifin H5A) magnesium
hydroxides. The coated magnesium hydroxide may be optionally used
to prevent loss of magnesium hydroxide during acidic processing
conditions. The different examples also contain magnesium hydroxide
particles having different surface areas. Comparing Examples 5, 6
and 7, Example 5 has a combination of 10 square meters per gram
surface area and 5 square meters per gram surface area sized
magnesium hydroxide, while Examples 6 and 7 have a combination of
10, 5 and 3 square meters per gram surface area (Magnifin H10, H5
and H, respectively). The particle surface area may be varied when
it is desirable to modify the particle packing fraction.
[0053] In summary, the data show thermosetting compositions with
UL-94 ratings of V-0 and V-1, with Example 4 achieving a V-1 rating
without use of additional flame retardant. In addition, dielectric
constants of less than about 4.5 and even less than about 4.0 can
be achieved. The dissipation factors of the compositions are less
than about 0.0065. Also, the water absorption is less than about
2.5 with many samples less than 0.2. The data thus clearly show
that the thermosetting compositions comprising magnesium hydroxide,
PTFE, and crosslinker possess acceptable UL-94 ratings, dielectric
constants, dissipation factors, and moisture absorption properties
with and without the addition of halogenated flame retardants.
[0054] While preferred embodiments have been shown and described,
various modifications and substitutions may be made thereto without
departing from the spirit and scope of the invention. Accordingly,
it is to be understood that the present invention has been
described by way of illustration and not limitation.
* * * * *