U.S. patent application number 10/227997 was filed with the patent office on 2003-05-01 for solid sheet material especially useful for circuit boards.
Invention is credited to Khan, Subhotosh, Levit, Mikhail R., Samuels, Michael R..
Application Number | 20030082974 10/227997 |
Document ID | / |
Family ID | 23226507 |
Filed Date | 2003-05-01 |
United States Patent
Application |
20030082974 |
Kind Code |
A1 |
Samuels, Michael R. ; et
al. |
May 1, 2003 |
Solid sheet material especially useful for circuit boards
Abstract
A solid sheet which contains an nonwoven fabric made from short
high tensile modulus fibers and a thermoplastic polymer having a
low moisture absorption matrix resin that is useful as a substrate
for circuit boards.
Inventors: |
Samuels, Michael R.;
(Wilmington, DE) ; Khan, Subhotosh; (Midlothian,
UG) ; Levit, Mikhail R.; (Richmond, VA) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1128
4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
23226507 |
Appl. No.: |
10/227997 |
Filed: |
August 26, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60315890 |
Aug 30, 2001 |
|
|
|
Current U.S.
Class: |
442/327 |
Current CPC
Class: |
H05K 1/0366 20130101;
B29B 13/10 20130101; H05K 2201/0278 20130101; B32B 27/12 20130101;
H05K 2201/0141 20130101; Y10T 442/60 20150401; H05K 2201/0129
20130101; H05K 2201/0293 20130101; B32B 15/04 20130101; H05K
2201/015 20130101 |
Class at
Publication: |
442/327 |
International
Class: |
D04H 005/00; D04H
001/00; D04H 013/00; D04H 003/00 |
Claims
What is claimed is:
1. A sheet, comprising: (a) a nonwoven fabric of short high tensile
modulus fibers; and (b) a thermoplastic polymer having a low
moisture absorption; said sheet having an apparent density which is
at least about 75% of its calculated density.
2. The sheet as recited in claim 1 wherein said apparent density is
at least about 90% of its calculated density.
3. The sheet as recited in claim 2 wherein at least some of said
high tensile modulus fiber is coated or encapsulated by said
thermoplastic polymer.
4. The sheet as recited in claim 3 wherein said thermoplastic
polymer is selected from the group consisting of perfluoropolymers
and liquid crystalline polymers.
5. The sheet are recited in claim 4 wherein said thermoplastic
polymer is a liquid crystalline polymer.
6. The sheet as recited in claim 5 wherein said high tensile
modulus fibers are an aramid.
7. The sheet as recited in claim 6 wherein said organic fibers are
an aramid.
8. The sheet as recited in claim 4 wherein said high tensile
modulus fibers are an aramid.
9. The sheet as recited in claim 2 wherein said high tensile
modulus fibers are an aramid.
10. The sheet as recited in claim 1 wherein a tensile modulus of
said sheet and a thermal coefficient of expansion of said sheet, in
a machine direction of said sheet is within about 20% of a tensile
modulus of said sheet and a thermal coefficient of expansion of
said sheet, respectively, in a transverse direction of said
sheet.
11. The sheet as recited in claim 1 wherein said thermoplastic
polymer absorbs no more than about 0.25 weight percent of
moisture.
12. A laminate comprising: the sheet of claim 1 and at least one
metal layer contacting one surface of said sheets.
13. A circuit board comprising the sheet of claim 1.
14. A process for the production of a solid first sheet material,
comprising the steps of heating and applying pressure to: (a) a
multilayer sheet structure, comprising, at least one layer
containing a nonwoven fabric of short high tensile modulus fibers,
and at least one other layer that comprises a thermoplastic polymer
having a low moisture absorption; to form a first sheet having an
apparent density of at least about 75% of its calculated
density.
15. The process as recited in claim 13 wherein said apparent
density is at least about 90% of said calculated density.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/315,890, filed Aug. 30, 2001.
FIELD OF INVENTION
[0002] The field of invention relates to solid sheets comprising
thermoplastic polymer having low moisture absorption and high
tensile modulus fibers, in which the thermoplastic polymer is the
matrix polymer, substrates for circuit boards made therefrom, and
methods of making the foregoing.
BACKGROUND
[0003] Circuit boards are important items of commerce, being used
in virtually every electronic device. The "board" or supporting
member of a circuit board or other electronic devices (such as the
interposer in a flip-chip package) is an important component of
such devices, and properties of the materials used to make such
boards are important to the functioning of the electronic or
electrical circuit.
[0004] As electronic components have become more sophisticated, the
demands placed upon the materials used for boards have increased.
For example, for many applications it is preferred that the board
have a coefficient of expansion which matches those of the chips
mounted on the board, and/or that the board have a low dielectric
constant, and low dissipation factor, especially when high
frequency devices are mounted on the board. These three factors are
often adversely affected by the absorption of moisture by the board
materials, which changes the dimensions of the board and/or changes
the dielectric constant and/or dissipation factor of the board
itself, and/or causes warpage.
[0005] The simplest boards for relatively nondemanding applications
are typically made from a thermoset resin such as an epoxy filled
with a fibrous reinforcement such as glass fiber. The glass fiber,
often in the form of a woven fabric, is saturated with liquid epoxy
resin to form a "prepreg", which is cured in form of a board. As
the demands on boards increase, the glass may be replaced by a
higher modulus infusible fiber such as an aramid. However, fibers
such as aramid fibers, and epoxy resins, absorb significant amounts
of moisture, and so are sometimes unsuitable for use together in
highly demanding circuit board uses. Thus there is a need for
improved circuit board materials.
[0006] Japanese Patent Application 2000-334871 describes the
preparation of a sheet from which a prepreg may be formed by
"laminating" a three layer structure in which the middle layer may
be an nonwoven sheet containing synthetic organic fiber and the two
outer layers may contain aramids or other infusible fibers. From
the way prepreg formation is described, it appears the sheet is
porous.
[0007] Japanese Patent Application 11-117184 describes the
preparation of a sheet from which a prepreg may be formed by
forming a nonwoven sheet from aramid and liquid crystalline polymer
(LCP) fibers, heating sheet under pressure to make the LCP flow,
and then adding a thermoset resin to form a prepreg. From the
reported densities of the sheets actually made, they are
porous.
[0008] Japanese Patent Application 9-21089 describes the
preparation of an LCP nonwoven sheet (paper) which is reported to
have low moisture absorption. Other fibers can also be present in
the sheet. The product, after being heated under pressure to
partially consolidate the sheet, is apparently still a paper-like
material.
[0009] Japanese Patent Application 11-229290 describes the
preparation of a paper made from LCP and aramid fibers which can be
impregnated with an epoxy resin which is then cured. The resulting
board may be used as a circuit board. No melting or flow under heat
and/or pressure of the LCP is described.
SUMMARY OF INVENTION
[0010] Our invention includes:
[0011] sheets, comprising(a) a nonwoven sheet of short high tensile
modulus fibers, and (b) a thermoplastic polymer having low moisture
absorption; the sheet having an apparent density which is at least
about 75% of its calculated density.
[0012] laminates made therefrom;
[0013] circuit boards made therefrom;
[0014] processes for the production of a solid sheet material,
comprising heating and applying pressure to, for a sufficient
amount of time,:
[0015] (a) a multilayer sheet structure, comprising, at least one
layer containing a nonwoven sheet of high tensile modulus fiber and
at least one other layer, and at least one of said layers present
comprises a thermoplastic polymer having low moisture absorption;
or
[0016] (b) a single layer sheet structure comprising a nonwoven
fabric comprising short lengths of a high tensile modulus fiber and
a thermoplastic polymer having low moisture absorption;
[0017] to form a sheet having an apparent density of at least about
75% of its calculated density.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0018] Herein certain terms are used. Some of these are defined
below.
[0019] By a "thermoplastic polymer having low moisture absorption"
(TP) is meant a thermoplastic plastic polymer which absorbs less
than 1.0 weight percent moisture (based on the weight of the
thermoplastic polymer) when measured on a sheet of pure
thermoplastic polymer by the method described below. Preferably the
moisture absorption of the thermoplastic polymer is about 0.5
weight percent or less, more preferably about 0.25 weight percent
or less, and especially preferably about 0.10 weight percent or
less.
[0020] By "high tensile modulus fibers" (HTMF) are meant these
product forms having a tensile modulus of about 10 GPa or more,
preferably about 50 GPa or more, more preferably about 70 GPa or
more, when measured in accordance with ASTM D885-85 method, using a
1.1 twist multiplier. HTMF herein include high tensile modulus
fibers, fibrils and fibrids, unless it is specifically indicated
not all three are included. The HTMFs are synthetic organic
materials, and this does not include carbon fibers of any kind.
[0021] By "LCP" is meant a polymer which is anisotropic when tested
by the TOT test as described in U.S. Pat. No. 4,118,372, which is
hereby incorporated by reference in its entirety. By thermotropic
is meant the LCP may be melted and is anisotropic in the melt, as
described in the TOT test.
[0022] By "nonwoven HTMF containing or comprising sheet" or
"nonwoven HTMF containing or comprising "fabric" or "nonwoven HTMF
containing or comprising paper" is meant a nonwoven sheet (or
fabric or paper) that contains (or comprises short HTMFs. In this
context herein the words "paper", "sheet" and "fabric" are used
interchangeably.
[0023] By "nonwoven sheet" herein is meant a nonwoven "fabric"
formed by any number of different methods, for example wet lay of
short fibers (often called a paper), dry lay, flash spun, melt
spun, mechanically needled felt, spunlaced. A preferred form of
nonwoven sheet is a paper as described in U.S. Pat. Nos. 4,886,578
and 3,756,908, each of which is hereby incorporated by reference in
its entirety. These patents describe aramid papers, but other HTMFs
may also be similarly used. This process also includes the optional
use of a binder, wherein such binders include, but are not limited
to, aramid fibrids and other binders known within the industry.
Dry-lay methods of manufacturing which are well known within the
art are described by U.S. Pat. No. 3,620,903 which is hereby
incorporated by reference in its entirety.
[0024] By "fiber" is meant an object having a length and a maximum
cross-sectional dimension, the maximum cross sectional dimension
typically being in the range of about 0.3 .mu.m to about 100 .mu.m
and an aspect ratio (length/width) of .gtoreq.50.
[0025] By "aramid fiber" herein is meant aromatic polyamide fiber,
wherein at least 85% of the amide (--CONH--) linkages are attached
directly to two aromatic rings. Optionally, additives can be used
with the aramid and dispersed throughout the polyfiber structure,
and it has been found that up to as much as about 10 percent by
weight of other polymeric material can be blended with the aramid.
It has also been found that copolymers can be used having as much
as about 10 percent of other diamines substituted for the diamine
of the aramid or as much as about 10 percent of other diacid
chlorides substituted for the diacid chloride of the aramid.
[0026] By "fibrils" herein is meant a fiber-like material having a
diameter of about 0.1 .mu.m to about 25 .mu.m, and an aspect ratio
of 3 to about 100.
[0027] By "fibrids" herein is meant very small, nongranular,
fibrous or film-like particles with at least one of their three
dimensions to be of minor magnitude relative to the largest
dimension. These particles are prepared by precipitation of a
solution of polymeric material using a non-solvent under high
shear.
[0028] The term "aramid fibrids", as used herein, means
non-granular film-like particles of aromatic polyamide having a
melting point or decomposition point above 320.degree. C. The
aramid fibrids typically have an average length in the range of
about 0.2 mm to about 1 mm with an aspect ratio of about 5 to about
10. The thickness dimension is on the order of a fraction of a
micrometer, for example about 0.1 .mu.m to about 1.0 .mu.m. In
addition to aromatic polyamide, aramid fibrids may optionally
additionally comprise one or more of dyes, pigments or other
additives such as those described in U.S. Pat. Nos. 5,965,072 and
5,998,309, each of which is hereby incorporated by reference in its
entirety.
[0029] By "short fibers" or "short lengths" of fibers herein is
meant fibers with an aspect ratio of less than about 2000,
preferably about 200-1000 and more preferably about 250-600.
[0030] By "powder" herein is meant a material having an aspect
ratio of less than 3. These particles typically have a maximum
dimension of about 5 .mu.m to about 1000 .mu.m. Powder particles
may have smooth or rough textured surfaces and may comprise fibrils
attached to a "central core" section.
[0031] By "apparent density" is meant the overall volume of a piece
of a sheet calculated as follows. Measuring thickness (if somewhat
uneven, an average value should be determined), length and width,
and multiplying these values to obtain a volume. The sheet is
weighed in air. This weight is then divided by the volume to obtain
an apparent density. A sheet which is porous will have an apparent
density lower than its calculated density.
[0032] By "calculated density" is meant the density of an object,
assuming it has no voids or pores, which is calculated from the
amounts and densities of the individual materials in that object.
For example, if an object was 60 weight percent of a material
having a density of 1.4, and 40 weight percent of a material having
a density of 1.6, the calculated density of that object would
be:
d=1.0/[(0.6/1.4)+(0.4/1.6)]=1.47
[0033] Calculations of this type are well known in the art.
[0034] By "solid" herein is meant that the material has an apparent
density which is at least about 75% of its calculated density.
[0035] By "a" or "an" herein, such as a TP or HTMF is meant one or
more.
[0036] By "comprising" herein is meant the named items (materials),
and any other additional materials or compositions may be
present.
[0037] Preferred "solid" or "consolidated" sheets are now
described.
[0038] A solid sheet is preferably formed from a multilayer (two or
more layers) or a single layer structure.
[0039] A preferred single layer structure comprises nonwoven HTMF
sheet or fabric which contains a TP. The TP may be present in a
number of ways. It may simply be a powder which is interspersed
between the fibers of the aramid nonwoven sheet. The HTMF nonwoven
sheet may contain TP (especially LCP) fibers (in other words the
sheet is a mixture of TP fibers and HTMF fibers). The HTMF sheet
may contain TP (especially LCP) pulps or mixtures of various forms
of TP such as powders, fibers and/or pulps. Preferably the TP and
the HTMF are both not an LCP, that is a lower melting LCP for the
TP and a higher melting LCP for the HTMF. "Fiber-shaped" LCPs may
be formed simply by wet pulping of pieces of LCPs such as pellets.
For example the pellets are mixed with water, and if desired one or
more surfactants, and the mixture subjected to relatively high
shear mixing. If the shear applied is high enough the pellets will
be broken up into LCP fiber-like particles.
[0040] If the solid sheet is formed from a multilayer structure, at
least one of the layers must include a nonwoven HTMF sheet or
fabric, and at least one of the layers must contain a TP (an "TP
layer"). For example, if two layers are present, one could be an
HTMF nonwoven sheet and the other could be either a nonwoven sheet
of TP or a TP film. The HTMF nonwoven sheet could also contain TP,
and/or vice versa. There may be more than one layer of a nonwoven
HTMF sheet or fabric, and/or TP layer present.
[0041] Typically a TP layer will be about 20 to about 95 percent by
weight, preferably about 30 to about 95 percent by weight, more
preferably about 40 to about 95 percent by weight, and especially
preferably about 70 to about 90 percent by weight, of the total
weight of HTMF and TP in a multilayer structure. For example aramid
papers typically weigh about 15 to about 200 g/m.sup.2.
[0042] In a TP layer, the TP may be present as a film, paper, short
fiber, fiber, fibrid, fibril, or powder, or any combination of
these. For example, because of the tendency of solid LCPs to
fibrilate when worked mechanically, combinations of the above forms
when the LCP is in particulate form may be employed. TPs which are
particulates and do not match any of the above particulate
definitions may also be used.
[0043] The amount of TP present in the single or multilayer
structure must be sufficient to form a solid sheet product.
Preferably, the TP will fill in essentially all the voids between
HTMFs of the HTMF nonwoven sheet, as well as any voids between
other materials which may be present, such as fillers. Since
nonwoven HTMF sheets or fabrics, especially papers, typically have
about 10 to about 70 percent by volume void space, the single or
multilayer structure to be consolidated into a solid sheet will
typically have at least about 20 percent by volume TP present, more
typically about 30 to about 95 percent by volume present. The
percent voids in a TP nonwoven sheet can be readily calculated by
measuring its apparent density, and using the TP's measured (solid)
density. These calculation methods are well known.
[0044] Other materials may also be present in the single or
multilayers, such as fillers, antioxidants, pigments, and/or other
polymers, as long as the final sheet is solid.
[0045] Conditions (assuming the single or multilayer structure has
enough TP present) for forming the first solid sheet are a
combination of temperature (heating), pressure and the amount of
time heating and pressure are applied. Generally, the higher the
temperature applied, the less the pressure needed and/or the less
time needed. The higher the pressure, the lower the temperature
needed and/or less time is needed. The longer the time used, the
lower the temperature and/or the lower the pressure which may be
needed. However, in most cases it may be necessary to heat the TP
to a temperature at least near its melting point. If too low a
temperature, or too low a pressure, or too short a time, or any
combination of these, is used, the TP may not flow enough to form a
solid sheet. In this case, the temperature and/or pressure should
be raised and/or the time increased. It is believed that the most
important variable is temperature, particularly when approaching
the melting point of the TP. Typically during the flowing of the TP
(at high temperature and/or pressure) the HTMF is at least coated
by, and in most instances, encapsulated by the TP. Although some of
the "fibers" of the HTMF in the HTMF nonwoven sheet may be moved
relative to one another, in the densified single or multilayer
sheet the HTMF nonwoven sheet structure is still present.
[0046] While applying heat and pressure to form the first solid
sheet, full or partial vacuum may also be applied to the single or
multilayer structure to remove air or other gases dissolved in the
materials of the single or multilayer structure or physically
present in the structure, as between the HTMF and TP particulates.
For example the single or multilayer structure may be placed in a
vacuum bag or vacuum chamber and then heat and pressure applied.
Using vacuum helps remove gases from the structure and avoid
trapping gas bubbles (voids) in the first solid sheet. With any of
the process variations described herein to consolidate the single
or multilayer structure, use of vacuum is a preferred option.
[0047] A variety of methods can be used to apply both higher
temperatures and pressures. A simple apparatus is a vacuum bag to
which heat and pressure may be applied. A press or autoclave may
also be used. A particularly preferred method is hot roll or hot
belt calendering. Temperatures, pressures, and time of treatment
(contact) with the hot roll(s) or belt(s) can be controlled fairly
well, as can the final thickness of the first sheet. Calendering is
a well known art, see for instance U.S. Pat. No. 3,756,908, which
is hereby incorporated by reference in its entirety. To help ensure
"complete" consolidation the calendering can be done in a
vacuum.
[0048] The consolidation (applying heat and pressure) into a solid
sheet may be carried out in one or more steps. For example, more
than one pair of calender rolls may be used to gradually
consolidate the sheet to a solid structure. Each step may also be
done individually, for example the sheet partially consolidated,
and then consolidated in a second separate step.
[0049] Metal layers on one or both sides of the sheet may be
applied in a single step process, or at any step of a multistep
process. For example, the sheet may be partially consolidated by a
pair of calender rolls or a press belt, metal sheets applied to one
or both surfaces of the sheet, and the consolidation finished in a
second pair of calender rolls or another press belt.
[0050] It is preferred that the resulting sheet is "balanced" in
the X-Y axes (sometimes referred to as the machine and transverse
directions) in the plane of the sheet. By balanced properties is
meant that the tensile modulus and/or coefficient of thermal
expansion (CTE) in one direction (machine or transverse) is no more
than twice than, more preferably no more than about 20%, and
especially preferably no more than about 10%, the tensile modulus
and/or CTE in the perpendicular direction. This is especially
preferred when the TP comprises an LCP, and very preferred when the
TP is an LCP (only). Sheeting formed by melt extrusion of TPs
containing short random lengths of HTMFs (but no in nonwoven sheet
form) tends to have larger differences in tensile moduli and CTEs
between the machine and transverse directions, especially if the TP
is LCP. This is disadvantageous for use in circuit and other
electronic board applications.
[0051] Any TP which has a low moisture absorption, such as
perfluorothermoplastics [for example, polytetrafluoroethylene;
copolymers of tetrafluoroethylene with hexafluoropropylene,
perfluoro(vinyl ethers) such as perfluoro(methyl vinyl ether)], or
ethylene; poly(ether-ether-ketones); poly(ether-ketone-ketones);
and poly(ether-ketones); polyesters such as poly(ethylene
terephthalate, poly(ethylene 2,6-napthalate, and polyesters from
bisphenol A and isophthalic/terephthalic acids; polycarbonates
especially those having higher temperature glass transition
temperatures; poly 4-methylpentene; poly(aryl sulfides);
poly(ether-imides); poly(aryl ethers); and LCPs are useful.
Preferred TPs are perfluoropolymers, particularly those mentioned
above, and LCPs are especially preferred. Among the preferred
properties for the TPs are very low moisture absorption, high
melting point, low dielectric constant and low dielectric loss
coefficient. LCPs have an excellent combination of such
properties.
[0052] Useful LCPs include those which are described in U.S. Pat.
Nos. 3,991,013, 3,991,014 4,011,199, 4,048,148, 4,075,262,
4,083,829, 4,118,372, 4,122,070, 4,130,545, 4,153,779, 4,159,365,
4,161,470, 4,169,933, 4,184,996, 4,189,549, 4,219,461, 4,232,143,
4,232,144, 4,245,082, 4,256,624, 4,269,965, 4,272,625, 4,370,466,
4,383,105, 4,447,592, 4,522,974, 4,617,369, 4,664,972, 4,684,712,
4,727,129, 4,727,131, 4,728,714, 4,749,769, 4,762,907, 4,778,927,
4,816,555, 4,849,499, 4,851,496, 4,851,497, 4,857,626, 4,864,013,
4,868,278, 4,882,410, 4,923,947, 4,999,416, 5,015,721, 5,015,722,
5,025,082, 5,086,158, 5,102,935, 5,110,896, 5,143,956, and
5,710,237, each of which is hereby incorporated by reference in its
entirety, and European Patent Application 356,226. Preferably the
TP such as an LCP has a melting point of about 180.degree. C. or
more, very preferably about 250.degree. C. or more, more preferably
about 300.degree. C. or more, and especially preferably about
325.degree. C. or more. Melting points are determined by ASTM
D3418-82, at a heating rate of 20.degree. C./min. The peak of the
melting endotherm is taken as the melting point. These higher
melting TPs will allow the circuit board to undergo high
temperature processing with less possibility of warping, for
example in reflow soldering. Low warpage is an important attribute
of the boards used in circuit boards. LCPs are also particularly
useful in this application since they have very low moisture
absorption and also the permeability of LCPs to moisture is very
low. Another preferred form of LCP is an aromatic polyester or
aromatic poly(ester-amide), especially an aromatic polyester. By an
"aromatic" polymer is meant that all of the atoms in the main chain
are part of an aromatic ring, or are functional groups connecting
those rings such as ester, amide, or ether (the latter of which may
have been part of a monomer used). The aromatic rings may be
substituted with other groups such as alkyl groups. Some
particularly preferred aromatic polyester LCPs are those found in
U.S. Pat. Nos. 5,110,896 and 5,710,237. More than one LCP
composition may be present in the first sheet, but one is
preferred.
[0053] Useful HTMFs include as aramids,
[0054] poly(phenylenebenzobisoxazole),
[0055] poly(phenylenbenzobisimidazole),
[0056] poly(phenylenebenzobisthiazole), poly(phenylene
sulfide),
[0057] LCPs, and polyimide. When calculating the concentration of
such fibers, the total of these types of fibers present will be
used, for example the total of aramid and
poly(phenylenebenzobisoxazole) fiber present. Among the preferred
properties are high modulus, high melting point and/or glass
transition temperature and low moisture absorption.
[0058] Aramids are preferred HTMFs. Useful aramids include
poly(p-phenylene terephthalamide), poly(m-phenylene
isophthalamide), and poly(p-phenylene/4,4'-oxydianiline
terephthalamide). Preferred aramids are poly(p-phenylene
terephthalamide), poly(m-phenylene isophthalamide), and
poly(p-phenylene terephthalamide) is especially preferred. A
description of the formation of aramid (short) fibers, fibrids and
fibrils of various types is found in U.S. Pat. Nos. 5,202,184,
4,698,267, 4,729,921, 3,767,756 and 3,869,430, each of which is
hereby incorporated by reference in its entirety. Description of
the formation of nonwoven aramid sheets, especially papers, is
found in U.S. Pat. Nos. 5,223,094 and 5,314,742, each of which is
hereby incorporated by reference in its entirety. More than one
aramid may be present in the first sheet.
[0059] The apparent density of the solid sheet is preferably at
least about 75% of its calculated density, more preferably at least
about 80% of its calculated density, even more preferably at least
about 90% of its calculated density, even more preferably at least
about 95% of its calculated density, and even more preferably at
least about 98% of its calculated density.
[0060] When applying heat and pressure to form the solid sheet(s),
metal layers, such as copper (or other metal) foil may be placed on
the outer surface(s) (one or both) of the single or multilayer
structure(s) to be consolidated so that a metal clad laminate is
produced. Often the metal layers are photolithographically etched
to create circuit lines. Combinations of different single or
multilayer structures may also be consolidated together with or
without metal layers.
[0061] The solid sheets, usually with metal layer(s) present may be
used as the supporting "board" for circuit boards. Such boards may
be formed by techniques known in the art, see for instance M. W.
Jawitz, "Printed Circuit Board Materials Handbook, McGraw-Hill Book
Co., New York (1997). For example it is known how to coat LCPs
(aside from consolidation with heat and pressure as described
above) with metals (other than by using metal foils), see for
instance U.S. Pat. No. 5,209,819, incorporated herein by reference
in its entirety, European Patent Application 214,827, World Patent
Application 9939021, and K. Feldmann, et al., Metalloberflaeche,
vol. 51, p. 349-352 (1997).
[0062] Alternatively, solid sheets without metal layers may first
be formed and metal layers attached to one solid sheet or more than
one solid sheet which have been plied up. Then metal layers may be
attached to the outer surface(s). The assembly with metal sheets
may be bonded together using heat and/or pressure, or adhesives may
be used.
[0063] If metal layers are present in and/or on the solid sheet, to
measure the apparent density the metal layer can first be removed
(as by acid etching) before measuring the apparent density, or the
metal layers may remain and their presence be taken into account by
calculation, using their thickness and (known) density, when
determining the apparent density of the solid sheet(s) present. If
more than one layer of solid sheet is present [for example
separated by metal layer(s)], the average apparent density (overall
apparent density) of the solid sheet(s) present will be used as the
benchmark for apparent density.
[0064] Circuit boards (including printed wiring boards and printed
circuit boards) produced from the above materials usually have low
moisture absorption, and/or good high temperature resistance,
and/or relatively low coefficients of thermal expansion, and/or low
dielectric constant, and/or low warpage, an excellent combination
of properties for a circuit board. Once the substrate boards are
formed they may be processed by normal methods to make circuit
boards.
[0065] "Densified" sheets containing one or more layers may also be
used in or as chip package substrates, chip carriers and chip
package interposers.
[0066] Procedure for Determining Equilibrium Moisture Absorption at
85.degree. C. and 85% Relative Humidity
[0067] Five specimens (5.times.5 cm) of the same sample dried to a
constant weight at 105.degree. C. are placed into a humidity
chamber set at 85.degree. C. and 85% relative humidity. After that,
weight gain of the specimens is measured at each day. When an
average weight gain for 3 consecutive days is less than 1% of the
total weight gain, specimens are deemed to be at equilibrium and
average moisture absorption (equal to the total weight gain) is
calculated by dividing the total weight gain by the original weight
of the sample and multiplying the result by 100.
EXAMPLES
[0068] The following Examples illustrate preferred embodiments of
our invention. Our invention is not limited to these Examples.
[0069] In the Examples, except as noted, all of the LCP used had
the composition as that of Example 4 of U.S. Pat. No. 5,110,896
derived from hydroquinone/4,4'-biphenol/terephthalic
acid/2,6-naphthalenedicarboxylic acid/4-hydroxybenzoic acid in
molar ratio 50/50/70/30/320.
[0070] Also in the Examples herein the poly(m-phenylene
isophthalamide) (PMIT) fibrids were made as described in U.S. Pat.
No. 3,756,908, which is hereby incorporated by reference in its
entirety. The poly(p-phenylene terephthalamide) (PPTA) had a linear
density of about 0.16 tex and a length of about 0.67 cm (sold by E.
I. du Pont de Nemours and Company under trademark KEVLAR.RTM.
49).
[0071] Poly(ethylene terephthalate) (PET) fiber used: 2.1 dpf, 6 mm
long, sold as Merge 106A75 by E. I. DuPont de Nemours & Co.,
Inc, Wilmington Del., U.S.A.
[0072] Glass fiber used: E-type glass fiber 6.5 .mu.m diameter and
6.4 mm long produced by Johns Manville Co., Denver, Colo. 80217,
USA, sold as type M189.
[0073] Poly(phenylene oxide) (PPE) resin used was type 63D from the
General Electric Co., Pittsfield, Mass., U.S.A.
[0074] Polybenzoxazole fiber used: 1.5 dpf produced by Toyobo Co.,
Ltd. (Kita-ku, Osaka 530-8230, Japan) under trademark Zylon.RTM.
(cut to length of 6.4 mm).
Example 1
[0075] The LCP used had the composition of the LCP of Example 9 of
U.S. Pat. No. 5,110,896, derived from
hydroquinone/4,4'-biphenol/terephthalic
acid/2,6-naphthalenedicarboxylic acid/4-hydroxybenzoic acid in
molar ratio 50/50/85/15/320. The particulate LCP was prepared by
grinding a melt blend mixture containing LCP (70 wt. %) and a
polytetrafluoroethylene powder (30 wt. %) in a Bantam.RTM. Micro
Pulverizer (model CF) along with liquid nitrogen until the
particles passed through about a 10 mesh screen. The particles were
reground in the same unit with additional liquid nitrogen until
they passed through a 40 mesh screen.
[0076] Two (2.00) g of para-aramid fiber was placed in a standard
laboratory pulp disintegrator(described in TAPPI Test Method T205
sp-95) together with 2500 g of water and agitated for 3 min.
Independently, 69.13 g of an aqueous, never-dried, meta-aramid
fibrid slurry (0.43% consistency and freeness 330 ml of
Shopper-Riegler) was placed in a same type of laboratory mixer
together with 2.25 g of the above described particulate LCP and
about 2000 g of water and agitated for 1 min. Both dispersions were
poured together into an approximately 21.times.21 cm handsheet mold
and mixed with addition of about 5000 g of water. The resulting
slurry had the following weight percent of solid materials:
[0077] meta-aramid fibrids 6.5%;
[0078] para-aramid floc 43.5%;
[0079] particulate LCP 50%.
[0080] A wet-laid sheet was formed. The sheet was placed between
two pieces of blotting paper, hand couched with a rolling pin, and
dried in a hand sheet dryer at about 190.degree. C.
[0081] A piece 7.1.times.7.1 cm was cut from the dried sheet,
covered on both sides with an aluminum foil treated with a mold
release Mono-Coat.RTM. 327W (sold by Chem-Trend Inc.) and placed in
the platen press MTP-20 (sold by Tetrahedron Associates, Inc.)
between two brass cover plates 1 mm thick each. The sheet was
compressed in the press under the following conditions:
[0082] temperature 360.degree. C., pressure 1.8 MPa for 2 min;
[0083] temperature 360.degree. C., pressure 89 MPa for 5 min;
[0084] The press plates were then cooled with water while
maintaining a constant pressure of 89 MPa. The final (compressed)
sheet had a basis weight of 108.8 g/m.sup.2, thickness of 81.3
.mu.m and an apparent density 1.34 g/cm.sup.3. With a calculated
density of about 1.52 g/cm.sup.3, the sheet was about 88% of the
calculated "solid" density.
Example 2
[0085] The final sheet (laminate) from Example 1 was placed between
two sheets of copper foil (20 .mu.m thick) and a metal-clad
laminate was prepared by hot compression in the same press and
using the same compression cycle as described in Example 1. The
polymer portion (without copper foil) in the final metal-clad
laminate had thickness 78.7 .mu.m and an apparent density of 1.38
g/cm.sup.3, which was about 91% of the calculated "solid"
density.
Example 3
[0086] Strand cut pellets of LCP were refined on a 30.5 cm diameter
Sprout-Waldron type C-2976-A single rotating disc refiner equipped
with plates in one pass with the gap between plates of about 25
.mu.m, a feed speed of about 60 g/min. and continuous addition of
water in quantity of about 4 kg of water per 1 kg of the pellets.
The resulting LCP pulp was additionally refined in a Bantam.RTM.
Micropulverizer, Model CF, to pass through a 30 mesh screen. A
water slurry was prepared by mixing LCP pulp and poly(p-phenylene
terephthalamide) floc. The slurry had the following percentages (as
a percent of total solids) of solid materials:
[0087] LCP pulp 65%;
[0088] poly(p-phenylene terephthalamide) floc 35%.
[0089] A continuous sheet was formed from the slurry on a Rotonier
(combination of Rotoformer and Fourdrinier) papermaking machine
equipped with a horizontal thru-air drier. The headbox consistency
was about 0.01%, forming speed about 5 m/min and temperature of air
in the drying section of about 338.degree. C. The formed paper was
calendered at ambient temperature between two metal rolls 86 cm
diameter each at a speed of about 7 m/min. and linear pressure of
about 6500 N/cm. Calendered material had basis weight of about 72.5
g/m.sup.2 and apparent density of about 0.82 g/cm.sup.3, which
corresponded to about 57% from calculated density. Tensile modulus
in the machine direction was 2.52 GPa and in the transverse
direction 1.65 GPa. Ten plies of calendered sheet (51.times.51 cm
each) were placed between two sheets of 17 .mu.m thick copper foil
and compressed in a platen press at the following conditions:
348.degree. C.-2.6 MPa-1 min>>348.degree. C.-34 kPa-1
min>>348.degree. C.-2.6 MPa-1 min>>149.degree. C.-2.6
MPa-1 min. The thickness of the final copper clad laminate was
0.541 mm, which corresponded to 0.507 mm thickness of polymeric
material (the rest was the copper foil). Based on basis weight of
10 plies of calendered material loaded in the press (725 g/m.sup.2)
and thickness of polymer material in the final laminate (0.507 mm),
apparent density of polymer material in the final copper clad
laminate was estimated to be 1.43 g/cm.sup.3, which corresponded to
about 99% of the calculated density. After etching of copper foil,
CTE in plane was determined as being in the range of +/.+-.1
ppm/.degree. C.
Example 4
[0090] Strand cut pellets of LCP were refined on 30.5 cm diameter
Sprout-Waldron type C-2976-A single rotating disc refiner equipped
with plates in one pass using a gap between plates of 25 .mu.m,
feeding speed of about 60 g/min. and continuous addition of water
in quantity of about 4 kg of water per 1 kg of the pellets. This
LCP pulp was additionally refined in a Bantam.RTM. Micropulverizer,
Model CF, to pass through a 60 mesh screen. The slurry was prepared
by mixing the LCP pulp with poly(p-phenylene terephthalamide) floc.
The resulting slurry had the following percentages (as a percent of
total solids) of solid materials:
[0091] LCP pulp 90%;
[0092] poly(p-phenylene terephthalamide) floc 10%.
[0093] A continuous sheet was formed from the slurry on a Rotonier
(combination of Rotoformer and Fourdrinier) papermaking machine
equipped with horizontal thru-air drier.
[0094] The headbox consistency was about 0.01%, forming speed about
5 m/min and temperature of air in the drying section of about 338
C. The formed material was calendered at ambient temperature
between two metal rolls 4 cm diameter each at speed about 5 m/min.
and linear pressure of about 2000 N/cm. Calendered material had a
basis weight of 66.1 g/m.sup.2 and apparent density about 0.66 g/ml
which corresponded to about 46% of the calculated density. Its
tensile modulus in the machine direction as 1.30 GPa, and about
0.93 GPa in the transverse direction. Ten plies of calendered sheet
were placed between two sheets of 17 .mu.m thick copper foil and
compressed in the platen press under the following conditions:
348.degree. C.-0.87 MPa-1 min>>348.degree. C.-34 kPa-1
min>>348.degree. C.-0.87 MPa-1 min.>>149.degree.
C.-0.87 MPa-1 min. Density of polymeric material in the final
copper clad laminate was 1.39 g/cm.sup.3, which corresponded to
about 96.5% of the calculated density. The CTE 23 ppm/.degree. C.
in the machine direction and 33 ppm/.degree. C. in the transverse
direction. Moisture absorption was 0.4 wt. %.
Example 4
[0095] Sheets (25 cm.times.21 cm) of THERMOUNT.RTM. reinforcement
type 2N710 available from I. E. DuPont de Nemours & Co.,
Wilmington, Del., U.S.A., which is an aramid paper containing a
majority of PPTA floc with some poly(m-phenylene isophthalamide
fibrids) were impregnated in two steps with a water dispersion of
Teflon.RTM. PFA [a thermoplastic copolymer of tetrafluoroethylene
and perfluoro(propyl vinyl ether) available from E. I. DuPont de
Nemours & Co., Wilmington, Del., U.S.A]. Each impregnation was
conducted in a bath having about 60% solids, followed by squeezing
between two glass rods and drying in an oven at 105.degree. C. PFA
content in the final impregnated sheets was about 77 wt. %.
Impregnated sheets were consolidated by compression in 2 plies in a
platen press under the following conditions: 316.degree. C.-3.9
MPa-5 min.>>149.degree. C.-3.9 MPa-1 min. Consolidated sheets
had basis weight 80.9 g/m.sup.2, thickness 0.145 mm and apparent
density 1.82 g/cm.sup.2, which corresponded to 91% of the
calculated density. Three consolidated sheets were compressed
together between two sheets of copper foil 17 .mu.m thick each at
the following conditions: 316.degree. C.-3.9 MPa-10
min>>149.degree. C.-3.9 MPa 1 min. In the final copper clad
laminate, apparent density of polymeric material was about 1.88
g/cm.sup.2, which corresponded to 94% of the calculated density.
Moisture absorption of this material at 85.degree. C. and 85%
relative humidity was 0.7 wt. %.
Example 5
[0096] One g of polybenzoxazole (PBO) fiber was placed in a
laboratory mixer (British pulp evaluation apparatus) with 2500 g of
water and agitated for 3 min. Independently, 69.77 g of an aqueous,
never-dried, poly(m-phenylene isophthalamide) fibrid slurry (0.43%
consistency and freeness 330 ml of Shopper-Riegler) was placed in
the same type of laboratory mixer together with 1.70 g of LCP pulp
(passed through a 30 mesh screen after grinding in a Bantam
Micropulverizer)) and about 2000 g of water and agitated for 1 min.
Both dispersions were poured together into an approximately
21.times.21 cm handsheet mold and mixed with addition of about 5000
g of water. The resulting slurry had the following percentages (of
total solids) of solid materials:
[0097] poly(m-phenylene isophthalamide) fibrids 10%;
[0098] PBO floc 33%;
[0099] LCP pulp 57%
[0100] A wet-laid sheet was formed. The sheet was placed between
two pieces of blotting paper, hand couched with a rolling pin, and
dried in a hand sheet dryer at about 190.degree. C. The dried sheet
had basis weight of about 68.8 g/m.sup.2. The dried sheet was
consolidated by calendering at ambient temperature between two
metal rolls 10 cm diameter each at a linear pressure of about 2000
N/cm and speed about 5 m/min. The calendered sheet had density of
about 0.69 g/cm.sup.3, which corresponded to about 48% of the
calculated density. The sheet was placed between two sheets of 17
.mu.m thick copper foil and compressed in a platen press at the
following cycle: 343.degree. C.-0.21 MPa-1 min>>343.degree.
C.-33.1 MPa-2 min>>93.degree. C.-33.1 MPa-1 min. Polymeric
material in the final copper clad laminate had apparent density of
about 1.34 g/cm.sup.3, which corresponded to about 93% of the
calculated density.
Example 6
[0101] Poly(p-phenylene terephthalamide) fiber (0.84 g) was placed
in a laboratory mixer (British pulp evaluation apparatus) with 2500
g of water and agitated for 3 min. Independently, 65.12 g of an
aqueous, never-dried, poly(m-phenylene isophthalamide) fibrid
slurry (0.43% consistency and freeness 330 ml of Shopper-Riegler)
was placed in the same type of laboratory mixer together with 1.68
g of PET floc and about 2000 g of water and agitated for 1 min.
Both dispersions were poured together into an approximately
21.times.21 cm handsheet mold and mixed with addition of about 5000
g of water. The resulting slurry had the following percentages (of
total solids) of solid materials:
[0102] poly(m-phenylene isophthalamide) fibrids 10%;
[0103] poly(p-phenylene terephthalamide) floc 30%;
[0104] poly(ethylene terephthalate) floc 60%
[0105] A wet-laid sheet was formed. The sheet was placed between
two pieces of blotting paper, hand couched with a rolling pin, and
dried in a hand sheet dryer at about 190.degree. C. The dried sheet
had basis weight of about 67.0 g/m.sup.2. Another sheet was
prepared by exactly the same procedure. Both sheets were placed
together between two sheets of aluminum foil with mold release on
their surfaces (see example 1) and compressed in the platen press
at the following cycle: 266.degree. C.-0.21 MPa-2
min>>266.degree. C.-15.9 MPa-2 min>>93.degree. C.-15.9
MPa-2 min. The consolidated sheet had an apparent density of about
1.28 g/cm.sup.3, which corresponded to about 91% of the calculated
density.
Comparative Example A
[0106] Aramid paper with basis weight of 31 g/m.sup.2 and a density
of 0.64 g/ml made from 87% by weight PPTA floc (2.25 denier per
filament, 6.7 mm cut length) and 13% by weight poly(m-phenylene
isophthalamide) fibrids was prepreged with commercial
multi-functional epoxy system L-1070 as in Example 2. Thirty-two
prepregs made by the above process were further laminated between
two Cu sheets (17 .mu.m thick) under the following conditions in a
vacuum press:
[0107] (a) Held for 1 h in vacuum (no external pressure or
temperature).
[0108] (b) Heated to 200.degree. C. (5.degree. C./min) from ambient
temperature under a pressure of 6.9 MPa.
[0109] (c) Held for 1 h at 200.degree. C. and 6.9 MPa.
[0110] (d) Cooled to room temperature fast (water quench on
platens) under pressure
[0111] Epoxy resin content in the polymer portion of the final
laminate was about 53% wt. %. After etching of copper foil,
properties of polymer portion of the laminate were measured. CTE e
was about 14.2 ppm/.degree. C. in the machine direction and 12.1
ppm/.degree. C. in the transverse direction, and moisture
absorption at 85.degree. C. and 85% humidity was about 2.1 wt.
%.
* * * * *