U.S. patent application number 10/460000 was filed with the patent office on 2003-11-20 for hole fill composition and method for filling holes in a substrate.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Farquhar, Donald S., Papathomas, Konstantinos I..
Application Number | 20030216490 10/460000 |
Document ID | / |
Family ID | 25342202 |
Filed Date | 2003-11-20 |
United States Patent
Application |
20030216490 |
Kind Code |
A1 |
Farquhar, Donald S. ; et
al. |
November 20, 2003 |
Hole fill composition and method for filling holes in a
substrate
Abstract
A composition usable in hole filling of a metal layer and to
planarize the metal layer is provided. The metal layer is part of a
substrate which can be part of a multilayer printed circuit board
or chip carrier. The composition comprises a fluoropolymer
dielectric metal, a filler material, and a coupling agent, the
filler material having at least a partial coating of the coupling
agent.
Inventors: |
Farquhar, Donald S.;
(Endicott, NY) ; Papathomas, Konstantinos I.;
(Endicott, NY) |
Correspondence
Address: |
DRIGGS, LUCAS BRUBAKER & HOGG CO. L.P.A.
DEPT. IEN
8522 EAST AVENUE
MENTOR
OH
44060
US
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
25342202 |
Appl. No.: |
10/460000 |
Filed: |
June 12, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10460000 |
Jun 12, 2003 |
|
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09863961 |
May 23, 2001 |
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6589639 |
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Current U.S.
Class: |
523/216 ;
524/492 |
Current CPC
Class: |
H05K 1/056 20130101;
Y10T 428/24917 20150115; H05K 2201/015 20130101; H05K 2201/0239
20130101; H05K 2201/0209 20130101; Y10S 428/901 20130101; Y10T
428/3154 20150401; H05K 3/445 20130101; Y10T 428/25 20150115; H05K
2203/143 20130101 |
Class at
Publication: |
523/216 ;
524/492 |
International
Class: |
C08K 003/34 |
Claims
We claim:
1. A hole fill composition comprising: a fluoropolymer dielectric
material; a filler material; and a coupling agent, said filler
material having at least a partial coating of said coupling agent
thereon.
2. The composition of claim 1 wherein said fluoropolymer dielectric
material is selected from the group consisting of polymers of
tetrafluoroethylene and its copolymers including
tetrafluoroethylene and perfluoroalkoxy, tetrafluoroethylene and
ethylene, and tetrafluoroethylene and at least 65 mole % of
perfluoro-2,2-dimethyl-1,3-- di-oxide; hexafluoropropylene;
perfluoro-2-2-dimethyl-1,3 dioxide; polymers and copolymers of
trifluorochloroethylene including trifluorochloroethylene and
ethylene; polymers of perfluoroalkyl vinyl ether; and
perfluorinated ethylene-propylene copolymers.
3. The composition of claim 1 wherein said fluoropolymer dielectric
material comprises about 40 percent by weight to about 90 percent
by weight of said composition.
4. The composition of claim 1 wherein said filler material
comprises about 9 percent by weight to about 60 percent by weight
of said composition.
5. The composition of claim 1 wherein said coupling agent comprises
about 1 percent by weight to about 10 percent by weight of said
composition.
6. The invention of claim 1 wherein said composition has a pH of
about 8 to about 11.
7. A hole fill composition comprising: a fluoropolymer dielectric
material; a surfactant; a filler material; and a coupling agent,
said filler material having at least a partial coating of said
coupling agent thereon.
8. The composition of claim 7 wherein said surfactant comprises a
non-ionic surface active agent.
9. A hole fill composition comprising: a fluoropolymer dielectric
material; a silica filler material; and a coupling agent, said
filler material having at least a partial coating of said coupling
agent thereon.
10. The composition of claim 9 wherein said fluoropolymer
dielectric material is selected from the group consisting of
polymers of tetrafluoroethylene and its copolymers, including
tetrafluoroethylene and perfluoroalkoxy, tetrafluoroethylene and
ethylene, and tetrafluoroethylene and at least 65 mole % of
perfluoro-2,2-dimethyl-1,3-- di-oxide; hexafluoropropylene;
perfluoro-2-2-dimethyl-1,3 dioxide; polymers and copolymers of
trifluorochloroethylene including trifluorochloroethylene and
ethylene; polymers of perfluoroalkyl vinyl ether; and
perfluorinated ethylene-propylene copolymers.
11. The composition of claim 9 wherein said fluoropolymer
dielectric material comprises about 40 percent by weight to about
90 percent by weight of said composition.
12. The composition of claim 9 wherein said silica of said silica
filler is selected from the group consisting of crystalline silica,
fumed silica, synthetic silica, precipitated silica, and amorphous
silica.
13. The composition of claim 9 wherein said silica filler material
comprises about 9 percent by weight to about 60 percent by weight
of said composition.
14. The composition of claim 9 wherein said silica of said silica
filler material is comprised of particles, each particle having a
size of from about 0.1 micron to about 40 microns.
15. The composition of claim 14 wherein said particles of silica
are substantially spherical or spheroidal.
16. The composition of claim 9 wherein said coupling agent
comprises about 1 percent by weight to about 10 percent by weight
of said composition.
17. The invention of claim 9 wherein said composition has a pH of
about 8 to about 11.
18. A hole fill composition comprising: a fluoropolymer dielectric
material; a surfactant; a silica filler material; and a coupling
agent, said filler material having at least a partial coating of
said coupling agent thereon.
19. The composition of claim 18 wherein said surfactant comprises a
non-ionic surface active agent.
20. A hole fill composition comprising: a fluoropolymer dielectric
material; a filler material; and a fluorosilane coupling agent,
said filler material having at least a partial coating of said
coupling agent thereon.
21. The composition of claim 20 wherein said fluoropolymer
dielectric material is selected from the group consisting of
polymers of tetrafluoroethylene and its copolymers, including
tetrafluoroethylene and perfluoroalkoxy, tetrafluoroethylene and
ethylene, and tetrafluoroethylene and at least 65 mole % of
perfluoro-2,2-dimethyl-1,3-- di-oxide; hexafluoropropylene;
perfluoro-2-2-dimethyl-1,3 dioxide; polymers and copolymers of
trifluorochloroethylene including trifluorochloroethylene and
ethylene; polymers of perfluoroalkyl vinyl ether; and
perfluorinated ethylene-propylene copolymers.
22. The composition of claim 20 wherein said fluoropolymer
dielectric material comprises about 40 percent by weight to about
90 percent by weight of said composition.
23. The composition of claim 20 wherein said filler material
comprises about 9 percent by weight to about 60 percent by weight
of said composition.
24. The composition of claim 20 wherein said fluorosilane coupling
agent includes alkoxy or halo groups attached to an Si group.
25. The composition of claim 20 wherein said fluorosilane coupling
agent comprises about 1 percent by weight to about 10 percent by
weight of said composition.
26. The invention of claim 20 wherein said composition has a pH of
about 8 to about 11.
27. A hole fill composition comprising: a fluoropolymer dielectric
material; a surfactant; a filler material; and a fluorosilane
coupling agent, said filler material having at least a partial
coating of said coupling agent thereon.
28. The composition of claim 27 wherein said surfactant comprises a
non-ionic surface active agent.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of application Ser. No.
09/863,961, filed May 23, 2001, now U.S. Pat. No. ______.
FIELD OF THE INVENTION
[0002] This invention relates to a composition for filling holes in
a substrate wherein the substrate can be part of a multi-layer
printed circuit board or chip carrier. Specifically this invention
defines anew and unique hole fill composition and method of filling
such holes in a substrate which provides a substantially planar
substrate surface at the filled hole locations wherein the filled
hole substrate can form part of the completed multi-layer printed
circuit board or chip carrier.
BACKGROUND OF THE INVENTION
[0003] Many known current printed circuit board constructions
require one or more external conductive layers, e.g., circuitry
and/or pads for mounting components thereon, and, given today's
increased functional demands, a plurality of internal conductive
planes, e.g., signal, power and/or ground. To provide effective
interconnections between such surface components and the board's
conductive circuitry, internal planes and/or pads, the use of
conductive through holes has been adopted wherein several such
holes are formed in the board and electrically coupled in a
selective manner to internal and external conductive elements. Such
holes typically include a conductive, e.g., copper, layer as part
thereof which in turn contacts the also typically copper circuitry,
pads and/or internal planes.
[0004] The term "through hole" or simply "hole" as used herein is
meant to include both conductive and non-conductive apertures which
may extend entirely through the circuit board or even only partly
therethrough (such partial holes are often also called "vias" in
the circuit board field), including between only one or more
internal layers without being externally exposed. Examples of
various circuit board structures which include holes of these types
are defined in several published documents, including the following
U.S. Letters Patents, issued on the dates identified:
1 U.S. Pat. No. Inventors Filing Date 4,704,791 Chellis et al. Nov.
10, 1987 4,435,480 Hart et al. Dec. 23, 1993 5,450,290 Boyko et al.
Sep. 12, 1995 5,487,218 Bhatt et al. Jan. 30, 1996 5,557,844 Bhatt
et al. Sep. 24, 1996 5,571,593 Arldt et al. Nov. 5, 1996 5,662,987
Mizumoto et al. Sep. 2, 1997
[0005] All of these patents are assigned to the same assignee as
the present invention and are incorporated herein by reference.
[0006] Printed circuit boards of all the above type are
particularly adapted for having one or more (usually several)
electrical components, e.g., semiconductor chips, capacitors,
resistors, etc., mounted on an external surface thereof and coupled
to various, selected internal conductive planes within the board's
dielectric substrate. As demands for increased levels of
integration in semiconductor chips and other electrical components
continue, parallel demands call for concurrent increased functional
capabilities, e.g., increased circuit densities, in printed circuit
boards adapted for use with such components. Such demands further
emphasize the growing need for more closely spaced electrical
components on the board's outer surfaces. For those boards
possessing greater functional capabilities and therefore which use
several through holes therein, it is highly desirable to position
the electrical components directly over the holes to maximize board
real estate while assuring a compact, miniaturized final board
product.
[0007] Increased demands such as those above are particularly
significant when it is desirable to couple what are referred to as
ball grid array.(BGA) or similar components directly onto the
board's outer conductive layer(s). These components typically
include a semiconductor chip electrically coupled to a plurality of
highly dense conductors, e.g., solder ball elements, closely
positioned in a fixed pattern on the component's undersurface. This
is also the case for directly mounted semiconductor chips (also
known in this technology as direct chip attach (or DCA components)
wherein a dense pattern of several minute solder balls are arranged
on the chip's small undersurface (that directly facing the
underlying circuit board). In this case, the circuit board may also
be referred to as a chip carrier.
[0008] In many of today's advanced chip carriers, the basic
building block of the chip carrier is a metal ground plane that has
been etched to form a personalized ground plane having clearance
holes. The personalized ground plane can then be laminated on both
sides with a fluoropolymer or other dielectric material and a metal
foil, preferably copper foil. The metal foil is then circuitized to
form a signal carrying layer. This circuitized structure may be
defined as a signal core. Subsequent additions of fluoropolymer or
other dielectric layers and metal foil layers are "built up" on the
signal core and can form power and additional signals layers which
are ultimately built up to a multilayer chip carrier structure. The
presence of clearance holes in a signal core may lead to a
non-planar signal core outside surface which can affect the
planarity of subsequent layers "built up" on the signal core (and
ultimately the planarity of the surface of the multilayer chip
carrier on which the semiconductor chip is to be mounted.) This is
believed to be caused by the limited flow characteristics of the
fluoropolymer or other dielectric material during the lamination
phase of signal core manufacture.
[0009] It is believed that a new hole fill composition and a method
of making a substrate having at least one hole (and possibly
several) therein which is filled with the new hole fill composition
will substantially prevent non-planarity of the signal core outside
surface and lead to a substantially planar multilayer printed
circuit board or chip carrier surface when the signal core is used
in the manufacture of the multilayer printed circuit board or chip
carrier. This would represent a significant advancement in the
art.
SUMMARY OF THE INVENTION
[0010] Accordingly, it is the object of this invention to provide a
new and unique composition which in turn may be used as a hole fill
in a metal layer of a substrate.
[0011] Another object of this invention is to provide a method of
making such a composition.
[0012] Yet another object of this invention is to provide a
substrate including a metal layer having at least one through hole
therein and a mixture of a fluoropolymer dielectric material and a
filler material substantially filling the through hole. The mixture
will provide a substantially planar filled hole substrate and will
improve the planarity of the multilayer printed circuit board or
chip carrier of which the substrate is a part.
[0013] Still yet another object of the invention is to provide a
method of making such a substrate.
[0014] The invention is adaptable to mass production and reduces
the defect level and lowers the cost of product made with this
invention.
[0015] According to one aspect of the invention, there is provided
a the fill composition comprising a fluoropolymer dielectric
material, a filler material, and a coupling agent, the filler
material having at least a partial coating of the coupling agent
thereon.
[0016] According to another aspect of the invention, there is
provided a hole fill composition comprising a fluoropolymer
dielectric material, a surfactant, a filler material, and a
coupling agent, the filler material having at least a partial
coating of the coupling agent thereon.
[0017] According to yet another aspect of the invention, there is
provided a hole fill composition comprising a fluoropolymer
dielectric material, a silica filler material, and a coupling
agent, the filler material having at least a partial coating of the
coupling agent thereon.
[0018] According to still yet another aspect of the invention,
there is provided a hole fill composition comprising a
fluoropolymer dielectric material, a surfactant, a silica filler
material, and a coupling agent, the filler material having at least
a partial coating of the coupling agent thereon.
[0019] According to another aspect of the invention, there is
provided a hole fill composition comprising a fluoropolymer
dielectric material, a filler material, and a fluorosilane coupling
agent, the filler material having at least a partial coating of the
coupling agent thereon.
[0020] According to yet another aspect of the invention, there is
provided a hole fill composition comprising a fluoropolymer
dielectric material, a surfactant, a filler material, and a
fluorosilane coupling agent, the filler material having at least a
partial coating of the coupling agent thereon.
[0021] According to still yet another aspect of the invention,
there is provided a method of making a hole fill composition
comprising the steps of providing a quantity of a filler material,
adding to the quantity of the filler material a quantity of
coupling agent to at least partially coat the filler material,
adding to the quantity of filler material at least partially coated
with the coupling agent a quantity of a fluoropolymer dielectric
material, and blending the filler material coated with the coupling
agent and the fluoropolymer material.
[0022] According to another aspect of the invention, there is
provided a method of making a hole fill composition comprising the
steps of providing a quantity of a filler material, dissolving a
quantity of coupling agent in a first solvent to form a solution,
mixing the filler material into the solution to at least partially
coat the filler material, drying the filler material at least
partially coated with the coupling agent, adding the filler
material at least partially coated with the coupling agent to a
second solvent, adjusting the pH of the second solvent, dispersing
a quantity of a fluoropolymer dielectric material into the second
solvent, adding a quantity of a surfactant to the second solvent,
and blending the filler material at least partially coated with the
coupling agent and the fluoropolymer material.
[0023] According to yet another aspect of the invention, there is
provided a substrate comprising a metal layer including at least
one through hole therein defined by at least one side wall within
the metal layer, and a mixture of a fluoropolymer dielectric
material and filler material at least partially coated with a
coupling agent positioned on the side wall of the through hole, the
mixture substantially filling the through hole in the metal
layer.
[0024] According to still yet another aspect of the invention,
there is provided a substrate comprising a metal layer including at
least one through hole therein defined by at least one side wall
within the metal layer, and a mixture of a fluoropolymer dielectric
material and a silica filler material at least partially coated
with a coupling agent positioned on the side wall of the through
hole, the mixture substantially filling the through hole in the
metal layer.
[0025] According to another aspect of the invention, there is
provided a substrate comprising a metal layer including at least
one through hole therein defined by at least one side wall within
the metal layer, and a mixture of a fluoropolymer dielectric
material and a filler material at least partially coated with a
fluorosilane coupling agent positioned on the side wall of the
through hole, the mixture substantially filling the through hole in
the metal layer.
[0026] According to yet another aspect of the invention, there is
provided a method of making a substrate comprising the steps of
providing a metal layer including at least one through hole therein
defined by at least one side wall within the metal layer,
positioning a mixture of a fluoropolymer dielectric material and a
filler material at least partially coated with a coupling agent on
the side wall of the through hole, and heating the metal layer, the
fluoropolymer dielectric material and the filler material at least
partially coated with the coupling agent to adhere the dielectric
material and the filler material to the side wall the dielectric
material and the filler material substantially filling the through
hole.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a much-enlarged sectional view in elevation of a
substrate in accordance with the prior art.
[0028] FIG. 2 is a much-enlarged sectional view in elevation of one
embodiment of the substrate of the present invention, illustrating
the substrate having a metal layer including at least one through
hole therein, and a mixture of a fluoropolymer dielectric material
and a filler material at least partially coated with a coupling
agent substantially filling the through hole.
BEST MODE FOR CARRYING OUT THE INVENTION
[0029] In accordance with the teachings of this invention, there is
provided a new composition for use as a hole fill in the
manufacture of a substrate usable as part of a multilayer printed
circuit board or chip carrier. In one embodiment, this hole fill
composition comprises a fluoropolymer dielectric material, a filler
material, and a coupling agent at least partially coating the
filler material. A fluoropolymer is defined as a carbon based
organic polymer with fluorine atoms replacing at least some of the
hydrogen atoms, covalently bound to the carbon atoms that form the
basic chemical structure. It has been discovered that when the hole
fill composition is utilized to fill through holes in a metal layer
during the manufacture of a substrate, it results in a planar
substrate surface.
[0030] Referring to FIG. 1, a known substrate is shown. A
non-planar substrate surface 2 can result when a fluoropolymer or
similar dielectric layer used in the manufacture of a multilayer
printed circuit board or chip carrier is laminated to a metal layer
6 having through holes 8 (only one shown in FIG. 1). A non-planar
substrate surface used in the manufacture of a multilayer printed
circuit board or chip carrier can result in a non-planar multilayer
printed circuit board or chip carrier outer surface of which the
substrate is a part. A non-planar board or chip carrier outer
surface can adversely affect assembly of components, such as
semiconductor chips, to the multilayer printed circuit board or
chip carrier surface and can result in increased assembly defect
levels and additional manufacturing costs.
[0031] A blistering defect between laminated dielectric layer 4 and
metal layer 6 of the substrate can occur during processing of the
multilayer printed circuit board or chip carrier due to voids 9
being present, after lamination, in the through hole locations.
These voids can occur because the properties of the dielectric
material may not allow substantial uniform filling of the through
holes in the metal layer during lamination.
[0032] The current hole fill composition substantially fills the
through holes in the metal layer of the substrate, provides a
substantially planar substrate surface and minimizes voids and
blisters in the through hole area, thereby reducing defect levels
during manufacture or assembly of components to the multilayer
printed circuit board or chip carrier of which the substrate is a
part.
[0033] The fluoropolymer dielectric material of this invention is
selected from the group consisting of polytetrafluoroethylene and
its polymers, copolymers of tetrafluorothylene,
hexafluoropropylene, copolymers of tetrafluoroethylene,
perfluoro-2-2-dimethyl-1,3 dioxide, polytrifluorochloroethylene,
copolymers of trifluoromonochloroethylene, polymers of
perfluoroalkyl vinyl ether, perfluorinated ethylene-propylene
copolymers, copolymer of tetrafluoroethylene and perfluoroalkoxy,
copolymer of tetrafluoro-ethylene and ethylene, copolymer of
chlorotrifluoroethylene and ethylene, polymers of
chlorotrifluorethylene, polymers of chlorotrifluoroethylene, and
copolymer of tetrafluoroethylene and at least 65 mole % of
perfluoro-2,2-dimethyl-1,3-di-oxide.
[0034] The fluoropolymer dielectric material comprises about 40
percent by weight to about 90 percent by weight of the composition.
Some examples of commercially available fluoropolymer dielectric
materials that are operable in this invention are TEFLON PTFE,
TEFLON FEP, TEFLON PFA, TEFZEL, HFB-430 and TEFLON AF (all
trademarks of E. I. Dupont de Nemours and Co., Wilmington, Del.),
HALAR (a trademark of Ausimont USA, Inc, Thorofare, N.J.), and
Neoflon (a trade mark of CTFE produced by Darkin, Orangeburg,
N.Y.).
[0035] The filler material that can be employed pursuant to the
present invention comprises silica. The filler material comprises
about percent by weight to about 60 percent by weight of the
composition. The silica, having the chemical formula Sio.sub.2, can
be selected from the group consisting of crystalline silica, fumed
silica, synthetic silica, precipitated silica and amorphous silica.
Crystalline silica and amorphous silica are obtained/mined (ground
and purified) from natural sources. Purification removes other
elements and ionic impurities. The purification step involves both
thermal and chemical processes. Synthetic silica and precipitated
silica can be obtained from sol (colloidal)/gel chemical processing
of silanes, which involves the polymerization of silanes into small
insoluble silica particles. Such a reaction permits the preparation
of highly pure silica (without natural mineral impurities) having
controlled size and shape. Fumed silica is a synthetic silica
prepared from the reaction of SiCl.sub.4, hydrogen, and oxygen in
the gas phase to form SiO.sub.2. The silica particles can have
substantially spherical or spheroidal shapes and have sizes of from
about 0.1 microns to about 40 microns. The addition of silica
particles of this shape and size facilitates the composition such
that it will readily flow into and conform to the through hole
shape of the metal layer and provides low thermal expansion
properties, a very important aspect of this invention.
[0036] A portion of each of the filler particles can include a
layer of a coupling agent positioned thereon to improve adhesion
and moisture resistance. Coupling agents such as fluorosilanes
including alkoxy or halo groups can be used in this invention.
Fluorosilane and alkoxy and halo fluorosilanes, take the form of
(R')--Si--(R", R'", R""). Silanes are organic based silicon
containing molecules. Typically the Si group is bound to an organic
functional group (R') such as alkane, alkene, phenyl or aromatic
groups or combinations thereof and may have fluoro, bromo, or
chloro (halo) groups replacing the hydrogen atoms. The R' group may
also have a chemically active pendant group, such as an epoxy,
amino, chloro, bromo, enabling it to react with other organic
molecules. The other three groups (R", R'", R"") attached to the Si
are typically chloro, bromo, methoxy, or ethoxy and can react with
each other in a displacement reaction to form a monolayer on a
silica or metal surface or together to form a network polymer. For
example, coupling agents, such as 1H, 1H, 2H, 2H
perflurooctyltriethoxysilane #12303-4 and 1H, 1H, 2H, 2H
perfluroalkyltriethoxysilane #12347-1, both available from PCR
Incorporated, Gainesville, Fla., can be used in this invention. An
amount of coupling agent which is from about 1% by weight to about
10% by weight of the composition has been found satisfactory. The
thickness of the coupling agent on the filler particles can be as
little as about a few monolayers.
[0037] Surfactants can be used to facilitate mixing of the filler
material with the fluoropolymer dielectric in solution. Suitable
surfactants include those of the non-ionic type, available under
the product name Triton X-100 from Rohm and Haas Co., Philadelphia,
Pa. Other surface active agents that can be used in this invention
include polyoxyethylene/polyoxypropylene block copolymers
commercially available under the trade name Pluronics, such as
Pluronic L-62, Pluronic 31R1, and Pluronic L-92 from BASF Inc.,
Parsippany, N.J.
[0038] The compositions of the present invention may have a pH of
from about 8 to about 11.
[0039] In accordance with another embodiment of this invention, a
method for making the hole fill composition defined above is hereby
provided. The method comprises the steps of providing a quantity of
filler material as defined hereinabove, adding to the quantity of
filler material a quantity of the above-defined coupling agent to
at least partially coat the filler material, adding to the quantity
of filler material at least partially coated with the coupling
agent a quantity of the fluoropolymer dielectric material of the
type defined above and then blending the filler material coated
with the coupling agent and the fluoropolmer dielectric material.
The filler material at least partially coated with the coupling
agent can be prepared by dissolving the coupling agent in a
suitable solvent, such as isopropyl alcohol, and mixing the filler
material into the coupling agent/solvent solution to form a slurry.
The slurry can then be poured into an open vessel, air dried for
about 12 hours, broken up into smaller particles, and further dried
in an air oven at about 125.degree. C. for about another 2 hours.
The step of blending the filler material at least partially coated
with coupling agent and the fluoropolymer dielectric material can
include slowly adding the dried filler material into a solvent,
such as deionized water, with vigorous agitation to form a slurry,
adjusting the pH of the deionized water/filler material slurry to a
pH of from about 8 to a pH of about 11 using ammonium hydroxide or
another suitable base, and dispensing the fluoropolymer dielectric
material into the pH adjusted deionized water/filler material
slurry. A quantity of surfactant, such as defined above, can be
added with stirring until the surfactant is dissolved.
[0040] In accordance with yet another embodiment of this invention,
referring to FIG. 2, there is also provided a substrate 10 which
includes a metal layer 16 including at least one through hole 18
therein defined by at least one side wall 20 within the metal
layer, and a mixture 22 of the above-identified fluoropolymer
dielectric material and the above-defined filler material at least
partially coated with a coupling agent, as described above,
positioned on the side wall of the through hole, the mixture
substantially filling the through hole in the metal layer. The
metal layer 16 of substrate 10 is selected from the group
consisting of nickel, copper, cobalt, molybdenum, iron and alloys
thereof. For example, one alloy that can be used as the metal layer
of this invention is Invar clad with a layer of copper. Invar can
be defined as an alloy having a composition of about 34% to about
0.38% nickel and about 62% to about 66% iron. A suitable alloy of
this type is available from Texas Instruments Incorporated
(Attleboro, Mass.).
[0041] In accordance with still yet another embodiment of this
invention, a method for making the substrate defined above is
hereby provided. The method comprises the steps of providing a
metal layer including at least one through hole therein defined by
at least one side wall within the metal layer, as defined
hereinabove, positioning a mixture of the above-defined
fluoropolymer dielectric material and a filler material of the type
defined above at least partially coated with the above-defined
coupling agent on the side wall of the through hole, and heating
the metal layer, fluoropolymer dielectric material, and filler
material to a temperature of up to about 80 degrees centigrade
above the fluoropolymer melting temperature to adhere the
dielectric material and filler material to the side wall of the
through hole, the dielectric material and the filler material
substantially filling the through hole. This will form a
substantially planar substrate surface. During the heating step,
the surfactant employed in the production of the fill composition
is substantially burned off. For example, when the fluoropolymer
dielectric material is TEFLON PTFE, its melting temperature is
about 327 degrees centigrade, so the heating temperature would be
in the range of about 327 degrees centigrade to about 407 degrees
centigrade.
[0042] The through hole in the metal layer can be provided by the
step of drilling, punching or etching.
[0043] The filler material and the fluoropolymer dielectric
material are adhered to the side wall of the through hole by fusion
during the heating step. Fusion is the process by which the
fluoropolymer dielectric material and the filler material are
heated above the fluoropolymer melt temperature so that the
fluoropolymer and filler adhere to the side wall by a combination
of mechanical and chemical interlocking once the temperature is
reduced below the melt temperature.
[0044] The invention provides a novel hole fill composition and
method of making the composition which can substantially fill
through holes in the metal layer of a substrate, provides a
substantially planar substrate surface, and minimizes voids and
blisters in the through hole area, thereby reducing defect levels
during manufacture or assembly of components to the multilayer
printed circuit board or chip carrier of which the substrate is a
part.
[0045] While there have been shown and described what are the
present considered preferred embodiments of the invention, it will
be obvious to those skilled in the art that various changes and
modifications may be made therein without departing from the scope
of the invention as defined by the appended claims.
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