llllll||I|||||||||||||||l||Illlllllllllllll|||||||||l|l||l||||lillll||||||l
`U5005506049A
`
`United States Patent
`
`[19;
`
`[11] Patent Number:
`
`5,506,049
`
`Swei et al.
`
`[45} Date of Patent:
`
`* Apr. 9, 1996
`
`3101490
`511930 Graudine,ll
`4,203,343
`.4231901x
`711930 Reed
`4,211,603
`4231143
`1211931 Blitsteiuetal.
`4,307,142
`.. 264149
`411933 Morenoetal.
`4,330,521
`.4231413
`711933 CDithflJIOII
`4,393.119
`5241431
`4,409,354 1011933 Namba etal
`264149
`4,434,116
`211934 Cavitch
`. 4231409
`,
`4,500,603
`211935 Freuudlich
`.. 4231421
`..
`4.555.543
`1111935 Efi’enbcrger et a1.
`4231245
`..
`4,610,913
`911936 Efi‘enbergeretal.
`264141
`4,692,237
`911937 ’l‘imrnons ...............
`4231421
`4,818,619
`411939 Stepparolaetal.
`42312097:
`4,324,511
`411939 Hartmannal.
`4231133
`4,347,135
`711939 Brena et 41.
`4231325
`4,349,234
`711939 Arthuretal.
`4231421
`4,333,716 1111939 Efl‘enbergeretal.
`4,333,245 1211939 Nitzlto ................................... .. 4231421
`
`
`
`(List continued on next page.)
`FOREIGN PATENT DOCUMENTS
`
`246844 1111937 European P143001.
`2071112
`91198] United Kingdom.
`
`Pit-imam: Examiner—Paul .l. Thibodeau
`Assistant Exmniner—H. Thi Le
`Attorney, Agent, or Firm—Fishman, Dionne & Cantor
`
`[57]
`
`ABSTRACT
`
`A particulate filled fluoropolymeric matrix composite article
`and method of making the same is presented. Preferably, the
`article comprises an electrical
`substrate material. The
`method for making the particulate filled polymeric matrix
`composite film includes mixing a polymeric matrix material
`with a dispersion of particulate filler in a carrier liquid to
`form a casting composition and adjusting the viscosity of the
`casting composition to retard separation of the particulate
`filler from the composition. A layer of the viscosity-adjusted
`casting composition is cast on a substrate and the layer is
`consolidated to form the particulate filled polymer matrix
`composite film. Films made by the method include very thin,
`e.g less than 1.0 mil, fluoropolymeric matrix films highly
`filled with very small diameter, preferably spherical, par-
`ticles for use as, eg. dielectric substrate materials in laminar
`electrical circuits.
`
`40 Claims, 1 Drawing Sheet
`
`[54] PARTICULATE FILLED COMPOSITE FILM
`AND METHOD OF MAKING SAME
`
`[75]
`
`Inventors: Gwo S. Swei, Northboro; David J.
`Arthur, Norwood, both of Mass.
`
`[73] Assignee: Rogers Corporation, Rogers, Conn.
`
`[*1 Notice:
`
`The portion of the term of this patent
`subsequent
`to Jun. 18, 2008, has been
`disclaimed.
`
`[21] Appl. No.: 177,198
`
`[22] Filed:
`
`Dec. 30, 1993
`
`Related U.S. Application Data
`
`[62] Division of Ser. No. 705,624, May 24, 1991, abandoned.
`
`Int. Cl.6
`[51]
`[52] U.S. Cl.
`
`B323 5116
`4281323; 4281325; 4281335;
`4281901
`4281323, 325.
`[58] Field of Search
`4281335, 403, 404, 405, 406, 407, 421,
`422, 457, 901
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`.
`
`611955 Hochberg
`2,710,266
`911958 Pctricllo ..
`2,852,811
`211960 Pettiello
`2,923,651
`711960 Evans et a].
`2945.831
`2,961,345 1111960 Peuiello
`2,980,965
`411961 lnfantino etal. ..
`3,054,716
`911962 Bergstein et al.
`3,054,761
`911962 Moore etal.
`3,292,725 1111966 Van Zalingo
`3,513,332
`611970 Skiarchuk
`3,556,161
`811970 Roberts
`3,577,508
`511971 Desaulniers .
`3.679.614
`711972 Shah et al.
`3,343,570 1011974 MmMa ..
`4,049,589
`911977 Sakane
`4,112,037
`911973 Parkeretal.
`4,183,991
`111980 Smiley et al.
`4,196,070
`411980 Chad etal.
`
`
`
`4281268
`264139
`4281461
`2601296
`4231212
`....... 18157
`2641212
`. 5241491
`2641215
`. 264149
`....... 1381141
`264133115
`521162
`521162
`521164
`.. 2641126
`4231220
`2041226
`
`mm 2
`4
`
`
`
`
`
`Dr. Reddy's - EX1018
`
`Page 1
`
`Dr. Reddy's - EX1018
`Page 1
`
`

`

`Page 2
`
`5,506,049
`Page 2
`
`1.1.8. PATENT DOCUMENTS
`
`
`
`1!]990 Suzuki
`4.895.756
`4235119
`
`4.915.983 M1990 Lake at 3.1.
`.. 430511 X
`4,985,296
`1:199! Mortimer. Jr.
`4281221)
`
`4.990544
`5.024.871
`5,051,543
`5,077,115
`5.198.295
`
`21'1991 Asaumi at a}.
`6(1991 Arthur et a1.
`10:1991 Aymaraal,
`[211991 Arthur et a1.
`3:1993 Anhure: a1.
`
`428l283 X
`4231209
`423mg
`. 423%?
`423823
`
`Page 2
`
`

`

`US. Patent
`
`Apr. 9, 1996
`
`5,506,049
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`m. 3
`
`
`
`*W
`
`Page 3
`
`
`
`.
`
`
`
`
`
`l'ullmmnl'nflflfi
`
`a
`
`
`
`
`
`
`
`
`
`
`
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`1‘76. 5
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`Page 3
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`

`

`1
`PARTICULATE FILLED COMPOSITE FILM
`AND METHOD OF MAKING SANEE
`
`This is a divisional of application Ser. No. 0?fl05,624
`filed on May 24, 1991., now abandoned.
`
`TECHNICAL FIELD
`
`The present invention relates to particulate filled polymer
`matrix composite materials and methods of manufacturing
`same and more particularly to thin films of highly filled
`polymer matrix composite materials.
`
`BACKGROUND OF THE INVENTION
`
`Laminated electrical circuit substrates which include a
`
`conductive layer supported on a dielectric fluoropolymer
`matrix composite layer are known. Driven by the continuing
`trend toward increasing circuit density, very thin films, cg.
`less than about 1.0 mil, of highly filled fluoropolymeric
`matrix composite substrate materials having a substantially
`uniform mierostructure have become desirable as allowing
`further reduction in the size of electronic circuits. It is
`technically and economically difficult to make such mate-
`rials by known methods.
`filled fluoropolymer
`Fluoropolymer and particulate
`matrix composite films are made by known papermakr‘ng,
`skiving, casting, melt extrusion and paste extrusion and
`calender-lug processes.
`Films produced by paper making processes required fiber
`reinforcement and are limited to thicknesses greater than
`about 2 mil.
`
`It is very ditiicult to produce thin high quality highly filled
`fiuoropolymer matrix films by striving due to abrasion of the
`skiving blade by the filler particles and tearing of the film
`associated with the resistance of the filler particles to the
`sltiving blade.
`The filler loading of films made by known casting pro-
`cesses is limited to less than about 15 volume percent.
`The high melt viscosity of neat fluoropolymers compli-
`cates the production of fluoropolymer films by melt extru-
`sion. Polyvinylidene fluoride (WP!) and polychlorotrifiuo-
`methylene (PCTFE) are melt exuudable only within a
`narrow processing window. Polyvinylfiuoride (PVF) film
`cannot be produced by melt extrusion due to thermal insta-
`bility. Polytetrafiuoroethyleue (FIFE) cannot be melt
`extruded due to its extraordinarily high melt viscosity.
`Fluorocopolymers are known which provide lower melting
`temperature and lower melt viscosity at extrusion tempera-
`tures, eg. copolymers of tetrafiuorocthylcne with hexafluo-
`ropropylene (FE?) or with ethylene, copolyrners of CTFE
`with vinylidene fluoride or hexafiuoropropylene.
`The introduction of fillers further complicates the melt
`extrusion of fluoropolyrners. In the presence of certain
`fillers. especially at high filler loading level, the melt pro-
`cessability of the melt extrudable fiuoropolymers is rapidly
`degraded due to the increase in melt viscosity associated
`with the presence of the filler or with filler-catalysed thermal
`degradation of the polymer matrix.
`A method of making highly filled PTFE composite mate-
`rials which exhibit excellent physical and electrical proper-
`ties by paste exrrusicn and calendering is set forth in
`coassigned U.S. Pat. No. 4,349,284 to D. J. Arthur, I. C.
`Mosko, C. S. Jackson and G. R. Trent, entitled “ELECTRI-
`CAL SUBSTRATE MATERIAL", the disclosure of which is
`incorporated herein by reference. However, it is techniwa
`
`10
`
`15
`
`‘15
`
`30
`
`35
`
`d0
`
`45
`
`50
`
`55
`
`611
`
`65
`
`5 ,5 06,049
`
`2
`
`to produce
`ditficult and economically extremely difficult
`thin, i.e. less than 2 mils, highly filled, i.e. greater than about
`40%. fiuoropclymer matrix composite films by the paste
`extrusion and calendaring process.
`What is needed in the art is a method which overcomes
`the above noted deficiencies of known processing methods.
`
`SUMMARY OF THE INVENTION
`
`A particulate filled fluoropolymer matrix composite
`article is disclosed. The article includes a fluoropolymer
`matrix and up to about 95 vol. % filler particles distributed
`throughout the matrix. wherein said particles have a maxi-
`mum equivalent spherical diameter of less than about 10
`microns.
`
`In an alternative embodiment, a particulate filled fluo-
`ropolymer matrix composite article comprises a fluoropoly-
`mer matrix and up to about 95 vol. % filler particles
`distributed throughout the matrix wherein none of the par-
`ticles have a single linear dimension greater than about 10
`microns.
`
`In a preferred embodiment a particulate filled finoropoly-
`mer matrix composite film comprises a nonfibrlllated finc-
`ropolymer matrix and greater than about 15 vol. percent
`filler particles distributed throughout the matrix. The film
`has a thickness less than about 2 rolls and is free of visually
`evident pin holes or tears.
`A porous fiuoropolymer film comprising a nonfibrillated
`fluoropolymer matrix having a void volume of greater than
`about 15 vol. % and a thickness of less than about 2 mils is
`disclosed.
`
`A method for making a particulate filled polymer matrix
`composite film is disclosed. The method comprises mixing
`the polymer with a dispersion of the particulate filler in a
`carrier liquid to provide a casting composition, wherein the
`casting composition includes relative amounts of polymer
`and filler effective to provide a film having greater than 15
`volume percent filler casting a layer of the casting compo-
`sition onto a substrate and consolidating the cast layer to
`form the particulate filled polymer matrix composite film.
`A caning composition is also disclosed. The casting
`composition includes a mixture of liquid carrier, a polymeric
`matrix material, and particles of a filler material.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows aphotomicrcgraph of a cross sectional view
`of a particulate filled polymer matrix composite film of the
`present invention.
`FIG. 2 shows a laminar circuit substrate made by the
`process of the present invention.
`FIG. 3 shows a cross sectional view of a conductive
`through-hole communicating between layers of a portion of
`a laminated electrical circuit
`
`FIG. 4 shows a cross sectional view taken along lines 4—
`4 of FIG. 3.
`
`FIG. 5 shows a cross sectional view of a portion of a
`laminar electrical circuit.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`Suitable fluoropolymer matrix materials include fluori-
`nated homopolymers, e.g. polytetrafluoroethylene (PTFE)
`and polychlorotrifluoroethylene (PCTFE)_ and fiuorinated
`copolymers, e.g. eopolymers cf tetrafiuoroethyleoefi/Eyarl
`
`Page 4
`
`Page 4
`
`

`

`5,506,049
`
`3
`monomer selected from the group consisting of hexafluo-
`ropropylene and perfluoroalkylvinyleurers, copolymers of
`tetrafiuoroethylene with a monomer selected from the group
`consisting of vinylidene fluoride, vinyl fluoride and ethyl-
`ene, and copolymers of chlorou-ifiuoroethylene with a
`monomer selected from the group of hexafiuoropropylene, .
`perfiuoroalltylvinylethers, vinylidene fluoride, vinyl fluoride
`and ethylene. Blends of the above listed fiuoropolymers and
`terpolymers formed from the above listed monomers are
`also suitable as the fluoropolymer matrix material of the
`present invention.
`Alternatively, polymer matrix material of the present
`invention may comprise a thermoplastic or thermosetting
`polymer other than a fluoropolymer. Suitable alternative
`polymeric matrix materials include, e.g. polyolefins, poly-
`imides, epoxy resins and cyanate esters. Specific examples
`of suitable polymer matrix materials include polyethylene,
`polymethylpentene, and polybutadiene.
`The particulate filler material of the present invention may
`include any organic or inorganic particulate material. The
`terms “particulate” and “particles” as used herein are
`intended to include fibers. Suitable inorganic filler materials
`include, e.g. glass particles, ceramic particles, metallic par-
`ticles, carbon particles and mineral particles. Specific
`examples of suitable particles include glass beads, glass
`microspheres. glass fibers, silica particles, carbon black,
`titanium dioxide particles and barium titanate particles.
`Silica particles, particularly amorphous fused silica particles
`and silica particles made by a sol gel process, and glass
`particles, are preferred filler particles for applications, e.g.
`dielectric layers of laminar electrical circuits, requiring a
`low dielectric constant.
`
`Specific examples of suitable polymeric particulate fillers
`include polymeurylmethacrylate particles, polystyrene par-
`ticles and polyimide particles. Suitable polymeric particles,
`e.g. LARC—TPI (Rogers, Corp), P-34 (Leaning).
`.
`The shape of the filler particles, the size of the filler
`particles and the size distribution of the filler particles are
`important parameters with regard to characterizing the par-
`ticle filled composite article of the present invention.
`In a preferred embodiment of the present invention all
`particlcs of the particulate filler exhibit an equivalent spheri-
`cal diameter'of less than about 10 microns (urn). As used
`herein the "equivalent spherical diameter" of a filler particle
`is the diameter of a sphere which occupies the same volume
`as that occupied by the filler particle.
`In an alternative preferred embodiment of the present
`invention, each of the filler particles exhibit no single linear
`dimension greater than about 10 um.
`For extremely thin films and in applications where a
`subSIantially uniform microstructure is an important char-
`acteristic of the film, it is preferred that all particles of the
`particulate filler exhibit an equivalent spherical diameter of
`less than about 5 our. Alternatively, it is preferred that all
`particles of the particulate filler exhibit no single linear
`dintension greater than about 5 pm
`In a preferred embodiment of the present invention each
`of the filler particles is substantially spherical. The use of
`spherical filler particles provides improved processability by
`minimizing the filler surface area for a given particle size
`and filler loading. Furthermore, spherical particles provide
`isotropic properties to the film since the spherical particles
`do not become oriented during processing.
`In a preferred embodiment of the present invention, the
`filler particles of the film are of a uniform size. The use of
`a monodisperse filler, i.e. wherein all the filler particles are
`
`10
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`15
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`35
`
`SI)
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`55
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`60
`
`65
`
`4
`of substantially the same size, provides a more homoge-
`neous film having substantially uniform properties through-
`out.
`
`In a particularly preferred embodiment of the present
`invention, the filler particles comprise Spherical silica par-
`ticles of asubstantially uniform size, i.e. all particles within
`plus or minus 10% of a nominal particle diameter. A pure
`silica powder known as GELSIL® produced by Gelteclt,
`Inc. and specified as :1 micron sphere size [i10%); density
`of 2.2 gramslcmzt free of hard agglomerations, has been
`found to be particularly suitable for use in the pracfice of the
`present invention.
`The particulate filler material may be treated with a
`surface treamrent to improve the moisture resistance and
`irnprove the mechanical properties of the composite film of
`the present invention.
`The hydrophobic coating of the present invention may
`comprise any coating material
`that is thermally stable,
`exhibits a low surface energy, and improves the moisture
`resistance of the composite of the present invention. suitable
`coating materials,
`include conventional silane coatings,
`titanate coatings and zirconate coatings. Preferred silane
`coatings include: phenyltrimethoxysilane, phenyln-iethox-
`ysilane, 3,3,3-uifluoropropyltrimethoxysilane,
`(tridecaf-
`luoro- I,l,2,2-tetrabydrodecy1)—l-triethoxysilane and mix-
`tures thereof. Further examples of suitable fluorinated silane
`compounds are set ferth ill unassigned U.S. application Ser.
`No 279,474,
`filed Dec. 2, 1988 and entitled “FLUO-
`ROPOLYMER COMPOSITE" by D. J. Arthur and G. S.
`Swei, the disclosure of which is incorporated herein by
`reference. Suitable titanate coatings include: neopentyl(dial-
`lyl)oxytrineodecanoyl titanate, neopentyl(dia]lyl)oxytri(di-
`octyl)phosphate
`titanate. Suitable
`zirconate
`coatings
`include: neopentyl(diallyl)oxyui(dioetyl)pyrophosphate zir-
`conate and neopentylidiallylloxyuim-ethylenediaminolet-
`hyl airconate. Further examples of suitable titanate and
`zirconate coatings are set forth in coassigned U.S. applica-
`tion Ser. No. 483.501, field Feb. 21, 1990, now 11.8. Pat. No.
`5,024,8?1, and entitled “CERAMIC FLUOROPOLYMER",
`by D. J. Arthur and G. S. Swei, the disclosure of which is
`incorporated herein by reference.
`The hydrophobic coating is used in an amount effective to
`render the surfaces of the filler particles hydrophobic and
`compatible with the matrix material. The amount of coating
`relative to the amount of inorganic particles coated will vary
`with the surface area coated and density of the inorganic
`particles. Preferably, the coated inorganic particles of the
`present invtion include from about 0.5 parts by weight
`(pbw) hydrophobic coating: 100 pbw inorganic particles to
`about 25 pbw hydrophobic coating: 100 pbw inorganic
`particles.
`-
`The polymer matrix material of the present invention is
`mixed with a first carrier liquid. The mixture may comprise
`a dispersion of polymeric particles in the first carrier liquid,
`a dispersion, in an emulsion, of liquid droplets of the
`polymer or of a monomeric or oligameric precursor of the
`polymer in the first carrier liquid or a solution of the polymer
`in the first carrier liquid.
`The choice of the fest carrier liquid is based on the
`particular polymeric matrix material and the form in which
`the polymeric matrix material is to be introduced to the
`casting composition of the present invtion. [fit is desired
`to introduce the polymeric material as a solution, a solvent
`for the particular polymeric matrix material is chosen as the
`canier liquid, e.g. N-methyl pyrrolidone (NM?) would be a
`suitable carrier liquid for a solution of a polyimide. If it is
`
`Page 5
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`Page 5
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`5
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`6
`
`5,506,049
`
`desired to introduce the polymeric matrix material as a
`dispersion, then a suitable carrier liquid is a liquid in which
`Ihe matrix material is not soluble, e.g. waler would be a
`suitable carrier liquid for a dispersion of PTFE particles and
`would be a suitable carrier liquid for an emulsion of
`polyamic acid or an emulsion of butadiene monomer.
`Preferably, a fiuoropolyrneric matrix material is intro-
`duced as an aqueous dispersion. A dispersion of PTPE in
`water known as Tefion® TE 30 made by DuPont has been
`found to be particularly suitable for use in the practice of the
`present invention.
`A dispersion of the particulate filler of the present inven-
`tion in a suitable second carrier liquid, i.e. a liquid in which
`the filler is not soluble. The second carrier liquid may be the
`same liquid or may be a liquid other than the first carrier
`liquid that is miscible with the first carrier liquid. For
`example, if the first carrier liquid is water, the second carrier
`liquid may comprise water or an alcohol. Preferably, the
`second carrier liquid is water.
`The dispersion of filler particles may include a surfactant
`in an amount efl'ectlve to modify the surface tension of the
`second carrier liquid to enable the second carrier liquid to
`wet
`the filler particles. Suitable surfactant compounds
`include ionic surfactants and nonionic surfactants. Triton
`X-100 (Rohm & Haas) has been found to bc a suitable
`surfactant for use in aqueous filler dispersions.
`Preferably, the filler dispersion comprises from about 10
`volume percent (vol 9b} to about 50 vol % filler particles.
`from about 0.1 vol 9'0 to about 10 vol % surfactant, with the
`remainder comprising the second carrier liquid.
`The mixture of the polymeric matrix material and first
`carrier liquid and the dispersion of the filler particles in the
`second carrier liquid are combined to form the casting
`composition of the present invention. Preferably, the casting
`composition comprises from about 10 vol % to about 60 vol.
`% of the combined polymeric matrix material and filler
`particles and from about 40 vol. % to about 90 vol. %
`combined first and second carrier liquids. The combined
`amount of polymeric matrix material and filler particles may
`include from 15 vol. % to about 95 vol. % filler particles.
`Preferably, the combined amount of polymeric matrix mate-
`rial and filler particles includes from about 30 vol. 96 to
`about 70 vol. 95 filler particles. Most preferably, the com-
`bined amount of polymeric matrix material and filler par-
`ticles includes from about 40 vol. % to about 65 vol. % filler
`
`particles.
`The viscosity of the casting composition of the present
`invention is adjusted by the addition of suitable viscosity
`modifier, chosen on the basis of its compatibility in a
`particular carrier liquid or mixture of carrier liquids, to
`retard separation, i.e. sedimentation or flotation, of the filler
`particles from the casting composition and to provide a
`casting composition having a viscosity compatible with
`conventicmal casting equipment. Conventional thickening
`agents are suitable and are chosen on the basis of the carrier
`liquid selected. Conventional viscosity modifiers suitable for
`use in aqueous casting compositions include, e.g. poly-
`acrylic acid compounds, vegetable gums and cellulose based
`compounds. Specific examples of suitable viscosity modi-
`fiers include polyacrylic acid, methyl cellulose, polyethyl-
`eneoxide, guar gum, locust bean gum, sodium carboxym-
`ethylcellulose, sodium alginate and gum tragacanth.
`
`5
`
`10
`
`15
`
`30
`
`35
`
`45
`
`50
`
`SS
`
`60
`
`65
`
`A minimum viscosity of the viscosity-adjusted casting
`composition is defined according to Stoke‘s law, i.e.
`
`'5? =
`
`st’ (9p - PL)
`1§tt
`
`wherein:
`
`v=terminal velocity of particle;
`g=gravitational constant;
`
`Dp=particle diameter;
`pp=particle density;
`pyzliquid density; and
`u=liquid viscosity;
`on the basis of the sine and density of the filler particles to
`provide a theoretical terminal viscosity, i.e. a filler separa-
`tion rate, that provides a casting composition that is stable
`within the time period of interest,
`i.e.
`the time period
`between mixing the casting composition and consolidating
`the film cast from the composition. For example, substitu-
`tion according to the above relationship reveals that an
`aqueous solution having a viscosity of 10,000 cp provides a
`theoretically terminal velocity of 6.5x10“1° ends for silica
`particles (density=2.2 glen?) having a diameter of 1 out. The
`viscosity of the viscosity-adjusted casting composition may
`be further increased, i.e. beyond the minimum viscosity, on
`an application by application basis to adapt the casting
`composition to the selected casting technique. For example,
`a viscosity of about 300 cp to about 1000 cp is preferred for
`metering rod casting.
`Preferably,
`the viscosity adjusted casting composition
`exhibits a viscosity between about 10 op and about 100,000
`cp. Most preferably, the viscosity adjusted casting compo-
`sition exhibits a viscosity between about 100 cp and 10,000
`op.
`Alternatively, the viscosity modifier may be omitted if the
`viscosity of the carrier liquid is sufiicient to provide a casting
`composition that does not separate during the time period of
`interest. Specifically, in the case of extremely small par-
`ticles, e.g. particles having an equivalent spherical diameter
`less than 0.1 urn, the use of a viscosity by modifier may not
`be necessary.
`A layer of the viscosity-adjusted casting composition is
`cast on a substrate by conventional methods, eg. dip coat-
`ing, reverse roll coating, knife-over-roll, knife-over-plate,
`and metering rod coating.
`Suitable substrate materials include, e.g. metallic films,
`polymeric films or ceramic films. Specific examples of
`suitable substrates include stainless steel
`foil, polyimide
`films, polyester films, fluoropolymer films.
`The carrier liquid and processing aids, i.e. the surfactant
`and viscosity modifier, are removed from the cast layer, e.g.
`by evaporation andlor by thermal decomposition, to con-
`solidate a film of the polymeric matrix material and the
`particulate filler. Preferably, the particulate filled polymeric
`matrix composite film of the present invention is consoli-
`dated by heating to evaporate the carrier liquid.
`The composition or the consolidated film corresponds to
`that of the combined amount of polymeric matrix material
`and filler particles set forth above in regard to the casting
`composition, i.e. the film may comprise from 15 vol. 96 to
`about 95 vol. % filler particles and from about 5 vol. % to
`85 vol. % matrix material, preferably comprises from about
`30 vol. % to about 70 vol. % filler particles and from 30 vol.
`% to about 70 vol. 9'» matrix material and most preferably
`comprises from about 40 vol. % to about 65 vol. % filler
`particles and from about 35 vol. 9’s to about 60 vol. % matrix
`material.
`
`Page 6
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`Page 6
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`

`

`5,506,049
`
`7
`The consolidated film of polymeric matrix material and
`particulate filler may he further heated to modify the physi-
`cal properties of the film, eg. to sister a thermoplastic
`matrix material or to cure andr'or post cure a therrnosening
`matrix material.
`
`The process of the present invention allows films having
`thickness below about 2 mils, and even below about 1 mil,
`to be economically produced. Film thicknesses are set forth
`herein in terms of “mils”, wherein one mil is equal to 0.001
`inch.
`Since the process of the present invention allows thin
`films to be produced without deforming the film, e.g. with-
`out calendaring or expanding the film, fiuoropolymer matrix
`films can be made without the fibrillation of the matrix
`material characteristic of expanded films and without the
`associated danger of tearing or forming pinholes in the film.
`If a porous film is being produced, the filler matmial is
`removed from the consolidated film. The method of removal
`is dependent upon the choice of filler material. If a filler
`material is dispersed in a matrix material wherein the matrix
`exhibits much higher temperature resistance than the filler
`material, e.g. a polymethyhnethacrylate filler in a PTFE
`matrix the filler material can be removed thermally during
`the consolidation and sintering steps. Alternatively, the filler
`material can be dissolved in a liquid in which the filler is
`soluble, but within the matrix material is insoluble Removal
`of filler materials from a fluoridated polymer matrices to
`form a porous fluoropolymer film is described in coassigned
`U.S. Pat. No. 4,937,274, entitled “COAXIAL CABLE
`lNSULATION AND COAXIAL CABLE MADE THERE-
`WTI'H”, by T. L. Miller, W. R. Zelanis, G. A. Woerner and
`A. F. Hum 111, the disclosure of which is incorporated herein
`by reference.
`It should be noted that the fluoropolymer matrix of the
`thin porous fluoropolymer film of the present invention does
`not exhibit the ribrillar structure characteristic of expanded
`porous FIFE films.
`The substrate and consolidated film may be used in
`combination as a laminar composite material or as a sub-
`strate for subsequent composite layers. Alternatively, the
`substrate may be removed from the film. The substrate may
`be deslmctively removed, e.g. by dissolution in a solvent, by
`chemical reaction, or thermal degradation, or the substrate
`may be reusably removed, e.g. by overcoming interfacial
`adhesion between the cast film and the substrate.
`
`The consolidated film may be used alone, e.g. as dis-
`cussed below, or as the substrate for subsequent casting of
`further layers of the casting composition to build up a
`multilayer film.
`The thin particulate filled fluoropolymeric matrix com-
`posite of films of the present invention have a wide range of
`potential applications.
`A laminar circuit substrate made by the process of the
`present invention is shown in FIG. 2. The substrate com-
`prises a conductive layer 2 laminated with a particle filled
`fluoropolymer composite layer 4. The laminar substrate
`shown in FIG. 2. can be made. e.g. by casting and consoli-
`dating layer 4 on a layer of the conductive film 2.
`As discussed above, the shape, size distribution of the
`filler particles is very important in several applications.
`Film thickness is a very important consideration in appli-
`cations where a particulate filled film is used as a dielectric
`substrate for a high density laminar electrical circuit. As the
`feature dimensions of the circuit are decreased, it becomes
`desirable to correspondingly reduce the thickness of the
`dielectric layer to thereby preserve the characteristic imped-
`ance of the circuit.
`
`10
`
`15
`
`3O
`
`35
`
`45
`
`SI]
`
`55
`
`In general, it is desirable that the longest characteristic
`dimension of the filler particles is significantly, e.g. by a
`factor of 10, less than the thickness of the particulate filled
`film to avoid bridging of particles between the surfaces of
`the film. As the desired film thickness decreases it becomes
`progressiver more difiicult to meet the criterion.
`Another outgrowth of increasing circuit density is illus-
`trated in FIGS. 3 and 4. A portion of a conventional laminar
`circuit 6 includes conductive layer 3 encased within dielec—
`tric layers 10, 12. A conductive through hole, i.e. a ‘
`’ ", is
`defined by a conductive sleeve 14. The conductive sleeve 14
`is separated from the conductive layer 8 by an insulating
`sleeve region 16 of dielectric mateIial formed by fusing the
`edges of the dielectric layers ll], 12. With increasing circuit
`density it is desirable to decrease the dimension of the
`conductive
`hole. As the distance between the con-
`ductive sleeve 14 and the conductive layer 8 is decreased,
`filler size must he correspondingly decreased to avoid bridg-
`ing of filler particles between the conductive sleeve 14 and
`conductive layer 3.
`A further aspect of increasing circuit density and decreas-
`ing via hole diameter is the need to drill smaller via holes.
`As the via hole diameter decreases, filler particle size
`becomes an important factor in hole quality. Laser drilling of
`particulate filled fiuuropolymer matrix films is described in
`coassigned U.S. Pat. No. 4,915,981. entitled “METHOD OF
`LASER DRILLING FLUOROPOLYMER MATERIALS”,
`by R. T. Traskos, C. A. Fleischer, C. A. Barton and D. B.
`Noddin, the disclosure of which is incorporated herein by
`reference. Laser drilling is eifective at removing precise
`amounts of matrix material but literally blasts whole chunks
`of filler particles from the hole being drilled. Consequently,
`the use of small filler particles allows higher quality, i.e.
`more precisely defined, small diameter holes to be laser
`chilled.
`FIG. 5 shows a portion of a laminar electrical circuit 16
`which includes a bondply layer 22 sandwiched between a
`pair of laminated circuit layers each comprising a conduc-
`tive layer 22 supported on a dielectric layer 20. The casting
`process of the present invention can be used with a lower
`melting fiuoropolymer matrix material, e.g. FEP, to produce
`very thin, highly filled bondplys for use in laminar electrical
`The. ability to make a highly filled finoropolymer
`matrix bmdply would provide electrical preperties similar
`to those of the substrate layers being bonded, while the
`ability to make a very thin bondey would minimize the
`detrimental effect of the bondply layer on the dimensional
`stability of the laminar circuit.
`The ability to produce very thin, highly filled fiuoropoly-
`rner films with an ordered nncrostructure is also of advan-
`tage in regard to circuit substrate materials for “nun-wave"
`applications which require very thin films having physical
`and electrical properties which, given the frame of reference
`provided by the short wavelength radiation involved, can be
`considered substantially uniform for purposes of the par-
`ticular application.
`An inorganic particle filled matrix composite layer may
`be cast onto a polyimide film to produce a composite film
`suitable for use in hex circuit applications. A flexible circuit
`including a microglass reinforced fiuoropolymer matrix
`composite layer sandwiched between a polyimr'de film and
`a copper conductive pattern is described in coassigned U.S.
`Pat No. 4,634,631, by S. Gazit and C. A. Fleischer entitled
`‘FLEXIIBLE CIRCUIT LAMINATE AND METHOD OF
`MAKING THE SAME”, the disclosure of which is incor-
`potated herein by reference.
`Porous films produced by the process of the present
`invention have a wide range of potential applications, e.g.
`filtration membranes. breathable fabrics.
`
`Page 7
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`Page 7
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`

`9
`EXAMPLE 1
`
`5,506,049
`
`'10
`
`The tensile properties of sample film of composition 1
`were determined. The film exhibited a tensile strength of
`0.731 kpsi, an elongation at break of 167.4% and a tensile
`modulus of 4.62 kpsi.
`A photomicrograph of a cross section of film composition
`4 is shown in the figure.
`
`EXAMPLE 2
`
`A porous thin film is made by the process set forth in
`Example 1 by using polymethyhnethacrylate particles hav-
`ing a nominal size of 0.2 um as the filler material to produce
`a 1.0 mil thick film having a filler loading of 60 volume
`percent.