19;
`United States Patent
`5,506,049
`Sweiet al.
`* Apr. 9, 1996
`(45) Date of Patent:
`
`[11] Patent Number:
`
`ACCAAAAA
`
`(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.
`
`{*] 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.
`[51]
`Int. C1.
`seettetstnseenineeetee
`. B32B 5/16
`[52] WS. Che ccvecseccsesnernee"428/323; 428/325; 428/335:
`428/901
`
`(58] Field of Search .
`ae
`.. 428/323, 325,
`428/335,“403, 404,‘405, 406, 407, 421,
`422, 457, 901
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`6/1955 Hochberg ....cssscsssssesesseseeessees 428/268
`2,710,266
`9/1958 Petricllo ......eccesessesseeessneersnees 264/39
`2,852,811
`
`
`2/1960 Petriello ....
`.. 428/461
`2,923,651
`7/1960 Evanset al.
`. 260/29.6
`2,945,831
`11/1960 Petriello........
`ve 428/212
`2,961,345
`4/1961 Infantino et al. c.cccssessecceccessee 18/57
`2,980,965
`9/1962 Bergstein etal.
`wa 264/212
`3,054,716
`
`9/1962 Moore etal. .....
`w. 524/491
`3,054,761
`
` 11/1966 Van Zane. - 264/215
`
`3,292,725
`6/1970 Skiarchuk .........:cssescssesssesseeesees 264/49
`3,518,332
`vee 138/141
`8/1970 Roberts ........
`3,556,161
`
` S/I971 Desaulniers ......cesseeeeee 264/331.15
`3,577,508
`TA97T2 Shah et al. wcccccscesssecseseeneee S21/62
`3,679,614
`. 521/62
`3,843,570 10/1974 Murayama...
`
`.........
`. 521164
`4,049,589
`9/1977 Sakane.
`.
`wa 264/126
`4,112,037
`9/1978 Parker et al.
`
`
`v..cessssessssssseseseeee 428/220
`4,183,991
`1/1980 Smiley et al.
`4/1980 Chao et al. wsceccesseesseeseesseene 204/226
`4,196,070
`
`4,203,848
`5/1980 Grandine, 1 oo... eessereseneee 310/490
`4,211,603
`T1980 Reed ......ceescsecssesesessseetseeres 428/901 X
`4,307,142
`12/1981 Blitstein etal.
`we 428/143
`
`
`4,380,521
`4/1983 Morenoetal. ..
`. 264/49
`
`4,393,119
`7/1983 Concannon .....
`. 428/413
`4,409,354
`10/1983 Nambaetal. ...
`. 524/431
`
`
`4,434,116
`2/1984 Covitch........
`w. 264/49
`4,500,603
`. 428/409
`2/1985 Freundlich ......
`
`4,555,543
`11/1985 Effenbergerct al.
`.. 428/421
`
`4,610,918
`9/1986 Effenbergeret al.
`428/245
`
`9/1987 Timmons............
`vw» 264/41
`4,692,287
`
`. 428/421
`4,818,619
`4/1989 Stepparola et al.
`.
`
`4,824,511
`‘428/209 xX
`.
`4/1989 Hartman et al.
`
`4,847,135
`.....
`wes 428/138
`7/1989 Brauset al.
`
`4,849,284
`7/1989 Arthur etal. ....
`« 428/325
`
`4,883,716 11/1989 Effenbergeretal.
`vee 428/421
`
`4,888,245
` 12/1989 NitZKO cocccacsnssussueernerneenne 428/421
`
`(List continued on next page.)
`
`FOREIGN PATENT DOCUMENTS
`
`246844
`2071112
`
`11/1987 European Pat. Off.
`9/1981 United Kingdom .
`
`.
`
`Primary Examiner—Paul J. Thibodeau
`Assistant Examiner—-H. Thi Lé
`Attorney, Agent, or Firm—Fishman, Dionne & Cantor
`
`(57)
`
`ABSTRACT
`
`A particulate filled fluoropolymeric matrix compositearticle
`and method of making the sameis 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, e.g. dielectric substrate materials in laminar
`electrical circuits.
`
`40 Claims, 1 Drawing Sheet
`
`2 4
`
`
`
`LLLLILLLLLLLLLALAAMA
`
`
`MOOWOOows
`
`Dr. Reddy's - EX1018
`Page 1
`
`Dr. Reddy's - EX1018
`Page 1
`
`

`

`5,506,049
`
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`4,895,756
`4,915,983
`4,985,296
`
`1/1990 Suzukieeccescsesessseseseeeee 428/317.9
`4/1990 Lake et al. wees430/311 X
`1/1991 Mortimer, Jreee 428/220
`
`4,990,544
`5,024,871
`5,061,548
`5,077,115
`5,198,295
`
`2/1991 Asaumi et al. 0.0.00... 428/283 X
`......eccseeseseeeeeee 428/209
`6/1991 Arthur et al.
`
`cccccccsccscccacsssesssess 428/209
`10/1991 Arthur et al.
`
`sovsrsneevene 428/137
`12/1991 Arthur etal.
`...
`
`3/1993 Arthur et al. owes 428/923
`
`Page 2
`
`Page 2
`
`

`

`US. Patent
`
`Apr. 9, 1996
`
`oe
`
`
`5,506,049
`
`Page 3
`
`Page 3
`
`

`

`5,506,049
`
`1
`PARTICULATE FILLED COMPOSITE FILM
`AND METHOD OF MAKING SAME
`
`This is a divisional of application Ser. No. 07/705,624
`filed on May 24, 1991, now abandoned.
`
`uA
`
`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, c.g.
`less than about 1.0 mil, of highly filled fluoropolymeric
`matrix composite substrate materials having a substantially
`uniform microstructure 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.
`fluoropolymer
`filled
`Fluoropolymer
`and particulate
`matrix composite films are made by known papermaking,
`skiving, casting, melt extrusion and paste extrusion and
`calendering processes.
`Films produced by paper making processes required fiber
`reinforcement and are limited to thicknesses greater than
`about 2 mil.
`
`Itis very difficult to produce thin high quality highly filled
`fluoropolymer matrix films by skiving dueto abrasion of the
`skiving blade by thefiller particles and tearing of the film
`associated with the resistance of the filler particles to the
`skiving 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 (PVF,) and polychlorotrifluo-
`roethylene (PCTFE) are melt extrudable only within a
`narrow processing window. Polyvinylfluoride (PVF) film
`cannot be produced by melt extrusion duc to thermalinsta-
`bility. Polytetrafluoroethylene (PTFE) 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, e.g. copolymersoftetrafluorocthylene with hexafluo-
`ropropylene (FEP) or with ethylene, copolymers of CTFE
`with vinylidene fluoride or hexafluoropropylene.
`The introduction of fillers further complicates the melt
`extrusion of fluoropolymers.
`In the presence of certain
`fillers, especially at high filler loading level, the melt pro-
`cessability of the meit extrudable fluoropolymersis rapidly
`degraded due to the increase in melt viscosity associated
`with the presenceofthe filler or with filler-catalyzed 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 extrusion and calendering is set forth in
`coassigned U.S. Pat. No. 4,849,284 to D. J. Arthur, J. C.
`Mosko, C. S. Jackson and G. R. Traut, entitled “ELECTRI-
`CAL SUBSTRATE MATERIAL”, the disclosure of whichis
`incorporated herein by reference. However,it is technically
`
`25
`
`35
`
`40
`
`45
`
`55
`
`60
`
`65
`
`2
`to produce
`difficult and economically extremely difficult
`thin, i.e. less than 2 mils, highly filled, ie. greater than about
`40%, fluoropolymer matrix composite films by the paste
`extrusion and calendering 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 fiuoropolymer 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 ahout 10
`microns.
`
`In an alternative embodiment, a particulate filled fluo-
`ropolymer matrix composite article compriscs 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 embodimenta particulate filled fluoropoly-
`mer matrix composite film comprises a nonfibrillated fluo-
`ropolymer matrix and greater than about 15 vol. percent
`filler particles distributed throughout the matrix. The film
`has a thickness less than about 2 mils and is free of visually
`evident pin holesortears.
`A porous fluoropolymer film comprising a nonfibrillated
`fluoropolymer matrix having a void volumeofgreater 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 ofthe 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 percentfiller 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 casting 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 a photomicrographof a cross sectional view
`of a particulate filled polymer matrix composite film ofthe
`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 polychlorotrifiuoroethylene (PCTFE) and fluorinated
`copolymers, e.g. copolymers of tetrafluoroethylene Svitliea
`
`Page 4
`
`Page 4
`
`

`

`5,906,049
`
`3
`monomer selected from the group consisting of hexafluo-
`ropropylene and perfluoroalkylvinylethers, copolymers of
`tetrafluoroethylene with a monomer selected from the group
`consisting of vinylidene fluoride, vinyl fluoride and ethyl-
`ene, and copolymers of chlorotrifluoroethylene with a
`monomerselected from the group of hexafiuoropropylene,
`perfluoroalkylvinylethers, vinylidene fluoride, vinyl fluoride
`and ethylene. Blends ofthe above listed fluoropolymers 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.
`Theparticulate 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 amorphousfusedsilica 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 particulatefillers
`include polymethylmethacrylate particles, polystyrene par-
`ticles and polyimide particles. Suitable polymeric particles,
`e.g. LARC-TP1 (Rogers, Corp.), P-84 (Lenzing).
`The shape ofthe filler particles,
`the size of the filler
`patticles 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
`particles of the particulate filler exhibit an equivalent spheri-
`cal diameter ofless than about 10 microns (um). As used
`herein the “equivalent spherical diameter”ofa filler particle
`is the diameter of a sphere which occupies the same volume
`as that occupied bythefiller particle.
`In an alternative preferred embodiment of the present
`invention, each ofthe filler particles exhibit no single linear
`dimension greater than about 10 um.
`For extremely thin films and in applications where a
`substantially 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 um. Alternatively, it is preferred that all
`particles of the particulate filler exhibit no single linear
`dimension greater than about 5 pm.
`In a preferred embodimentof 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 becomeoriented during processing.
`In a preferred embodimentof the present invention, the
`filler particles of the film are of a uniform size. The use of
`a monodispersefiller, ic. wherein all the filler particles are
`
`10
`
`20
`
`40
`
`50
`
`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 a substantially 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 Geltech,
`Inc. and specified as :1 micron sphere size (+10%); density
`of 2.2 grams/cm*; free of hard agglomerations, has been
`foundto be particularly suitable for use in the practice of the
`present invention.
`The particulate filler material may be treated with a
`surface treatment to improve the moisture resistance and
`improve 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, phenyltricthox-
`ysilane,
`3,3,3-trifluoropropyltrimethoxysilane,
`(tridecaf-
`luoro- 1,1,2,2-tetrahydrodecy!)-1-triethoxysilane and mix-
`tures thereof. Further examples ofsuitable fluorinated silane
`compoundsare set forth ill coassigned U.S. application Ser.
`No 279,474,
`filed Dec. 2, 1988 and entitled “FLUO-
`ROPOLYMER COMPOSITE”by D. J. Arthur and G. 8.
`Swei, the disclosure of which is incorporated herein by
`reference. Suitable titanate coatings include: neopenty|(dial-
`lyl)oxytrineodecanoy] titanate, neopentyl(diallyl)oxytri(di-
`octyl)phosphate
`titanate.
`Suitable
`zirconate
`coatings
`include: neopentyl(dially])oxytri(dioctyl)pyrophosphatezir-
`conate and neopentyl(diallyloxytri(N-ethylenediamino)ct-
`hyl zirconate. 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 U.S. Pat. No.
`5,024,871, 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 amounteffective to
`render the surfaces of the filler particles hydrophobic and
`compatible with the matrix material. The amountof coating
`relative to the amountof inorganic particles coated will vary
`with the surface area coated and density of the inorganic
`particles. Preferably, the coated inorganic particles of the
`present invention 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,
`i.e. an emulsion, of liquid droplets of the
`polymer or of a monomeric or oligomeric precursor of the
`polymerin thefirst carrier liquid or a solution of the polymer
`in the first carrier liquid.
`The choice of the first 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 invention.If it is desired
`to introduce the polymeric material as a solution, a solvent
`for the particular polymeric matrix material is chosen as the
`carrier liquid, e.g. N-methyl pyrrolidone (NMP) would be a
`suitable carrier liquid for a solution of a polyimide.If it is
`
`Page 5
`
`Page 5
`
`

`

`5,506,049
`
`20
`
`25
`
`30
`
`35
`
`5
`desired to introduce the polymeric matrix material as a
`dispersion, then a suitable carrier liquid is a liquid in which
`the matrix material is not soluble, e.g. walter would be a
`suitable carrier liquid for a dispersion of PTFE particles and
`would be a suitable carrier liquid for an emuision of
`polyamic acid or an emulsion of butadiene monomer.
`Preferably, a fluoropolymeric matrix material is intro-
`duced as an aqueous dispersion. A dispersion of PTFE in
`water known as Teflon® 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 carrierliquid,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 carrerliquid 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 effective to modify the surface tension of the
`second carrier liquid to enable the second carrier liquid to
`wel
`the filler particles. Suitable surfactant compounds
`include ionic surfactants and nonionic surfactants. Triton
`X-100 (Rohm & Haas) has been found to be a suitable
`surfactant for use in aqueousfiller dispersions.
`Preferably, the filler dispersion comprises from about 10
`volume percent (vol %) to about 50 vol % filler particles,
`from about 0.1 vol % 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 ofthe 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
`amountof polymeric matrix material andfiller 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. % to
`about 70 vol. % 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. sedimentationor flotation, of the filler ~
`particles from the casting composition and to provide a
`casting composition having a viscosity compatible with
`conventional casting equipment. Conventional thickening
`agents are suitable and are chosen onthe basis of the carrier
`liquid selected. Conventional viscosity modifiers suitable for
`use in aqueous casting compositions include, e.g. poly-
`acrylic acid compounds, vegetable gumsand cellulose based
`compounds. Specific examples of suitable viscosity modi-
`fiers include polyacrylic acid, methyl cellulose, polyethyl-
`eneoxide, guar gum, locust bean gum, sodium carboxym-
`ethylceliulose, sodium alginate and gum tragacanth.
`
`40
`
`45
`
`50
`
`65
`
`6
`A minimum viscosity of the viscosity-adjusted casting
`composition is defined according to Stoke’s law, i.e.
`
`_ gD,? (Pp — Pz)
`~
`18u
`
`wherein:
`
`v=terminal velocity of particle;
`g=gravitational constant;
`D,=particle diameter;
`p,=particle density;
`p,=liquid density; and
`u=liquid viscosity;
`on the basis of the size and density of the filler particles to
`provide a theoretical terminal viscosity, ic. 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 6.5x107'° cm/s forsilica
`particles (density=2.2 g/cm>) having a diameter of 1 um. The
`viscosity of the viscosily-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 cp and about 100,000
`cp. Most preferably, the viscosity adjusted casting compo-
`sition exhibits a viscosity between about 100 cp and 10,000
`cp.
`Alternatively, the viscosity modifier may be omitted if the
`viscosity of the carrier liquid is sufficientto 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 um, 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, e.g. 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.
`Thecarrier liquid and processing aids, i.e. the surfactant
`and viscosity modifier, are removed from thecastlayer,e.g.
`by evaporation and/or 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 of 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. % 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. % matrix material and most preferably
`comprises from about 40 vol. % to about 65 vol. % filler
`particles and from about 35 vol. % to about 60 vol. % matrix
`material.
`
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`

`7
`
`5,006,049
`
`10
`
`20
`
`8
`The consolidated film of polymeric matrix material and
`it is desirable that the longest characteristic
`In general,
`dimension of the filler particles is significantly, e.g. by a
`particulate filler may be further heated to modify the physi-
`factor of 10, less than the thickness of the particulate filled
`cal properties of the film, e.g.
`to sinter a thermoplastic
`film to avoid bridging of particles between the surfaces of
`matrix material or to cure and/or post cure a thermosetting
`the film. As the desired film thickness decreases it becomes
`matrix material.
`progressively more difficult to meet the criterion.
`The process of the present invention allows films having
`Another outgrowth of increasing circuit density is illus-
`thickncss below about 2 mils, and even below about 1 mil,
`trated in FIGS. 3 and 4. A portion of a conventional laminar
`to be economically produced. Film thicknessesare set forth
`circuit 6 includes conductive layer 8 encased within dielec-
`herein in terms of “mils”, wherein one mil is equal to 0.001
`tric layers 10, 12. A conductive through hole, i.e. a “via”, is
`inch.
`defined by a conductive sleeve 14. The conductive sleeve 14
`Since the process of the present invention allows thin
`is separated from the conductive layer 8 by an insulating
`films to be produced without deforming the film, e.g. with-
`sleeve region 16 of dielectric material formed by fusing the
`out calendering or expandingthe film, fluoropolymer matrix
`edges ofthe dielectric layers 10, 12. With increasing circuit
`films can be made without the fibrillation of the matrix
`density it is desirable to decrease the dimension of the
`material characteristic of expanded films and without the
`conductive through hole. As the distance between the con-
`associated danger oftearing or forming pinholesin thefilm.
`ductive sleeve 14 and the conductive layer 8 is decreased,
`If a porous film is being produced, the filler material is
`filler size must be correspondingly decreased to avoid bridg-
`removed from the consolidated film. The method of removal
`ing offiller particles between the conductive sleeve 14 and
`is dependent upon the choice offiller material. If a filler
`conductive layer 8.
`material is dispersed in a matrix material wherein the matrix
`A further aspect of increasing circuit density and decreas-
`exhibits much higher temperature resistance than the filler
`ing via hole diameter is the need to drill smaller via holes.
`As the via hole diameter decreases, filler particle size
`material, e.g. a polymethylmethacrylate filler in a PTFE
`becomes an importantfactor in hole quality. Laser drilling of
`matrix the filler material can be removed thermally during
`particulate filled fluoropolymer matrix films is described in
`the consolidation and sintering steps. Alternatively, the filler
`coassigned U.S. Pat. No. 4,915,981, entitled “METHOD OF
`material can be dissolved in a liquid in whichthefiller is
`LASER DRILLING FLUOROPOLYMER MATERIALS”,
`soluble, but within the matrix material is insoluble. Removal
`by R. T. Traskos, C. A. Fleischer, C. A. Barton and D. B.
`of filler materials from a fluorinated polymer matrices to
`Noddin, the disclosure of which is incorporated herein by
`form a porousfluoropolymerfilm is described in coassigned
`reference. Laser drilling is effective at removing precise
`U.S. Pat. No. 4,987,274, entitled “COAXIAL CABLE
`amounts of matrix material butliterally blasts whole chunks
`INSULATION AND COAXIAL CABLE MADE THERE-
`of filler particles from the hole being drilled. Consequently,
`WITH”, by T. L. Miller, W. R. Zelanis, G. A. Woerner and
`the use of small filler particles allows higher quality, i.e.
`A. FE. Horn IU, the disclosure of whichis incorporated herein
`more precisely defined, small diameter holes to be laser
`by reference.
`drilled.
`It should be noted that the fluoropolymer matrix of the
`FIG. 5 shows a portion of a laminar electrical circuit 16
`thin porous fluoropolymerfilm of the present invention does
`which includes a bondply layer 22 sandwiched between a
`not exhibit the ribrillar structure characteristic of expanded
`pair of laminated circuit layers each comprising a conduc-
`porous PTFE films.
`tive layer 22 supported on a dielectric layer 20. The casting
`The substrate and consolidated film may be used in
`process of the present invention can be used with a lower
`combination as a laminar composite material or as a sub-
`melting fluoropolymer matrix material, e.g. FEP, to produce
`strate for subsequent composite layers. Alternatively, the
`very thin, highly filled bondplys for use in laminar electrical
`substrate may be removed from the film. The substrate may
`circuits. The. ability to make a highly filled fluoropolymer
`be destructively removed, e.g. by dissolution in a solvent, by
`matrix bondply would provide electrical properties similar
`chemical reaction, or thermal degradation, or the substrate
`to those of the substrate layers being bonded, while the
`may be reusably removed, c.g. by overcoming interfacial
`ability to make a very thin bondply would minimize the
`adhesion between the cast film and the substrate.
`detrimental effect of the bondply layer on the dimensional
`The consolidated film may be used alone, e.g. as dis-
`stability of the laminar circuit.
`cussed below, or as the substrate for subsequent casting of
`The ability to produce very thin, highly filled fluoropoly-
`mer films with an ordered microstructure is also of advan-
`further layers of the casting composition to build up a
`multilayer film.
`tage in regard to circuit substrate materials for “mm-wave”
`The thin particulate filled fluoropolymeric matrix com-
`applications which require very thin films having physical
`posite of films of the prescnt invention have a wide range of
`and electrical properties which, given the frame of reference
`potential applications.
`provided by the short wavelength radiation involved, can be
`A laminar circuit substrate made by the process of the
`considered substantially uniform for purposes of the par-
`present invention is shown in FIG. 2. The substrate com-
`ticular application.
`prises a conductive layer 2 laminated with a particle filled
`An inorganic particle filled matrix composite layer may
`fluoropolymer composite layer 4. The laminar substrate
`be cast onto a polyimide film to produce a composite film
`shown in FIG. 2 can be made, e.g. by casting and consoli-
`suitable for use in flex circuit applications. A flexible circuit
`dating layer 4 on a layer of the conductivefilm 2.
`including a microglass reinforced fluoropolymer matrix
`As discussed above, the shape, size distribution of the
`composite layer sandwiched between a polyimide film and
`filler particles is very important in several applications.
`a copper conductive pattern is described in coassigned U.S.
`Film thickness is a very important consideration in appli-
`Pat. No. 4,634,631, by S. Gazit and C. A. Fleischer entitled
`“FLEXIBLE CIRCUIT LAMINATE AND METHOD OF
`cations whereaparticulate filled film is used as a dielectric
`MAKING THE SAME”,the disclosure of which is incor-
`substrate for a high density laminar electrical circuit. As the
`feature dimensionsof the circuit are decreased, it becomes
`porated herein by reference.
`desirable to correspondingly reduce the thickness of the
`Porous films produced by the process of the present
`dielectric layer to thereby preserve the characteristic imped-
`invention have a wide range of potential applications, e.g.
`ance of the circuit.
`filtration membranes, breathable fabrics.
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
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`9
`EXAMPLE1
`
`5,506,049
`
`5
`
`10
`The tensile properties of sample film of composition 1
`were determined. The film exhibited a tensile strength of
`Thin films of particulate filled fluoropolymeric matrix
`0.731 kpsi, an elongation at break of 167.4% andatensile
`composite material were