JPH08259764A - Adhesive and filled polymer film composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a thin fluoropolymer film composite material suitable for producing electronic device by causing a paste contg. a thermosetting or thermoplastic adhesive resin and a particulate filler to be injected into or absorbed in voids of a porous polymer.

SOLUTION: The composite material is a nonwoven bonded composite material contg. at least one porous fluoropolymer substrate layer 1 having a void volume of at least 30 vol.%; and an adhesive 4 and a particulate filler 5 evenly dispersed in the whole voids of the substrate layer. The amts. of the adhesive 4 and the filler 5 are such that the vol. of the fluoropolymer substrate accounts for about 5-40 vol.% of the composite material. The material can be used e.g. for a printed circuit board by bonding a metal layer 6 to the adhesive film 1. An epoxy resin, a cyanate ester resin, a polybutadiene resin, etc., are pref. as the adhesive. Examples of the pref. filler are SiO₂, TiO₂, and ZnO, and the like.

COPYRIGHT: (C)1996,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to thin film composites formed from a polymeric substrate imbibed with a mixture of filler and adhesive. The absorbed filler imparts thermal and / or mechanical and / or electrical properties to the film composite. In particular, the present invention provides a thin fluoropolymer film composite material, wherein the fluoropolymer voids comprise a mixture of filler and adhesive. This absorbed film composite material of the present invention is suitable for use in the fabrication of electronic devices.

[0002]

Polymer films containing fillers are used in the electronics industry for the production of electronic substrates, chip packages, circuit boards and other electronic devices, and for separation techniques in which filters, separators or membranes are required. Suitable for The end use of the film and the particular properties it exhibits will determine the choice of a particular filler. For example, activated carbon can be incorporated into the film to provide a filter or separator. The electrical properties of the polymer film can be imparted by incorporating fine particles of a metal that impart conductivity. Often, the film is a polymeric adhesive and the metal particles give the film the necessary electrical properties. Thermal conductivity can be obtained by adding ceramic and / or metal and / or diamond in the adhesive.

Adhesive films can be formed from (1) a solution or paste that polymerizes to form a "polymer" film, or (2) a polymeric substrate with an adhesive added to it. In either case, as the amount of filler is increased to provide the desired electrical / thermal properties, the physical properties of the adhesive drop to the point of limited utility. For example, a typical conductive adhesive is 40-60%
Will have (v / v) filler. However,
These adhesives are very weak and brittle and are only useful when applied as a paste / liquid. Even if films could be made from these compositions, they were difficult to handle in the "B" stage configuration,
Their size and thickness are limited.

One approach to overcoming the disadvantages of filled adhesives is to limit the amount of filler added. Another approach is to add reinforcement such as woven glass fiber. However, in both of these approaches, doing this would result in
The performance of the filled adhesive is severely degraded. as a result,
Less than the desired amount of filler is used. The sheet-like adhesive obtained is usable, but does not have the desired optimum properties and performances. Therefore, existing filled adhesives sacrifice performance for usability.

In addition, sheet-like adhesives filled with particles suffer from a phenomenon known as "particle settling" or settling. Heavy particles (up to 10 times the density of the resin) will sink to the bottom of the film, leaving a resin-rich surface. This phenomenon results in undesired inhomogeneities and poor reliability. High bonding pressure is often required to ensure that excess surface resin is forced into the film.
Even so, surface irregularities will result in resin-rich regions of imperfect nature provided by the particles.

Attempts have been made to prepare adhesive-filled films, but there are significant drawbacks and therefore their preparation is limited. The amount of filler that can be added is controlled by the physical limitations of (1) polymer film or substrate, and (2) filler and adhesive additives. Often, the use of the desired amount of filler makes handling of the adhesive and filler additives impossible.

Absorption of thermosetting resins into substrates has been practiced to provide structural integrity to otherwise brittle layers. For example, a knitted or woven glass fiber substrate can be imbibed with a thermosetting or thermoplastic adhesive. However, this approach presents significant drawbacks when fillers are also added. For example, hollow glass microspheres were dispersed in a thermosetting adhesive and then imbibed on a woven substrate. However, the amount of filler that can be incorporated into the substrate is limited. Because the resulting adhesive film has poor flexibility and operability, it is difficult to adapt this adhesive film to the desired application.

Another drawback of such composite materials is the limited homogeneity possible with woven structures. In every gap of the knitted fabric there is a composition that is different from the volume defined between the gaps. This leads to inhomogeneities in physical properties, electrical properties, and compatibility. It would be desirable to have a homogeneous, flexible filled adhesive sheet with a wide range of filler amounts.

Curable additives have also been added to pressure sensitive adhesives which have been absorbed into foamed polyurethanes, but the nature of this scaffolding has presented numerous limitations. After all, it is very difficult to make thin composites, and also flexible, thermally stable composites. For use as a flame retardant flexible circuit board, flame retardant particles were dispersed in an adhesive which was then absorbed into a non-woven polyimide and ester substrate. In general, these prior arts have not been able to add the best amount of additives to the adhesive for performance purposes while at the same time providing the adhesive as a thin sheet.

By adding the filler directly to the fluoropolymer prior to extrusion and stretching, the fluoropolymer, eg, porous and expanded polytetrafluoroethylene (PTFE), is also loaded. It was Thickness 0.1 to 5.0 mils (2.54 to 12.7 μm
), A thin and porous polytetrafluoroethylene film substantially free of pinholes and filled with an inorganic filler also has a low capacitance polytetrafluoroethylene layer for a printed wiring board (PWB). Is known as. This porous polytetrafluoroethylene used is G
It can be prepared according to the teachings of US Pat. No. 3,953,566 to Ore. In each case, the filler is mixed prior to extrusion and stretching.

Polytetrafluoroethylene which is not expanded and thus does not contain expanded fibril-nodular microstructures of polytetrafluoroethylene can also contain fillers. An extruded composite tape having a dielectric, ceramic filler and polytetrafluoroethylene was prepared by adding the filler to polytetrafluoroethylene prior to extrusion. Silane compounds may also be desirable in order to provide homogeneity and improved dispersibility when preparing aqueous polytetrafluoroethylene-filler dispersions. Lever
See U.S. Pat. No. 3,929,721 to Ett and U.S. Pat. No. 4,038,244 to Ogden et al. In addition to silanes, other organic compounds are known that render hydrophilic fillers hydrophobic for better dispersibility. Kawachi et al., U.S. Pat. No. 4,440,879 and Morozumi, U.S. Pat.
See 4143110.

The composite materials formed in these patents must be bonded at "sintering" temperatures-that is, at very high temperatures or at high temperatures and pressures. As a result, these composites were not used to the extent expected. This was especially the case because of the difficulties encountered when the composite material was processed further. Other materials that are bonded to these composites are
This is especially the case when they cannot withstand these high temperatures and pressures.

Other attempts have been made to avoid these drawbacks, but the results have not been satisfactory.
Landi U.S. Patent Nos. 3407096 and 3407.
Porous microfibrillated polytetrafluoroethylene was prepared according to the technique taught in H.249. Lan
In the di patent, inorganic or organic fillers are added into the network of unsintered polytetrafluoroethylene fibers. The Landi process involves preparing a mixture of extruded polytetrafluoroethylene and an organic polymer. Subsequently, the organic polymer is dissolved in a suitable solvent and removed. The resulting structure eliminates the ingress of particulate filler due to its very fine network of fibers.

In Sato's US Pat. No. 5141972, gas-containing microhollow spheres or spheres are used to form an insulating porous composite material using polytetrafluoroethylene. In the Sato patent, the polytetrafluoroethylene substrate has a porosity of about 75% and is immersed in a liquid containing ultrasonically agitated micro hollow spheres, which is allowed to flow into the pores. The absorbed substrate is heated unrestrained, thus causing the porous polytetrafluoroethylene to shrink and immobilize the microspheres in the pores. The manufactured product, according to the Sato patent, is useful as a porous, compression resistant, low dielectric material. The sphere fills the hole and thus prevents it from collapsing.
Using the same approach, Sato's US Patent No. 508
At 7641, a porous polytetrafluoroethylene composite material having polytetrafluoroethylene particles sintered into the pores is manufactured. In each case, Sato's composite material does not absorb the resin satisfactorily and, as such, is very difficult to use as an adhesive.

While the prior art produced substrates containing fillers, the addition of adhesive to the particles produced did not result in an acceptable product. For example, S. In JP-A-6140328 of Hamasaki et al., Silicone rubber is absorbed in a porous and expanded polytetrafluoroethylene structure for use as a thin electric insulating material having a thickness of 50 μm or less. There is. This silicone rubber is absorbed as a solution, yielding a transparent, eg unfilled, product which is subsequently cured. However, the structural integrity of this cured product is poor. With the intention of reinforcing the structure of this Hamasaki patent, H. Kato et al., JP 62-100359 teaches a silicone rubber article made by first adding a ceramic to a dispersion of polytetrafluoroethylene. The filler is added directly into the nodes of the node and the fibrils, after which the silicone resin is absorbed into the fibril structure as described above. In both of these examples, the final product is a rubber-like cured sheet.

Similarly, M. Hatakayama is GB-
2195269B (EP-0248617B1) describes an article and method in which a thermosetting resin is absorbed in expanded polytetrafluoroethylene, which is useful as an adhesive for a printed wiring board (PWB). The inorganic filler could be incorporated into the expanded and expanded porous polytetrafluoroethylene node- and-fibril structure.
See also U.S. Pat. No. 4,784,901 to Hatakayama et al. Here, a resin without a filler is impregnated in polytetrafluoroethylene.

Unfortunately, these approaches make it difficult to achieve high ceramic loadings because the ceramic weakens the knots and fibril structure. It is difficult to make thin films of polytetrafluoroethylene reinforced with fillers. This is because the filler / microfiber particles create pinhole cracks as the material thickness decreases. Furthermore, the incorporation of inorganic fillers, especially in the range greater than 30% by volume, makes the mixing and paste extrusion of these composites very difficult. Even more unfortunate is that the ceramic reinforcement is not evenly distributed throughout the composite structure.

[0018]

There is a need for a uniformly reinforced, thin adhesive sheet composite which can carry large amounts of reinforcement. That is, in order to maximize the desired properties without sacrificing structural integrity,
There is a need for an adhesive film that contains the maximum amount of filler possible, is structurally reliable, and is filled with filler. These films should be as thin or thick as possible, easy to use, and have a convenient sheet-like morphology, which should not be brittle, have uniform hardness, and be pinhole free. is there. The invention described below overcomes the drawbacks of the prior art.

[0019]

SUMMARY OF THE INVENTION The present invention is directed to a porous polymeric substrate that has absorbed a large amount of filler and a thermoplastic or thermosetting adhesive derived from the original voids of the original polymeric substrate. . In particular, fluoropolymers such as Gore
The porous, expanded polytetrafluoroethylene materials of U.S. Pat. No. 3,953,566 of Bowman et al. And U.S. Pat. No. 4,482,516 of Bowman et al., Which are incorporated herein by reference, may be used in the present invention. , Absorbing a paste mixture of adhesive and filler to provide a composite material for use in the electronics industry and other industries.

Accordingly, a primary object of the present invention is to form a composite film in which a thermosetting or thermoplastic adhesive resin and a particulate filler combined as a paste is injected or absorbed into the voids of a porous polymer. It is to be. The porous polymeric substrate has an initial void volume of at least 30%, preferably at least 50%, most preferably at least 70%, and a thermosetting or thermoplastic adhesive resin and a particulate filler paste are placed in the interstices. It facilitates containment while providing a flexible reinforcement to prevent brittleness and particle settling of the overall composite.

One aspect of the invention is about 5 to about 40% by volume.
Of the polymer substrate and 10 absorbed in the voids of the substrate
-95% by volume of a particle-filled adhesive and a polymer composite are provided.

Another aspect of the invention is a composite in which 5 to 85% by volume of inorganic particulate filler is contained in the composite material, within the structure of the porous polymer, or within the adhesive, or both. Provide materials and methods of making them.

Yet another aspect of the present invention is a film of expanded polytetrafluoroethylene having a void volume of at least 50%, containing a uniformly dispersed adhesive-filler paste mixture, The filler is to provide 5 to 85% by volume of the volume of the composite material.

Yet another aspect of the invention is a film of expanded polytetrafluoroethylene having a void volume of at least 30%, comprising a paste mixture of an adhesive and a filler, said filler being 5 to 5 of the volume of the composite material
The polytetrafluoroethylene occupies 85% by volume, and the average pore diameter of the polytetrafluoroethylene is 2.5 times or more the average diameter of the granular filler. Alternatively, the pore size and particle size (pa
The minimum pore size of PTFE may be 1.4 times or more of the maximum particle size when calculating the particle size).

An additional aspect of the present invention is a fluoropolymer substrate having a thermosetting or thermoplastic adhesive and having nodes interconnected by fibrils, and voids of the fluoropolymer substrate. Provided is a composite material having ceramic particles disposed therein.

It is an object of the present invention to provide an adhesive and filler containing substrate for an electronic device having one or more layers of composite material, at least one layer containing a conductive metal. Is to provide.

Various objects of the invention will be apparent from a review of the following description. The operation of the present invention will become apparent from the following description when considered in conjunction with the accompanying drawings that do not limit the present invention.

Porous substrates having an initial void volume of 30-95%, preferably at least 50%, and often more than 70% provide a scaffold for absorbing filler-containing adhesives and are good. It has been found to provide a substrate having a controlled thickness. Porous stretched and expanded polyolefin such as ultra high molecular weight (U
HMW) polyethylene, fluoropolymers such as porous expanded polytetrafluoroethylene (including those with and without its copolymers), porous inorganic or organic foams, microporous Cellulose acetate and the like are some examples of substrates that can be used in the present invention. These materials provide a scaffold with voids, which allows thermoplastic or thermoset resins with or without fillers to be absorbed into the voids of the scaffold.
As a result, the presence of large amounts of inorganic fillers in the thermosetting or thermoplastic adhesives, such as granular or fibrous ceramic fillers, powdered metals, is made possible by the invention described herein, On the other hand, a sheet adhesive that is compliant, supple, convenient to use, easy to handle, and has no tears or pinholes in a thin film can be made. This result was unexpected. It is a common sheet of adhesive filled with filler that is very fragile and brittle,
This is because it cannot be handled at all. This surprising result comes from the flexibility of the expanded substrate, such as expanded polytetrafluoroethylene.

Traditionally, "strong" stiffeners have been used to anchor composite materials. In contrast,
The present invention uses a low modulus reinforcement with a much lower percentage of composition than could be achieved with a strong reinforcement. This gives a much higher percentage of filler than previously thought possible.

The substrate of the present invention is a scaffold formed from fine interconnected networks of fibrils and nodes that serve as interpenetrating networks within the filler-filled adhesive. An additional unexpected advantage is that the thickness of the adhesive film made of expanded polytetrafluoroethylene is tightly controlled by the thin film substrate / scaffold thickness. Therefore, controlling the paste thickness during the coating process is not a control parameter of the present invention, which is advantageous. This is because the properties of this paste, such as viscosity and thickness, are susceptible to many variables. Instead, the scaffold is made of composite material.
The thickness and structure of the starting substrate controls the absorption process and the properties of the final product, even when making up as small a percentage. As a result, very finely controlled thicknesses of adhesives, in particular filler-filled adhesives, can be produced with high reliability. This is important for dielectric layers in electronic and microelectronic devices.

Another unexpected advantage of the present invention is the ability to introduce a uniform dispersion of particles in the adhesive into the microporous structure. This reduces the migration of particles due to the toughening effect of the microporosity of the substrate and the fact that the dispersion remains uniformly dispersed (ie the particles are more or less accommodated by the scaffold). It provides a number of important advantages, including homogenization effects due to its tendency to

More particularly, the composite material composition of the present invention comprises (but is not limited to) 5-40% by volume of polytetrafluoroethylene and 10-95% by volume.
A porous filled expanded polytetrafluoro with or without a filler containing a particle-filled adhesive adsorbed within the porous structure of the polytetrafluoroethylene web. Includes a film of ethylene. The filler may be dispersed throughout the adhesive in the form of particles suspended in the adhesive. Alternatively or additionally, polytetrafluoroethylene may include the same or different particulate fillers in the film's fibril-nodular structure to provide thermal and / or electrical conductivity. May be. In all cases,
The particulate filler constitutes 5-85% by volume of the total composite.

Particle-filled adhesives are those in which are suspended one or more of the following:
Metals and alloys such as, but not limited to, nickel, copper, aluminum, silicon, solder, silver, gold; metal plated particles such as silver plated copper, silver plated nickel, silver plated Glass microspheres; inorganic compounds such as BaTiO ₃ , SrTiO ₃ , SiO ₂ ,
Al ₂ O ₃ , BN, ZnO, TiO ₂ , MnO, Cu
O, Sb ₂ O ₃ , WC, fused silica, fumed silica, amorphous fused silica, sol-gel silica, sol-gel titanate, mixed titanates; ion exchange resins; lithium-containing ceramics; hollow glass microspheres; carbon-based materials , Eg carbon, activated carbon, carbon black, ketchem black, diamond powder; elastomers such as polybutadiene, polysiloxane;
Semi-metals; as well as ceramics. Particularly preferred fillers for use in the present invention are BaTiO ₂ , SiO ₂ , Al
₂ O ₃ , ZnO, TiO ₂ , nickel and solder, especially SiO ₂ , TiO ₂ and ZnO.

The particles have one or more specific properties for the adhesive, such as thermal conductivity, electrical conductivity, dimensional stability, low dielectric constant, high dielectric constant, ion exchange capacity, galvanic potential, and flame retardancy. Gender, etc. "Granular" means a filler that can have any aspect ratio. Thus, this term includes both fillers and powders. This filler may have been treated by well known techniques, for example by a silane coating which renders the filler hydrophobic.

The adhesive itself may be thermosetting or thermoplastic and may be polyglycidyl ether, polycyanurate, polyisocyanate, bis-triazine resin, poly (bis-maleimide), norbornene terminated polyimide. , Acetylene-terminated polyimides, polybutadienes and their functionalized copolymers, polysiloxanes, polycisqualox
ane), functionalized polyphenylene ethers, polyacrylates, novolac polymers and copolymers, fluoropolymers and copolymers, melamine polymers and copolymers, poly (bisphenylcyclobutane) and mixtures thereof. The adhesives described above may themselves be blended with each other or compounded with other polymers or additives to provide flame retardancy or enhanced toughness.

In the present invention, expanded porous filled or unfilled substrates include nonwoven papers, polymer fibers, nonwoven foams, in addition to expanded polytetrafluoroethylene and polyolefins. , Which are used as scaffold / matrix materials to form films. Nonwoven papers contemplated herein include, but are not limited to, those made by the "wet-lay" and "spunbond" processes, such as cellulose paper, aramid paper. Fiber scaffolds may include chopped fiber mats and ceramic paper. The foam may be an aerosol ceramic foam or an open cell polymer foam,
Or it may comprise poly (ethylene terephthalate) foam. The expanded scaffold material may include expanded polyethylene, microporous polymers such as cellulose acetate and the like. These materials impart extra strength to the adhesive-containing film due to the expanded morphology of the scaffold or matrix and due to their low modulus.
This matrix serves as a scaffold and holds the otherwise weaker ceramic and adhesive paste / dispersion together.

In the present invention, the expanded and expanded polytetrafluoroethylene acts as a binder, and as a result,
The adhesive need only exhibit good adhesive properties. The low modulus of the expanded polytetrafluoroethylene structure and the intricate network of nodes and fibrils help strengthen the overall composite, like the inversion phase in phase separated polymer alloys. This also allows for compositional ratios of components that would normally not be practical because people classically rely on adhesives as both binders and glues.

Another key feature of the present invention is thickness control. Stretched and expanded polytetrafluoroethylene can be made very uniform. And once the resin is absorbed, it does not change its final thickness. Therefore, overall thickness control is obtained. In addition, the thickness of the expanded polytetrafluoroethylene is precisely controlled so that the resulting scaffold film can be very thin or very thick. Very thin substrates have the additional advantage of allowing the preparation of composite materials with several layers.

An important aspect of the present invention is the extraordinary ability to stretch and expand polytetrafluoroethylene to form a porous material having interconnected channels formed of nodes and microfibers. Lies in the use of features. It is well known to stretch polytetrafluoroethylene to form a porous material and is described in US Pat. No. 395.
3566 and 4482516. The void space in the expanded and expanded polytetrafluoroethylene is
It occupies at least 50%, often more than 70% of the volume, while at the same time remains very strong. When this void space is replaced by a filler, such as SiO ₂ , TiO _2, etc., it gives a composite material which is very highly packed and yet retains strength and handleability.

In the present invention, the average flow pore size (Me
an Flow Pore Size) and minimum pore size by Coulter ™ Porometer II
(Coulter Electronics Lt
d. , Luton UK). This instrument reports its value directly.

The average particle size and the maximum particle size are Macrotra
c Light scattering particle size analyzer Model No. FRA (Mic
rotrac Division of Leeds
& Northup, North Wales, P
A, USA). Average particle size (APS)
Is defined as the value at which 50% of the particles are larger. Maximum particle size (LPS) is defined as the largest particle that can be detected in a Microtrac histogram.

Apparent density (Observed Dens)
(ty) (ρobs) is the apparent weight in grams (o)
Calculated by dividing the bserved weight by the calculated volume in cubic centimeters (cc).
The sample volume was calculated by multiplying the average thickness, length and width. Each average consisted of at least 5 separate measurements. The uncertainty associated with these measurements has been rounded up through multiple calculations.

The calculated density (ρcalc) was calculated by the following formula: ρcalc = Σ (vi) ^* (ρi); where vi is the volume fraction of the i-th component, and ρi is the density of the i-th component. Is.

The prepreg resin content (RC) is calculated by dividing the weight of the prepreg swatch by the weight of the same swatch after thorough extraction of all adhesive with solvent, drying and weighing. did.

Dielectric constant (Dk) (at frequencies below 3 GHz) is Hewlett-Packard 8753A.
Network Analyzer (Hewlett
-Packard Corp. , San Jose,
CA) was used to obtain the substrate resonance method for copper coated laminates.

Dielectric constant (Dk) and dielectric loss tangent (dissi)
partition factor (Df) (at frequencies above 5 gigahertz) is a GDK product (GDK Pro).
cucts, Inc. , Cazonova, NY) and Hewlett Packard 8510 Netw.
ork Analyzer (Hewlett-Pack)
ard Corp. , San Jose, CA) developed resonance mode (resonant mod)
e) Dielectrometer
er).

The copper peeling value is the Applied Test.
Systems Model No. 1401 Computer-controlled tensile tester (Applied Test)
Systems, Inc. , Butler, PA, U
The copper-clad laminate fixed to a rigid sliding plane substrate bonded to SA) was measured using the 90 ° peel morphology.

The weight composition is Galbraith Lab.
It was measured by elemental analysis by oratories (Knoxville, TN). The compositions of SiO ₂ , TiO ₂ and Ni were measured by using the inductively coupled plasma spectral ash melting decomposition analysis method, and the respective amounts of Si, Ti and Ni were determined by using this. The PTFE composition was measured in a similar manner, but Schniger Flas was used to measure fluorine directly.
k / Specificion Electrode A
Fluorine from Nalysis was used. The amount of adhesive was calculated by the difference in mass balance.

The void volume (VV) or "% air volume" was calculated by dividing the apparent density by the calculated density and subtracting this from 1, while exerting on it a suitable degree of uncertainty.

The volume fraction (VF) of each component was calculated by multiplying the volume (1-VV) of dense particles in the composite material by the volume fraction of each component. It is calculated by the formula: VF
_i = (1-VV) ^* (volume of i-th component / total volume of composite material) = ([(ρobs) / (ρcalc))]
^* [((W _i ) ^* (ρ _i )] (VV + Σ (W _i )
(Ρ _i )]; where VF _i is the volume fraction of the i-th component, ρ obs is the apparent density in g / cc,
ρ calc is the calculated density in g / cc, W _i is the weight fraction of the i-th component, and ρ _i is the density of the i-th component in g / cc.

In general, the method of the present invention comprises:
(A) Stretching the lubricated and extruded preform to stretch and expand the polytetrafluoroethylene sheet to a microstructure sufficient to allow the microparticles and adhesive to freely flow into the void or pore volume. , (B) forming a paste from a polymeric material, such as a thermosetting or thermoplastic material and a filler, and (c) making the paste of adhesive and filler highly porous by dipping, coating or compressing. Absorbing on a quality scaffold, such as expanded polytetrafluoroethylene.

The following examples show how the invention can be made and used, but they are not intended to limit the scope of the invention.

In one of the preferred embodiments of the present invention, stretched, porous, filler-filled or unfilled polytetrafluoroethylene is used as a matrix material to make a film. It is due to the exceptional strength provided by its expanded configuration and due to its low modulus. This matrix holds together and serves to provide a void volume that can otherwise accept the weaker paste / dispersion ceramic and adhesive. As already mentioned, due to the low modulus and the network of interconnected nodes and fibrils, the expanded polytetrafluoroethylene structure, like the conversion phase in phase-separated polymer alloys, has a large overall structure. Helps to strengthen composite materials. This also allows compositional ratios of components that would normally not be practical because one has traditionally relied on adhesives as both binders and glues. In the present invention, the expanded and expanded polytetrafluoroethylene acts as a binder,
After all, the adhesive need only exhibit good adhesive properties.
Another key feature is thickness control. Stretched and expanded polytetrafluoroethylene can be made very uniform.
And once the resin is absorbed, it does not change its final thickness. Therefore, overall thickness control is obtained. In addition, the expanded polytetrafluoroethylene can be very thin or very thick. In the case of very thin films, several phases can be combined into a composite material.

An important aspect of the present invention is that when polytetrafluoroethylene is stretched and expanded, the interconnected channels formed by nodes and microfibers.
s) in the use of the unusual feature of forming a porous material. The void spaces in expanded polytetrafluoroethylene occupy at least 30%, often more than 50%, more often more than 70% of the volume and still remain very strong. This void space is then replaced with an adhesive containing filler, which gives the desired improvement in properties. For example, a nickel filled adhesive is
Exhibits high electrical and thermal conductivity, fused silica (Si
The O ₂ ) -filled adhesive exhibits high dimensional stability and a relatively low coefficient of thermal expansion (CTE), and the lithium-filled adhesive exhibits high ion-exchange properties, such as titanium oxide (T
Adhesives filled with io ₂ ) or titanates exhibit high dielectric constants, and so on. If mechanical integrity is deemed necessary, the particles themselves may have a thin coating of primer or other surface modifying layer such as a silane coating, titanate, zirconate, sizing on the adhesive itself. .

Although the features of the present invention will be described with reference to FIGS. 1 to 3, the present invention is not limited thereto.

In FIG. 1, film 1 does not include particulate filler and shows stretched or expanded polytetrafluoroethylene film 1, which is described in Section 2 (indicated by irregular circles). ) Are interconnected by fibrils 3 (indicated by lines). That is, FIG. 1 shows a node-and-microfiber structure.

In FIG. 2, the continuous voids defined by the nodes and microfiber structures have been replaced by an adhesive 4 filled with particles 5. This node-and-microfiber structure serves as a scaffold for the adhesive.

FIG. 3 shows that the nodes of the film 1 also have particles, and the same particles are not necessarily dispersed in the voids.

To prepare the filled adhesive film of the present invention, the particulate filler is mixed in a solvent or aqueous solution or molten adhesive to give a finely dispersed mixture. Fillers in the form of small particles typically have a size of 40 μm
Is less than 1 and preferably has an average particle size of 1 to 10 μm
Is. The average pore size of the polytetrafluoroethylene node- and-microfiber structures should be large enough to allow proper penetration of the particles. If the substrate is expanded polytetrafluoroethylene,
Structures similar to those taught in Bowman et al., U.S. Pat. No. 4,482,516 are preferred. Preferably, the mean flow pore si
ze) (MFPS) is about 2-5 smaller than the largest particle size.
It should be double or more, and it is especially preferred that the MFPS is greater than about 2.4 times the size of the filler.

Alternatively, another mechanism for determining relative pore size and particle size may be calculated such that the minimum pore size is about 1.4 times greater than the maximum particle size.

Table 1 shows the average flow pore size (MF) of the substrate.
The effect of the relationship between PS) and particle size is shown. Poor results are obtained when the ratio of mean flow pore size (MFPS) to maximum particle size is less than 2.0. In this case, no homogeneous composite material is observed and most of the particulate filler does not evenly penetrate the microporous substrate. A uniform composite material is obtained when the MFPS to maximum particle ratio is greater than about 2.0. The higher the ratio of MFPS to the largest particles, the more often the homogeneous dispersion is absorbed into the microporous substrate.

[Table 1] Substrate Poise Size Particle Poise Size Minimum MFPS Average Maximum (Average Poise Size) / (Minimum Poise Size) Details (μm) (μm) (μm) (μm) (Average Particle Size) / (Maximum Particle Size) Results PP266-81a 4 7 5 10 1.4 0.4 Bad PP266-81b 4 5 5 10 1.0 0.4 Bad PP266-85 --58 5 10 12.4 N / A ^* Good PP266-92 18 32 6 10 5.3 1.8 Good PP266-92 18 32 1 1 32.0 18.0 Good PP266-94 17 24 6 10 4.0 1.7 Good PP266-118 0.2 0.4 0.5 1.6 0.8 0.125 Bad PP279-74 --60 18 30 3.3 --- Good PP279-112 14 11 0.5 1.6 22.0 8.8 Good PP289-4 14 29 4 8 7.3 1.8 Good PP289-4 14 29 5 10 5.8 1.4 Good * N / A: No data.

The film having voids can easily absorb the resin filled with particles. In this case, all or part of the voids that currently contain air are replaced with a resin / adhesive filled with particles. If only a portion of the air voids are replaced with resin, the final composite will be properly compressed into a very thin void-free composite. This composite material has excellent adhesion, excellent thickness control, and excellent flexibility and compressibility. In this way, it is possible to produce unusually thick, well-controlled thickness, unusually high loading adhesives that were previously unattainable.

FIG. 4 shows a composite material that can be made using the present invention. Contains nodes 2 interconnected by fibrils 3,
The adhesive film 1 with the adhesive 4 and the particles 5 is attached to at least one layer 6 of metal. The structure serves a variety of applications, such as printed circuit board substrates, embedded capacitors, endothermic materials and the like. A metal layer can also be applied to the other side of this material to create a sandwich structure.

[0065]

【Example】

Example 1 Polyglycidyl ether based on bisphenol-A (Nelco N-4002) flame retarded and catalyzed by dicyanamide / 2-methylimidazole.
5, Nelco Corp. 20) dissolved in MEK
% (W / w) solution with 281.6 g of TiO ₂ (Tl
Pure R-900, DuPont Compan
A fine dispersion was prepared by mixing y).
The dispersion was continuously stirred to ensure homogeneity. The expanded PTFE swatch was then immersed in the resin mixture. The web is tensioned at 165 ° C for 1 hour.
It was dried for a minute to make a flexible composite material. The partially cured adhesive composite material produced in this way is 57 wt.
% TiO ₂ , 13 wt% PTFE and 30 wt% epoxy adhesive. Place several stacks of this adhesive sheet between copper foils in a vacuum assisted hydraulic press at 600 psi (4.1 MPa), 2
It was pressed at 25 ° C. for 90 minutes and cooled under pressure. This results in a copper laminate with a dielectric constant of 19.0, which has an average stack thickness of 100 µm (0.0039 "(3.9 mils) dielectric laminate thickness and withstands solder shock at 280 ° C for 30 seconds. It was

(Example 2) 44 g of Ni powder (Aldric
h Chemical Co. , Catalog # 2
6,698-1), 17.4 g of platinum cured poly (dimethylsiloxane-methylsiloxane) thermosetting silicone elastomer (Sylgard 4105, Do.
w Chemical Co. ) And 40 g of MEK to prepare a fine dispersion. The dispersion was continuously stirred to maintain homogeneity. A sample of expanded PTFE was then dipped into the resin mixture. After removing this sample, excess resin was wiped off the surfaces on both sides. The web was dried for 1 minute at 165 ° C. with tension applied to obtain a flexible composite material. This composite material is 39 wt% Ni, 10 wt% PTF
E, and 51 wt% silicone, and has a conductivity of less than 100 milliohms for a 3 square inch sample and a thermal impedance of 1.33 ° C./W.
mal impedance) was shown.

Example 3 165 g of ZnO powder (Nort
h American Oxide) to poly (1,2
-Butadiene-co-styrene) (R-104, Rico
n Resins dissolved in MEK 20% (w /
w) A fine dispersion was prepared by mixing in the solution. The dispersion was continuously stirred to maintain homogeneity. Then, an expanded PTFE sample filled with 0.0004 "copper (US Patent Application No. 19604).
8 (filed on February 14, 1994 by Ameen et al.)
(Filled to a level of 40% according to the teachings of 1.) was immersed in the resin mixture. After removing this sample, excess resin was wiped off the surfaces on both sides. The web was dried for 1 minute at 165 ° C. with tension applied to obtain a flexible composite material.

Example 4 200 g of bismaleimide triazine resin (BT206OBJ, Mitsubishi Gas Chemical) and 38
Phenyltrimethoxysilane (04330, Huls / Pe) was added to a manganese-catalyzed solution of 8 g of MEK.
386 g of SiO ₂ (HW) pretreated with
-11-89, Harbison Walker Co
rp. ) Was mixed to prepare a fine dispersion. The dispersion was continuously stirred to ensure homogeneity.
A 0.0002 ″ sample of expanded PTFE was then dipped into the resin mixture, removed, and dried under tension for 1 minute at 165 ° C. to make a flexible composite material. Some of this prepreg Place the stack between copper foils in a vacuum assisted hydraulic press at 250 ps.
i (1.7 MPa), pressed at 225 ° C. for 90 minutes and cooled under pressure. The dielectric thus obtained consists of 53 wt% SiO ₂ , 5 wt% PTFE and 42 wt% adhesive, has good adhesion to copper, dielectric constant 3.3 (at 10 GHz) and dielectric loss tangent (at 10 GHz). )
It was 0.005.

Example 5 In a solution of 274.7 g of bismaleimide triazine resin (BT2060BJ, Mitsubishi Gas Chemical) and 485 g of MEK using manganese as a catalyst,
483 g of SiO ₂ (HW-11-89, Harbis
on Walker Corp. ) Was mixed to prepare a fine dispersion. The dispersion was continuously stirred to ensure homogeneity. Then 0.0002 "
A (5.1 μm) sample of expanded PTFE was dipped in the resin mixture, removed and tensioned at 165
It was dried at 0 ° C for 1 minute to make a flexible composite material. Several stacks of this prepreg were placed between copper foils in a vacuum assisted hydraulic press at 250 psi (1.7
(MPa), pressed at 225 ° C. for 90 minutes and cooled under pressure. The dielectric thus obtained is 57 wt% of SiO ₂ ,
Consisting of 4 wt% PTFE and 39 wt% adhesive,
Shows good adhesion to copper, dielectric constant (at 10 GHz) 3.2 and loss tangent (at 10 GHz) 0.0.
It was 05.

Example 6 3.30 kg of bismaleimide triazine resin (BT206OBJ, Mitsubishi Gas Chemical) and 1
In a solution of 5.38 kg of MEK in a manganese-catalyzed solution, 15.44 kg of TiO ₂ (Tl Pure R-9
00, DuPont Company) to prepare a fine dispersion. The dispersion was continuously stirred to ensure homogeneity. Then, the stretched expanded PTFE of filled with TiO ₂ 0.0004 "(10.2μm) swatch (TiO ₂ was added 40%, except that no compressing the film last U.S. Patent Mortimer No.
(Filled according to the teachings of 4985296) was dipped into the resin mixture, removed, and then 165 under tension.
It was dried at 0 ° C for 1 minute to make a flexible composite material. Place several stacks of this prepreg between the copper foils,
In a vacuum-assisted hydraulic press, 500 psi (3.
5 MPa), 220 ° C. for 90 minutes, and cooled under pressure. The dielectric thus obtained had good adhesion to copper, a dielectric constant of 10.0 and a dielectric loss tangent of 0.008.

While particular embodiments of the present invention have been illustrated and described herein, the present invention is not limited to such description and description. It is obvious that variations and modifications are included and embodied as part of the present invention within the scope of the claims of this specification.

[Brief description of drawings]

FIG. 1 is an illustration showing a stretched or stretched polytetrafluoroethylene film 1 containing nodes 2 interconnected by fibrils 3 without the particulate filler.

FIG. 2 is an illustration showing a stretched or stretched polytetrafluoroethylene film containing an adhesive in which the voids defined by the nodes and microfiber structures are filled with particles.

FIG. 3 Stretch-expanded wherein the voids defined by the knot- and fibril structures contain a particle-filled adhesive and filler particles are also located in the fibril-knot structure. An explanatory view showing a stretched polytetrafluoroethylene film.

FIG. 4 is an illustration showing a composite material of the present invention adhered to a metal layer.

[Explanation of symbols]

 1 ... Film 2 ... Section 3 ... Microfiber 4 ... Adhesive 5 ... Particles 6 ... Metal

Claims (10)

[Claims] 1. A non-woven fabric comprising at least one porous fluoropolymer substrate layer having a void volume of at least 30% by volume; and an adhesive and a particulate filler uniformly dispersed throughout the voids of the substrate. A composite adhesive, wherein the adhesive and filler are present in the substrate such that the volume of the fluoropolymer substrate is about 5-40% by volume of the composite. material. 2. The composite material according to claim 1, wherein the adhesive is a thermosetting or thermoplastic compound. 3. The adhesive is at least one of an epoxy resin, a cyanate ester resin or a polybutadiene resin.
The composite material according to claim 2, wherein 4. The fluorine-containing polymer is stretched and expanded polytetrafluoroethylene, and the filler is Si.
The composite material according to claim 1, which is at least one of O ₂ , TiO ₂ , and ZnO. 5. The composite material of claim 4, wherein there is a plurality of substrate layers. 6. The composite material of claim 5, wherein a metal layer is adhered to the adhesive material. 7. The adhesive and the filler are sufficient to provide a composite having from about 5 to about 40 volume% expanded polytetrafluoroethylene. The composite material according to the item. 8. The composite material according to claim 1, wherein 10 to 95% by volume of the adhesive and the filler are absorbed in the base material. 9. The composite material according to claim 1, wherein the composite material contains 5 to 85% by volume of a filler. 10. At least one porous polymeric substrate layer having an initial void volume of at least 30%, said voids comprising an adhesive and a filler, wherein said filler throughout said voids of said substrate. The adhesive and filler are present in the substrate such that the volume of the polymer substrate is about 5 to about 40% by volume of the composite material, evenly distributed throughout.
The composite material adhesive.