JPH06283831A - Circuit board material of compounded fluoropolymer containing filler, and manufacture thereof - Google Patents

Abstract

PURPOSE: To obtain an electronic board material having excellent tensile characteristics in which the density, melt flow and alkaline solution resistance are enhanced while reducing bore by composing the board material of fluoropolymer matrix filled with a specified quantity of a ceramic filler applied with hydrophobic coating. CONSTITUTION: A multilayer board 10 comprises a plurality of layers of board materials 12, 14 and 16 comprising a composite material of mixed fluoropolymer filled with a ceramic filter. The composite material comprises a fluoropolymer matrix filled with 26-70 vol.% of a ceramic filter applied with hydrophobic coating and the matrix comprises a mixture of polytetrafluoroethylene (PTFE) and one or more kind of fluoropolymer component having fusion viscosity lower than that of the PTFE. Consequently, in the composite material of mixed fluoropolymer, only the PTFE has uniform and improved characteristics as compared with conventional characteristics of fluoropolymer matrix.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates generally to fluoropolymer composites containing fillers. The invention particularly relates to a fluoropolymer composite material for use as an electronic substrate material comprising a fluoropolymer matrix filled with coated ceramic particles. The fluoropolymer matrix is a mixture of polytetrafluoroethylene (PTFE) and one or more fluoropolymers having a low melt viscosity unlike this. The invention further relates to a new process for the preparation of composites of compounded fluoropolymers containing fillers.

[0002]

The use of highly filled fluoropolymer composites in the manufacture of circuit boards is well known for their use in a variety of other applications. Generally these fluoropolymer composites consist of a fluoropolymer substrate filled with a surface-treated ceramic filler. Preferably, the ceramic filler comprises silica particles and the surface treatment comprises a silane coupling agent. Examples of fluoropolymer composites of the type described above are disclosed in US Pat. Nos. 4,849,824 and 5,061,548 (both assigned to the assignee of the present application and incorporated herein by reference). US Patent Application No. 641,427, filed Jan. 17, 1991, filing date 198.
No. 279,474, Dec. 2, 1996, filing date 1991
No. 705,624 on May 24, 1994, No. 704,320 on May 22, 1991 (all assigned to the assignee of the present application and incorporated herein by reference) ) Is disclosed.

US Pat. No. 4,849,284, Ro
RO-2800 from Gers Corporation
A ceramic-filled fluoropolymer-based electronic substrate material sold under the trademark is described.
The electronic substrate material preferably comprises silica and polytetrafluoroethylene filled with a small amount of microfiberglass. An important feature of this material is that the ceramic filler (silica) is treated with a silane coating to make the surface of the ceramic hydrophobic and to enhance tensile strength, peel strength and dimensional stability. U.S. Pat. No. 4,84
No. 9,284 is for composite materials (assuming no voids)
It discloses that at least 50% by volume of filler is used as a circuit board or tie layer.

In US Pat. No. 5,024,871, the percentage of ceramic filler in the circuit board material disclosed in US Pat. No. 4,849,284 is about 45 volume percent, assuming no voids. It has been discovered that it retains sufficient thermal, mechanical, and electrical properties to be used as a tie layer in multilayer circuit materials and as a filler in rigid structures. US Patent No. 5,
The 024,871 ceramic-filled fluoropolymer composite improves the flowability of the material according to U.S. Pat. No. 4,949,284 and further provides an extremely high coefficient of thermal expansion (CTE) in the Z-axis of the material. Useful for applications that require filling access holes and shapes with resin flow without multiplication.

According to US Pat. No. 641,427, fluoropolymer composites rich in filler (eg, 50% or more) of US Pat. No. 4,849,284 are extended to high pH baths. It has been discovered that the severe chemical degradation of the material believed to occur with time exposure can be reduced and / or mitigated by using a low loading of about 26% by volume, assuming no voids. The resulting ceramic-filled composites have excellent mechanical and electrical properties and show a significant improvement in alkali resistance (for highly filled composites). Thus, in U.S. Patent Application No. 641,427, 26-45
A fluoropolymer composite filled with vol% silane coated silica is described.

The preferred silane coating of US Pat. No. 641,427 consists of a blend of phenylsilane and fluorosilane. This combination has excellent chemical resistance to alkaline baths and enhances laser drilling performance. Also, the combination of this relatively inexpensive phenylsilane and the more expensive fluorosilane gives a very economical coating. US Patent Application No. 279,474 and US Patent Application No. 704,320 generally describe the use of fluorosilane coatings and the very good physical properties provided to fluoropolymer composites by using fluorosilanes. There is.

US Pat. No. 705,624 discloses about 1
Particles of coated silica having no single linear dimension greater than 0 micron are loaded in an amount of at least 15 volume percent to about 95 volume percent, a thickness of about 2
Sub-mil fluoropolymer matrix composite thin film.

US Pat. No. 5,024,871 and US Patent Application No. 7 both filed on May 22, 1991
Nos. 04,303 and 703,633, all assigned to the assignee of the present application and incorporated herein by reference, are fluoropolymers filled with zirconate or titanate coated ceramic fillers. Regarding composite materials.

[0009]

Since the fluoropolymer composite material containing the above-mentioned filler is porous, a solvent having a low surface energy (eg, xylene, isopropanol, etc.), a semi-aqueous fluid, a surfactant is used. Aqueous processing fluids, including, can penetrate into the composite material. It is well known that alkaline solutions attack the filler (silica), although hydrophobic coatings on the filler surface (eg silanes, titanates, zirconates) significantly slow the permeation rate. This creates problems with the processing and performance of the material when manufacturing electronic circuit boards from the material and then during its subsequent end use. on the other hand,
The low volume fraction materials of US Patent Application No. 641,427 address this problem, but by doing so, some mechanical and thermal properties are lost. Therefore, there is a strong need to eliminate or reduce the pores in filled fluoropolymer materials of the type described above.

PTFE is known to exhibit a very high melt viscosity. Therefore, US Pat. No. 4,84
It is believed that the standard, highly filled material of 9,284 is only dense and not flowable. Therefore, there are many limitations in satisfying fine lines and shapes when manufacturing circuit boards containing such composite materials. The high flow composites of US Pat. No. 5,061,548 or US Pat. No. 641,427 were made to address this problem by reducing the amount of filler. However, as noted above, other important properties such as coefficient of thermal expansion have been lost.

[0011]

SUMMARY OF THE INVENTION The deficiencies and other deficiencies of the prior art described above are overcome or ameliorated by the novel fluoropolymer composites of the present invention and methods of making the same. In accordance with the present invention, a filler-containing fluoropolymer composite material used in electronic substrate materials comprises a fluoropolymer matrix filled with a coated ceramic filler, the fluoropolymer matrix comprising polytetrafluoroethylene (PTFE). )When,
One or more low melt viscosity fluoropolymers such as copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ether (PFA), copolymers of hexafluoropropylene and tetrafluoroethylene (FEP), or poly (ethylene- Co-chlorotrifluoroethylene) (ECTFE) or polychlorotrifluoroethylene (CTFE).

The resulting compounded fluoropolymer composites containing the fillers of the present invention have very uniform and improved properties over conventional commercial composites in which only PTFE is used as the fluoropolymer matrix. These improved properties include reduced porosity, improved density, high melt flow, significant improvement in alkali solution resistance, and excellent tensile properties.

According to another important feature of the invention,
The compounded fluoropolymers of the invention (eg, PTFE / PFA) are dramatically improved when the separate fluoropolymers are compounded in an aqueous dispersion rather than a powder. That is, when compounded in powder, the resulting compounded fluoropolymer composite exhibits two distinct melting points (indicative of incompatible compounding), but when compounded in an aqueous dispersion, Shows only one melting point (indication of compatible formulation). Thus, according to a preferred practice of the present invention, PTFE and one or more lower melt viscosity fluoropolymers are formulated in an aqueous dispersion. It then follows a co-coagulation process that "quenches" the morphology of the compounded fluoropolymer, thus minimizing phase separation. This composite material was subsequently described in US Pat. No. 4,849,2.
Sheets or thin films are made using the paste extrusion method described in No. 84.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The above and other features of the present invention will be understood by those skilled in the art upon reading the following detailed description with reference to the accompanying drawings.

The fluoropolymer composite material containing the filler of the present invention comprises a fluoropolymer matrix (30 to 74) filled with a ceramic filler (26 to 70% by volume).
%) And the ceramic filler is coated with a hydrophobic coating.

The fluoropolymer matrix comprises PTFE having a melt viscosity of about 10 GP and at least one lower melt viscosity PFA, FEP, ECTFE or CTFE.
And blends with fluoropolymers including, but not limited to. Other suitable low melt viscosity fluoropolymers include poly (ethylene-co-tetrafluoroethylene) and polyvinylidene fluoride. Focusing on the fluoropolymer matrix component, PTFE preferably comprises 10-95% by volume in the total fluoropolymer matrix, while the remaining lower melt viscosity components make up 90-5% by volume in the total fluoropolymer matrix. .

The ceramic filler is preferably silica, more preferably amorphous fused silica. The polymer matrix is loaded with greater than 40 volume percent fused silica or other ceramic filler to achieve a target coefficient of thermal expansion (CTE) of less than 75 ppm ° C. Fused amorphous silica is the preferred ceramic filler due to its extremely low coefficient of thermal expansion (0.6 ppm / ° C over a wide temperature range) and relatively low dielectric constant and weight loss, but many ceramic materials (fine crystalline silica). , Glass spheres, complete or hollow glass microspheres, TiO ₂ or BaTiO ₃ )
Any of these will yield useful products according to the present invention.

The hydrophobic coating of the present invention may be comprised of any coating agent that is thermally stable, exhibits low surface energy and improves the water resistance of the composite material of the present invention. Suitable coating agents include common silane coatings, titanate coatings, zirconate coatings. Preferred silane coatings include phenyltrimethoxysilane, phenyltriethoxysilane, (3,3,3-trifluoropropyl) trimethoxysilane, (trideca-fluoro-1,1,2,2-
Tetrahydrodecyl) -1,1-triethoxysilane,
(Heptadecafluoro-1,1,2,2-tetrahydrodecyl) -1-triethoxysilane and mixtures thereof. Suitable titanate coatings include neopentyl (diallyl) oxytrineodecanoyl titanate, neopentyl (diallyl) oxytri (dodecyl) benzene-sulfonyl titanate, and neopentyl (diallyl) oxytri (dioctyl) phosphate titanate. Suitable zirconate coatings include neopentyl (diallyl) oxytri (dioctyl) -pyrophosphate nizirconate,
And neopentyl (diallyl) oxytri- (N-ethylenediamino) ethyl zirconate.

The hydrophobic coating is used in an amount effective to render the surface of the filler particles hydrophobic and compatible with the matrix material. The amount of coating relative to the amount of coated inorganic particles depends on the surface area coated and the density of the inorganic particles. Preferably, the coated inorganic particles of the present invention comprise about 3 parts by weight (pbw) hydrophobic coating: 100 pbw ceramic particles to about 15 pbw hydrophobic coating:
Includes 100 pbw ceramic particles.

To coat the filler, stir in the coating solution, remove from the solution and finally heat to evaporate the solvent from the coating and allow the coating to react with the surface of the filler.

Composite materials of the present invention having a compounded fluoropolymer matrix are disclosed in US Pat. Nos. 4,355,180 and 4,84, which are incorporated herein by reference.
Mixing may be done according to the procedure outlined in the specification of 9,284. Briefly, the procedure involves mixing particles of the coated ceramic with a fluoropolymer dispersion, coagulating the mixture with a coagulant, filtering the coagulated mixture and then heating to a high temperature (600 ° F). ~ 800 ° F) High pressure (100 psi ~ 3)
000 psi) and consolidating the mixture to form a composite substrate. Alternatively, the fluoropolymer powder may be mixed with the particles of the coated filler, and the mixture thus prepared may be consolidated under high temperature and high pressure conditions to form a composite substrate.

For reasons detailed below, the preferred method of making the composite material of the present invention incorporates the fluoropolymer component as an aqueous dispersion (rather than a dry powder mix). Such aqueous dispersions are commercially available. For example, the PTFE dispersion is I
Trade name Fluon AD7 from CI Americas
It is marketed as 04. A PFA dispersion is also available from DuPont under the tradename Teflon® PFA. Prior to mixing the coated (eg, treated) filler with the fluoropolymer dispersion (eg, PTFE and at least one lower melt viscosity fluoropolymer), the treated filler is mixed with a surfactant ( Example, Union Carbi
Disperse with Triton X-100) of de.
The amount of surfactant is adjusted so that the blended compounded polymer dispersion and filler form a uniform co-coagulated composite. The amount of this surfactant is generally 1 wt% with respect to the filler and is effective in dispersing the treated filler without stabilizing the polymer and filler mixture. As a result, filler / polymer co-coagulation occurs instantly when the polymer dispersion is added to the filler dispersion. After co-coagulation, a composite fluoropolymer composite layer or thin film (eg, 1 to 30 mils) can be made by the paste extrusion method described above.

Compounded polymers can be defined as a mixture of polymers without covalent bonds. Compatible polymer blends (2
It is possible to have the performance (ie mechanical, thermal, chemical, rheological) of both polymers sought, when the seed polymers are intimately mixed. However, polymer incompatibility arises from the very small entropy obtained by mixing different types of long chains and molecular weights. Simple blending of the two polymers very often results in incompatible blended polymers. Differential scanning calorimetry (DSC) is an effective method for assessing polymer compatibility. A compatible compounded polymer should have only one melting endotherm.

According to an important feature of the invention, PTFE /
PFA dispersion mixture (eg 50/50)
Was found by DSC to have one melting endotherm (a sign of a true compatible formulation). On the other hand, PTFE / P
The FA powder mixture (50/50) does not give a compatible formulation (2 endotherms in DSC).

The four DSC measurement results are shown in FIGS. 1 to 4 and support the above results. In Figure 1, PT
The FE dispersion and PFA dispersion were mixed. DSC shows the initial melting peak of PTFE and PFA (33
9 ° C., 313 ° C.). Compound PTFE / PFA
FIG. 2 which is the second DSC measurement result of the dispersion.
Shows only one melting peak at 319 ° C.
Thus, FIG. 2 shows compatible formulations.

FIG. 3 shows a mixture of PTFE powder and PFA powder. DSC melts PTFE at 335 ° C,
It shows that FA melts at 308 ° C. This PTF
The second DSC measurement of the E / PFA powder formulation, FIG. 4, still shows two distinct melting peaks. This is a sign of incompatibility.

Importantly, the examples of FIGS. 1 through 4 were made using samples without ceramic filler. The fact that the preferred blended fluoropolymers thus improved are made from aqueous dispersions is beneficial whether or not they contain a filler.
PTFE / P mixed with filler by the new method of the present invention
The improvement results obtained by mixing the FA dispersions, the synergistic effect on the porosity, fluidity and other properties of the composite material are shown in the following examples.

[0028]

EXAMPLES Samples of compounded fluoropolymer composites (PTFE / PFA) made according to the preferred manufacturing method described above.
/ SiO ₂ filler) and prior art composite material sample (PT
FE only / SiO ₂ filler) with a filler of 30, 40, 5
The comparison was made by including 0 volume%. The volume% ratio of filler / PTFE / PFA in each example is 30/35/3
5, 40/30/30 and 50/25/25. Tables 1 to 3 below summarize the differences in important material properties. Table 1 is a measure of the absorption of the solvent (xylene) and thus an indirect measure of porosity. Table 2 shows NaOH
Measurement of mass defect after immersion in (pH = 13) for 24 hours, while Table 3 is a measurement of water absorption after immersion for 24 hours in NaOH.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

The results in Table 1 show that the compounded fluoropolymer composite material containing fillers was found to contain PTFE containing fillers of the prior art.
It has been shown to have significantly improved density and reduced porosity over the bare composites. In Tables 2 and 3, the compounded fluoropolymer composites of the present invention have significantly improved alkaline solution (NaOH) resistance over prior art PTFE-only composites, and among these improvements are , 400 of mass loss after soaking in NaOH
% Improvement (50% by volume example) and only slight water uptake after NaOH soaking is shown to be included.

In Table 4, several types of PTFE / PFA /
The tensile properties of the SiO ₂ composite are shown. These tensile properties are excellent, particularly for electronic substrate material applications, and are preferred over prior art PTFE-only composite materials.

[0034]

[Table 4]

In Table 5, a disk having a diameter of 0.50 "is used.
The results of a squeeze flow test carried out at a thickness of 0.060 ″, 500 psi and 700 ° F. are shown. Flowability was examined by decreasing the thickness of the discs tested and increasing the surface area.

[0036]

[Table 5]

From Table 5, it is clear that the more PFA in the composite material, the higher the flow performance of the composite material. Prior art 1
Is a sample of PTFE only (50% by volume) / phenylsilane-coated silica filler (50% by volume). Prior art 2 is a sample of PTFE only (50% by volume) / fluorosilane coated silica filler (50% by volume).

Whereas the above table shows the PTFE / PFA formulations, the following Table 6 shows similar results and properties for the PTFE / FEP formulations.

[0039]

[Table 6]

As noted above, the compounded fluoropolymer composites of the present invention are particularly useful as single or multi-layer circuit board materials (where the present invention is used as a thin tie layer). Turning to FIG. 5, such a multilayer circuit board is shown generally at 10. The multilayer substrate 10 is made of substrate materials 12, 1
4, 16 multiple layers, all of which are electronic substrate materials, preferably compounded fluoropolymers filled with the ceramic filler of the present invention or other US Pat. No. 4,84.
It comprises a suitable fluoropolymer composite material such as that disclosed in 9,284 and sold under the trademark RO-2800. Each of the substrate layers 12, 14, 16 has a conductive pattern 1
There are 8, 20, 22, and 24, respectively. Here, a board layer having a circuit pattern is defined as a circuit board. The plated through holes 26 and 28 connect the selected circuit patterns to one another in a known manner.

According to the invention, the separate sheets 30 and 32, which are substrate materials of the composition according to the invention, are used as an adhesive or tie layer for bonding different circuit boards together. According to a preferred method for making such laminates, one or more tie layers and circuit boards are alternately stacked. This stack of layers
Fused at temperatures below 500 ° F. and pressures below 300 psi, the entire multilayer is melted and blended into a homogeneous composition whose electrical and mechanical properties do not change throughout. Adhesive bond layers 30 and 32 may be used to bond circuit boards comprised of materials other than fluoropolymer composites with the coated fillers described herein.

Although the preferred embodiments have been shown and described, various modifications may be made to the present invention without departing from the scope of the present invention. Accordingly, the present invention is exemplary and not limiting.

[Brief description of drawings]

FIG. 1 of PTFE / PFA dispersion mixture
It is a third DSC measurement diagram.

FIG. 2 is a second DSC measurement diagram of the PTFE / PFA dispersion mixture of FIG.

FIG. 3: First DSC of PTFE / PFA powder mixture
FIG.

FIG. 4 is a second DSC measurement diagram of the PTFE / PFA powder mixture of FIG.

FIG. 5 is a cross-sectional front view of a multi-layer circuit using the compounded fluoropolymer composite material of the present invention.

[Explanation of symbols]

 10 Multilayer Circuit Board 12, 14, 16 Substrate 18, 20, 22, 24 Conductive Pattern 26, 28 Through Hole 30, 32 Adhesive Bonding Layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display location C08L 27/12 LGH 9166-4J 27/18 LGB 9166-4J H01L 23/12 23/14

Claims (23)

[Claims] 1. Polytetrafluoroethylene (PTF)
A fluoropolymer matrix comprising a blend of E) and one or more fluoropolymer components having a lower melt viscosity than PTFE; a ceramic filler in an amount of about 26-70% by volume of the total substrate material; Electronic substrate material consisting of the hydrophobic coating of. 2. The material of claim 1, wherein the PTFE is present in about 10 to 95 volume percent based on the total fluoropolymer matrix. 3. The fluoropolymer component is a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether (PFA), a copolymer of hexafluoropropylene and tetrafluoroethylene (FEP),
Poly (ethylene-co-chlorotrifluoroethylene),
A material according to claim 1, characterized in that it is selected from the group consisting of polychlorotrifluoroethylene, poly (ethylene-co-tetrafluoroethylene), polyvinylidene fluoride. 4. The fluoropolymer matrix is
The material of claim 1, wherein the material is made by blending the PTFE and an aqueous dispersion of the one or more fluoropolymer components. 5. The material of claim 1, wherein at least one layer of conductive material is disposed on at least a portion of the electronic substrate material. 6. The material according to claim 1, wherein the ceramic filler comprises silica. 7. The material of claim 6, wherein the silica comprises amorphous fused silica powder. 8. The ceramic filler comprises particles,
The material of claim 1, wherein its average particle size varies from about 10 to 15 microns. 9. The composite material of claim 1, wherein the hydrophobic coating is selected from the group consisting of silane coating, zirconate coating, titanate coating. 10. The ceramic filler coating comprises:
The composite material of claim 9, wherein the coating is about 3 parts by weight to about 15 parts by weight with respect to 100 parts by weight of the filler. 11. The coating is phenyltrimethoxysilane, phenyltriethoxysilane, (3,3,3).
-Trifluoropropyl) trimethoxysilane, (tridecafluoro-1,1,2,2-tetrahydrooctyl) -1,1-triethoxysilane, (heptadecafluoro-1,1,2,2-tetrahydrodecyl) The composite material according to claim 9, comprising -1-triethoxysilane or a mixture thereof. 12. The coating comprises neopentyl (diallyl) oxytrineodecanoyl titanate, neopentyl (diallyl) oxytri (dodecyl) benzene-
10. Composite material according to claim 9, characterized in that it consists of sulfonyl titanate, neopentyl (diallyl) oxytri (dioctyl) phosphate titanate. 13. The coating according to claim 9, wherein the coating comprises neopentyl (diallyl) oxytri (dioctyl) -pyrophosphate = zirconate, neopentyl (diallyl) oxytri- (N-ethylenediamino) ethyl = zirconate. Composite material. 14. A multilayer circuit including at least a first circuit layer and a second circuit layer, wherein an adhesive layer is sandwiched between the first and second circuit layers, the adhesive layer comprising: A fluoropolymer matrix, which is a blend of tetrafluoroethylene (PTFE) and one or more fluoropolymer components having a lower melt viscosity than PTFE, and a ceramic filler included in an amount of about 26 to 70 volume percent in the total substrate material. A multilayer circuit comprising a hydrophobic coating on a ceramic filler. 15. The multilayer circuit of claim 14 including at least one plated through hole. 16. The multilayer circuit of claim 14, wherein the PTFE is present in about 10 to 95 volume percent based on the total fluoropolymer matrix. 17. The fluoropolymer component is a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether (PFA), a copolymer of hexafluoroalkyl vinyl ether and tetrafluoroethylene (FEP), poly (ethylene-co-chlorotri). 15. The multilayer circuit according to claim 14, wherein the multilayer circuit is selected from the group consisting of fluoroethylene), polychlorotrifluoroethylene, poly (ethylene-co-tetrafluoroethylene), and polyvinylidene fluoride. 18. The multilayer circuit of claim 14, wherein the fluoropolymer matrix is made by blending the PTFE and an aqueous dispersion of the one or more fluoropolymer components. 19. Polytetrafluoroethylene (PTF)
E) and one or more kinds of aqueous dispersions of fluoropolymer components having a lower melt viscosity than PTFE are mixed to form a compounded fluoropolymer dispersion, and the compounded fluoropolymer dispersion is co-coagulated to form a uniform composite material. A method of manufacturing an electronic substrate material, comprising: 20. The method of claim 19 including dispersing the filler with a surfactant and mixing the filler dispersion with the compounded fluoropolymer during the co-coagulation step. 21. The amount of surfactant for dispersing the filler is selected such that it effectively disperses the filler without stabilizing the blended fluoropolymer and filler mixture. The method according to claim 20, wherein 22. The method of claim 20 including the step of coating the filler with a hydrophobic coating. 23. The method of claim 19 including the step of paste extruding the uniform sheet of composite material.