FR2671932A1 - FLUOROPOLYMER COMPOSITE MATERIAL FOR CERAMIC FILLERS. - Google Patents

Abstract

A composite material comprising a fluoropolymer containing ceramic fillers is presented, wherein the ceramic is coated with a silane and the ceramic is a volume% fraction of about 26 to 45. The composite of the present invention exhibits excellent resistance to chemicals, particularly alkaline environments. Preferably, the silane comprises a mixture of at least one phenylsilane and at least one fluorosilane. Preferably, the silane is coated to obtain a content of 10% of the total weight of the ceramic filler material. The present invention finds particular utility in the filling of openings (52), for example ground planes (50), and in the bonding of multilayer printed circuit boards or in the construction of printed circuit boards by laminating sheets. .

Description

Fluoropolymer composite material containing filler materials

  The present invention relates to an electrical substrate material comprising a fluoropolymeric material and ceramic filler materials, which is particularly suitable for use as a bonding layer in a multilayer printed circuit board, as well as in other applications of electronic circuits, which require flowability, as well as good thermal, mechanical and electrical properties The fluoropolymer composite material of the present invention also exhibits resistance to degradation caused by chemicals, in particular

  especially in high p H (alkaline) environments.

  In the patent of the United States of America

4,849,284,

  an electrical substrate material based on fluoropolymer containing ceramic filler materials (sold by Rogers

  Corporation under the trade name RO-2800).

  Preferably, this electrical substrate material comprises polytetrafluoroethylene containing, as fillers, silica, as well as a small amount of glass microfibers. In an important characteristic of this material, ceramic fillers (silica) are coated with a silane coating material which makes the ceramic surface hydrophobic and which provides improvement in tensile strength, chipping resistance and dimensional stability The composite material of the patent of the United States of America 4,849,284 discloses a filler material fraction in volume percent (on a void-free basis) of at least 50, for use as a substrate for printed circuits or as a

bonding layer.

  The electrical substrate material of U.S. Patent 4,849,284, based on fluoropolymer containing ceramic fillers, is well suited for shaping rigid substrate material for printed circuit boards an improvement in its electrical performance compared to other printed circuit board materials Likewise, the low coefficients of thermal expansion and the elastic nature of this material of electric substrate, give rise to improved reliability with regard to mounting in surface as well

  improved reliability with regard to metallized holes.

  As is known, individual sheets of this electrical substrate material must be stacked to obtain a multi-layer wafer for printed circuits. In fact, thin film formulations of the material disclosed in US Patent 4 can be used. 849 284 (and sold by Rogers Corporation under the trade name RO-2810), as a bonding layer for bonding to each other several layers of substrate stacked so as to obtain the multilayer wafer for printed circuits. It will be understood that high volume fractions (greater than 55% by volume) as to the ceramic fillers will adversely and significantly affect the rheology (e.g., flow) of the fluoropolymer composite containing fillers. ceramic This characteristic is of particular importance when the composite is used as a bonding film or to fill openings made in previously rigid structures. Although fractions by volume of ceramic filler materials of the order of 50 to 55% provide Theological properties greatly improved compared to higher fractions of fillers, there has been a need to provide the fluoropolymer composite with even better flow properties, without appreciably altering the excellent thermal, mechanical and electrical properties. In addition to the detrimental effects on rheology, it was also possible to determine that fractions of ceramic filler materials of 50% and more by volume also had a negative impact on the chemical resistance of the fluoropolymer composite containing filler materials, by compared to certain hostile environments, in particular baths with high p H (alkaline) One needs such baths with high p H (for example, a p H greater than 12) to obtain a deposit of chemical copper which constitutes a highly desirable and frequently used in the manufacture of circuit components in the form of thin lines (i.e. flake modules) It has been found that high contents of ceramic filler (50% by volume and more) could give fluoropolymer material for printed circuit boards poor chemical resistance upon long-term exposure in such alkali baths alins The resulting degradation, caused by poor resistance to alkaline baths, gives rise to a reduction in the hydrophobic character of the fluoropolymer composite In turn, this reduction gives rise to more intense moisture absorption, accompanied by a decrease corresponding and highly undesirable electrical properties of the

  composite material for printed circuits.

  In the patent of the United States of America

5,061,548

  it has been discovered that the ceramic filler content of the material disclosed in U.S. Patent 4,849,284 could be as low as 45% by volume on a void-free basis, the material still retaining thermal properties , mechanical and electrical, suitable for use as a bonding layer in multilayer materials for printed circuits and as a filler for certain rigid structures The fluoropolymer composite material containing ceramic filler materials of the United States patent 5,061,548 exhibits improved rheology compared to US Patent 4,849,284 material and is useful in applications which require access holes and characteristic filling by flow of resin, without giving rise to an excessive increase in the coefficient of expansion

  thermal of the material's z-axis.

  The object of the present invention is to reduce and / or decrease the significant degradation caused by chemicals, associated with fluoropolymer composites with a high filler content (for example, 50% and more) of the United States patent. of America 4 849 284 during exhibition

  long-term at high p H baths.

  In accordance with the present invention, this object is achieved by using lower contents of ceramic filler as low as about 26% by volume on a void-free basis,

  said fillers being coated with silane.

  The resulting composite containing ceramic filler materials exhibits excellent mechanical and electrical properties, and it exhibits a significant improvement (compared to composites with higher contents of

  charge) as for resistance to alkalis.

  In accordance with another important characteristic of the present invention, it has been found that relatively large amounts of silane coating of up to 2-10% (of the total weight of the ceramic filler) give rise to improved properties, in particular, with regard to laser drilling to obtain metallized holes, as well as subsequent solid connections The use of a coating at a rate of 10% (and preferably, at a rate of 6%) is surprising and unexpected , since it was generally believed (as described in U.S. Patent 4,839,284) that the silane levels should be between 1 and 2% and that no improvement was achieved

  appreciable with high contents going up to 6-

10%.

  The preferred silane coating comprises a mixture of phenylsilane and fluorosilane. This combination gives excellent resistance to chemicals in alkaline baths and at the same time promotes the ability to be drilled using the laser. Similarly, the combination of relatively cheaper phenylsilane and more expensive fluorosilane provides

  coating extremely interesting in terms of cost.

  Those skilled in the art will understand and appreciate the features and advantages of the present invention mentioned above, as well as others to

  from the detailed description below and

  drawings in which: FIGS. 1A and 1B are respective views in cross section and in elevation of a rigid structure provided with openings, before and after filling with the composite material of the present invention; Figure 2 is a cross-sectional elevational view of a multilayer printed circuit board, which uses the thermoplastic composite material according to the present invention as a thin bonding film layer; FIG. 3 is a graph representing the effect of the silane and of the content (%) of coated silica filler materials on the laser treatment capacity of the composite material at 248 nm, the energy of the ray = 3.9 J / cm 2; and FIG. 4 represents a view in cross section and in elevation of a plate for

  printed circuits according to the present invention.

  The fluoropolymer composite material of the present invention, containing ceramic fillers, is essentially similar to the composites described in U.S. Patents 4,849,284 and 5,061,548 with the exception that (1), in a first embodiment, the ceramic is present, on a void-free basis, in an amount as low as about 26% by volume; and (2) in a second embodiment, the ceramic fillers are coated with silane up to% (relative to the total weight of the ceramic fillers) Preferably, all of these embodiments use a mixture of phenylsilane and fluorosilane for coating ceramic fillers and said fluoropolymer material is chosen from the group comprising:

  polytetrafluoroethylene, hexafluoropropene, tetra-

  fluorethylene and perfluoroalkylvinyl ether.

  In a preferred embodiment, the first embodiment of the present invention comprises a composite of particulate ceramic fillers present in a volume fraction of about 0.26 to less than 0.45 and the fluoropolymer (e.g. , PTFE) present in a volume fraction of 0.74 to 0.55 on a void-free basis The preferred ceramic filler is molten amorphous silica All other composition characteristics, as well as manufacturing methods are the same as those disclosed in U.S. Patent 4,849,284 (including the fact that the ceramic is coated with silane), except for preferred higher weight percentages for coating with silane and preferred mixtures of silane, these two characteristics being described below. Reference will therefore be made to United States patents 4,849,284 for these details. the materials comprising the present invention, either by "wet mixing" of PTFE polymer in dispersion with the ceramic fillers and by coagulation, or by dry mixing of fine PTFE powders with

  ceramic fillers.

  The reduction in the filler content to as low as about 26% by volume gives rise to a significant increase in the resistance of the fluoropolymer composite material to alkaline environments In the comparison of Examples 1 and 2 shown in Table I below, Example 1 relates to a composite of the type described in United States patent 4,849,284, which has a composition of fluoropolymer PTFE in an amount of 50%, of the fillers in silica at a rate of 50% and of a coating of fillers with phenylsilane corresponding to 2% by weight. Example 2 relates to a composition according to the present invention, namely a composition of 37.1% of fillers of silica, 62.9% PTFE fluoropolymer and a mixture of phenyl and fluorosilanes (3: 1 ratio) of 6% by weight (relative

  the total weight of the fillers).

  TABLE i Example 1 Example Dle 2 Absorption of xylene (%) 5.3 2.7 Absorption of H 20 (%) 0.05 0.02 Absorption of H 20 * (%) 1.7 0.07 Insulation resistance ** (M ohm) 90 + than 300 Coefficient of thermal expansion (ppm / C) 40 60 Laser ablation threshold (J / cm 2) 1.7 1, 3 * After 24 hours in Na OH 0.1 M, 1% Triton, 23 C ** After 8 hours in 0.1 M Na OH, 1% Triton, 60 C The results in Table 1 clearly indicate that the absorption of H 20 (after treatment in an alkaline bath) decreases significantly when the quantity of fillers decreases (for example, 0.07% for the present invention against 1.7% for the material of the patent of the United States of America 4,849,284) It will be understood that an absorption acceptable H 20 should be less than about 0.1% by weight. The results of Table 1 are verified in additional examples 3-12 of Table 2 In Examples 6-11, the silane coating comprises a mixture of phenylsilane and fluorosilane In Example 12,

  a phenylsilane coating is used.

o 1 l Example silica% / silane%

3 30 / O

dried up

4 40/0

dried up

50/0

dried up

6 29 3

dried up

7 39

dried up

8 48 6

dried up

9 1 27 9

  dry 37.1 dry 46.1 dry 48.6 dry, H20 absorption control (24 hours 2 H20 absorption (24 hours weight v <

2.2047

2.1970

2.1452

2.1971

2.1800

2.1201

2.1859

2.1654

2.1163

2.1130

* es, 50 C) res, 50 C)

Table 2

  ol absorption 1 initial absorption 2 of H 90 (%) conditioned by H 20

0.5152 0 5895

1.1160 1 2474

2.3566 2 0443

0.0435 0 0428

0.0361 0 0886

0.0774 0 4099

0.0458 0 0500

0.0140 0 0727

0.0613 0 5869

0.0400 1 7640

  without preconditioning by alkaline bath.

  after 24 hours in Na OH O, 1 M, triton at 1,

0.23 C.

  N b 9 il In Table 2, we see once again that a decrease in the content of fillers gives rise to an increase in the resistance to chemicals during treatment at high p H, as indicated by the decrease in water absorption when the filler content decreases A comparison between the examples in which there are equal coatings of silane (such as examples 3-5, 6-8 and 9-11 ) indicates that the increase in resistance to chemicals is provided, at least in part, by the lower filler rates. It will be understood that the low rates (for example, 27 and 37% by volume) according to the present invention are improved significantly over the 50% volume percent associated with the composite of US Patent 4,849,284 Thus, a composite of a fluoropolymer material of the present invention, intended for circuits print ies and containing fillers, which has a fillers content of approximately 26 (it should be noted that Table 3 shows examples having contents of fillers which drop to approximately 26% by volume) at less than 45% by volume, provide a significant advantage over the materials of the patent of the United States of America 5,061,548 (contents of filler materials

  less than 50% by volume) and the United States patent

  United States of America 4,849,284 (content of

load of 50% by volume and more).

  In accordance with yet another feature of the present invention, it has been found that higher coating rates of up to 10% (and preferably 6%) by weight of the total ceramic filler content contribute to improved results in laser ablation This discovery is unexpected, since it was thought and suggested in US Patent 4,849,284 that silane coating rates of 1 to 2% were preferred and that above 2%, the effect of the silane coating was negligible Two criteria used to determine the suitability for laser treatment of materials intended for printed circuits, include (1) the rate of energy required for ablation (lower rates are preferred); and (2) the deviation with respect to walls of perfectly rectilinear holes (not conical) having undergone ablation (a deviation of O being preferred) In FIG. 4, the cross section of a printed circuit board is shown, which has a hole 2 obtained by laser ablation and made in a substrate 4 (made from the composite of the present invention), on which a layer 6 has been deposited. The angle "a" represents the distance from a wall rectilinear In Table 3, the laser ablation results are represented for a series of coating values and quantities of ceramic filler materials for compositions mixed dry and in the wet state In Examples 13-30 and 32-38, silica filler materials are used, while in Examples 31 and 39, silica filler materials are used

quartz charge.

Table 3

  Laser ablation threshold at 248 nm for various PTFE / ceramic compositions SEC dry mixing process i M II) DL Ii UMIDE l WET DRY TO DRY

WET

I WET

IHIUMIDE

H WET

  A SEC A SEC Load content 46.1 46.1 37.1 43.8 37.1 27.9 35. 3 27.9 26.7 48.6 48.6 48.6 Coating

6% 3: 1

6% 3: 1

6% 3: 1

% 3: 1

6% 3: 1

6% 3: 1

% 3: 1

6% 3: 1

% 3: 1

2% 3: 1

2% 6124

2% 6124

Dimension of

materials of ch.

  l Or lou l Or 1.5 u lou l Or 1.5 u l Or 1.5 u l Or l Or l Or Ablation threshold (J / cm) 1.3 1.3 1.3 1.3 1.3 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 ce a) r ,, N c 1

Example

  The results in Table 3 indicate that high contents of fillers and high values of coating, provide the best laser ablation results (in terms of the lowest threshold energy for ablation). as for laser ablation deteriorate as either the filler content, or the coating content or both, decrease Thanks to the coating of the filler materials, the threshold of the ablation even for low filler contents, such as of the order of 26% This characteristic becomes quite obvious when comparing Examples 18 and 20 with Example 36 In Table 3, the coatings indicated by the ratio 3: 1 relate to three parts of

  phenylsilane for part of fluorosilane.

  The coating identified by the number 6124 constitutes phenyltrimethoxysilane and the fluorosilane is tridecafluoro-l, 1-2,2-tetrahydrooctyl-1-triethoxysilane whose chemical formula is C 6 F 13 CH 2 CH 2 Si (OCH 2 CH 3 ) 3 and it is designated below by the abbreviation C 6 F. In FIG. 3, this effect of the composition on the ability to be treated with laser is also indicated (at 248 nm for a ray energy of 3.9 J / cm 2), the diagonal lines representing the deviation from walls of rectilinear holes having undergone

  laser treatment (lower corner preferred).

  In FIG. 3, the "contents of silica filler materials" include the contribution in% by volume made by the coating to silane. In FIG. 3, it is indicated that higher quantities of silane and / or higher quantities of materials of ceramic filler give rise to improved laser ablation (quality of the walls of the holes) It should be noted Mixing method A SEC A SEC

WET

WET

  Charoe mat content 48.6 39.0 39.0 48.6

Table 3

Coating

2% 3: 1

2% 3: 1

2% 3: 1

2% 3: 1

  (contd.) Threshold of TV set at room temperature (J / cm) u 1 7 l Ou u l Ou 1.7 2.7 2.7

2% 3: 1

2% 3: 1

2% 6124

2% 3: 1

2% 3: 1

% 3: 1

  untreated untreated untreated untreated untreated l Or l Or Quartz l Or l Or 1.5 u l Or l Or l Or l Or Quartz

Example

0, N (O -e A SEC A SEC A SEC A SEC

I IUIMIDE

WET

IIU Mi DE A SEC

WET

  A SEC A SEC 48.6 39.0 29.3 29.3 29 3 35.3%%%%% 2.7 2.7 2.7 2. 7 2.7 2.7 3.9 3.9 3.9 3.9 3.9 that preferably, when using low levels of ceramic filler, we uses high silane contents. In accordance with yet another characteristic of the present invention, it has been found that the silane coating preferably constitutes a mixture of phenylsilane and of fluorosilane. The fluorosilane confers resistance as to chemicals when exposed to alkalis, while phenylsilane promotes laser drilling, while being less expensive than fluorosilane In Table 4, we demonstrate the superiority of fluorosilane over phenylsilane to confer resistance to degradation due to alkalis The preferred mixture relates to a ratio

  weighted phenylsilane: fluorosilane 3: 1 preferably

  rence, the silane coating is chosen from the group

  including p-chloromethylphenyltrimethoxysilane, amino-

  ethylaminotrimethoxysilane, a mixture of phenyltrimethoxy-

  silane and aminoethylaminopropyltrimethoxysilane, fluorosilane and a mixture of at least one fluorosilane and at

minus a phenylsilane.

-Example Process Content

mixing ch mat.

  48 6 dry 41 47 3 dry 42 46 1 dry 43 47 3 dry H20 absorption (48 hours,

2 2

Absorption of IH 0 (48 hours,

230 C 2

Example 4

1 2

  Weight Rate Type Absorptionlini Absorption 2 condi-

  silane% specific silane H 20 (%) tted H 20 (5%)

C 6 F 2 2 142 0 03 O 33

C 6 F 4 2 143 0 04 0 41

C 6 F 6 2 139 0 04 0 50

6124 4 2,097 0 02 0 99

   C) without alkaline preconditioning C) after 24 hours in 0.1 M aqueous Na OH, 1% by weight of Triton X-100, N (O r- HI By this reduction as regards the content of fillers, the rheology of the material of the present invention is improved to the point that it will "flow" and fill larger openings in the metal sheets or the inner layers of the circuit components, which cannot be filled with some of the materials to be high filler content (greater than a fraction

  55% by volume), revealed in the United States patent

United States of America 4,849,284.

  An important characteristic of the present invention relates to the fact that the rheology is improved without excessively increasing the coefficient of thermal expansion (CTE) of the x-axis of the material. The CTE of the axis of the materials has been measured. x of the formulation of fillers at a rate of 30 to 45% by volume, as being considerably lower than that of fiber-reinforced PTFE and used in

  a large measure, in the temperature range of -

  55 to + 1250 C (specifically, around 200 ppm / 0 C) (see Table 5) Multilayer printed circuit boards, made from RO-2800 laminates bonded together using bonding layers of the present invention will manifest an overall CTE considerably lower than that of fiber-reinforced PTFE wafers The reduction in the CTE is significant in order to increase the reliability of the metallized holes and of the connections in order to withstand the assembly. thermal and

high temperature.

L 9

TABLE 5

  Example Material -55 / + 125 silane% / mat of ch% ppm / oc

44 2/30 94

2/40 68

46 2/50 41

47 6/30 84

48 6/40 72

49 6/50 47

  The present invention extends to a number of applications in which PTFE composite materials containing ceramic filler materials can be used to construct useful boards for printed circuits. The present invention has the particular utility of filling openings in already rigid structures such as engraved ground or voltage planes for integrated circuits and holding cores, or even

  circuit components bonded to such structures.

  For example, in FIG. 1A, a rigid structure of mass plane in cross section at 50 is described, provided with several openings 52. The sheets 54, 56 of the present invention are then positioned (for example, having a ceramic fraction of 0 , 26 to 0.45 by volume) on each side of the ground plane 50 In FIG. 1 B, the laminate 58 of FIG. 1 A is branched out under the action of heat and pressure The composition of the present invention will allow a good flow so as to completely fill the openings, while also providing thermal, mechanical and

excellent electrics.

  Furthermore, with reference to FIG. 2, the composite of the present invention can be treated to obtain a sheet in its non-densified and non-sintered form and use it to bond multilayer printed circuit boards or to construct boards. printed circuits by branching of sheets Turning to FIG. 2, such a multilayer wafer for printed circuits is represented, in general, by the number 10 The wafer comprises several layers of a substrate material 12, 14 and 16, each being made of an electrical substrate material, preferably the fluoropolymer material containing ceramic fillers of the United States patent

  4,849,284, sold under the trade name RO-

  2800 On each substrate layer 12, 14 and 16, a selective metal plating 18, 20, 22 and 24 is then applied, respectively. It should be noted that a layer of substrate on which a selective plating of printed circuits is applied, defines a circuit substrate Metallized holes 26 and 28 interconnect selective circuit plating

printed in a known manner.

  In accordance with the present invention, separate sheets 30 and 32 comprising a substrate material, the composition of which corresponds to that of the present invention, are used as an adhesive or bonding layer for laminating to each other individual circuit substrates. In a preferred method for obtaining such a laminate, a laminate of circuit substrates is produced which alternate with one or more layers of bonding thicknesses. This laminate is then glued by fusion by melting and bringing to fusion the whole of the multilayer assembly to obtain a homogeneous construction having stable electrical and mechanical properties from end to end As an important remark, it will be noted that the adhesive layers 30 and 32 with bonding thicknesses can be used to laminate circuit substrates comprising other materials as the fluoropolymer of United States patent 4,849,284, containing materials silane coated ceramic filler However, in a preferred embodiment, a multilayer printed circuit board includes circuit substrates which are all made of

  electric substrate material of the United States patent

United States of America 4,849,284.

  Composites with high contents of fillers, which are mentioned in US Patent 4,849,284 (for example, fillers in the proportion of 50% by volume and more), are very suitable for most models of printed circuit boards (for example, large multi-layer boards for CPUs (CPU boards), military surface mount assemblies and assemblies

  glued to microwave circuit boards).

  However, for specific applications of multiline wafers requiring thick planes of voltage with respect to the dielectric thickness (for example, dk S thick power planes, thick holding sheets for adjusting the CTE), we need a lower filler content (for example, 45 to 50% by volume) to provide adequate flow, as noted in the aforementioned U.S. Patent 5,061,548 The lower amounts of filler at the right rate from about 26% to less than 45% in accordance with the present invention, constitute a response to the evolution of technology for processing printed circuits for the manufacture of glitter modules which specifically require laser drilling of small holes, a good flow and alkali resistance for autocatalytic baths The low amounts of fillers of the present invention may not as a good conventional multilayer wafer (as the material described in United States patent 4,849,284 would do), but the material in United States patent 4,849,284 is not suitable for some applications for glitter modules, which are emerging as the preferred compaction technology for high speed / high models

density.

Claims (9)

  1 Electric substrate material comprising a fluoropolymer material and ceramic filler materials, characterized in that the filler material represents an amount of at least about 26 to at least% by volume of the total substrate material, said filler material ceramic being coated using a silane coating.   2 Material according to claim 1, characterized in that said fluoropolymer material is chosen from the group comprising   polytetrafluoroethylene, hexafluoropropene, tetra-   fluorethylene and perfluoroalkylvinyl ether.   3 Material according to claim 1 or 2, characterized in that said filler material ceramic includes silica.   4 Material according to any one of   claims 1 to 3, characterized in that said   coating of silane is chosen from the group comprising p-chloromethylphenyltrimethoxysilane, aminoethylaminotrimethoxysilane, a mixture of   phenyltrimethoxysilane and aminoethylaminopropyl-   trimethoxysilane, fluorosilane and a mixture of   at least one fluorosilane and at least one phenylsilane.   5 Material according to any one of   claims 1 to 3, characterized in that said   coating with silane represents a level greater than 2 and up to approximately 10% by weight relative to the weight of the ceramic filler.   6 Material according to claim 5, characterized in that said silane coating comprises a mixture of at least one fluorosilane and at least one phenylsilane. 7 Material according to claim 1, characterized in that there is at least one layer of conductive material (6) on at least one   portion of said electrical substrate material (4).   8 Material according to any one of   claims 1 to 6, characterized in that it forms a   adhesive layer (30, 32) interposed between at least a first and a second layer in a circuit multilayer.   9 Material according to any one of   Claims 1 to 6, characterized in that it is used   to fill at least one opening (52) made in a rigid substrate (50).