DE4200583A1 - FLUOROPOLYMER COMPOSITE MATERIAL WITH CERAMIC FILLER - Google Patents

Description

The present invention relates to a electrical substrate material made of fluoropolymer and a ceramic filler, and especially is well suited for use as an adhesive layer a multilayer circuit board and other circuit board Applications that have good fluidity, as well as good ones thermal, mechanical and electrical properties require. The fluoropolymer composite material of the front lying invention is also resistant to about chemicals, especially (alkaline) media with high pH.

In U.S. Patent 4,849,284, which is incorporated by reference in the present invention is incorporated electrical substrate material based on fluoropolymer a ceramic filler (that of the Rogers Corporation under the trademark RO-2800 is distributed). This electrical substrate material preferably contains polytetrafluoroethylene, which with Silica and a small amount of micro fiberglass filled is. An important feature of this material is that the ceramic filler (silica) with a silane coating is provided, the surface of the ceramic particles makes hydrophobic and a greater tensile strength, peeling strength and dimensional stability. The network material of U.S. Patent 4,849,284 contains a fill content of at least 50 percent by volume (on hollow space-free base) when used as a PCB Substrate or adhesive layer.

The electrical substrate material on fluoropolymer base with ceramic filler, according to the US patent 48 49 284, is well suited for the production of Substrate materials for rigid printed circuit boards and exhibits better than other circuit board materials electrical properties. In addition, the low coefficient of thermal expansion and the compliant speed of this electrical substrate material is a larger one  Surface mounting and hole plating Reliability. As is known, can individual foils from this electrical substrate material can be stacked to create a multi-layer Form circuit board. Thin film formulations of the in U.S. Patent 4,849,284 (described by from Rogers Corporation under the trademark RO-2800 is indeed available as an adhesive layer used to be a variety of one above the other arranged substrate layers to glue together, wherein the multilayer circuit board is obtained.

High volume fractions (over 55 volume percent) ceramic filler have a very unfavorable Influence on the rheological properties (like e.g. the fluidity) of the fluoropolymer Composite material. This is especially important if that Composite material as an adhesive film or for filling Openings in previously rigid structures are used. Although proportions of ceramic filler from 50-55 Volume percent compared to higher filler proportions result in much better rheological properties, it is necessary to adjust the flow properties of the To further improve fluoropolymer composite material, but without the excellent thermal, mechanical and change electrical properties significantly.

In addition to the unfavorable influence on the rheological properties it was found that a Ceramic filler content of 50 percent by volume or about it also has an adverse effect on the chemical resistance of the filler provided fluoropolymer composite material certain aggressive media, especially (alkaline) Baths with a high pH. Such baths with a high pH value (e.g. above pH = 12) are for the currentless Copper deposition required during manufacture of printed circuit boards with fine conductor tracks (e.g.  Multichip modules) a very desirable and often ver process used. It was found that a high Portion (50 volume percent or above) of ceramic Filler poor chemical resistance of the fluoropolymer circuit board material at long Exposure to such alkaline baths. The Decomposition due to poor resilience compared to the alkaline baths leads to a ver reduction in the hydrophobic properties of the fluoropolymer Composite material. This reduction in turn has one increased moisture absorption with a corresponding very undesirable deterioration in electrical PCB composite material properties Episode.

In U.S. Patent Application 3,676,241, filed on June 16, 1989, today U.S. Patent 5,061,548 (issued by Reference fully incorporated into this patent is indicated that the content of ceramic Filler of that described in U.S. Patent 4,849,284 Materials up to 45 volume percent on void-free Base can be reduced, and still adequate thermal, mechanical and electrical properties can be obtained using the material as an adhesive layer Multilayer printed circuit boards, and as filler for to use certain rigid structures. The one ceramic filler provided fluoropolymer composite material of U.S. Patent 5,061,548 points to that Material of U.S. Patent 4,849,284 better rheological Properties on without an excessive increase in Coefficient of thermal expansion in the Z direction, and it is useful for the applications, the access holes require, into which the resin must flow.

The aim of the present invention is the strong chemical decomposition associated with the high filler content (e.g. 50% and above) the fluoropolymer composite materials of US Patent 48 49 284 at long in  effect of baths associated with high pH reduce and / or eliminate.

According to the present invention, this object achieved by using a lower percentage of ceramic filler, and only from 26 percent by volume on a void-free basis, said filler with Silicone coated.

The resulting composite material with ceramic Filler has excellent mechanical and electrical Properties and exhibits a (compared to composite materials with higher filler content) essential greater resistance in alkaline media.

According to another important feature of the previous lying invention was found to be a relative large silane content of 2-10% (based on the total weight of the ceramic filler) for better properties leads, especially with regard to the laser drilling for the production of plated-through holes and of bushings for fixed supports. These Results using 10% (preferably 6%) silane are surprising and unexpected because (as in the U.S. Patent 4,849,284) was widely adopted was that the silane content is between 1 and 2% should, and that at high proportions of 6-10% none substantial improvement is obtained.

The preferred silane coating consists of a Mixture of phenylsilane and fluorosilane. That combination gives an excellent chemical resistance against alkaline baths and also has an effect favorably on laser drilling. In addition, at Combination of the relatively inexpensive phenylsilane and expensive fluorosilane a very inexpensive coating receive.

The above and other features and advantages of the present invention will become apparent to those skilled in the art become visible and understandable in this area  based on the following detailed description and the Drawings showing:

FIGS. 1A and 1B are vertical sectional views of an apertured rigid structure before and after the filling these openings with the composite material of the present invention.

Fig. 2 is a vertical sectional view of a multi-layer circuit board in which the thermoplastic composite material according to the present invention is used as a thin adhesive layer.

Fig. 3 is a graph showing the effect of silane and the percentage of coated silica filler on the machinability of the composite material with a laser at a wavelength of 248 nm and a beam energy of 3.9 J / cm ² is.

The Fig. 4 is a vertical sectional view of a printed circuit board according to the present invention.

The fluoropolymer composite material with ceramic Filler according to the present invention corresponds in essentially that in U.S. Patents 4,849,284 and 50 61 548 (both by reference to the present Patent fully included) described composite material, the difference being that (1) in a first embodiment, the ceramic filling fabric, on a void-free basis, only a percentage of makes up about 26 percent by volume; and (2) one second embodiment of the ceramic filler with up to 10% silane (based on the total weight of the ceramic filler) is coated. With all of these Execution is used to cover the ceramic Filler preferably a mixture of phenylsilane and Fluorosilane used.

In the first embodiment of the present The composite material preferably has one Percentage of approximately 26 to 45 percent by volume  particulate ceramic filler, and a proportion from about 74 to 55 percent by volume of fluoropolymer (e.g. PTFE) on a void-free basis. The preferred ceramic filler is amorphous quartz powder. All other components and manufacturing processes (including the silane coated ceramic filler) are the same as in that U.S. Patent 4,849,284, except for the larger one Silane portion for the silane coating, and the preferred Silane mixtures, which are discussed below. Therefore reference is made to the U.S. patent for these details 48 49 284. To the materials of the present Manufacturing invention can either in PTFE polymer Dispersion with the ceramic filler "wet mixed" and cause coagulation, or it can fine PTFE powder with the ceramic filler be mixed dry.

The reduction in the filler content down to approximately 26 volume percent results in a significant one Increase the resilience of the fluoropolymer Composite material in alkaline media. In the after Table 1 above is a comparison between two Reproduced examples. Example 1 is a Composite material of the type described in U.S. Patent 4,849,284 described type, made of 50% PTFE fluoropolymer, 50% Silica filler, and 2 weight percent phenylsilane as Filler coating. Example 2 is a composite material according to the present invention, from 37.1% silica Filler, 62.9% PTFE fluoropolymer, and 6% (based on the total weight of the filler) of a mixture Phenyl and fluorosilanes (ratio 3: 1).  

Table 1

From Table 1 it is clear that the H₂O absorption (after treatment in an alkaline bath) decreases significantly with decreasing filler content (z. B. 0.07% in the composite material of the present invention versus 1.7% in the composite material of the U.S. Patents 4,849,284). It is clear that an acceptable H ₂ O absorption should be less than about 0.1%. The results of Table 1 are checked in further Examples 3-12 of Table 2. In Examples 6-11, the silane coating consists of a mixture of phenylsilane and fluorosilane. Example 12 uses a phenylsilane coating.

From Table 2 it also follows that a decreasing filler content to an increase in chemical resistance to treatment in a bath with a high pH, as from the decrease water absorption with decreasing filler content can be seen. A comparison of examples with same silane coating (as Examples 3-5, 6-8 and 9-11) shows that the increased chemical resistance ability at least partially on the lower Filler content. It can be seen that the low proportions (e.g. 27 and 37 percent by volume) for composite materials of the present invention bring significant improvement over the share of 50 volume percent for the composite material of the U.S. patent 48 49 284. A fluoropolymer-printed circuit board assembly material according to the present invention, with a Filler content of approximately 26 to 45 percent by volume (In Table 3 are examples with a filler content of only about 26 percent by volume) a significant advantage over the material U.S. Patent 5,061,548 (filler content from 45 to 50 Volume percent), and the material of the US patent 48 49 284 (filler content of 50 percent by volume and about that).  

Table 2

According to a further feature of the present invention, it has been found that higher coating proportions of up to 10 percent by weight (preferably 6 percent by weight) of the entire ceramic filler result in better laser deposition. This is an unexpected result because US Patent 4,849,284 stated that a silane coating level of 1 to 2% is preferred and that if the level is greater than 2% the additional effect is negligible. Two criteria used to determine the laser machinability of circuit board materials are (1) the energy level required for the deposition (with lower energy levels preferred); and (2) the deviation from completely straight (non-conical) melted hole walls (a deviation of 0 degrees being preferred). FIG. 4 shows a section of a printed circuit board which has a laser-burned hole 2 in a substrate 4 (consisting of the composite material of the present invention) to which a copper layer 6 has been applied. The angle "a" indicates the deviation from a straight wall. Table 3 shows the laser melting results for dry and wet mixtures with different proportions of coating material and ceramic filler. Silica filler was used in Examples 13-30 and 32-38, and quartz filler in Examples 31 and 39.

Table 3

Laser melting threshold at 248 nm for different compositions (PTFE / ceramic filler)

From Table 3 it can be seen that high Filler proportions and high coating material proportions best laser melting results (expressed as lowest melting threshold energy). The Laser melting results will be worse if the Filler portion or the coating material portion, or decrease both proportions. The filler coating can Reduce the melting threshold significantly, even at a low filler content of, for example, 26%. This is quite evident when Examples 18 and 20 can be compared with Example 36. In the table 3 consist of the ratio 3: 1 Coatings of three parts phenylsilane and one part Fluorosilane. The coating identified by 6124 is Phenyltrimethoxysilane, and that is fluorosilane Tridekafluoro-1,1,2,2-tetrahydrooctyl-1-triethoxysilane with the chemical formula C₆F₁₃CH₂CH₂Si (OCH₂CH₃) ₃, hereinafter referred to as C₆F.

This effect of the composition on the laser workability (at 248 nm and a beam energy of 3.9 J / cm ² ) can also be seen from FIG. 3, in which the oblique lines show the deviation from the straight hole wall when baked in with the laser play (the smaller angle is preferred). In Fig. 3, the "silica filler portions" also contain the silane coating material. From Fig. 3 it can be seen that higher proportions of silane and / or ceramic filler result in better laser melting (hole wall quality). It should be noted that high levels of silane are preferably used for low levels of ceramic filler.

Table 4

According to another feature of the present Invention, it has been found that the silane coating material preferably a mixture of phenylsilane and Is fluorosilane. The fluorosilane gives chemical resistance resistance to alkaline media, while the Phenylsilane also favors laser drilling is less expensive than fluorosilane. Table 4 is illustrates that fluorosilane has greater resistance ability towards alkaline media causes as Phenylsilane. The preferred mixing ratio is 3 Parts by weight of phenylsilane to 1 part by weight of fluorosilane. Examples of suitable phenylsilanes and fluorosilanes are in U.S. Patent Application 2,779,474, filed December 2, December 1988 (now US patent ......) reproduced, and are incorporated by reference into the present invention fully involved.

By reducing the filler content the rheological properties of the invention modern material improved to such an extent that it "flows" and comparatively large openings in thick Metal foils or inner layers of the circuit board that does not match any of those described in U.S. Patent 4,849,284 described materials with high filler content (above 55 volume percent) can be filled.

An important feature of the present invention is that the rheological properties improve be without the material of thermal expansion coefficient increases excessively in the direction of the Z axis. It it was found that the coefficient of thermal expansion in the direction of the Z axis when formulated with 30-45 Volume percent filler over the temperature range of -55 to + 125 ° C is considerably lower (a typical one Value is about 200 ppm / ° C) than that common used glass fiber reinforced PTFE (see table 5). Multi-layer printed circuit boards made from RO 2800 laminate adhesive layers according to the invention were glued together,  give a total coefficient of thermal expansion that is significantly lower than the thermal expansion coefficient of a glass fiber reinforced PTFE circuit board. The lower coefficient of thermal expansion is important for the reliability of plated-through holes and bushings so that the circuit boards Temperature changes and assembly endure high temperature.

Table 5

The present invention increases the number of applications in which PTFE composite materials with a ceramic filler can be used to produce reliable circuit boards. The present invention is particularly useful for filling openings in already rigid structures, such as in etched CIC voltage or base layers and holding cores, or in conductor tracks glued to such structures. In FIG. 1A, for example, the reference number 50 shows a structure with different openings 52 with a rigid base layer in vertical section. The films 54 , 56 of the present invention (for example with a proportion of 45 to 50 percent by volume of ceramic filler) are then applied to both sides of the base layer 50 . In Fig. 1B, the stack assembly 58 of Fig. 1A was laminated under heat and pressure. The composition according to the invention has good fluidity so that the openings are completely filled, while also offering excellent thermal, mechanical and electrical properties.

In addition, according to FIG. 2, the composite material according to the invention can be processed in its undensified, unsintered form into a film which can be used for gluing multilayer printed circuit boards or for producing printed circuit boards by film lamination. Such a multilayer printed circuit board is given again in FIG. 2 at the general reference number 10 . The multilayer printed circuit board 10 has a plurality of substrate material layers 12 , 14 and 16 , all of which consist of an electrical substrate material, preferably the fluoropolymer composite material with ceramic filler, according to US Pat. No. 4,849,284, which under the trademark RO-2800 is distributed. Conductive patterns 18 , 20 , 22 and 24 are applied to the substrate layers 12 , 14 and 16 . It should be noted that a substrate layer on which a conductor pattern is applied represents a conductor substrate. The plated-through holes 26 and 28 connect selected conductor pattern in a known manner.

According to the present invention, separate foils 30 and 32 made of substrate material with a composition according to the invention are used as an adhesive layer in order to glue individual conductor substrates together. In a preferred method for producing such a laminate, interconnect substrates with adhesive layers arranged in between are stacked one above the other. This stack arrangement is then fused together, whereby a homogeneous structure with uniform electrical and mechanical properties is obtained. It is important to note that adhesive layers 30 and 32 can be used to laminate conductor substrates which are made of materials other than the fluoropolymer with silane-coated ceramic filler according to US Pat. No. 4,849,284. In a preferred embodiment, however, the multilayer printed circuit board has conductor track substrates, all of which consist of the electrical substrate material according to US Pat. No. 4,849,284.

The composite specified in U.S. Patent 4,849,284 materials with a high filler content (e.g. over 50 Volume percent) are suitable for most conductors board designs (e.g. large multilayer printed circuit boards for central computer, military surface mounting units, and glued microwave circuit boards units). For special multilayer printed circuit boards Applications that require thick layers of stress in Comparison to the dielectric thickness (e.g. thick Current layers, thick holding foils for mastery thermal expansion), however, is a lower fill substance content (e.g. 45-50 volume percent) required to to get sufficient fluidity, as in the aforementioned U.S. Patent 5,061,548. The lower filler content of approximately 26 to 45% according to the present invention is an answer to that Further development of PCB processing technology for manufacturing multichip modules that especially laser drilling small holes, a good one Fluidity, and resistance to require alkaline baths for electroless plating. With the low filler content according to the present Invention may not be a good conventional one Get multilayer circuit board (in contrast to that material specified in U.S. Patent 4,849,284), but the material of US patent 48 49 284 is not suitable for certain multichip module applications that become one preferred packaging technology for high speed Develop high-density designs.

Claims (9)

1. Electrical substrate material made of fluoropolymer material and ceramic filler, characterized in that said filler makes up approximately 26 to 45 percent by volume of the total substrate material and is provided with a silane coating. 2. Material according to claim 1, characterized net that said fluoropolymer material from the group is selected from polytetrafluoroethylene, hexafluoro propene, tetrafluoroethylene and perfluoroalkyl vinyl ether consists. 3. Material according to claim 1 or 2, characterized characterized in that said ceramic filler Silica exists. 4. Material according to any one of claims 1 to 3, characterized in that the silane for said Silane coating is selected from the group consisting of P-chloromethylphenyltrimethoxysilane, aminoethylamino trimethoxysilane, a mixture of phenyltrimethoxysilane and aminoethylaminopropyltrimethoxysilane, 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 silane coating about 2 to 10 weight percent of the ceramic fill matters. 6. Material according to claim 5, characterized net that said silane coating from a mixture at least one fluorosilane and at least one phenyl there is silane. 7. Material according to claim 1, characterized in that at least one layer ( 6 ) of conductive material is applied to at least part of the electrical substrate material ( 4 ). 8. Material according to any one of claims 1 to 6, characterized in that it forms an adhesive layer ( 30 , 32 ) which is sandwiched between at least a first and a second layer in a multilayer printed circuit board. 9. Material according to any one of claims 1 to 6, characterized in that it is used to fill at least one opening ( 52 ) provided in a rigid substrate ( 50 ).