GB2083478A - Epoxy resin moulding compositions - Google Patents

Abstract

An epoxy resin moulding composition which is particularly suitable as an encapsulant for microelectronic devices, comprises epoxy resin, a hardener therefor, and from 40 to 80% by weight of filler, from 25 to 100% by weight of the filler being an anisotropic polycrystalline sintered ceramic material which is relatively non- abrasive and free of ionic contaminants and which has cordierite as its primary phase and consists, on an oxide analysis basis, of 11.5-16.5% RO, 33-41% Al2O3, and 46.6-53% SiO2.

Description

SPECIFICATION Epoxy resin moulding composition This invention is concerned with epoxy resin moulding compositions which are suitable for use as encapsulants for electrical and electronic devices, particularly microelectronic components, such as semiconductors.

Electrical and electronic devices have been encapsulated in a variety of resins, including epoxy, silicone and phenolic resins. Thus, it is known to provide epoxy resin moulding compositions which comprise epoxy resin, hardener therefor the inorganic filler as the essential ingredients thereof, to which various additives, such as catalysts, mould release agents, pigments, flame retardants and coupling agents may be added.

The following performance characteristics are required of resinous encapsulants for microelectronic devices: a. good device compatability with no chemical, physical and electrical interference with the performance of the semiconductor device by the resinous encapsulant used; b. adequate sealing of leads to prevent penetration of moisture and ionic contaminants along leads; c. low moisture penetration through the encapsulant; d. low level of ionic contaminants, such as Li+, Na+, K+, and Cl-; e. a high glass transition temperature; f. a low coefficient of thermal expansion; g. a high thermal conductivity; and h. long term dimensional stability.

While requirements a, b, c, d, e and h are largely fulfilled by epoxy resins cured or hardened with anhydrides, phenol formaldehyde condensates, cresol formaldehyde condensates, polyamines or combinations thereof, with or without catalysts and coupling agents, the crucial factors of low coefficient of thermal expansion and high thermal conductivity, together with the required low level of ionic contaminants and minimal abrasiveness are influenced directly and significantly by the choice of the inorganic filler or fillers.

The importance of a low coefficient of thermal expansion in an epoxy moulding composition cannot be overemphasized. The tremendous progress in the microelectronics industry has enabled the production of semiconductor chips of increasing size, functionality, complexity and circuit density. Such large semiconductor chips are more vulnerable to thermally-induced stress than smaller and simpler chips with the result that the use of an encapsulant composition which does not have a low coefficient of thermal expansion causes premature failure due to cracking of the chips, wire breakage, cracking of the passivation layer, and parametric shift. Such defects are all related to a large thermally induced internal stress, the result of a high, rather than a low, coefficient of thermal expansion in the epoxy moulding composition employed.

In addition to the requirement for a low coefficient of thermal expansion, it is equally important that the epoxy moulding composition should have a high thermal conductivity. Semiconductor devices with a high circuit density generate more heat per unit area than devices of low circuit density, requiring the rapid dissipation of heat through the encapsulant in order to ensure cool operation and a long operating life. It is widely accepted in the electronics industry that an increase of 100C in junction temperature decreases the life expectancy of a semiconductor device by one half. Therefore, the property of high thermal conductivity, i.e. rapid dissipation of heat, is necessary to the efficient operation and long life of a microelectronic device.

The inorganic fillers currently in use for epoxy moulding compositions include fused silica, - quartz, alumina, glass fibre, calcium silicate, a variety of earths and clays, and various combinations thereof. These fillers, which are present to the extent of from 40 to 80% by weight of the total epoxy composition, exert the greatest influence on the thermal expansion coefficient and thermal conductivity properties. Thus, fused silica has a low coefficient of thermal expansion, but also has a low thermal conductivity. It must therefore be used in conjunction with a filler having a high thermal conductivity to provide these dual properties.

Another widely used filler is cr-quartz which has a high thermal conductivity, but also a high coefficient of thermal expansion, requiring that it be used in combination with a filler with a low coefficient of thermal expansion to overcome this deficiency.

Although alumina does exhibit the dual properties of a low coefficient of thermal expansion and a high thermal conductivity, its excessive abrasiveness precludes its use as it causes an unacceptably excessive and rapid wear of manufacturing and moulding equipment.

The prior art fails to disclose a practical, usable filler which has both a low coefficient of thermal expansion, which is here defined as less than 23 x 10-6/0C below the glass transition temperature, and a high thermal conductivity, here defined as one greater than 25 x 10-4 cal./ C per centimeter per second. The procedures for determining the coefficient of thermal expansion and the thermal conductivity are described hereinafter in Example 1.

We have now found that a particular anisotropic polycrystalline sintered ceramic material which has both a low coefficient of thermalexpansion and a high thermal conductivity and which is relatively non-abrasive andfree of ionic contaminants, is an excellent filler for epoxy resin encapsulant compositions and when so used provides encapsulant compositions having a desirable combination of properties.

According to the present invention, there is provided an epoxy resin moulding composition, which comprises epoxy resin, a hardener therefor, and from 40 to 80%, based on the total weight of the composition, of filler, from 25 to 100% by weight of the filler being an anisotropic, polycrystalline sintered ceramic product (a) which has cordierite as its primary phase, (b) which comprises, on an oxide analysis basis,11.5 to 16.5% RO, 33 to 41% Al2O3, and 46.6 to 53% SiO2, (c) RO consisting of MgO and, optionally, NiO in an amount less than 25% of the RO total, or CoO in an amount less than 1 5% of the RO total, or FeO in an amount less than 40% of the RO total, or MnO in an amount less than 98% of the RO total, orTiO2; in an amount less than 15% of the RO total, (d) which has a coefficient of thermal expansion in at least one direction of less than 11.0 x 10-7 in./in./0C over the temperature range 250 to 10000C, and (e) which is relatively non-abrasive and free of ionic contaminants, the proportion of the sintered ceramic product being such as to impart to the moulding composition a linear thermal expansion coefficient below the glass transition temperature of less than 23 x 10-6/OC and a thermal conductivity of more than 25 x 10-4 cal./0C/cm./sec.

The anisotropic polycrystalline sintered ceramic product used according to the present invention is fully described in U.S. Patent 3,885,977. The present invention is based on the discovery that the orientation of cordierite crystallites in a fired ceramic within a compositional area of 41-56.5% SiO2, 3050% Al203 and 920% MgO provides a very low expansion parallel to the oriented c-axes of the crystals. The resultant monolithic fired ceramic product in honeycomb form is said to be particularly adapted for use as a catalyst support matric for internal combustion engine emission control.

The invention also comprises a method of making an epoxy resin moulding composition according to the invention, which comprises mixing the epoxy resin, the hardener therefor, and the filler, and subjecting the mixture to momentary heat and pressure to compact and densify same.

The inventions further comprises a semiconductor device encapsulated with an epoxy resin moulding composition according to the invention.

It is preferred that the RO component of the sintered ceramic product should be MgO alone and further that this product should constitute 100% by weight of the filler.

The epoxy resins used in the composition of the present invention are those having more than one epoxide group and may be of any of those customarily used in moulding compositions, such as the diglycidyl ethers of bisphenoi A, glycidyl ethers of phenolformaldehyde resins, and aliphatic, cycloaliphatic, aromatic and heterocyclic epoxies. These epoxy resins are commercially available under a variety of trade marks, such as "Epon", "Epi-Rez", "Genepoxy" and "Araldite", to name a few.

Epoxylated novolac resins are also useful in this invention and are available commercially under the trade marks "Ciba ECN" and "Dow DEN". The epoxy resins disclosed in U.S. Patent 4,042,550 are useful in the practice of this invention.

Hardeners, also known as curing agents, which may be used herein are any of those customarily used for the purpose of cross-linking the epoxy resin and causing it to form a hard and infusible mass.

Suitable hardeners are well known in the art and the use of any particular one or combination thereof is not critical to the present invention.

Some hardeners or curing agents which may be used are the following: Anhydrides Any cyclic anhydride of a dicarboxylic or other polycarboxylic acid suitable for cross-linking the epoxy resin at cure temperatures. These include, but are not limited to, the following: phthalic anhydride, tetrachlorophthalic anhydride, benzophenonetetracarboxylic dianhydride (BTDA), pyromellitic dianhydride (PMDA), the dianhydride of 1 ,2,3,4-cyclopentanetetracarboxylic acid (CPDA), trimellitic anhydride, trimellitic double anhydride, nadic anhydride, i.e. endomethylene tetrahydrophthalic anhydride, chlorendic anhydride, and hexahydrophthalic anhydride. Other useful anhydride curing agents are those available under the trade mark "Amoco", for example Amoco TMX 220 which is apparently the reaction product of trimellitic acid with the diacetic acid derivative of ethylene glycol, and Amoco TMX 330 which is the reaction product of triacetin with trimellitic anhydride.

Novolacs Cresol or phenol novolacs are useful and are formed by reacting formaldehyde with cresols or with phenols to form condensates containing phenolic hydroxyl groups.

Amines Any of the polyamines conventionally used are operable, such as for example, the diamines, including aromatic amines represented by methylene dianiline, m-phenylene diamine, and m-tolylene diamine.

Generally from 10 to 200%, preferably from 20% to 100%, of hardener, based on the stoichiometric amount of the epoxy group employed, is used.

A variety of additives may be added to the epoxy moulding composition to provide special properties. Thus, catalysts, mould release agents, pigments, flame retardants, and coupling agents are generally employed in addition to the epoxy resin, hardener and filler.

A catalyst functions to accelerate the rate of cure or hardening of the epoxy resin. Thus, although not essential to the hardening of the epoxy resin per se, a catalyst is useful commercially on a production basis as it shortens the length of time necessary to bring about the thermoset condition of the moulding composition. Some catalysts which have been used are amines, such as dimethylamine and dimethylaminoethylphenol; metal halides, such as boron trifluoride, zinc chloride, and stannic chloride; acetylacetonates; and a variety of imidazoles. The quantity of catalyst used may be from 0.05 to 10% by weight of the epoxy resin.

Mould release agents are useful to prevent sticking of the composition in the mould and provide easy release therefrom after the moulding operation. Waxes, such as carnauba and montan wax, and various silicones, polyethylenes and fluorinated compounds are suitable for this purpose. Certain fatty acid metal salts, such as zinc, magnesium and calcium stearates, and glyceryl fatty acid compounds can also be used. Other lubricants may be used where deemed necessary, though in many moulding operations it may not be necessary to incorporate a mould release agent in the epoxy composition itself.

The most widely used pigment or colouring agent for epoxy moulding compositions is carbon black. As is readily understood, a great variety of pigments other than carbon black may be employed as desired for special colouring effects. Pigments which also serve as flame retardants include metalcontaining compounds where the metal is antimony, phosphorus, aluminium or bismuth. Organic halides are also useful for providing flame retardancy.

Coupling agents may be used to improve the water resistance or the wet electrical properties of the moulding composition. In general, the preferred coupling agents are silanes, such as those commercially available from Dow Chemical Company under the designation "Z-6040", which has the formula

and "Z-6070", which is methyl trimethoxy silane. Silanes are also available from Union Carbide under the following designations: A162 Methyl triethyoxy silane A163 Methyl trimethoxy silane A172 Vinyl-tris-(2-methoxyethoxy) silane A186 Beta-[3,4-epoxy-cyclohexyl] ethyl trimethoxy silane A187 Gamma-glycidoxypropyl trimethoxy silane A1100 Gamma-aminopropyltriethoxy silane.

Also useful are: KBM-202 Diphenyl dimethoxy silane - available from Shinetsu Chemical Co., and PO--330 Phenyl trimethoxy silane - available from Petrarch Systems, Inc, When used, a suitable quantity of coupling agent is from 0.05 to 3% by weight based on the epoxy moulding composition.

In order that the invention may be more fully understood, the following examples are given by way of illustration; of these examples, Examples 1, 9, 10, 1 2-1 6 and 19 are examples of the invention and the other examples describe compositions not in accordance with the invention for the purpose of comparison.

EXAMPLE 1 The following epoxy composition was prepared by dry blending the pulverized ingredients in the indicated proportions at ambient temperature until a homogeneous blend was obtained. For convenience, small quantities of catalyst, release agent, pigment and silane were added. The resulting mixture was then densified on a hot differential two-roll mill, cooled to room temperature and ground to provide an epoxy moulding composition in coarse granular form which, for encapsulating purposes, can be converted to a thermoset condition by the application of heat and pressure. The specific anisotropic polycrystalline sintered ceramic filler used according to the invention is referred to in this and following examples as "Present Filler".

EPOXY MOULDING COMPOSITION Component % By Weight Polyglycidyl ether of o-cresol formaldehyde novolac (epoxy resin) 18.25 Phenol formaldehyde novolac (hardener) 7.60 Present Filler 73.00 2-heptyldecyl imidazole (catalyst) 0.25 Carnauba wax (release agent) 0.30 Carbon black (pigment) 0.20 Silane '7-6040" (coupling agent) 0.40 The filler content of this and the subsequent examples is held constant at 55% by volume because measurements of the linear coefficient of thermal expansion and of thermal conductivity are based on volume percent rather than weight percent. For example, the density of the Present Filler is 2.6 gicc.

The density of the remainder (27%) of the composition is about 1.18 g./cc. Therefore, the volume of Present Filler is equal to: 73 2.6 =55% 73 + 27 2.61.18 This composition was tested for its thermal conductivity and for its linear coefficient of thermal expansion according to the following methods.

THERMAL CONDUCTIVITY Thermal conductivity is a measure of the capacity of a material for conducting heat. The Cobra Thermoconductometer is used, based upon a method devised by Dr. J. Schroeder (German Patent 1,145,875) to measure the thermal conductivity of plastics materials.

In this method, a cylindrical sample of test material is placed between two boiling chambers containing two different pure liquids having a 1 0-200C difference in boiling points. The liquid in the lower chamber is heated to boiling and the heat transfers through the test material to boil the liquid in the upper chamber. The time is measured for a given quantity of heat to flow through the sample to cause1 ml of liquid from the upper boiling chamber (cold side) to evaporate and condense 1 ml of liquid by passing heat through the test sample is compared to a known standard.

To test for thermal conductivity, a 0.70" x 1/8" disc of the material to be tested is moulded. This disc is placed in the thermoconductomer and tested as aforesaid.

The thermal conductivity ( t) of the test material in ca!./ C/cm./sec. is calculated as follows: O h A t.(TATB) F where 0 = heat of vaporization for 1 ml of liquid B.

t = time in seconds for distilling 1 ml.

TATB = temperature difference in C which is given by the boiling points of the two liquids.

h = sample height in cm.

F = sample cross-section in cm2.

A ,l value greater than 25 x 10-4 is highly desirable for encapsulants for electronic devices.

The thermal conductivity of the above epoxy moulding composition was found to be 30 x 10-4 cal./0C/cm./sec.

THERMAL EXPANSION The coefficient of linear thermal expansion is a measure of reversible heat induced expansion of a material. A Thermal Mechanical Analyzer is used to measure the expansion characteristics of a moulded epoxy composition.

Plastics materials at some temperature reach a glossy state where the polymer chains begin to relax. This temperature is referred to as the Glass Transition Temperature (Tg) of the plastic. The average coefficient of thermal expansion below Tg is called a1. The average coefficient of thermal expansion above isca called a2.

To determine a1, a2' and Tg of a plastics material, a cylindrical test sample 0.2" x 0.2" is moulded in a transfer moulding press using a temperature of 3500F and a pressure of 1000 psi. This test specimen is post-cured at a temperature and for a period of time predetermined for each material.

The post-cured specimen is then placed into the quartz tube chamber of the Thermal Mechanical Analyzer. A quartz displacement probe is positioned on top of the specimen. The chamber is then heated at a predetermined rate (usually 5 C/minute). The expansion of the plastic is sensed by a transducer which transfers the information to an X Y recorder. The Thermogram produced shows displacement versus temperature.

To determine Tg, the best tangent lines for the lower part of the displacement/temperature curve and the upper section are drawn. The temperature at the intersection of these two tangent lines is the glass transition temperature.

and a2 can be calculated as follows: cr=L1 xA xF Lo x T Where a2' = Average linear coefficient of thermal expansion in inchesAnch/0C.

L1 = Displacement in inches A = Sensitivity of the Y' axis a = Original length of sample in inches T = Temperature range used for determining thermal expansion F = Calibration factor Although both a1 and a2 values are determined in this and in all subsequent examples, the ai value, the coefficient of linear thermal expansion below the glass transition temperature (T,) is the significant thermal expansion coefficient for evaluating the performance of epoxy moulding compositions for encapsulating electronic devices. An a1 value less than 23 x 10-6 is highly desirable for an encapsulant for electronic devices.

The values for a1, Lo and Tg for the above epoxy moulding composition were found to be as follows: a1 18.3 x 10-B/CC a2 74.4 x 10-B/CC T 164 C EXAMPLE 2 The composition and procedure of Example 1 were repeated except that crystalline silica was substituted forth Present Filler.The following results were obtained for a1' cr2, T and A: α1 30.1 x 10-6 a2 82.8 x 10-6 Tg 1590C A 34 x 10-4 EXAMPLE 3 The procedure of Example 1 was repeated with the following composition: Component % By Weight Polyglycidyl ether of o-cresol formaldehyde novolac (epoxy resin) 14.10 Phenol formaldehyde novolac (hardener) 7.60 Tabular alumina 79.00 2-heptyldecyl im idazole (catalyst) 0.20 Carnauba wax (release agent) 0.30 Carbon black (pigment) 0.20 Silane "Z-6040" (coupling agent) 0.40 The following results were obtained for α1, α2, Tg and A:: α1 16.2 x 10-6 α2 57.1 x 10-6 Tg 178 C A 57 x 10-4 EXAMPLE 4 The procedure of Example 1 was repeated with the following composition: Component % By Weight Polyglycidyl ether of o-cresol formaldehyde novolac (epoxy resin) 17.95 Phenol formaldehyde novolac (hardener) 7.40 Cordierite glass 73.50 2-heptyldecyl imidazole (catalyst) 0.25 Carnauba wax (release agent) 0.30 Carbon black (pigment) 0.20 Silane "Z-6040" (coupling agent) 0.40 The following results were obtained for a1, a2, Tg and A: α1 23.0 x 10-6 α2 74.0 x 10-6 Tg 155 C # 20 x 10-4 EXAMPLE 5 The procedure of Example 1 was repeated with the following composition:: Component % By Weight Polyglycidyl ether of o-cresol formaldehyde novolac (epoxy resin) 17.45 Phenol formaldehyde novolac (hardener) 7.20 Cordierite Crystal 74.20 2-heptyldecyl imidazole (catalyst) 0.25 Carnauba wax (release agent) 0.30 Carbon black (pigment) 0.20 Silane "Z-6040" (coupling agent) 0.40 The following results were obtained for α1, α2, Tg and #: a1 23.9 x 10-6 a2 79.0 x 10-6 Tg 158 C 26 x 10-4 EXAMPLE 6 The procedure of Example 1 was repeated with the following composition:: Component % By Weight Polyglycidyl ether of o-cresol formaldehyde novolac (epoxy resin) 17.03 Phenol formaldehyde novolac (hardener) 7.05 Wallastonite 74.80 2-heptyldecyl imidazole (catalyst) 0.22 Carnauba wax (release agent) 0.30 Carbon black (pigment) 0.20 Silane "Z-6040" (coupling agent) 0.40 The following results were obtained for a1, a2, Tg and A: a1 22.6 x 10-6 a2 76.7 x 10-6 Tg 1670C # 25 x 10-4 EXAMPLE 7 The procedure of Example 1 was followed with the following composition:: Component % By Weight Polyglycidyl ether of 0-cresol formaldehyde novolac (epoxy resin) 11.95 Phenol formaldehyde novolac (hardener) 4.95 Zircon 82.00 2-heptyldecyl imidazole (catalyst) 0.20 Carnauba wax (release agent) 0.30 Carbon black (pigment) 0.20 Silane "Z-6040" (coupling agent) 0.40 The following results were obtained for a1, a2,T and A: a1 24.0 x 10-6 α2 86.3 x 10-6 Tg 1640C A 30x 10-4 EXAMPLE 8 The procedure of Example 1 was followed for the following composition: : Component % By Weight Polyglycidyl ether of o-cresol formaldehyde novolac (epoxy resin) 21.10 Phenol formaldehyde novolac (hardener) 8.70 Fused Silica 69.00 2-heptyldecyl imidazole (catalyst) 0.30 Carnauba wax (release agent) 0.30 Carbon black (pigment) 0.20 Silane "Z-6040" (coupling agent) 0.40 The following results were obtained for a1, a2, Tg and A:: α1 22.6 x 10-6 α2 77.6 x 10-6 Tg 159 C # 17 x 10-4 The resultsof Examples 1-8 are tabulated in Table 1. TABLE 1

--------------------------------------------------------------------------------------------------------------------- EXAMPLES ----------------------------------------------------------------------------------- 1 2 3 4 5 6 7 8 ------------------------------------------------------------------------------------ COMPONENT % By Weight ---------------------------------------------------------------------------------------------------------------------- Polyglycidyl ether of o-cresol formaldehyde novolac 18.25 18.25 14.10 17.95 17.45 17.03 11.95 21.10 ----------------------------------------------------------------------------------------------------------------------- Formaldehyde novalac 7.60 7.60 5.80 7.40 7.20 7.05 4.95 8.70 --------------------------------------------------------------------------------------------------------------------------- Present Filler 73.00 ------------------------------------------------------------------------------------------------------------------------------ Crystalline Silica 73.00 --------------------------------------------------------------------------------------------------------------------------- Tabular alumina 79.00 -------------------------------------------------------------------------------------------------------------------------------- Cordierite glass 73.50 ---------------------------------------------------------------------------------------------------------------------- Cordierite crystal 74.20 -------------------------------------------------------------------------------------------------------------------------------- Wallastonite 74.80 -------------------------------------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------------------ Fused silica 69.00 ----------------------------------------------------------------------------------------------------------------------------- Additives* 1.15 1.15 1.10 1.15 1.15 1.12 1.10 1.20 ----------------------------------------------------------------------------------------------------------------------------a1 x 10-6/ C 18.3 30.1 16.2 23.0 23.9 22.6 24.0 22.6 --------------------------------------------------------------------------------------------------------------------------------------a2 x 10-6/ C 74.4 82.2 57.2 74.0 79.0 76.7 86.3 77.6 ----------------------------------------------------------------------------------------------------------------------------------- Tg( C) 164 159 178 155 158 167 164 159 ----------------------------------------------------------------------------------------------------------------------------------- # x 10-4 cal./ C/cm./sec. 30 34 57 20 26 25 30 17 --------------------------------------------------------------------------------------------------------------------------------------- *The total of the catalyst, carnauba wax, carbon black and silane.

As summarized in Table 1, the compositions of Examples 1, 3, and 6 which respectively use the Present Filler, tabular alumina and Wallastonite had (E1 values below 23 x 10-6/ C and thermal conductivity, ,1, values above 25 x 1 0-4 cal./cm./sec./0C. The compositions of Examples 2, 4, 5, 7 and 8 had either a1 values above 23 x 10-6/OC or A values below 25 x 1 0-4 cal./cm/sec./ C, and are therefore less useful where the dual properties of a low coefficient of thermal expansion and a high thermal conductivity are required.

The epoxy moulding composition of Example 3 is of little practical significance primarily because of the excessive abrasiveness of tabular alumina which causes undesirably rapid wear of both manufacturing and moulding equipment. The composition of Example 6 contains Wallastonite as a filler.

This filler usually has a high level of ionic contaminants, such as sodium ion, and degrades the reliability performance of semiconductor devices encapsulated therewith. The composition of Example 7 uses zircon as a filler which has a high dielectric constant and is often contaminated with heavy radioactive elements, making it undesirable as a component of an encapsulant for semiconductor devices. Only an epoxy moulding composition that uses the Present Filler, as represented by Example 1, is of practical significance for encapsulating microelectronic devices since the Present Filler is essentially free from the defects pointed out for tabular alumina, Wallastonite and zircon.

The compositions of Examples 4 and 5 use as fillers Cordierite Glass and Cordierite Crystal respectively in place of the Present Filler of Example 1. The overall chemical composition is similar for Cordierite Glass, Cordierite Crystal and the Present Filler, their principal common constituent being high cordierite (2MgO.2AI203.5SiO2), identified by its X-ray diffraction pattern. However, Cordierite Glass and Cordierite Crystal contain noticeable quantities of quartz and spinel (MgAl2O4), while the Present Filler is free from such contaminants. Cordierite Crystal is less amorphous than Cordierite Glass, while the Present Filler is essentially pure high cordierite with its characteristic X-ray diffraction pattern.

EXAMPLE 9 The procedure of Example 1 was followed for the following composition: Component % By Weight Polyglycidyl ether of o-cresol formaldehyde novolac (epoxy resin) 18.25 Phenol formaldehyde novolac (hardener) 7.60 Present Filler 36.50 Crystalline silica 36.50 2-heptyldecyl imidazole (catalyst) 0.25 Carnauba wax (release agent) 0.30 Carbon black (pigment) 0.20 Silane "Z-6040" (coupling agent) 0.40 The following results were obtained for 1 a2, T6 and A:: a1 22.7 x 10-6 a2 82.6 x 10-B 1650C A 34 x 10-4 It is noted that the use of crystalline silica as the sole filler in Example 2 gave an a1 value which was 30.1 x 1 0-6, an unacceptably high value, whereas the use of a combination of fillers consisting of crystalline silica and the Present Filler resulted in a reduction of the a1 value to a desirable value of 22.7 x 10-6.

This demonstrates the usefulness and versatility of the Present Filler which can be used as the sole filler (100% of the total filler) in an epoxy moulding composition, or can be admixed with other conventional fillers in a proportion down to 25% by weight of the total filler to impart the dual attributes of a low coefficient of thermal expansion below the glass transition temperature (a1) and a high therrr conductivity (A).

EXAMPLE 10 The procedure of Example 1 was followed with the following composition: Component % By Weight Polyglycidyl ether of o-cresol formaldehyde novolac (epoxy resin) 15.85 Phenol formaldehyde novolac (hardener) 6.80 Present Filler 38.20 Calcined alumina 38.20 2-heptyldecyl imidazole (catalyst) 0.25 Carnauba wax (release agent) 0.30 Carbon black (pigment) 0.20 Silane "Z-6040" (coupling agent) 0.40 The following results were obtained for a1, aZ2, Tg and A: a1 17.3 x 10-6 a2 75.0 x 10-6 Tg 169 C # 40 x 10-4 This demonstrates that the Present Filler may be combined with calcined alumina to provide the desired a1 and A values; EXAMPLE 11 The procedure of Example 1 was followed with the following composition:: Component % By Weight Polyglycidyl ether of o-cresol formaldehyde novolac (epoxy resin) 19.65 Phenol formaldehyde novolac (hardener) 8.20 Present Filler 35.50 Fused silica 35.50 2-heptyldecyl imidazole (catalyst) 0.25 Carnauba wax (release agent) 0.30 Carbon black (pigment) 0.20 Silane "Z-6040" (coupling agent) 0.40 The following results were obtained for a1, a2, Tg and # : (r1 21 x10-6 a2 78.9 x 10-B Tg 1630C A 22 x 10-4 When fused silica was the sole filler, as in Example 8, the A value was an unacceptable 17 x 1 0-4.

When the Present Filler is admixed with fused silica in a 1:1 ratio, the A value is increased appreciably to 22 x 10-4, which is only just below the acceptable value.

EXAMPLE 12 The procedure of Example 1 was followed with the following composition: Component % By Weight Polyglycidyl ether of o-cresol formaldehyde novolac (epoxy resin) 17.55 Phenol formaldehyde novolac (hardener) 7.30 Present Filler. 37.00 Wallastonite 37.00 2-heptyldecyl imidazole (catalyst) 0.25 Carnauba wax (release agent) 0.30 Carbon black (pigment) 0.20 Silane "Z-6040" (coupling agent) 0.40 The following results were obtained for a1, aS2, Tg and A:: at1 17.4 x 10-6 a2 69.6 x 10-6 Tg 1720C # 25 x 10-4 This example, when compared with Example 6, demonstrates the reduction in at, value obtained by the use of a filler composition comprising equal quantities of the Present Filler and Wallastonite.

EXAMPLES 13-15 These examples demonstrate that it is possible to use epoxy resins other than the polyglycidyl ether of o-cresol formaldehyde novolac and hardeners other than phenol formaldehyde novolac in epoxy moulding compositions using the Present Filler to obtain the desired a and A values. The compositions and results obtained by testing according to the methods described in Examplel are tabulated in Table 2.

TABLE 2

Examples - % By Weight Component 13 14 15 Polyglycidyl ethe of o-cresoi formaldehyde novolac 17.25 Polyglycidyl ehte of phenol formaldehyde novolac Diglycidyl ether of bis-phenol A 9.60 Cresol formaldehyde novolac 9.20 6.70 Brominated diglycidyl ether of bis-phenol A 1.40 Present Filler 73.00 73.00 72.00 Antimony Oxide 1.00 2-heptyldecyl imidazole 0.20 0.25 0.25 Camauba wax 0.30 0.30 0.30 Carbon black 0.20 0.20 0.20 Z6040 (silane) 0.40 0.40 0.40 at X 10610C 19.7 17.0 16.8 a2 x 10-6/ C 68.7 7 5.8 72.8 Tg - OC 183 149 169 Ax10"4cal.10C/cmisec. 31 31 30 EXAMPLES 16-21 Examples 1621 demonstrate that it is possible to use anhydrides or amines as hardeners for epoxy resins or mixtures of epoxy resins together with the Present Filler to obtain the desired el and .1 values, even where the additives are different from those in Example 1.

Similarly, the use of the same anhydride hardeners with the same epoxy resins in combination with fillers other than the Present Filler, that is in combination with crystalline silica or fused silica respectively, results in unacceptably high a1 and unacceptably low A values.

The composition of Examples 16-21 and the results obtained'by testing for (x, and A values according to the methods described in Example 1 are tabulated in Table 3.

TABLE 3 %By Weight

--------------------------------------------------------------------------------------------- EXAMPLE ----------------------------------------------------------- Component 16 17 18 19 20 21 ---------------------------------------------------------------------------------------------- Polyglycidyl ether of o-cresol formaldehyde novolac 9.23 9.23 10.80 19.00 19.00 21.80 ------------------------------------------------------------------------------------------------- Diglycidyl ether of bis-phenol A 12.96 12.96 15.10 3.00 3.00 3.80 -------------------------------------------------------------------------------------------------- Benzophenone tetra carboxylic dianhydride 5.76 5.76 6.00 ------------------------------------------------------------------------------------------------- Methylene dianiline 4.90 4.90 5.60 ------------------------------------------------------------------------------------------------ Present Filler 69.50 69.50 ------------------------------------------------------------------------------------------------- Crystalline silica (a quartz) 69.50 69.50 ----------------------------------------------------------------------------------------------- Fused silica 65.20 -------------------------------------------------------------------------------------------------- Zinc Stearate 1.90 1.90 2.00 ---------------------------------------------------------------------------------------------- Carbon black 0.19 0.19 0.20 0.30 0.30 0.30 ----------------------------------------------------------------------------------------------- Z-6040 (silane) 0.28 0.28 0.30 --------------------------------------------------------------------------------------------- Stearyl alcohol 0.38 0.38 0.40 ---------------------------------------------------------------------------------------------------- Chlorendic anhydride 1.50 1.50 1.50 --------------------------------------------------------------------------------------------------- Calcium stearate 2.00 2.00 2.00 -------------------------------------------------------------------------------------------------a1 x 10-6/ C 21.5 34.7 27.4 21.1 30.6 24.5 ------------------------------------------------------------------------------------------------------a2 x 10-6/ C 85.9 82.8 86.6 76.9 78.2 73.5 ------------------------------------------------------------------------------------------------------ Tg 177 153 166 179 176 173 ----------------------------------------------------------------------------------------------------- # x 10-4cal./ C/cm./sec. 28 32 17 25 28 15 -------------------------------------------------------------------------------------------------- Examples 16 and 19 show that the Present Filler can be used with a combination of epoxy resins, anhydride hardener and an amine hardener respectively to obtain a low 1 and a high A value. Example 17 is identical in composition to Example 16 with the exception that the filler is crystalline silica instead of the Present Filler, with the result that the a1 value is unacceptably high.

Example 18 is similar in composition to Example 16, except that the filler is fused silica instead of the Present Filler. Here again, the a, value is too high for use in an epoxy moulding composition for a semiconductor or other electronic device.

Examples 20 and 21 are similar in composition to that of Example 19 except that the fillers in Examples 20 and 21 are crystalline silica and fused silica respectively. The , values of Examples 20 and 21 are too high and the A value of Example 21 is too low.

Claims (4)

1. An epoxy resin moulding composition, which comprises epoxy resin, a hardener therefor, and from 40 to 80%, based on the total weight of the composition, of filler, from 25 to 1 00% by weight of the filler being an anisotropic, polycrystalline sintered ceramic product (a) which has cordierite as its primary phase, (b) which comprises, on an oxide analysis basis,11.5 to 16.5% RO, 33 to 41% Al2O3, and 46.6 to 53% SiO2, (c) RO consisting of MgO and, optionally, NiO in an amount less than 25% of the RO total, or CoO in an amount less than 1 5% of the RO total, or FeO in an amount less than 40% of the RO total, or MnO in an amount less than 98% of the RO total, or TiO2 in an amount less than 15% of the RO total, (d) which has a coefficient of thermal expansion in at least one direction of less than 11 ,0 x 10-7 in./in./0C over the temperature range 250 to 1000 C, and (e) which is relatively non-abrasive and free of ionic contaminants, the proportion of the sintered ceramic product being such as to impart to the moulding composition a linear thermal expansion coefficient below the glass transition temperature of les than 23 x 10-6/OC and a thermal conductivity of more than 25 x 10-4 cal./0C/cm./sec.

2. A methqd of making an epoxy resin moulding composition according to claim 1, which comprises mixing the epoxy resin, the hardener therefor, and the filler, and subjecting the mixture to momentary heat and pressure to compact and densify same.

3. An epoxy resin moulding composition substantially as herein described in any of Examples 1, 9, 10, 12to 16, and 19.

4. A semiconductor device encapsulated with a thermoset composition according to claim 1 or 3.