Polysiloxane modified thermoset compositions

Abstract

A polysiloxane-modified epoxy-based encapsulation composition comprising an epoxy resin, a curing agent for the epoxy resin, a polylactone-polysiloxane block copolymer, and a filler is described. The powder molding compositions provide a low internal stress epoxy composition without significantly sacrificing T.sub.g.

Description

BACKGROUND OF THE INVENTION

This invention relates to polysiloxane-modified epoxy resin compositions. In a specific aspect, the invention relates to molding powder formulations from such compositions, suitable for use as encapsulates for semiconductor devices, and articles made from such formulations.

Encapsulation of semiconductors and other components with an epoxy resin, is widely used in the electronics industry to provide physical integrity and environmental protection to electrical components.

Encapsulation is generally a process in which an electrical component, or an assembly of small discrete units, is cast with, or imbedded in, a molten film, sheath, or foam of an encapsulation composition, which is then subjected to conditions effective to solidify the composition. Once the encapsulation composition is solidified, the encapsulated component will have physical integrity and environmental protection. The most commonly used encapsulation technique is transfer molding. In this process, the component to be encapsulated is placed into the cavity of a mold and an encapsulation composition, liquefied by heat and pressure, is forced into the cavity where it solidifies to encapsulate the component.

An encapsulation composition must not soften during the normal usage of the encapsulated component, must not develop excessive internal stress during the encapsulation process, and must have minimal moisture gain. An encapsulation composition that softens during the normal usage of the encapsulated component will jeopardize the integrity of the encapsulated component. The softening of the encapsulation composition during the normal usage of the encapsulated component can be prevented by incorporating into the composition an encapsulation resin with a sufficiently high glass transition temperature (T.sub.g). Encapsulation compositions that develop high internal stress tend to break apart during normal usage. The trend in electronics technology is toward larger die sizes, increased capacity, smaller packages with higher pin counts and finer pitches, which in turn requires resins with low internal stress properties for very large scale integrated (VLSI) circuit chip encapsulation. Thus in encapsulation, as in many other epoxy applications, it is important that the composition used have low internal stress and high T.sub.g.

The internal stress (.sigma.) of a composition can be estimated by the following equation:

.sigma.=k.intg.E .alpha.dT wherein E is the modulus of the material, k is a constant, T is temperature, and .alpha. is the coefficient of thermal expansion. Since the internal stress is proportional to both the modulus and the coefficient of thermal expansion, this suggests that the internal stress can be lowered by reducing the coefficient of thermal expansion, the modulus or both.

The common approach towards lowering internal stress has been to modify the epoxy resin with an elastomer. However, with increasing amounts of elastomer modifier, with filled or unfilled material, the modulus tends to decrease while the coefficient of thermal expansion tends to increase. Thus the reduction in internal stress is marginal due to the opposing trends of the modulus and the coefficient of thermal expansion. In addition, the T.sub.g, which for encapsulation must generally be at least about 150.degree. C., will many times vary proportionally with the modulus. Sometimes the lowering of the modulus results in too great a reduction in the T.sub.g for encapsulation application.

It is therefore an object of the invention to provide an epoxy-based encapsulation composition. In one embodiment, it is an object of the invention to provide a low internal stress epoxy composition without significantly sacrificing T.sub.g. It is another object to provide molding powders and articles made therefrom.

BRIEF SUMMARY OF THE INVENTION

According to the invention, there is provided a composition comprising an epoxy resin, a curing agent for the epoxy resin, a polylactone-polysiloxane block copolymer, and a filler. Also according to the invention, there are provided molding powders made from such compositions and articles made from such molding powders. The molding powder compositions provide low internal stress epoxy compositions without significantly sacrificing T.sub.g.

DETAILED DESCRIPTION OF THE INVENTION

The invention compositions include a polylactone-polysiloxane AB or ABA block copolymer. Although the invention is not limited to any particular polylactone-polysiloxane block copolymer, suitable block copolymers useful in the present invention are described in U.S. Pat. No. 4,663,413 and U.S. Pat. No. 3,691,257. In both AB and ABA type block copolymers, solubility parameters of the polysiloxane block B, will affect the selection of the polylactone block A. Preferably, for a polysiloxane segment at a solubility parameter of about 7 to about 8, more preferably about 7.3 to about 7.5, the solubility parameter of block A is preferably about 9 to about 10. The number average molecular weight ratio of all block A to B is preferably greater than or equal to 1 in order to obtain a block copolymer easily dispersible in the epoxy resin. Solubility parameter is defined as square root of energy of evaporation of 1 mole of liquid over the molar volume. The polymer solubility parameter can be measured indirectly from equilibrium-swelling measurements in solvents of differing solubility parameters as described in May, Epoxy Resins: Chemistry and Technology (1988) 604-05.

The preferred block copolymers useful in the present invention are ABA type block copolymers described in U.S. Pat. No. 4,663,413, the disclosure of which is hereby incorporated by reference, and have the following general formula (I). ##STR1## wherein n is an integer from 1 to about 200; R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently linear or branched alkyl, alkenyl, haloalkyl, or haloalkenyl of 1 to 6 carbon atoms; aryl of 5 to 7 carbon atoms; aralkyl of 6 to 8 carbon atoms;

A and A' are independently ##STR2## p is an integer from 0 to 6; m is an integer from 1 to about 250; R.sub.6 is hydrogen or linear or branched alkyl of 1 to 6 carbon atoms; R'.sub.5 is ##STR3## R.sub.5 is ##STR4## R.sub.7, R.sub.9 and R.sub.11 are independently --CH.sub.2).sub.q, q is an integer from 1 to 20; ##STR5## where r, t and w are independently integers from 1 to 6 and v is an integer from 1 to about 100; R.sub.8 and R.sub.10 are independently hydrogen or alkyl of 1 to 6 carbon atoms.

The preferred polysiloxane-polylactone copolymers useful in the invention are characterized as block copolymers. By the term "block" is meant that there is at least one repeating monomeric unit in the copolymer which repeats on the order of about 10 to 200 times. In particular, this means that in the formula given above, either n, m or v must be of a magnitude sufficient to define a block.

Referring to the formula above, R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently linear or branched alkyl, alkenyl, haloalkyl or haloalkenyl of 1 to 6 carbon atoms, aryl of 5 to 7 carbon atoms or aralkyl of 6 to 8 carbon atoms. Exemplary alkyl groups are methyl, ethyl, propyl, isopropyl, butyl, and the like. Exemplary alkenyl groups are ethenyl, 1-prop-2-enyl, and the like. For the haloalkyl and haloalkenyl groups, the halo group is preferably fluoro. Illustrative haloalkyl groups are trifluoromethyl 1,1,2,2-tetrafluoroethyl, and the like. Representative haloalkenyl groups are 1,2-difluoroprop-1-enyl, and the like. Illustrative aryl groups are phenyl and substituted-phenyl. Representative aralkyl groups are benzyl, 2-phenylethyl, and the like. Preferably R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are alkyl of 1 to 6 carbon atoms. Most preferably, R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are methyl. The block copolymer will most preferably have number average molecular weights in the order of about 5,000 to about 25,000.

The moieties A and A' are derived from a lactone which is used as a starting material for forming the copolymers useful for the present invention. Thus, if an .epsilon.-caprolactone is used as a starting material, then p in the formulas A and A' will be 4 and R.sub.6 will be hydrogen. This is the preferred moiety for A and A'. The group R.sub.6 may, however, be other linear or branched alkyl groups of 1 to 6 carbon atoms, such as methyl, ethyl, isopropyl, propyl and the like. The integer m may be of a magnitude which describes a block as described above, however, if there is at least one other block in the copolymer, then m may be as low as 1.

A preferred class of compounds are those in which R.sub.5 and R.sub.5' are the groups --R.sub.7 --O--. The group R.sub.7 may be a linear alkylene group --(CH.sub.2)--.sub.q, where q is an integer from 1 to 20; or R.sub.7 may be cycloalkylen-1,4-yl, or a linear polyalkylene ether of the formula --(CH.sub.2).sub.t --(--O--(CH.sub.2).sub.r --O--).sub.v --(CH.sub.2).sub.w --, where r, t and w are independently integers from 1 to 6 and v is an integer from 1 to about 100. Preferably, R.sub.7 is a linear alkylene group wherein 2 is an integer from 1 to 20. A second class of preferred R.sub.5 and R.sub.5' groups are --R.sub.7 --NR.sub.8 --. The group R.sub.7 will be as defined above. The compounds where R.sub.7 is a linear alkylene group wherein q is an integer from 1 to 20 is preferred. The substituent R.sub.8 may be hydrogen or alkyl of 1 to 6 carbon atoms, such as methyl, ethyl, isopropyl, n-propyl, butyl, t-butyl and the like. Preferably, R.sub.8 is hydrogen.

The groups R.sub.5 and R.sub.5' may also be ##STR6## wherein R.sub.9 and R.sub.11 are defined as the same group of substituents for R.sub.7 above. The group R.sub.10 may be hydrogen or alkyl of 1 to 6 carbon atoms such as methyl, ethyl, isopropyl, n-propyl, t-butyl and the like. Preferably R.sub.10 is hydrogen and R.sub.9 and R.sub.11 are independently linear alkylene groups wherein q is an integer from 1 to 20.

The epoxy resin composition will generally comprise an amount of polylactone-polysiloxane modifier within the range of about 1 to about 50, preferably about 5 to about 40, most preferably more than 10 to about 35 weight percent modifier based on the weight of the epoxy resin. These polymers are readily dispersible in epoxy resins and unexpectedly gave good physical properties to the molding powder compositions within the range of about 10 to about 30 weight percent based on the modified epoxy resin. The modifier imparts toughness and lower modulus to the epoxy resin composition without significantly affecting the T.sub.g, which is important in encapsulation technology. Further, it provides compositions which have lower levels of ionic contaminants which are typically present in conventional commercial carboxy-terminated butadiene acrylonitrile modifiers. The polysiloxane-modified composition also provides improved toughness and better processability compared to conventional sticky compositions.

Generally, suitable epoxy resins include a broad range of liquid or solid resins characterized by the presence of, on average, at least one 1,2-epoxy group (i.e. vicinal epoxy group) per molecule. Examples of suitable epoxy resins include the polyglycidyl ethers of both polyhydric alcohols and polyhydric phenols; polyglycidyl amines, polyglycidyl amides, polyglycidyl imides, polyglycidyl hydantoins, polyglycidyl thioethers, epoxidized fatty acids or drying oils, epoxidized polyolefins, epoxidized diunsaturated acid esters, epoxidized unsaturated polyesters, epoxy novolacs, and copolymers and mixtures thereof. The composition will generally comprise an amount of epoxy resin within the range of about 1 to about 60, preferably about 20 to about 40, weight percent epoxy resin based on the weight of the composition.

Suitable epoxy curing agents include anionic initiators, cationic initiators, carboxy functionalized polyesters, polyamides, amidoamines, polyamines, melamine-formaldehydes, phenol-formaldehydes, urea-formaldehydes, dicyandiamide, polyphenols, polysulfides, ketimines, novolacs, anhydrides, blocked isocyanates, anhydrides, and imidazoles. Preferably polyamines, novolacs, or anhydrides, most preferably novolacs such as an epoxidized ortho creosol novolac, are used as curing agents in encapsulation application. The composition will generally contain from about 1 to about 60, preferably about 30 to about 60, weight percent curing agent based on the epoxy resin composition. The polylactone-polysiloxane modifier can be added to the curing agent as long as the modifier can be added before curing.

The invention composition must also contain a filler. In compositions comprising only epoxy resin and the polysiloxane-polylactone modifier, increasing amounts of modifier will result in an increase in the coefficient of thermal expansion and a decrease in the modulus. By contrast, in compositions including a filler, the polysiloxane-polylactone modifier, and an epoxy resin, increasing amounts of modifier will result in the desired reduction of both the coefficient of thermal expansion and the modulus and thus lowering the internal stress of the composition. The composition must contain an amount of filler sufficient to produce this desired property of decreasing both the coefficient of thermal expansion and modulus with increasing amounts of modifier. The amount of filler is also a function of the application in which the composition is being used. In encapsulation applications, the composition will generally contain at least about 55 weight percent filler, preferably about 70 weight percent filler. Generally the compositions will not contain more than about 95 weight percent The invention molding powder composition will generally comprise an amount of polylactone-polysiloxane modifier within the range of about 1 to about 40, preferably about 2 to about 30, most preferably about 2 to about 20, weight percent modifier based on the weight of the composition.

Suitable fillers are any filler which has low coefficient of thermal expansion such as metal oxide fillers and mineral fillers. They include, for example, silica, iron oxide, mica, alumina, talc, antimony trioxide, titanium oxide and the like, depending on the desired application. The coefficient of thermal expansion of the filler is preferably less than about 6.times.10.sup.-6 .degree. C.sup.-1 to achieve the desired low stress. Preferably the composition comprises a mineral filler such as silica for VLSI encapsulation so the property of the encapsulate will be similar to the silicon-based substrate.

Other thermosettable resins that may optionally be included in the composition include for example, polyurethanes, polyureas, polyamides, brominated epoxies, phenoxy resins, polyesters, polyester-polyether copolymers, bismaleimides, polyimides, and mixtures and copolymers thereof.

The invention molding powder composition may include other additives, such as stabilizers, extenders, plasticisers, pigments, reinforcing agents, flow control agents and flame retardants.

Methods for formulating an encapsulation composition are well known. Generally the first step is to grind the ingredients, i.e., the resin, curing agent, polycaprolactone-polysiloxane, and any filler, typically with a grinder or hammer mill. The particles are then screened and dry blended. Next, the dry blended mixture is melt mixed, in a roll mill or extruder, at a room temperature above the softening point of the mixture, generally about 15.degree. C. to about 30.degree. C. above the softening point of the mixture. In addition, the block copolymer may be introduced into the system by first dry blending or melt mixing the block copolymer with the curing agent, the resin or both.

The filler is preferably pretreated prior to blending in order to improve interfacial adhesion between epoxy matrix and filler. Preferably, the filler is coated with a coupling agent, such as silane coupling agents, which is sprayed on the surface of the filler and mixed in a mixer prior to blending in the molding powder formulation.

The curing agent may be melt mixed or dry blended with from about 1 to about 50, preferably about 5 to about 40 weight percent polysiloxane-polylactone block copolymer, based on the weight of the curing agent. Likewise, the epoxy resin may be melt mixed or dry blended with from about 1 to about 50, preferably about 5 to about 40, weight percent polysiloxane-polylactone block copolymer, based on the weight of the epoxy resin.

The melt blending can be accomplished using a twin screw extruder or a two or three roller heated roll mill at temperatures in the range of about 100.degree. to 120.degree. C. depending on the melt characteristics of the molding powder. The molding powders are typically milled and screened.

For ease of handling, preforms can be made by using any suitable method to produce a pellet, for example, by hydraulic pressing in a mold. Transfer molding is most commonly used for encapsulation. The desired article can be obtained by placing an electrical component in a cavity and casting preforms in a transfer molding machine under conditions that the preforms will gel and flow to fill the cavity, which is typically operated at a temperature of about 160.degree. to about 180.degree. C., a transfer pressure of about 500 to about 1000 psi, and mold clamp pressure of about 1000 to about 2000 psi. Optionally, the preforms can be heated in a radio frequency oven before being placed in the molding machine, which may be desirable if the preform size is large. The articles may be post cured at elevated temperatures to develop maximum physical properties.

The composition may find use in coating applications in which low stress properties are desired. For coating applications, the composition will generally contain at least about 40 weight percent filler to produce the desired property.

Specific embodiment of the curable epoxy resin compositions of the present invention are further described in detail in the following examples.

EXAMPLE 1

Run numbers 1-4 in Table 2 below describe polysiloxane-modified epoxy resin compositions at various block copolymer concentrations to demonstrate the superior toughness of the compositions. Run numbers 5-7 in Table 2 describe the polysiloxane-modified low stress epoxy resin invention compositions.

The neat casting of run 1 was made by melting 74.80 grams of phenolic novolac curing agent in a 800 ml glass beaker in a 150.degree. C. forced air oven, adding and mixing 0.3 gram of triphenylphosphine (TPP) catalyst and then adding 120 grams of 3,3',5,5'-tetramethylbiphenyl(4,4'-diglycidyl ether). After mixing, the mixture was placed in a 150.degree. C. vacuum oven. The mixture was poured in oven between glass plates coated with a thin layer of SurfaSil (silicone mold release agent manufactured by Pierce Chemical Co.), separated with 1/8 inch diameter Teflon.RTM. rope as a spacer and held by binder clips. The casting was cured for 2 hours at 150.degree. C. followed by 4 hours at 200.degree. C. The casting was removed from the oven, cooled to room temperature, and removed from the glass mold.

For run number 2, 141.45 grams of the diglycidyl ether of tetramethylbiphenol and 7.44 grams of SMA-423 supplied by Goldschmit Chemical (linear polycaprolactone-polysiloxane-polycaprolactone block copolymer having a number average molecular weight of each block of approxinately 2000, 3000 and 2000, respectively) were placed in a 1 liter rotary evaporating flask. Both components were purified prior to use by heating at 150.degree. C. in a rotary evaporator under vacuum. The mixture was heated in an oil bath at 150.degree. C. under vacuum for approximately 11/2 hours. The mixture was decanted in a forced air oven operating at 150.degree. C. and cooled to room temperature under nitrogen atmosphere. Subsequently, the casting was made in a similar manner to run 1, except 70.98 grams of phenolic novolac curing agent was used and 120 grams of the biphenyl/SMA blend instead of the diglycidyl ether of tetramethylbiphenol was used.

For run number 3, 154.98 grams of diglycidyl ether of tetramethylbiphenol and 17.22 grams of SMA-423 were placed in a 1 liter rotary evaporating flask. The mixing conditions were similar to run number 2, except the mixture was allowed to blend for approximately 21/2 hours. The casting was made in a similar manner to run 2, except 67.19 grams of phenolic novolac curing agent was used.

For run number 4, 145.40 grams of the diglydidyl ether of tetramethylbiphenol and 25.66 grams of SMA-423 were placed in a 1 liter rotary evaporating flask. The mixing conditions were similar to run number 3. The casting was made in a similar manner to run 2, except 63.78 grams of phenolic novolac curing agent was used.

The properties of the polysiloxane-modified epoxy resin castings of runs 1-4 are shown in Table 2. The glass transition temperature (T.sub.g) of runs 1-4 in Table 2 are low possibly due to the use of old phenolic curing agents, which may contained a significant amount of moisture. But for comparison purpose, this should not affect the trend in the T.sub.g.

The resin/SMA-423 mixtures used in runs 5-7 were obtained in a similar manner to run 2, except the following amounts of components were used.

______________________________________ Diglycidyl ether ofRun No. tetramethylbiphenol (grams) SMA-423 (grams)______________________________________5 150 06 142.5 7.57 127.5 22.5______________________________________ The resin/SMA-423 products were milled in a hammer mill and passed through a 35 mesh sieve. Brominated epoxy novolac and phenolic novolac curing agent (obtained from Borden Chemical Co.) were purified prior to use by heating at 150.degree. C. in a rotary evaporator under vacuum, milled in a hammer mill and passed through a 35 mech sieve. Carnuba Wax and triphenylphosphine (TPP) were pulverized and passed through a 35 mesh sieve. 2.016 grams of (3-glycidoxypropyl)trimethoxysilane coupling agent (obtained from Petrach Systems) was sprayed on the surface of 840 grams of fused silica by an atomizer type sprayer at low pressure, and mixed in a Turbula mixer.

Table 1 below describes the molding powder formulations. The ingredients listed in Table 1, except treated silica, were first mixed in a Turbula mixer for about one hour. Treated silica was then added and mixed for an additional one hour. The resulting powder formulations were melt blended in a twin screw extruder at temperature of about 105.degree. C. The material was cooled to room temperature, milled in a Waring blender, and passed through a 16 mesh sieve. These powders were stored at 4.degree. C. under nitrogen purge.

TABLE 1______________________________________(grams)Run # 5 6 7______________________________________Resin/SMA-423 75 80 90Brominated epoxy novolac 7.50 8.00 9.00phenolic novolac 50.48 51.08 51.75Antimony oxide 7.50 8.00 9.00Carnuba wax 1.50 1.60 1.80Triphenylphosphine 2.25 2.40 2.70Fused Silica (treated) 336.54 352.53 383.24______________________________________

Preforms were made using a Hull transfer molding press operated at room temperature at 4000 psi on the plunger with pressure held for 45 seconds. The preforms were heated in a radio frequency oven at 90.degree. C. Pieces were cast in a two piece metal book mold, 1".times.3".times.1/8" thick, in a Hull transfer molding press at 175.degree. C. operated at 1000 psi pressure with a molding time of 3.5 minutes. They were released from the mold, cooled to room temperature and postcured in a forced draft oven clamped between clean plate glass for 4 hours.

The properties of these polysiloxane-modified molding compositions are shown in Table 2.

TABLE 2__________________________________________________________________________Run # 1 2 3 4 5 6 7__________________________________________________________________________% SMA in Epoxy 0 5 10 15 0 5 15% Silica in Formulation -- -- -- -- 70 70 70Tg, .degree.C., Tan Delta 123 123 123 123 174 174 170Tg, .degree.C., TMA 109 107 103 110 149 151 151CTE, ppm/.degree.C..sup.1 50-100.degree. C. Range 68 68 79 90 24.8 22.7 19.7 220-240.degree. C. Range 203 207 209 208 86.1 85.0 84.2Flex PropertiesStrength, ksi 20.7 19.1 17.9 16.8 18.7 18.2 19.0Modulus, ksi 533 508 478 475 2033 1815 1679% Elongation 6.0 5.8 5.8 5.7 1.0 1.09 1.42Water Absorption.sup.2 2.41 2.35 2.25 2.12 0.6 0.6 0.6Dielectric Constant, 1 MHz 3.74 3.68 3.68 3.66 -- -- --Dissipation Factor, 1 MHz .021 .020 .020 .020 -- -- --Fracture Tough, psi* in 1/2 679 1598 2056 2142 -- -- --CTE * Modulus, psi/.degree.C. 36.4 34.8 37.7 42.8 50.42 41.2 33.1% Internal Stress Reduction -- -- -- -- -- 18 34__________________________________________________________________________ .sup.1 Coefficient of thermal expansion. .sup.2 % Weight gain, immersed in water for 2 weeks at 93.degree. C.

As can be seen from Table 2, the polysiloxane-modified epoxy resin compositions have excellent fracture toughness above about 10% SMA without significant decrease in T.sub.g. From Table 2, a decrease in both coefficient of thermal expansion and modulus can be observed in runs 6 and 7, indicating the low internal stress value for these polysiloxane-modified molding powder formulations.

EXAMPLE 2

Run numbers 1-4 and 9-12 in Table 3 below describe carboxyterminated butadiene acrylonitrile (CTBN)-modified epoxy resin compositions at similar block copolymer concentrations as in Example 1. Run numbers 5-8 in Table 4 describe powder molding compositions modified by CTBN and silica. Run numbers 1-4 were melt blended and run numbers 5-12 were formed by adduct formation of CTBN and the resin.

Run numbers 1-4 were prepared in a similar manner to example 1, except CTBN (Hycar.RTM. 1300X8 available from BF Goodrich Co.) was used in place of SMA-423 as listed below.

______________________________________ Diglycidyl ether ofRun No. tetramethylbiphenol (grams) CTBN (grams)______________________________________1 100.0 0.02 302.00 15.903 278.28 30.924 259.53 45.80______________________________________

Run numbers 5-8 were prepared by adduct formation between the resin and CTBN. The ingredients listed below were placed in a 1 quart metallic container and mixed after 45 minutes in a 150.degree. C. forced air oven. TPPEI (triphenylphosphine ethyl imidazole) was subsequently added and allowed to react for 1.5 hours while stirring every 30 minutes. After 1.5 hours, the product was cooled by removing the container from the oven.

______________________________________ Diglycidyl ether ofRun No. tetramethylbiphenol (grams) CTBN (grams) TPPEI______________________________________5 100.0 0.06 95.0 5.0 0.0957 90.9 10.1 0.09088 90.57 16.0 0.0907______________________________________ These CTBN-containing epoxy resins of runs 2-4 and 8 were too sticky to grind into powders. Neat casting of run 5-8 were prepared in a similar manner to Example 1, except CTBN-containing epoxy resins were used instead of the SMA-containing resins.

Molding powder run numbers 9-11 were prepared in a similar manner to Example 1, except CTBN/epoxy powders formed in a similar manner to runs 5-8 above were used instead of SMA/epoxy powders.

______________________________________ Diglycidyl ether ofRun No. tetramethylbiphenyl (grams) CTBN (grams) TPPEI______________________________________ 9 100.0 0.010 137.18 7.22 0.137211 118.8 13.20 0.118812 113.33 20.00 0.1133______________________________________ The ingredients listed in Table 3 were blended in a similar manner to Example 1, except CTBN-modified epoxy resin was used.

In run number 12, the 15% CTBN-containing epoxy blend molding powder was too sticky to grind into a powder, therefore, the sample was melt blended by melting 12.5 grams of brominated epoxy novolac and 69.54 grams of phenolic novolac curing agent in a forced draft oven separately and mixing in a container placed in a dry ice bath to rapidly cool them to prevent advancement of the resin. The mixture was milled in a hammer mill, and passed through a 35 mesh sieve. 95.23 grams of this powder (marked * in Table 3), 5.75 grams of antimony oxide, 1.15 grams of carnuba wax and 1.73 grams of triphenylphosphine were mixed for one hour on the Turbula mixer. Then treated fused silica (see example 1 for treatment) was added to the formulation and mixed for another hour on the Turbula mixer. The mixture was then melt blended, preformed and molded under same procedures as Example 1.

TABLE 3______________________________________(grams)Run # 9 10 11 12______________________________________Resin/CTBN 75.00 75.00 61.62 95.23*Brominated epoxy novolac 7.50 7.50 6.16Phenolic novolac 50.48 47.59 36.36Antimony oxide 7.50 7.50 6.16 5.75Carnuba wax 1.50 1.50 1.23 1.15Triphenylphosphine 2.25 2.25 1.85 1.73Fused Silica (treated) 336.54 329.8 264.35 242.32______________________________________

Attempts were made to prepare acceptable CTBN-modified epoxy resin molding powders from the melt blended samples from CTBN-modified epoxy resins obtained in runs 5-8. But, these attempts were not very successful due to its difficulties in handling and unevenness in the melt blended products.

The properties of these CTBN-modified compositions are shown in Table 4 and 4A.

TABLE 4______________________________________Run # 1 2 3 4______________________________________% CTBN 0 5 10 15Tg, .degree.C., Tan Delta 143 143 143 143Tg, .degree.C., TMA 124 116 116 113CTE, ppm/.degree.C.50-100.degree. C. Range 67 70 76 79220-240.degree. C. Range 209 199 202 202Flex PropertiesStrength, ksi 18.8 17.3 16.0 14.6Modulus, ksi 474 446 420 382% Elongation 6.9 6.5 6.2 6.2Water Absorption 1.91 1.95 1.91 1.92Dielectric Constant, 1 MHz 3.65 3.68 3.78 3.84Dissipation Factor, 1 MHz .020 .025 .030 .035Fracture Tough, psi* in 1/2 838 1434 1581 1661CTE * Modulus, psi/.degree.C. 31.6 31.4 31.7 31.4% Internal Stress Reduction -- -- -- --______________________________________ TABLE 4A__________________________________________________________________________Run # 5 6 7 8 9 10 11 12__________________________________________________________________________% CTBN in Epoxy 0 5 10 15 0 5 10 15% Silica in Formulation -- -- -- -- 70 70 70 70Tg, .degree.C., Tan Delta 143 143 143 143 174 174 174 170Tg, .degree.C., TMA 124 120 118 115 149 140 143 146CTE, ppm/.degree.C. 50-100.degree. C. Range 67 69 76 82 24.8 23.1 20.8 20.5220-240.degree. C. Range 209 202 197 202 86.1 83.2 64.3 69.8Flex PropertiesStrength, ksi 18.8 17.6 16.6 14.9 18.7 17.5 16.9 16.8Modulus, ksi 474 458 433 390 2033 1959 1873 1774% Elongation 6.9 6.3 6.4 6.3 1.0 .95 1.07 1.01Water Absorption 1.91 1.97 2.0 1.92 0.58 0.59 0.58 0.62Dielectric Constant, 1 MHz 3.65 3.66 3.80 3.85 -- -- -- --Dissipation Factor, 1 MHz .020 .025 .030 .040 -- -- -- --Fracture Tough, psi*in 1/2 838 1457 1710 1722 -- -- -- --CTE * Modulus, psi/.degree.C. 31.6 31.3 33.0 32.0 50.42 45.3 38.9 36.4% Internal Stress Reduction -- -- -- -- -- 10 23 28__________________________________________________________________________ As can be seen from Table 2 and Table 4A, the decrease in Tg of the polysiloxane-modified epoxy resin compositions is slightly less than that for the CTBN-modified epoxy resin compositions. The polysiloxane-modified formulations exhibit a higher percent internal stress reduction than the CTBN-modified formulations. In addition, the CTBN-modified epoxy resin compositions were sticky and difficult to handle. The SMA-modified epoxy resin compositions have better processability due to their lack of stickiness and improved flow properties.

The polysiloxane-modified epoxy resin compositions have improved fracture toughness compared with the CTBN-modified epoxy resin above 10 weight percent. The improvement is significant above about 15 percent modifier as evidenced by the significant increase in fracture toughness at 2142 psi* in 1/2 in run 4 Table 2 compared to run 4 in Table 4 at 1661 or run 8 in Table 4A at 1722 psi* in 1/2. This suggests that the molding powder formulations will also exhibit improved toughness at these percent modification levels.

Fraction change in length during the first thermal mechanical analysis (TMA) for 15% CTBN containing molding powders and 15% SMA-423 containing molding powders were measured between 50.degree. to 200.degree. C. For run number 5 in example 1 (no modifier), the fraction change in length was 72 .mu.m/m. Surprisingly, for run number 7 in example 1 (15% SMA-423), the change was 57 .mu.m/m, which is less than the non-modified powder, compared to run number 12 in example 2 (15% CTBN adduct) at 82 .mu.m/m, which is greater than the non-modified powder. The low fraction change value of the SMA-423 modified molding powder suggests less expansion of the molded powders at higher temperature and results in retention of the original size of the shaped object during varying temperatures suggesting less mold-in-stress.

EXAMPLE 3

1,1',5,5'-tetrakis(4-glycidyloxyphenyl)pentane (GDA-E) and SMA-423 as listed in Table 5, were placed in a 2 liter evaporating flask. The flask was placed on a rotary evaporator, equipped with a condenser and heated oil bath at 150.degree. C. After the contents of the flask melted, the mixture was allowed to blend for approximately one hour under vacuum. The produce was decanted into a metal pan in a 150.degree. C. forced air oven, then allowed to cool to room temperature by removing the pan from the oven. The resulting solid was ground to a powder form.

100 parts of the powder, 10 parts of brominated epoxy resin, 50 parts of Durite.RTM. SD-1731 (a phenolic novolac available from Borden Chemical Co.) were melted in a rotary evaporator under vacuum to remove volatile components until completion. After cooling, the resulting solids were milled in a hammer mill to a particle size of less than 35 mesh size. The solids, 70 percent treated fused silica (see Example 1 for treatment) based on total mixture, 1.0 phr based on epoxy of triphenylphosphine accelerator, 2 parts Carnuba Wax and Siloxane coupling agent were place in a rotary type dry blender and blended for one hour. The mixture was next melt blended in a twin screw extruder at about 100.degree. to 120.degree. C. The resultant blended product was cooled and milled in a rotary blade type mill and passed through a 35 mesh sieve. Preform was made from the resulting powder using a hydraulic press. The preforms were placed in a hydraulic resin transfer molding machine operated at a temperature of 175.degree. C., a transfer pressure of 500 to 1000 psi, and a molding clamp pressure of 2000 psi for 4 minutes. These pieces were post-cured in a forced air oven for about four hours at 175.degree. C. The properties of the molded test pieces are listed in Table 5 below.

TABLE 5______________________________________Percent SMA 423 in Epoxy 0% 5% 10% 15%______________________________________GDA-E (grams) 75 75 75 75SMA-423 (grams) -- 3.95 8.33 13.24Tg, .degree.C., Rheometrics 213 213 213 213Tg, .degree.C., TMA 161 182 180 174CTE 50-100.degree. C..sup.1 27 28 26 24220-240.degree. C. 74 93 86 83Flex Properties, 25.degree. C.Strength, ksi 20 18 17 15Modulus, ksi 2207 2022 1946 1725% Elongation 1.0 1.0 1.1 1.1Water Absorption.sup.2 0.7 0.7 0.7 0.7CTE * Modulus, psi/.degree.C. 59.6 56.6 50.6 41.4% Reduction of CTE * 5 15 31Modulus______________________________________ .sup.1 Coefficient of thermal expansion (X 106m/m/.degree.C.). .sup.2 Weight gain, immersed in water for 2 weeks at 93.degree. C.

As can be seen from Table 5, the formulations containing at least about 10% SMA-423 are particularly suitable for molding powder formalations as shown by the significant reduction in the internal stress expressed by decrese in % reduction of CTE multiplied by modulus. T.sub.g remained substantially the same for all of the above formulations.

EXAMPLE 4

Compositions containing EOCN 1027 (epoxidized orthocresol novolac available from Nippon Kagaku KK) and SMA-423 as listed in Table 6 were placed in a 2 liter evaporating flask. The flask was placed on a rotary evaporator, equipped with a condenser and heated oil bath at 150.degree. C. After the contents of the flask melted, the mixture was allowed to blend for approximately one hour under vacuum. The product was decanted into a metal pan in a 150.degree. C. forced air oven, then allowed to cool to room temperature by removing the pan from the oven. The resulting solid was ground to a powder form.

The molding powder formulations and test pieces were prepared as described in Example 3, except modified EOCN 1027 powder described above was used instead of modified GDA-E. The properties are listed in Table 6 below.

TABLE 6______________________________________Percent of SMA 423 in Epoxy 0% 5% 10% 15%______________________________________EOCN 1027 (grams) 60 57 54 51SMA-423 (grams) -- 3 6 9Tg, .degree.C., Rheometrics 216 216 216 216Tg, .degree.C., TMA 173 175 175 177CTE 50-100.degree. C..sup.1 24 23 22 20220-240.degree. C. 80 82 81 82Flex Properties, 25.degree. C.Strength, ksi 20 21 20 19Modulus, ksi 2349 2170 2121 2031% Elongation 0.9 1.0 1.1 1.1Water Absorption.sup.2 0.7 0.7 0.7 0.7Dielectric Constant, 1 MHz 3.8 3.8 3.9 3.8Dissipation Factor, 1 MHz .008 .009 .008 .008CTE * Modulus, psi/.degree.C. 56.38 49.91 46.60 40.60Reduction of CTE * Modulus 11 17 28______________________________________ .sup.1 .times. 106m/m/.degree. C. .sup.2 % Weight gain, immersed in water for 2 weeks at 93.degree. C.

As can be seen from Table 6, the formulations containing from about 10% SMA-423 are particularly suitable for molding powder formulations, as suggested by the significant reduction in the internal stress expressed as decrease in % reduction of CTE multiplied by modulus. The T.sub.g was substantially constant for all of these formulations.

EXAMPLE 5

The neat resin properties of various epoxy resins modified by various number average molecular weight SMA block copolymers are described in Table 7 below. The neat resins were made in a similar manner to example 1, except EPON.RTM. Resin 828 (glycidyl ether of bisphenol-A available from Shell Chemical Co.) were used in place of diglycidyl ether of tetramethylbiphenol (TMB) in runs 1, 2 and 3 as listed in Table 7. In runs 3 and 6, SMA-446 (linear polycaprolactone-polysiloxane-polycaprolactone block copolymer having number average molecular weight of each block of approximately 4000/6000/4000 supplied by Goldschmit Chemical) was used in place of SMA-423 as listed in Table 7.

The properties of these polysiloxane-modified epoxy resin castings are shown in Table 7. As can be seen from Table 7, both SMA block copolymers decrease modulus compared to unmodified resin castings without a significant decrease in T.sub.g, suggesting that these epoxy resins and SMAs are suitable for use in low-stress encapsulation formulations when blended with a filler as in Example 1.

TABLE 7__________________________________________________________________________Run # 1 2 3 4 5 6__________________________________________________________________________EPON .RTM. Resin 828 100 100 100TMB 100 100 100SMA 423 5 5SMA 446 5 5Tg, .degree.C., tan Delta 130 130 130 160 150 150Tg, .degree.C., TMA 120 118 117 145 141 141CTE<Tg 69 74 76 67 67 66>Tg 189 192 194 180 186 188Dielectric Constant, 1 MHz 3.75 3.75 3.73 3.58 3.60 3.55Dissipation Factor, 1 MHz 0.026 0.026 0.026 0.022 0.022 0.022Flex Properties, DryStrength, ksi 18 16 16 15 15 15Modulus, ksi 428 403 408 391 385 378% Elongation 7.2 6.5 6.6 7.3 6.9 7.0Flex Properties, WetStrength, ksi 0.9 0.7 0.6 8.2 7.4 7.2Modulus, ksi 50 73 79 293 279 263% Elongation (No Break) 4.72 7.22 6.53 3.75 3.77 3.79% Moisture Gain.sup.1 2.3 2.3 2.3 1.7 1.7 1.7Fracture Toughness, Kg 629 1662 1590 1366 1458 1352Fracture Energy, Gic,in-lb/in.sup.2__________________________________________________________________________ .sup.1 % Weight gain, immersed in water for 2 weeks at 93.degree. C.

EXAMPLE 6

The neat resin properties of EPON.RTM. HPT Resin 1071 (tetraglycidyl diamine resin available from Shell Chemical Co.) and EPON.RTM. HPT Resin 1079 (diglycidyl ether of bisphenol fluorenone available from Shell Chemical Co.) modified by SMA-423 block copolymer are described in Table 8 below.

In run number 1, 100 g of EPON.RTM. HPT Resin 1071 was melted in a 150.degree. C. circulating air oven. 61.0 g of EPON.RTM. HPT Curing Agent 1062 was melted at 170.degree. C. in a circulating air oven and added to the EPON.RTM. HPT Resin 1071 while hand mixing. It was then degassed in a 160.degree.-170.degree. C. vacuum oven, poured into a preheated (150.degree. C.) glass mold and cured for 2 hours at 150.degree. C. then 4 hours at 200.degree. C.

In run number 2, 110 g of EPON.RTM. HPT Resin 1071 and 11.0 g of SMA-423 were charged into a 500 ml rotary evaporating flask and placed under vacuum at 155.degree. C. When the foaming stopped, 0.1% (0.12 g) of triphenylphosphine was added and held at 155.degree. C. for 11/2 hours under vacuum. 110 g of the EPON.RTM. HPT Resin 1071/SMA-423 mixture was heated to 150.degree. C. in a circulating air oven. 61.0 g of EPON.RTM. Curing Agent 1062 was melted in a 170.degree. C. circulating air oven and added to the mixture while mixing. It was then degassed in a 160.degree.-170.degree. C. vacuum oven, poured into a preheated (150.degree. C.) glass mold and cured for 2 hours at 150.degree. C. then 4 hours at 200.degree. C.

In run number 3, 100 g of EPON.RTM. HPT Resin 1079 was melted at 150.degree. C. in a circulating air oven. 52.0 g of EPON.RTM. HPT Curing Agent 1062 was melted at 170.degree. C. in a circulating air oven and added to the EPON.RTM. HPT Resin 1079 while hand mixing. It was then degassed in a 160.degree.-170.degree. C. vacuum oven, poured into a preheated (150.degree. C.) glass mold and cured for 2 hours at 150.degree. C. then 4 hours at 200.degree. C.

In run number 4, 110 g of EPON.RTM. 1079 and 11.0 g of SMA-423 was charged into a 500 ml rotary evaporating flask and placed under vacuum at 155.degree. C. When the foaming stopped, 0.1% (0.12 g) of triphenylphosphine was added and held at 155.degree. C. for 11/2 hours under vacuum. 110 g of the EPON.RTM. HPT Resin 1079/SMA-423 mixture was heated to 150.degree. C. in a circulating air oven. 52.0 g of EPON.RTM. HPT Curing Agent 1062 was melted in a circulating air oven at 170.degree. C. and added to the mixture while mixing. It was degassed in a 160.degree.-170.degree. C. vacuum oven under vacuum, poured into a preheated (150.degree. C.) glass mold and cured for 2 hours at 150.degree. C. then 4 hours at 200.degree. C. in a circulating air oven.

The properties of these polysiloxane modified resin compositions are shown in Table 8. As can be seen in Table 8, the polysiloxane-modified epoxy resin compositions have improved fracture toughness compared with unmodified compositions. It suggests the compositions to be suitable for use as low stress epoxy molding powder formulations when blended with a filler as in Example 1, shown by the decrease in modulus without sacrificing T.sub.g.

TABLE 8______________________________________Run # 1 2 3 4______________________________________EPON .RTM. Resin HPT 1071 (grams) 100 110EPON .RTM. Resin HPT 1079 (grams) 100 110SMA 423 (grams) 11.0 11.0Tg, .degree.C., tan Delta 231 231 208 209Flex Properties, DryStrength, ksi 17 15.2 17.9 16.0Modulus, ksi 498 435 467 424% Elongation 3.8 4.0 7.8 4.7% Moisture Gain.sup.1 1.6 1.5 1.3 1.3Fracture Toughness, Kg 517 897 529 952Fracture Energy, Gic, 1.6 1.5 0.60 2.14in-lb/in.sup.2______________________________________ .sup.1 % Weight gain, immersed in water for 2 weeks at 93.degree. C.

Claims

1. A process comprising:

(a) casting an electrical component with a composition comprising a solventless intimate mixture of an epoxy resin, a curing agent for the epoxy resin, at least about 55 weight percent, based on the weight of the composition, of a filler, and at least about 1 weight percent, based on the weight of the composition, of an AB or ABA block copolymer wherein B is a polysiloxane segment having greater than about 10 monomeric repeating units and having a solubility parameter of about 7 to about 8, A is a polylactone segment having a solubility parameter of about 9 to about 10, and the number average molecular weight ratio of total A to B is greater than or equal to 1, and

(b) subjecting the casting composition to conditions effective for curing the epoxy resin and hardening the casting composition around the electrical component.

2. The process of claim 1 wherein the filler is silica.

3. The process of claim 1 wherein the filler is pretreated with a silane coupling agent.

4. The process of claim 1 wherein the block copolymer is a linear polysiloxane-polylactone block copolymer having the formula: ##STR7## wherein n is an integer from 1 to about 200; R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently selected from the group consisting of linear or branched alkyl, alkenyl, haloalkyl and haloalkenyl of 1 to 6 carbon atoms; aryl of 5 to 7 carbon atoms; and aralkyl of 6 to 8 carbon atoms;

A and A' are independently ##STR8## in which p is an integer from 0 to 6; m is an integer from 1 to about 250; R.sub.6 is hydrogen or linear or branched alkyl of 1 to 6 carbon atoms;

R'.sub.5 is ##STR9## R.sub.5 is ##STR10## R.sub.7, R.sub.9 and R.sub.11 are independently --CH.sub.2 q, in which q is an integer from 1 to 20; ##STR11## where r, t and w are independently integers from 1 to 6 and v is an integer from 1 to about 100; and R.sub.8 and R.sub.10 are independently hydrogen or alkyl of 1 to 6 carbon atoms.

5. The process of claim 4 wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently linear or branched alkyl of 1 to 3 carbon atoms.

6. The process of claim 5 in which each of R.sub.1, R.sub.2, and R.sub.3, and R.sub.4 is methyl.

7. The process of claim 4 wherein

R.sub.5 ' is --R.sub.7 --O--;

R.sub.5 is --O--R.sub.7 --; and

R.sub.7 is a linear alkylene group --(CH.sub.2)--.sub.q.

8. The process of claim 7 wherein R.sub.6 is hydrogen and p is 4.

9. The process of claim 4 wherein R.sub.5 ' is --R.sub.7 --NR.sub.8 --; R.sub.5 is --NR.sub.8 --R.sub.7 --; and R.sub.7 is a linear alkylene group --(CH.sub.2)--.sub.q.

10. The process of claim 1 in which the casting is preformed in a transfer molding machine.

11. The process of claim 10 in which the casting composition is heated at a temperature within the range of about 160.degree. to about 180.degree. C. and a pressure within the range of about 500 to 1000 psi.

12. The process of claim 1 in which the epoxy resin comprises an epoxidized orthocresol novolac.

13. The process of claim 1 in which the epoxy resin comprises 3,3',5,5'-tetramethylbiphenyl(4,4'-diglycidyl ether).