GB2028344A - Heat-curable filled moulding composition - Google Patents

Abstract

A heat curable moulding composition which comprises: a) 100 parts of a heat curable moulding resin; and b) up to 400 parts of a filler wherein 5 to 80 weight percent of filler b) consists of a spherical inorganic filler having an average particle size of 1 to 800 millmicrons, and a process for the preparation thereof. The spherical filler may be fumed silica. The composition has low coefficient of thermal expansion and high flowability during moulding.

Description

SPECIFICATION A heat curable resin moulding composition The present invention relates to a heat curable resin moulding composition which possesses a low coefficient of thermal expansion and a high flowabil ity during the processes.

Large dies for low pressure transfer moulding have recently been developed in the semiconductor field, and in order to avoid a premature filling of such large dies, and furthermore to produce satisfactory moulding characteristics, moulding materials must be used which have excellent flow characteristics and an EMMI spiral flow length at least exceeding 40 inches.

Several methods have been proposed for reducing the viscosity of the resin composition in order to induce higher flowability in the moulding process.

For example, the amount of filler used in the composition has been reduced, but even though flowability was enhanced, the lack of filler inherently increased the resin/filler ratio which often led to moulding compositions with a very high coefficient of thermal expansion. In addition, it is undesirable from an economic point of view to leave out the low cost fillers.

A second known method of increasing the flow ability of moulding compositions is by control ofthe cure rate by adjusting the level of curing agent and auxiliary curing agent. This method suffers generally from variability in the finished part because of the inability to control the curing agents precisely. Both electrical and mechanical properties of the part are affected by inadequate cure. Furthermore, controlling the flow properties by reduced curing, creates variability in the mechanical properties of the part.

Moreover, the flowability is not significantly altered by this method.

Athird known method for increasing flowability is the use of resins having low melt viscosities, or to blend high melt viscosity resins with liquid resins.

These compositions, however, cause resin bleeding in the final product which also leads to reduced moulding efficiency.

A fourth known method for increasing flowability is to use fillers having a very fine particle size. For example, silicone resins containing large quantities of filler having a particle size below 10 microns can improve the flowability of the moulding materials.

With epoxy resins, the flowability of the moulding material can be improved by combining, in the proper ratio a filler having an average particle size between 45 and 100 microns with another filler having a particle size below 44 microns. Even though this method is effective, it is not completely satisfactory, if a composition with a high spiral flow is needed.

If the spiral flow of a moulding compound can be improved, better moulding characteristics can be obtained. If the spiral flow can be improved and the amount of filler increased at the same time, better electrical and mechanical properties can be obtained.

It is therefore an aim of the present invention to increase the filler content of resinous moulding compounds thereby enhancing the electrical and mechanical properties of the moulded parts.

It is a further aim of the present invention to improve the flowability of the moulding compound so that greater moulding efficiency is achieved.

Accordingly, the present invention provides a heat curable moulding composition which comprises[A] 100 parts of a heat curable moulding resin and [B up to 400 parts of a filler, wherein 5 to 80 weight percent of filler[B] consists of a spherical as herein defined inorganic filler having an average particle size of from 1 to 800 millimicrons.

The above moulding composition has improved spiral flow, better moulding characteristics, and also the quantity of fillter is increased over conventional moulding compounds such that the electrical and mechanical properties are improved. The moulded products have a relatively low coefficient of thermal expansion which improves the adhesion of the compounds to metals and ceramics. In addition, the moisture resistance of the moulded parts is improved.

Various techniques for improving the spiral flow of moulding materials have been investigated and it has now been found that the addition of spherical inorganic fillers in accordance with the present invention can significantly improve the flowability during moulding. Spherical inorganic fillers have not previously been used as fillers for moulding materials because they are too fine and because their use does not improve the flowability when used alone.

In other words, this invention is concerned with a heat curable resin [A] which contains a filler[B] with an average particle size exceeding 1 , and, spherical (as herein defined) inorganic filler with an average particle size of 1 to 800 m. The spherical as herein defined, inorganic filler comprises 5 to 80 weight% of the total filler, that is, 5 to 80 weight percent of [B] is a spherical as herein defined, inorganic filler. The total quantity of[B] in the composition is preferably 100 to 400 parts per 100 parts of [A], more preferably 200 to 400 parts of[B].

By the term "spherical" when used to describe the inorganic filler with an average particle size of 1 to 800 m,a is meant particles which are completely spherical and/or which are semispherical. The filler particles must be homogeneous. A non-spherical inorganic filler with an average particle size within the above-mentioned range may reduce the flowability during moulding, but it certainly cannot increase the flowability. Even when spherical particles are used, and secondary particles form in the inorganic filler, the flowability during moulding may be reduced and then cannot be recovered.

If the average particle size of the spherical inorganic filler exceeds 800 mp, the improvement in flowability during moulding is reduced. On the other hand, it is difficult to obtain fillers with an average particle size below 10 m,u and although particles of size below 10 m,a may be used in the present invention, the preferred range for the average particle size is 10 to 500 m,a.

The amount of spherical as herein defined, inorganic filler used varies according to the following factors: 1] its average particle size, 2] the average particle size and type of the other filler[B] with aver age particle sizes exceeding 1 ,, and 3J the type of heat curable resin. The spherical inorganic filler con sists of 5 to 80 wtO/o of the total filler[B], preferably 10 to 60 wt% of the total filler[B].

Any inorganic substance which can form fine spherical, as herein defined, particles may be used in the present invention.

In addition to the above, suitable surface treat ments may be carried out depending upon the affinity of the filler toward the resins and the properties of the other filler.

An example of a spherical as herein defined, inorganic filler is a fumed silica produced by the thermal reduction of silica with coke at about 1,200"C and which is oxidized by air at high temperatures to produce silicon dioxide. This silicon dioxide is a completely spherical, as herein defined, non-crystalline silica and can be easily and inexpensively produced.

The conventional fillers [B] with an average particle size exceeding 1 y which may be used with the spherical, as herein defined, inorganic filler are crystalline silica, non-crystalline silica, natural silica, talc powder, calcium carbonate, diatomaceous earth, calcium silicate, aluminum silicate, magnesium silicate, zirconium silicate, alumina, ammonium hydroxide, titanium oxide, glass beads, glass balloons and fibrous fillers such as glass fibre, asbestos fibre, synthetic fibre or natural fibre.

The heat curable resins used in the present invention are not of critical importance. Any of the wellknown moulding resins can be used. Examples of such resins are: silicone resins, epoxy resins, phenol resins, polyester resins, polyimide resins, polyurethane resins, copolymers of diallylphthalate with the above resins, and mixtures of the above.

Silicone resins, epoxy resins, silicone epoxy copolymer resins and mixtures thereof are particu larlypreferable.

Curing agents may be used in the present invention and these include any curing agent which can cure the heat curable resins used. The ratio between the heat curable resins, the filler and the curing agent will vary with the particle sizes and component types used and the composition will therefore be determined on the basis of providing optimal conditions. The order in which the filler and the curing agent may be added in any order since this is not a critical factor. Mould releasing agents, pigments, curing accelerators, curing inhibitors, flame retardants, auxiliary flame retardants and bonding agents may also be added when desirable.

The heat curable resin composition of the present invention is prepared by analogous methods to those used for preparing known heat curable resin moulding materials. All the ingredients are melted and blended in a roll mill, kneader-mixer, Banbury mixer or extruder. The melted and blended mixture is then cooled to bring about solidification and the solidified product is then crushed to the desired size.

The present invention is further illustrated by the following non-limiting Examples.

In the Examples, "Parts" and "%" indicate "parts by weight" and "weight%" respectively.

Example 1 Acresol novolakeDoxy resin[100 parts] [ECN;1280 produced by Ciba-Geigy Co., Ltd.], a phenol novolak epoxy resin [30 parts] [HT-9490 produced by Ciba-Geigy Co., Ltd.], 2-methylimidazole [0.5 parts], carnauba wax[3 parts] and filler[300 parts] were placed in a double roll mill and blended thoroughly at about 90"C. The filler used was a mixture of fused silica powder [specific gravity 2.2, 60% of the powder passing through a 325 mesh sieve] and spherical non-crystalline silica having an average particle size of 50 mCL [specific gravity 1.95]. The filler compositions are given in Table I. The blended material was formed into a sheet and cooled, and this was then crushed for use as a moulding material.

The flowability during moulding was measured by the EMMI spiral flow length at 175"C. The movement of the plunger was recorded electrically, and the flow time was measured as the time elapsed until movement of the plunger stopped.

The moulding was carried out at 1750for3 minutes at a moulding pressure of 60 kg/cm2. The completion of curing was determined using the Barcol hardness [measured with a Barcol hardness tester 935] 10 seconds after releasing the moulding pressure.

Table I shows the spiral flow length, the flow time and the hot Barcol hardness for the various ratios between the two filler types.

It was found that when the spherical, as herein defined, non-crystalline silica comprises 30% of the total filler, the spiral flow length increases by 50 /O overthat of a sample lacking spherical, as herein defined, non-crystalline silica.

The spiral flow length reached a maximum as the percentage of spherical non-crystalline silica increased. The results in the following Examples were obtained with a moulding material containing spherical, as herein defined, non-crystalline silica at the percentage giving the maximum spiral flow length.

Example 2 Solid phenylmethylpolysiloxane resin [100 parts] [ratio of phenyl groups to silicon atoms 0.6:1, ratio of methyl groups to silicon atoms 0.5:1, 6% siliconbound hydroxy groups], glass fibre with an average length of about 1.6 mm [100 parts], fused silica powder[180 parts, more than 99.5% passing through a 325 mesh sieve], spherical as herein defined, noncrystalline silica with an average particle size of 30 m,u 20 parts, 6.7% of the total filler, specific gravity 1.95 calcium stearate[l part], lead carbonate [1 part and benzoic acid [1 part] were placed in a double roll mill and blended thoroughly at 900C. The blended material was formed into a sheet, cooled and then crushed. The crushed material was designated moulding material [I].

The same components, with the exception of the spherical, as herein defined, non-crystalline silica which was replaced with fused silica powder[200 parts 99.5% passing through a 325 mesh sieve], were blended, and a moulding material was prepared as described above. This particular material was designated moulding material [Il].

The spiral flow length, flow time and hot Barcol hardness of these two moulding materials were measured as described in Example 1. The results are given in Table II.

Example 3 The ratio between the fused silica powder [99.5% passing through a 325 mesh sieve] and the spherical, as herein defined, non-crystalline silica was the same as that used in Example 2, but the silicone resin content was reduced to 20%. Thus, solid phenylmethylpolysiloxane resin[100 parts],fused silica powder[240 parts], spherical, as herein defined, non-crystalline silica [60 parts], glass fibre with an average length of 1.6 mm [100 parts], cal cium stearate[1 part], lead carbonate[1 partl and benzoic acid[1 part] were blended, and a moulding material designated[llI],was prepared in accordance with the procedure of Example 2.

Material (III) was moulded at 175"C. for 3 minutes at a moulding pressure of 60 kg/cm2. Postcure was 15 hours at 175"C. The coefficient of thermal expansion of the moulded product was then measured.

For the purposes of comparison, the coefficient of thermal expansion was measured for moulding material (II), and these results are given in Table III.

The spiral flow length ofthe resulting moulding material was about 100 cm, and its coefficient of thermal expansion was relatively low.

Example 4 A phenol novolak epoxy resin (Epicoat 154 produced by Shell Chemical Co., Ltd. 'Epikote' is a Registered Trade Mark) (50 parts),the same phenylmethylpolysiloxane as used in Example 2 (50 parts), fused silica powder (99.5% passing through a 325 mesh sieve) (240 parts), spherical, as herein defined, non-crystalline silica having an average particle size of 30 m, (specific gravity: 1.95) (60 parts, 20% of the total silica filler), stearic acid (3 parts), and aluminum benzoate (1.5 parts) were placed in a dou ble roll mill and blended thoroughly at 600C. The blended material was formed, cooled and then crushed to obtain a moulding material designated (IV).

For the purpose of comparison, a moulding material designated (V) was prepared by replacing the spherical, as herein defined, non-crystalline silica used for material (IV) with fused silica powder so that fused silica powder comprised the total silica filler.

The resulting spiral flow length, flow time and hot Barcol hardness at 175"C. are given in Table IV.

It was found that the spiral flow length of the moulding material containing 20% of spherical, as herein defined, non-crystalline silica of the total filler was 77% greater than the spiral flow length of the moulding material prepared without spherical, as herein defined, non-crystalline silica.

TABLEI Experiment No.

1 2 3 4 5 Fused silica powder (parts) 300 270 240 210 180 Spherical, as herein defined, non-crystalline 0 30 60 90 120 silica (parts) Spiral flow length (cm) 84 102 114 127 109 Flow time (seconds) 17 16 17 17 18 Hot Barcol Hardness 76 75 75 74 67 TABLET Moulding Moulding Material (I) Material {IIJ Spiral flow length (cm) 130 114 Flowtime (seconds) 19 22 Hot Barcol Hardness 60 60 TABLE lIl Moulding Moulding material (III) Material flV Silicon resin content (%) 20 25 Spiral flow length (cm) 99 114 Flow time (seconds} 18 22 Hot Barcol Hardness 62 60 Coefficient of thermal expansion (30 to 1500C) 2.7 x 10-3 3.2 x 10-3 TABLE IV Moulding Moulding material IV Material V Spiral flow length (cm) 94 53 Flowtime (seconds) 11 12 Hot Barcol Hardness 80 80

Claims (9)

1. A heat curable moulding composition which comprises: a) 100 parts of a heat curable moulding resin; and b) up to 400 parts of a filler wherein 5 to 80 weight percent of filler b) consists of a spherical (as herein defined) inorganic filler having an average particle size of 1 to 800 millimicrons.

2. A heat curable moulding composition as claimed in claim 1 wherein filler b) has an average particle size in excess of 1 /1.

3. A heat curable moulding composition as claimed in claim 1 or claim 2, wherein the total quantity of filler b) in the composition is from 100 to 400 parts per 100 parts of a).

4. A heat curable moulding composition as claimed in claim 3 wherein the total quantity of filler b) in the composition is from 200 to 400 parts per 100 parts of a).

5. A heat curable moulding composition as claimed in any of claims 1 to 4 wherein the Spherical (as herein defined) inorganic filler has an average particle size of 10 to 500 mull.

6. A heat curable moulding composition as claimed in any of claims 1 to 5, wherein 10 to 60 weight as percent of filler b) consists of Spherical (as herein defined) inorganic filler.

7. A heat curable moulding composition as claimed in any of claims 1 to 6 wherein the Spherical (as herein defined) inorganic filler is silica.

8. A heat curable moulding composition as claimed in any of claims 1 to 7 wherein the resin a) in a silicone resin, an epoxy resin, a silicone-epoxy copolymer resin or mixtures thereof.

9. A heat curable moulding composition as claimed in any of claims 1 to 8 wherein filler b) comprises 90 to 40 weight percent based on the total weight of b) of glass fibre and 10 to 60 weight percent of Spherical silica.

9. A heat curable moulding composition as claimed in any of claims 1 to 8 wherein filler b) comprises 90 to 40 weight percent based on the total weight of b) of glass fibre and 10 to 60 weight percent of Spherical (as herein defined) silica.

10. A heat curable moulding composition as claimed in claim 1 substantially as herein described with reference to the Example.

11. A process for preparing a heat curable moulding composition as claimed in claim 1 which comprises: i) melting and blending the resin a) and the filler b); ii) cooling the mixture obtained to bring about sol- idification; and iii) crushing the solidified composition.

New claims or amendments to claims filed on 30 Jan 1979

1. A heat curable moulding composition which comprises: a) 100 parts of a heat curable moulding resin; and b) up to 400 parts of a filler wherein 5 to 80 weight percent of filler b) consists of a spherical inorganic filler having an average particle size of 1 to 800 millimicrons.

5. A heat curable moulding composition as claimed in any of claims 1 to 4 wherein the Spherical inorganic filler has an average particle size of 10 to 500 m.

6. A heat curable moulding composition as claimed in any of claims 1 to 5, wherein 10 to 60 weight as percent of filler b) consists of Spherical inorganic filler.

7. A heat curable moulding composition as claimed in any of claims 1 to 6 wherein the Spherical inorganic filler is silica.