GB2062646A

GB2062646A - Molding compound for semiconductor devices

Info

Publication number: GB2062646A
Application number: GB8034992A
Authority: GB
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1979-11-07
Filing date: 1980-10-30
Publication date: 1981-05-28
Also published as: DE3042093C2; GB2062646B; DE3042093A1; JPS5667948A

Abstract

A molding compound for semiconductor device having a Barcol hardness of 80 or more after curing contains as a base resin a thermosetting resin and as a filler a silicate having a chain combination structure or a two-dimensional network structure. The silicate is suitably enstatite, wollastonite; rhodonite, anthophyllite, tremolite, kaolinite or talc.

Description

SPECIFICATION Molding compound for semiconductor devices The present invention relates to an encapsulating resin for semiconductor devices which is capable of reducing the strain of the sealed semiconductor devices.

An inorganic filler is generally contained in a base resin for sealing the semiconductors for the purpose of improving: (1) the thermal conductivity, (2) the volume or bulking effects, and (3) the reduction in the thermal expansion coefficient in order to approach it to those of the other containing materials.

Silica is generally used as such a filler since it is easy to obtain in relatively highly purified form and its thermal expansion coefficient is small.

With such a conventional sealing resin containing silica, however, a great distortion such as 1 200-1,500 kg/cm2 is disadvantageously caused by the stress. This presented problems especially with some types of bipolar linear ICs in that the diffusion resistance, hence, the overall characteristics change or the manufacturing margin (fraction non-defective) is reduced. Such resin has been also defective in that the increase in the low frequency noise figure leads to difficulties in adoption of the low noise ICs, manufacturing cost cannot be reduced and the noise of the resin-encapsulated devices increases upon sealing.

In order to solve these problems, it has been proposed to use a soft, flexible resin, e.g., silicone resin as the base resin.

However, this method has also been proved to be defective in that the elements tend to break and the characteristics change when the resin sealing elements are packaged on an electronic device and are tightened with screws.

It is, therefore, the primary object of the present invention to provide a molding compound for semiconductor devices with which the distortion of the semiconductor elements may be reduced to the minimum and various characteristics of the semiconductor devices such as the diffusion resistance and the low frequency noise figure may not be adversely affected.

To the above and other ends, the present invention provides a molding compound for semiconductor devices characterized in that silicate having a chain combination structure or a twodimensional network structure is dispersed as a filler in a base resin.

The present inventors have found that the distortion of the molding resin may be significantly reduced by using a silicate having a chain combination structure or a two-dimensional network structure in place of the crystallized silica or the fused silica having a three-dimensional network structure which has been conventionally used as a filler for the sealing resins. The silica which has been conventionally used has a three-dimensional network structure of tetrahedron, i.e., Six, as the crystal structure. It is considered that the distortion increases since such a structure cannot cope with the stress when the hardness is high.

On the other hand, with a silicate having a chain combination structure or a two-dimensional structure, considerable amount of displacement is produced within the chain combination structure or the two-dimensional network structure against an external pressure reducing the distortion.

As the base resin to be used in the present invention, a thermosetting resin whose hardness in combination with a filler mired therewith is over 80 (Barcol hardness) after curing may be used. More particularly, phenol novolak type epoxy resins; or other hard resins used as the base resins for conventional sealing resins such as acid anhydride type epoxy resins, silicone resins, silicone polymers may be used.

Representatives of the silicates having the chain combination structure used in the present invention are the pyroxene group represented by the rational formula M"SiO3 such as enstatite (MgSiO3), wollastonite (CaSiO3), and rhodonite (MnSiC); or the amphibole group such as anthophyllite [(Mg, Fe), (OH2) (Si4011)2 ] and tremolite [ Ca2Mg2(OH)2(Si4011)2J. Representatives of the silicates having the two-dimensional network structure are kaolinite, talc and so on which are easy to cleave. Among these silicates, enstatite is most preferable since the distortion may be most reduced and the high temperature volume specific resistance is great.

It is preferable to use the silicates of higher purity and particularly those of less than 500 ppm alkali content (K and/or Na) since they do not corrode aluminum electrodes.

It is preferable to add a silicate in the amount of about 6080% based on the sum of the silicate and the base resin. When the silicate content is less than this lower limit (60%), the overall thermal expansion coefficient of the resin cannot be made sufficiently small. On the other hand, when it exceeds the upper limit (80%), it is not preferable since the viscosity becomes too great during hot pressing (molding), frequently resulting in damages to the lead wires.

In addition to the silicate, it is possible to add suitable amounts of a flame resistance increasing agent such as antimony trioxide and other conventional additives such as a colorant and a mold releasing agent.

The present invention will now be described with reference to its examples.

EXAMPLE Phenol novolak type epoxy resin 100 parts by weight (230 epoxy equivalent) Phenol novolak resin (curing resin) 50 parts by weight (700-800 molecular weight) 2-heptadecylimidazole (curing promotor) 3 parts by weight Carbon black (colorant) 0.5 part by weight Carnauba wax (mold releasing agent) 365 parts by weight The silicates as shown in the table below were used as the filler. The each filler was added in the amount shown above. After the mixture was kneaded with a kneading roll heated to 800C for 10 minutes, it was ground while cooled to provide a sealing resin composition powder.

This sealing resin composition powder was used to seal a bipolar IC. For sealing, it was molded at 1 700C for 3 minutes (low pressure transfer molding) and thereafter heated to cure at 1 700C for 8 hours. The Resin was formed in a form of a 1 6 pin DIP in a conventional manner and its distortion characteristic and the high temperature volume resistance were measured. The measurements are shown in the table below.

TABLE

Sillcates Characterlstics of Moided Products Purlty Straln High Tempèrature Crystal Kind (Impurity Characteristic Volume Reslstance Structure (Mineral) Content) (Stress) (100 C) Chain Crystal Woliastonite Less than 1000 - 1100 kg/cm 5 x 1012 #.cm 500 ppm Enstatite Less than 900 - 1000 kg/cm 5 x 1013 #.cm 500 ppm Rhodonlte Less than 1000 - 1100 kg/cm 3 x 1012 #.cm 1000 ppm Two-dimensional Kaolinite Less than 1000 - 1050 kg/cm 5 x 1012 #.cm Network Crystal 500 ppm Talc Less than 850 - 950 kg/cm 7 x 1012 #.cm 500 ppm Three-dimenslonal Crystallized 500 - 1000 ppm 1400 - 1500 kg/cm 4 x 1013 #.cm Network Crystal Sillca Fused Sllica Less than 1100 - 1200 kg/cm 5 x 1012 #.cm 500 ppm As may be apparent from the above example, the molding resin of the present invention is far improved in the distortion characteristic as compared with the conventional molding resins so that the fluctuation in the characteristics of the bipolar IC and the noise of the low noise IC may be reduced which have been attributable to the conventional sealing resins.

Claims

1. A molding compound for semiconductor device characterized in that a silicate having a chain combination structure or a two-dimensional network structure is dispersed as a filler in a base resin.

2. A molding compound as claimed in claim 1, wherein the composition of the base resin and the filler has a Barcol hardness of over 80 after curing.

3. A molding compound as claimed in claim 1, wherein a thermosetting resin is selected from the group consisting of acid anhydride type epoxy resins, silicone resins and silicone epoxy polymers.

4. A molding compound as claimed in claim 1, wherein the silicate having a chain combination structure is selected from the group consisting of the pyroxene group and the amphibole group.

5. A molding compound as claimed in claim 4, wherein the silicate having a chain combination structure is enstatite.

6. A molding compound as claimed in claim 1, wherein the silicate having a two-dimensional network structure is kaolinite or talc.

7. A molding compound as claimed in any one of the preceding claims, wherein the silicate is mixed in an amount 6080% of the sum of the silicate and the base resin.

8. A molding compound for semiconductor devices, substantially hereinbefore described with reference to Examples.