Lowering Thermal Stress in Molding Compounds

Thermal stress in resin encapsulated LSI packages is produced by the differences in thermal expansion coefficients between encapsulation materials and the insert materials such as silicon chips, lead frames, etc. The thermal stress ct generated can be estimated by the following equation, which is approximately derived from Eq. (1). 

Linear thermal expansion coeffiejents and elastic moduli of encapsulation materials change greatly at temperatures nrar Tg, however, they do not change vay much above or below Tg. Therefore, Eq. (10) can be reduced to the following  

1) Lowr the linear thermal eiq)ansion coefficient of molding compounds to those of inserts. 

Most of the low thennal stress molding compounds now on the market are based on epoxy resins having rubber particles dispersed as flexibilizers to lower the elastic modulus in the cured state Although this method has been successful so 

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