Correlations of dynamic mechanical measurements to the stress formation by molding compounds

Semiempirical estimation of stress by the integrated value of the products from shear modulus and the coefficients of thermal expansion are not suitable to differentiate between commercially used low-stress molding compounds. A modified evaluation procedure is presented. Prior to multiplying the curves of shear modulus and thermal expansion, one must shift to the same glass transition temperature (T/sub g/) because of all of the values are frequency dependent. The conclusion is that the T/sub g/ of improved compounds should be situated outside of all the occurring temperatures at given frequencies. Another influence on stress that must be considered is the adhesion strength between the molding compound and substrate (silicon, leadframe, etc.). The authors applied nondestructive testing methods for composites to the combination of the silicon and the compound. The data obtained by dynamic mechanical experiments are contradictory to published data. Post-cure increases the adhesion of standard compounds to the substrate, whereas adhesion of siloxane-modified low-stress compounds is weakened.<
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