Numerical and Experimental Analysis of Resin Cracking in LSI Packages under Temperature Cyclic Loading. An Observation of Initial Site of the Edge-Delamination and the Effect of Delamination Length.:An Observation of Initial Site of the Edge-Delamination

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An experimental study using Kr<SUP>85</SUP>radioactive tracer techniques is made to determine the initial site of the edge-delamination between dissimilar materials occurring in LSI plastic packages with either Cu alloy (Cu-2%Sn) or alloy 42 (Fe-42%Ni) leadframe under temperature cyclic loading. It is found from the Kr<SUP>85</SUP>penetration test that the initial edge-delamination is expected to occur at the upper corner of the die pad edge for Cu alloy leadframe packages whereas it occurs at the lower corner of the die pad edge for alloy 42 leadframe packages. Numerical stress analysis on the effect of delamination length on the encapsulant resin cracking in the packages is also carried out. The delamination is assumed to be located along the top surface of the die pad for Cu alloy leadframe packages and along the bottom surface of the die pad for alloy 42 leadframe packages. The results of numerical stress analysis show that, in both Cu alloy and alloy 42 leadframe packages, resin cracking starting from lower corner of the die pad edge becomes more likely to occur and cracking direction changes toward the bottom surface of the packages as the delamination extends.
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