Numerical stress analysis of resin cracking in LSI plastic packages under temperature cyclic loading. II. Using alloy 42 as leadframe material

For pt. I see ibid., vol. 19, p. 593-600 (1996). In the present paper, we apply the previous analysis to the case where alloy 42 (Fe-42%Ni) is used as the leadframe material. Based on the linear fracture mechanics approach to the bimaterial problem we demonstrate that the delamination occurring between dissimilar materials in alloy 42 leadframe packages quantitatively determines: (a) the degree to which resin cracking occurs; (b) the cracking direction at both the upper and lower wedges of the die pad. The procedure of the analysis and the targeted package are the same as those considered in the previous study. Temperature cyclic tests using actual packages are then also performed to verify the validity of analytical results. The impact of interfacial delamination on resin cracking in alloy 42 leadframe packages is quantitatively determined. It is concluded that the delamination which most easily produces resin cracking is that between the bottom surface of the die pad and the resin while other interfacial delamination (e.g., those at the upper and lower wedge of the die pad) has little impact on resin cracking.