Effect of lead frame material on plastic-encapsulated IC package cracking under temperature cycling

Differences in the package cracking mechanisms among lead frame materials are studied both by analysis and experiment. The results of thermal stress analysis indicate that encapsulant stress in the Alloy 42 lead frame package is increased by delamination of the chip pad´s bottom surface. Conversely, stress in the copper lead frame package is mainly determined by delamination of the die bonding layer. The mechanisms predicted for both packages are experimentally verified by ultrasonic inspection of the chip pad´s bottom surfaces and thermal-deformation-based observation of package cross sections. The effect of material properties on cracking is also studied to find ways to prevent cracking. Recommendations are made for lead-frame, encapsulant, and die-bonding materials