Investigations of Large PLCC Package Cracking During Surface Mount Exposure

Surface mount technology imposes severe strains on plastic leaded chip carriers. An examination of package cracking during solder reflow and the factors that affect this problem are presented. The major factor inducing package cracking is found to be water vapor absorption from the ambient. It was found that the cracking problem could be circumvented by reducing the absorbed moisture level through a minimum 6 h 150°C air bake followed by surface mounting within 8 h to prevent reabsorption of water from the environment. Other factors affecting this problem are the absorptivity of the plastic encapsulant, the plastic brittleness, the rigidity of the lead frame flag, the plastic to lead frame bond strength, the package thickness, and the die size.