New analytical study for popcorn phenomenon

Package crack during mounting on the printed circuits is a major concern in package design and material development by engineers. This package crack (the so-called popcorn phenomenon) is caused by evaporation and expansion of absorbed moisture in the package at the temperature of reflow soldering for mounting on printed circuits. This package crack has been assumed to start from delamination between the encapsulant and the leadframe. But a new crack mode was found starting from the delamination of the silver paste. In order to evaluate this new crack mode, the following items were investigated: (1) the mechanism of package cracking, (2) stress, generated during the soldering process, and (3) the design of physical properties of a molding compound that has resistance of the new crack mode. Using these studies the authors developed a new molding compound that has excellent resistance to the new crack mode