Investigation of the adhesion strength between molding compound and leadframe at higher temperatures

The popcorn effect is still a main failure source where the reliability of surface mounted devices is concerned. For thin packages such as P-TSOPs or P-TQFPs, it was found that after preconditioning to level 3 or level 1, the popcorn effect starts from the back side or the top side of the die pad, respectively. Adhesion tests at room temperature could not enlighten this difference, but raised even more questions. To clarify the situation, we investigated the adhesion strength between molding compound and leadframe and between Ag coating and chip adhesive as a function of temperature, Ag coating and moisture content. We also report on investigations of the temperature dependence of different molding compounds and leadframes, with particular emphasis on leadframes with a special coating which showed increased adhesion strength in comparison to uncoated leadframes in popcorn experiments and adhesion tests at room temperature.