The impact of die attach material on type II popcorn cracking

Recent advances in packaging design, processes and materials have been effective in eliminating or reducing the occurrence of type I and II popcorn failures. However, type II popcorn failures remain prevalent. This paper features a vigorous investigation on the properties of various die attach materials and attempts to correlate the measured properties to the type II popcorn failure rate using a TQFP-208 package. Of the properties evaluated, a high adhesion strength under “hot-wet” conditions consistently exhibited superior popcorn performance. The test measures the adhesion strength between the die and the die-pad at an elevated temperature, after samples have been moisture pre-conditioned. Additionally, the impact of the die attach material properties on package stress and moisture distribution was investigated using finite element analysis. It was found that die attach materials with a high modulus at temperatures above their glass transition temperatures experience less strain due to thermal loading. Moisture diffusion modelling showed that a high moisture absorption die attach material having a high “hot-wet” adhesion can still perform satisfactorily in the popcorn test