Effects of assembly methodology on manufacturing-induced stresses in μBGA packages

46-ball μBGA packages assembled by two different packaging methodologies, one utilizing nubbin structure (type A) and the other using pre-made elastomer film (type B), were investigated for the evaluation of the manufacturing induced stresses in the packages. Moire interferometry was utilized to exam the package topology changes while the package was heated from room temperature to 170°C as well as having the package substrate removed. The induced stresses were found from the obtained experimental results. It shows that the induced stresses in the chip in the package with nubbin structure are only around 43% of those induced in the one with pre-made elastomer film. From the experiments, it also reveals that some of the manufacturing-induced stresses relaxed since the stress free state was found below the curing temperature. In type A packages, the higher percentage of stress relaxation may be resulted from the nature of the silicone elastomer