Manufacturing stresses in die due to die attach process

Manufacturing of the electronic packages consisting of different materials leads to the development of the residual stresses due to mismatch in the coefficients of thermal expansion. Thus, to properly assess service life of the packages, those stresses must be taken into account. An experimental technique, the digital image analysis enhanced moire interferometry ( DIAEMI), was used to measure the in-situ out-of-plane displacements of the die due to the die-attach process. This information was related to the residual stresses in the die. Several test dies, with and without coating, were prepared and two different bonding materials, "low-stress" and "high-stress", were used for analysis of the induced stresses. The initial and final (after die-attach) surface contour patterns of the dies were observed and recorded. Out-of-plane displacements of the dies were obtained and induced stresses were calculated by a hybrid finite element method. The results show that stresses in die induced by high-stress bonding material are on average five times higher than the stresses induced by low-stress material. It was also found that during die-attach some of residual stresses induced by chip's coating were released. The obtained results were compared with the straight forward finite element method prediction. It shows that the stresses predicted by the straight forward finite element analysis are much higher than the stresses obtained by the hybrid method.<
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