Manufacturing stresses in the die due to the die-attach process

During the die-attach process, residual stresses are developed in components of the die-attach assembly due to the mismatch of coefficients of thermal expansion of different materials. To properly assess the service life of the assembly, those stresses must be taken into account. Several test dies, with and without chip's protective coating, were prepared, and two different bonding materials, "low-stress" and "high-stress", were used for analysis of the die-attachment induced stresses. An experimental technique, the digital image analysis enhanced moire interferometry (DIAEMI), was utilized to observe the initial and final (after die-attach) surface contour patterns of dies. This information was used to obtain the in-situ out-of-plane displacements of the die due to the die-attach process, and the induced stresses were calculated by a hybrid finite element method. The results show that stresses in die induced by high-stress bonding materials are on average five times higher than the stresses induced by low-stress materials; during the process some of the residual stresses induced by the chip's coating were released. By comparing the results with the straightforward finite element method prediction, it is shown that the induced stresses are much lower than those stresses predicted by the straightforward finite element calculation.<
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