A study on solder joint reliability including FEM simulations on silicon substrate MCM-D

Within the TWiCS project, the concept of direct module attach (DMA) has been designed and produced. Silicon substrate multichip modules equipped with large eutectic solder balls have been assembled on FR4 printed circuit boards and the reliability has been evaluated through thermo-mechanical testing. Along with the tests, nonlinear FEM simulations of DMA reliability were performed. Among the parameters in the simulations were solder pad size, solder joint height and shape and various underfill properties. The results from the tests and the FEM simulations confirm the major gain in reliability when using an underfill material on the DMAs. Underfill materials on or slightly below the CTE of solder seem to give the best results. Underfill adhesion is identified as a key factor. The tests and the FEM simulations indicate that the use of an underfill with a CTE higher than the solder is more likely to lead to silicon cratering.