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Generally, the viscoelastic properties of packaging materials used in the simulation models are obtained from the materials after postcuring. However these properties were observed to change during humidity conditioning and the thermal cycling. Two kinds of packaging materials are tested, one is molding compound and another is underfill. All samples are cured according to the curing procedure, postcured at 180degC. Before the test, first the samples are pre-dried at 125degC for 24 hours and then preconditioned at 60degC/60%RH for 40 hours. Secondly, one reflow at 260degC. Finally, all samples are subjected to thermal cycling. Thermal cycling temperature range is from -65degC to 150degC and every cycle is finished in 30 minutes. For the DMA test, a TA Instrument Q800 is used. Test results show the glass modulus, rubber modulus and glass transition temperature increase with the number of thermal cycles. This change in materials after humidity and thermal treatment is here referred to as aging. The finite element software Marc is used to simulate the internal change of stress and displacement. The simulation result shows that the total warpage has increased a little at the corner of passive die, which is where the critical cracks and crazes were found in our qualification tests. And the Von Mises stresses increase after thermal cycling.
Date of Conference: 20-23 April 2008