The reliability research of lead-free solder joint of Flip-chip

Based on the minimum potential energy theorem and the Theory of solder joint shape, 3-D (Three-dimensional) predicting model of Flip-chip lead-free solder joints shape are established. According to different technologic parameters, the 3-D solder joint shape is predicted. The nonlinear finite element analyses of the lead-free solder joint is performed by ANSYS under thermal cycles and the stress/strain distributions within the key solder joints and the maximum plastic strain range of the solder joints are determined. Based on the calculated maximum plastic strain range, the thermal fatigue life of the Sn96.5-Ag3.5 and Sn95.5-Ag3.8-Cu0.7 solder joints are calculated using Coffin-Manson equation. Based on the results of the calculated thermal fatigue life, the rules influencing thermal fatigue life of lead-free solder joints under the different technologic parameters are derived, which can be used in the hatch design of stencil and the dimension design of pad.