研究目的

To investigate the reliability of the SAC305 solder joint used in a LED CSP, the 3D modeling of solder joints with randomly distributed voids was firstly established in this study with statistical methods. The mechanical strength and heat dissipation performance of solder joints considering the effect of random voids were then investigated with finite element simulations. Finally, the thermal shock experiment and simulation were designed to evaluate the fatigue failure of solder joints in LED CSP.

研究成果

The results indicate the following: (1) after a long-term thermal shock test, the void rate of solder joints increases and its shear strength degenerates with an exponential trend; (2) as stress is always concentrated near the voids, the first principle stress of a solder joint is obviously influenced by the void position, especially when the through-hole voids are formed at the corner of solder joints; (3) when the void rate grows during the thermal shock aging test, the thermal resistance of solder joint also increases at the same time; (4) the formation of voids in solder joints always affects their reliability. The proposed lifetime estimation method by inserting the 3D randomly distributed void model into the Anand and Coffin–Manson models can increase the accuracy of fatigue failure prediction for solder joints in LED CSP.

研究不足

The study acknowledges the large uncertainties in both voids measurement and shear force measurement, which may affect the relationship between the void ratio increase and shear force decrease. Additionally, the Z coordinates of voids in the X-ray images could not be determined, and the void position in the Z axis was assumed to be randomly distributed within solder joints.