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Reliability of SAC 105 and SAC1205N under Drop Tests
Keywords: drop test, solder joint fatigue life, SAC105 and SAC1205N
In this paper, the solder joint failure and the solder joint fatigue life in the TFBGA Package (Thin-profile Fine-pitch Ball Grid Array) was investigated by performing the drop test and implementing a simulation model. Owing to the need to meet the increasing demands for functionality, microelectronic package reliability can be compromised and has become the key issue when executing drop tests. During impact in drop test, the deformation of PCB due to bending and mechanical shocks will cause solder joint failure. While this is a well known issue, observing the solder joint responses during the test execution can be a challenge. Therefore, in this work, a simulation model approach has been developed to investigate the stress and strain of the solder joint during the drop test. In this research, the JEDEC Condition B drop test was simulated, characterized by 1500G peak acceleration and 0.5 ms duration. The drop test simulation model was successful in predicting the solder joint fatigue life with different solder joint materials, such as SAC105 and SAC1205N, while also facilitating result comparison to identify the most optimal structure. The finite element model implemented in this work incorporates the ANSYS, and is fully parametric with respect to all relevant dimensions and material properties. The drop test simulation was performed using 1500G peak acceleration and 0.5 ms duration, applied on the screw hole. To investigate the resulting solder joint stress and strain and propose strategies for improving the solder joint fatigue life, the finite element method and design of experiment were performed in the research. The simulation results of the TFBGA package are characterized by a single layer of silicon chips, of 11.8 mm 11.8 mm size, with SAC105 as the solder joint material. By observing the failure of solder joints, the location of the maximum von-Mises stress can be identified. The study findings show that, in this case, it occurred on the outer solder joint. More specifically, the von-Mises stress at the outer solder joint is concentrated on the top surface, where a crack occurred. To establish the fatigue life model for SAC105 and SAC1205N as solder joint materials, the simulation results and the experimental testing results were compared and statistically analyzed. The solder joint fatigue life was calculated by analyzing the stress and strain of the critical solder joint. The fatigue life results reveal that the greatest discrepancies between the simulation results and experimental testing results do not exceed 10%, with the maximum error of 17%. Therefore, the accuracy of fatigue life model is deemed acceptable, suggesting that it can be used to predict the solder joint fatigue life.
Jia-Shen Lan,
National Sun Yat-sen University
Kaohsiung, Kaohsiung

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