Study of Residual Stress in Packaging Process on Solder Joint Life under Thermal Shock

Since the packaged device is composed of materials with different thermal properties, the package will be subjected to multiple thermal and mechanical loads during the packaging process, resulting in stress and deformation. The stresses may cause delamination or cracking of the electronic device even before the package processing is completed. Therefore, it is crucial to consider the process step continuity during the packaging process to improve the reliability of the packaged devices.In this paper, the three-dimensional structural model of the auxiliary transformer is established by ANSYS Workbench software. Three sequential process steps, reflow soldering, molding and thermal shock, are simulated using the method of killing activating elements, and the fatigue life of solder joints under thermal shock is predicted based on the Coffin-Manson fatigue model. The results show that at the moment of peak reflow, the stress at the contact location between the Magnetic mold and the T-core of the auxiliary transformer reaches a maximum value of 121 MPa, with a possible risk of cracking failure. The predicted fatigue life of solder joints in thermal shock reliability is 580 cycles.