Comprehensive Influences of Manufacturing Process Integrated With Thermal Cycling Test Loading on Mechanical Responses of Power Module

Although the power module has been developed and used for decades, the effects of large deformation and residual stress during the manufacturing process remain as critical issues. These issues also affect the reliability of a power module. Therefore, a process-oriented simulation methodology based on the finite element method is proposed to estimate warpage variation and residual stress during the process of a power module. The mechanical behavior of the thermal cycling test (TCT) is estimated in accordance with the deformation and residual stress from the process. The chemical shrinkage characteristic of the molding material is included in the simulation due to the large deformation of the molding process. The warpage of the power module from the experiment is measured during the process to verify the simulation methodology. Experimental measurements of the major procedures, including prebending, reflow, housing, and molding, of the power module, are conducted in sequence. Warpage error between the experiment and the simulation during the process is less than 5%. The effects of residual stress and deformation from the process are subsequently considered for TCT to investigate the effects on the corresponding mechanical behavior. In addition, static electrical and insulation characteristics are measured. The measured results of the insulation voltage reveal that the aluminum nitride (AlN) ceramic layer fails due to cracking between 150 and 250 cycles, verifying the prediction of the simulated results on the basis of the first principle stress of ceramic. Moreover, the failure of the ceramic is observed with scanning acoustic tomography. The simulation results compare the effects of deformation and residual stress from the manufacturing process. The simulation result that has not considered the process shows that the ceramic fails immediately at the first cycle of TCT. This finding is inconsistent with the experiment results. The results indicated that the effect of the manufacturing process should be considered when estimating the mechanical behavior for the subsequent reliability test.