Design and optimization of lead-forming for CFP package based on finite element analysis

With the development and application of ceramic packages, the thermal fatigue failure, which comes from the mismatch of thermal expansion coefficient (CTE) between different materials, becomes one of the main failures to modules during temperature cycling. In this paper, the model of a typical assembling module, which includes a ceramic flat package (CFP) soldered on the PCB, was established. And then, the finite element analysis software was used to simulate the thermal stress of solders and leads in the assembling module.To analyze the effect of the lead-forming parameters, the shoulder, the height and the angle were selected as analysis variables. Then, a series of forming parameter combinations was designed. Accordingly, all the over-molded assembling modules were simulated in the same thermal condition to analyze the trends of the stress. Based on the simulation results and actual lead-forming condition, a better combination of lead-forming parameters which resulting in the minimum stress of solders was chose as the final scheme. Comparing with the typical assembling module, the maximum stress of the solders in the final scheme decreases 1.8MPa (5.7%), and the maximum stress of the lead decreases 55.4MPa (37.9%).Generally, the possible failure point during the temperature cycling is on the solder. The fatigue life of the solder joint was calculated using Engelmaier’s model. Lastly, the simulation and experiment results show that the final lead-forming scheme meets the application environment and realizes the structure optimization of CFP16 package well.