TO220 package lead frame optimization for reducing trim and form delamination by simulation

In this paper, a transient non-linear dynamic finite element framework is developed and utilized for the optimization of trim and form process for TO220 package. The objective of this paper is to optimize the TO220 lead frame structure by modeling the complete trim and form process through explicit finite element code LS-DYNA. A non-linear rate dependent material constitutive relation is presented for the copper based lead frame. A surface contact eroding algorithm is utilized to simulate the dynamic cut process by introducing a lead frame failure mechanism. Modeling discloses the stress impact to the interface between the mold compound and lead frame, different parameters of heat sink and heat sink bars, including different type of pre-made grooves in the heat sink bars, distance between mold compound and lower heat sink bar, heat sink bar´s width and notch in the heat sink between heat sink bars are considered and simulated. The simulation results show that decrease upper heat sink bar´s width can reduce delamination. While move lower heat sink bar farther away the mold compound and make notch in the heat sink and small pre-made groove in the lower heat sink bar, has also reduce delamination. There is an optimized shape of heat sink and heat sink bars that may reduce delamination during trim and form process.