Consideration of buckling characteristics for optimal design of stiffened punch in the blanking process of lead frame

The recent technical trend of semiconductor, chip size and high performance package technology, requires the IC lead frame to be of more multi-leads and fine pitch, and the corresponding punch thickness has been narrow. The members with high slenderness ratio such as a lead frame punch can be broken suddenly due to buckling. It is the major aim of the present work to suggest a practical optimization procedure to design the punch with the optimal number and position of stiffeners considering the maximum buckling load of punch. The various cases of punches have been also analyzed using finite element method and theoretical model, and the results have been confirmed by buckling test. It is shown that the analytical and theoretical results are in good agreement with the experimental ones. Finally, a guideline to design the punch with stiffeners is proposed through analysis of cross-section of lead frame punch such as moment of inertia and eccentricity.