Studies Of Crystal Plasticity In The Micro-Forming Of Cu Alloy Ultra-Thin Chip Leads By Finite Element Simulation

In this research,a NovaPack chip with ultra-thin CuFe₂P leads was studied,which is a typical Quad Flat Package?QFP?.During the process of packaging,the leads was deformed into a shape of"gull wing"extending from each of the four sides.As the leads are made of micro scale ultra-thin metal sheets,the size effect will appear in the micro-forming and it will be much different from the metallic plastic deformation in the macro scale.The size,location and orientation of grains in the chip leads will have a significant influence on the micro-forming.As a result,the knowledge and tools developed for analysis of macro-forming will not be adapted in the case of micro-forming.Thus,new models and theories are needed to explain the mechanic problems of micro-forming of ultra-thin leads.This paper focus on developing a grain level model to realize the finite element simulation of the micro-forming of ultra-thin chip leads and explore the effect of grain size and mesh size on micro mechanic properties.In particular,the measurement of springback angles has been done to reveal the influence of grain size on the elastic return of the leads.The results of simulation indicate that the maximum value of stress and true strain in the leads increase slowly with the decrease of the grain size.There is an average stress fall of 161MPa after the micro-forming.Besides,the standard error of all the results will become smaller when the element number per grain increases,which means a small element size can improve the precision of calculation.However,the relationship between the grain size and elastic return seems more complicated.With the increase of ratio T/D,the springback angle decreases,the trend of the evolution of the springback angle has been proved by related experiments.The complexity of calculation augment rapidly with the refining of the crystalline grains.Thus,this research has applied the cluster computing to realize the whole process of the simulation.This method can not only be used in the micro-forming of chip leads,but also in the micro mechanic problems of other micro parts in the electronic industries.