Study On Tin Whisker Growth Behavior And Growth Mechanism Of Microbumps With Small Diameter In 3D Packaging

In electronic device packaging,with the requirement of lead-free in electronic solders and the development trend towards minimizing device size,the growth of tin whisker has always been a threat to the reliability of electronic devices and thus,has drawn a lot of attentions in the industry.Microbumps have been the main form for inter-connection because the diameter could be as small as 10 ?m,which is advantagrous comparing 100?m in diameter in BGC technique.However,the decrease of solder size might influence the properties of solder,one of which being the growth of tin whiskers.Therefore,it is necessary to understand the tin whisker growth behavior in small diameter microbumps.However,few researches focus on this matter.In this present work,the tin whisker growth behavior of isolated microbumps with the different diameters of 5 ?m,7 ?m and 10 ?m are investigated under different temperatures: 25°C,55°C,85°C and 115°C.Continuous compressive force was used to simulate the unevitable strain existed in the real application with the existence of heat or electric expansion.The experimental results show that the length of tin whisker increases with the increase of temperature.The reason might be higher temperature helps increase the diffusion rate of tin atoms.Besides,while conducting deeper research on microbumps with 10?m in diameter,a non-uniform copper oxide layer with several hundred nanometers thick was observed covering the surface of the microbump.The weak spots on the copper oxide layer,as localized stress relief centers,were found to be the place where tin whiskers grow from.The Highresolution TEM results also present the existence of twin grain boundary between tin whisker and neighboring grain.Near the twin grain boundary,it was observed that a lot of dislocations exist.The dislocations provide paths for the tin atoms to slip over.Under the driving force of internal stress,tin atoms slop from the microbump solder cap grains into tin whisker grain.This present study has significant meaning for 3D electronic packaging.