In situ measurement of electromigration-induced transient stress in Pb-free Sn-Cu solder joints by synchrotron radiation based x-ray polychromatic microdiffraction

In situ synchrotron x-ray white beam microdiffraction is used for studying the electromigration-induced hydrostatic elastic stress in Pb-free SnCu solder joints. The compressive stress gradient between the cathode and the anode is much larger than that is required for initiating Sn whisker growth and the effective charge number of [beta]-Sn derived from the electromigration data has agreed well with the calculated value.