Effects of Different Printed-Circuit-Board Surface Finishes on the Formation and Growth of Intermetallics at Thermomechanieatty Fatigued,Small Outline J Leads/Sn-Ag-Cu Interfaces

摘要

The effects of printed-circuit-board(PCB)surface finish and thermomechani-cal fatigue(TMF)on the formation and growth of intermetallic compounds(IMCs)between small outline J(SOJ)leads and Sn-3.OAg-0.5Cu solder were investigated.The thickness of the IMC layer formed initially at the as-soldered SOJ/Sn-Ag-Cu interface over a Ni/Au PCB surface finish was about 1.7 times of that over the organic solderability preservative(OSP)PCB surface finish.The parabolic TMF-cycle dependence clearly suggests that the growth processes are controlled primarily by solid-state diffusion.The diffusion coeffi-cient for the growth of the total IMC layer at the SOJ/Sn-Ag-Cu interface over the Ni/Au PCB surface finish is the same as that over the OSP PCB surface finish,and thus,the total IMC layer at the SOJ/Sn-Ag-Cu interface over the Ni/Au PCB surface finish is thicker than that over the OSP PCB surface finish.Using the Cu-Ni-Sn ternary isotherm,the anomalous phenomenon that the presence of Ni retards the growth of the Cu_3Sn layer while increasing the initial growth of the Cu_6Sn_5 layer can be addressed.