Growth kinetics of intermetallic compounds in chip scale package solder joint

The formation of the peaky/spiky Ni₃Sn₄ layer and thick Cu-Sn intermetallic compounds (IMC) at solder/plated-Ni PCB and solder/Cu component-pad, during soldering CSP component on Au/Ni plated substrated respectively is presented. The Ni-SN IMC and Cu-SN IMC growth complies with following equation: x(mm) = 0.9869×10^-3±0.0167 t^0.497 exp(-29.54×10³/RT), and x(mm) = 0.244×10^-3±1.85 t^0.463 exp(-45.4×10³/RT) respectively. The temperature that the assembly experiences is main factor including intermetallic layer thicken. The estimation of the IMC layer thickness with the proposed equations can be used to predict the solder joint reliability. The 0.6 μm thick Ni-SN IMC or 2.5 μm thick Cu-Sn IMC should decrease the solder joint lifetime about 2/3.