Reliability Analysis of Aging in Joint Microstructures for Sn-Ag-Cu Solder Joints During Thermal Cycling

Abstract

This study illustrates test results and comparative literature data on the influence of isothermal aging and thermal cycling associated with Sn-1.0Ag-0.5Cu (SAC105) and Sn-3.0Ag-0.5Cu (SAC305) ball grid array (BGA) solder joints on three board finishes (ImAg, ENIG, ENEPIG). The resulting degradation shows that the characteristic lifetimes for both SAC105 and SAC305 decrease in the order ENIG > ENEPIG > ImAg. SAC305, with a higher relative fraction of Ag3Sn IMC within the solder, performs better than SAC105. SEM and EDX analysis shows continuous growth of Cu-Sn intermetallic compounds (IMC) on SAC/ImAg systems and Cu-Ni-Sn IMC on SAC/ENIG/ENEPIG systems at board side solder joints, which eventually cause fatigue failures.

Packaging Reliability Effect of ENIG and ENEPIG Surface Finishes in Board Level Thermal Test under Long-Term Aging and Cycling

“…Figure 12 shows the cross-polarized image of 10 mm SAC105 solder balls, the crack which might be effect by grain boundaries. This is due to the formation of a continuous network of high-angle (grain) boundaries by local recrystallization increasing grain structure movement along the interfacial region, enhancing cracks nucleation and propagation through the recrystallized solder interconnections [ 23 , 24 ].…”