Degradation Of Tab Outer Lead Contacts Due To The Au Concentration In Eutectic Tin/lead Solder

Abstract

The influence of the Au-concentration in OLB-solder fillets on the contact reliability is shown. The quantitative analysis of the AUcontent is in accordance with the estimated concentrations using the geometrical data. The Au-concentration is the major influence factor on the thermal aging behaviour of OLB-contacts. A change in the failure mechanism due to Kirkendall porosity is observed if a AUconcentration of 9 wt% in the solder fillet is reached. The pores formed during diffusion at the interface between copper and the temary intermetallic compound CugAugSng cause a strong degradation of pull forces. For low Au-concentrations. the degradation of pull-forces and the growth of the ternary compounds CuAugSng and CuAuqSng have comparable activation energies in the range of 0.3 eV. For higher Au-concentrations the two effects show different values. "he activation energy of pull-force degradation increases significantly up to 0.67 eV, whereas the growth constant of the temary compound shows a small increase to 0.4 eV. The investigations show evidence of a critical Au-concentration in OLBcontacts. Kirkendall pore formation causes higher activation energies for the pull-test degradation compared to the activation energy for the growth rate of the temary compound.