Reliability of thermally aged Au and Sn plated copper leads for TABinner lead bonding

摘要

After thermal aging, three tape metallizations consisting of tin,gold, and nickel-gold were inner lead bonded (ILB) to chips with goldbumps. The degradation of bond strength was measured in a pull test.Auger depth profiles and microprobe WDS analysis, of the tapes and theILB-contacts were performed. The formation of the intermetallic compoundCu₃Sn is the main degradation mechanism for eutectic Au-Snsoldering. The Cu₅Sn₆ phase is dissolved in theeutectic solder, forming a ternary (AuCu)Sn alloy. Arrhenius plots fordifferent failure criteria in pull test result in an activation energyof 0.76-0.8 eV. A shelf life of at least two years at 20° C can beestimated for a tape with 0.7 μm electroless deposited Sn. Incontrast to eutectic Au-Sn soldering, bulk processes such as theformation of intermetallic compounds are not the limiting factor ofthermocompression bonding. Because no significant degradation was foundeven after 2000 hours at 150 ° C, an Arrhenius plot was not possible.With an activation energy of 0.55 eV, a shelf life of at least 15 yearsat 50° C can be estimated for 1 μm electroplated Au on copperleads, so that a Ni-diffusion barrier is not required