RELIABILITY INVESTIGATIONS OF DIFFERENT TAPE METALLIZATIONS FOR TAB-OUTER LEAD BONDING

An important reliability aspect of TAB technology is the aging behavio r of OLB contacts performed with different tape metallizations. During the OLB process tin or gold plated copper leads are connected with th e bond pads on the substrate. For soldering the OLB pad metallization consists of tin or eutectic tin/lead. Gold, tin and copper can form va rious intermetallic compounds, which may affect the long term reliabil ity of the OLB contacts. The investigations were performed with two ta pe metallizations: Sn and Au. The tapes were outer lead bonded to diff erent substrates; printed wiring board and ceramic. The pad metallizat ion for both substrates consists of eutectic tin-lead (60/40) solder. The bond process was performed by gang bonding with a thermode and sin gle point bonding with a Nd:YAG laser. The optimal bond parameters for both tape metallizations were determined. Accelerated aging was perfo rmed by high temperature storage and thermal cycling. The degradation of the contacts was measured in pull test. The different failure modes were investigated by SEM and metallographic cross sections. Quantitat ive analysis of the contact metallurgy and diffussion profiles were pe rformed with a microprobe. A comparison of the failure mechanisms for the different type metallizations and substrates with regard to the ap plied OLB process (thermode or laser) is presented.