Abstract:

Sn-3.0 Ag-0.5Cu (SAC305) alloy is the most widely used solder in electronic assemblies. However, issues associated with cost and drop/ shock durability have resulted in a search for alternative lead-free solder alloys. One approach to improve the drop/shock reliability has been to reduce the silver content in Sn-Ag-Cu alloys. Another approach is doping Sn-Ag-Cu solder with additional elements. In 2008, the International Electronics Manufacturing Initiative (iNEMI) started the ‘Characterization of Pb- Free alloy Alternatives' project to provide a comprehensive study of 15 tin based solder interconnect compositions benchmark against the eutectic tin-lead solder. For this study temperature cycle durability was the primary focus and solders were selected to study the effect of varying silver content, micro-alloy additions and ageing. This papers reports findings from one of the test conditions conducted under the iNEMI project. The cycles to failure for a temperature cycling test conditions from -15 degree C to 125 degree C, with dwell times of 60 Min at both extremes, are presented. The test assembly consisted of 16 of the 192 I/O BGAs and 16 of the I/O BGAs soldered onto an LG451HR laminate. Test results revealed that the reduction of silver resulted in a reduction cycles to failure. In all cases, the 15 tin based solders were more durable than eutectic SnPb solder. Ageing at 125 degree C for 10 d did not effect the cycles to failure SAC105 solder; however, the cycles to failure decreased with ageing in SAC305 solder. In addition, ageing resulted in a wider distribution of cycles to failure in 192 I/O BGAs. Failure analysis was carried out on all solder materials to identify the failure site and failure mode.