Semiconductor Die Attach with Nano-Ag: A Case Study of Commercial Application

ABSTRACT Because of the expectation that the current exemption from the EU RoHS Directive for solders with more than 85% lead will not be extended beyond 2016 the identification of a practicable lead-free alternative to high-lead high-melting-point solders has been one of the most urgent challenges for the electronic component industry. So far all attempts to formulate a lead-free solder alloy that could replace the high-lead solders have involved compromises in the ease of processing and/or service reliability. Since nano-silver can be sintered at temperatures similar to those used in reflowing the high-lead solders it has been increasingly considered as one of the most promising replacement candidates. Because, once sintered the melting point returns to the 961.8°C of bulk silver joints made with nano silver have physical and mechanical properties comparable with those of silver. That means that joints effected with nano-silver have higher reliability at elevated temperature and in thermal cycling and higher electrical and thermal conductivity than the high-lead solders they replace. In a previous paper, the authors reported the stabilization of reactive nano silver by alcohol derivatives and compared the performance of joints between copper and silicon in thermal cycling with those joints made with Pb-5Sn. The cost of making joints with nano silver can be reduced by the addition of micro particles of copper and in this paper the authors will present data obtained in a successful commercial application of this combination in semiconductor die attach. Basic physical properties and performance in thermal cycling test will be reported and compared with the properties and performance of joints made with pure nano-silver and Pb-5Sn.