Soft solder die bonding of multiple die devices

The aim of the work presented in this paper is to study the soft solder die attach of multiple die devices by a multiple pass process. With a multiple pass process we mean a procedure which needs as many die bonder furnace passes as there are different types of dice to be bonded into a package. The main focus of the investigation is on the effect of the necessary multiple furnace passes on the reliability of the soft solder attachment layer. As this behavior may depend on the specific type of device or package (i.e., solder alloy-substrate combination, die size, package geometry), it is analyzed relative to the one of an identical die processed in one single furnace pass. A real package (TO-220) is used as test vehicle and processed on standard equipment. A detailed analysis of the multiple pass process relative to a single pass process with appropriate equipment is performed. It is concluded that a multiple pass process may be slightly less efficient for throughput. However it gives more process flexibility and allows using standard equipment which is available on the market. The result of this investigation strongly supports the feasibility of multiple die devices with a multiple pass process. No reliability limiting influence of the additional furnace passes causing a repeated re-melting and re-solidifying of the solder layer is found. It is, however, necessary to investigate the capability for any other specific device or package again.