Authors: Traian C. Cucu, Ph.D., Ioan Plotog, Ph.D., Mihai Branzei, Ph.D. Company: Alpha Assembly Solutions, Politechnica University of Bucharest Date Published: 9/17/2017
Abstract: Environmental issues are increasingly becoming important to the organizations and individuals alike. Electronic assembly industry, as everyone else, is becoming more conscience about environmental friendly processes and materials. This movement brings back in the spotlight the low temperature processes and materials, as they can help with the decrees in energy consumption and, consequently, the reduction of the carbon footprint, for the assembly processes. The tin/bismuth alloys have been used for a while in the lead-free assembly processes in electronic assembly, one of the main concerns being the compatibility with the SAC spheres from BGA/CSP type of components. Due to the lower process temperatures, new chemistry platforms for solder paste need to be developed, to fulfill both the assembly process requirements and the final assembly reliability. The solder joints are the result of the soldering process consisting of the temperature gradient action over the solder paste volume at the interface between pins and pads [1, 3]. The solder joint overall performance is described by the intermetalic formation at the interface of pad and solders volume as well as the pin and solder volume [2, 4]. The reduction of carbon footprint and the potential dollar savings add to the appeal of the low temperature process . This paper is looking at the performance of two low melting point Sn/Bi alloys (42%Sn57.6%Bi0.4%Ag and HRL1-non-eutectic Sn/Bi alloy with additives with a pasty range of 139°C-151°C) used in solder paste when used to assemble BGA type of components with SAC alloy spheres and the advantages a low temperature process brings over the regular SAC assembly process. The paper will evaluate the solder paste capability, process wise, and evaluate the performance of a joint formed with a low melting point alloy solder paste and a SAC305 spheres and look at the process advantages and the material capability. The pastes used for the low temperature process were OM-550 with HRL1 alloy and CVP-520 for the 42%Sn57.6%Bi0.4%Ag alloy.