Process and Material Selection for zero defects and superior adhesion Lead Free SMT soldering

Researchers on this project formed an industry-led “UMASS Lead-Free Consortium ” to evaluate various emerging alternatives to lead-based Solders and finishes. The consortium members donated expertise, time, materials and equipment to this lead free project. The various alternatives of lead free materials, surface finishes and manufacturing processes were evaluated as factors in a set of designed experiments and analyzed, in comparison to a baseline of standard leaded processes, using the quality characteristics of visual, mechanical and thermal testing criteria. The Manufacturing Research Laboratory facilities at UMASS Lowell were utilized to test and analyze the performance of alternatives based on the principles of Design of Experiments. Results were analyzed using statistical techniques resulting in determining whether a particular factor was significant to the quality characteristic being measured. This paper discusses the mechanical reliability tests of the lead free process, outlines the testing decisions made and the techniques used. Results show that the reliability of the lead free joints as measured after 2000 thermal cycles by pull tests have been shown to be of equivalent quality to the lead based solder joints baseline. Additional testing and cross-sectioning of the lead free solder joints are yet to be performed at the time of authoring this paper. Key words: lead-free, design of experiments, PW