Solderability testing of alternate component termination materials with lead free solder alloys

The impending introduction of environmental legislation aimed at reducing the quantity of heavy metals disposed of into landfill sites has caused many organisations to look at their choice of interconnect media. A response to this challenge has been the recent activity to find drop-in replacements for tin/lead solders which do not contain lead. Switching from a well characterised and mature interconnection medium, such as the tin-lead and tin-lead-silver alloys, includes a number of potential risks if the proposed alternatives are not sufficiently understood. Candidate materials will have to satisfy a number of demands, such as those relating to reliability and manufacturing compatibility. Reliability demands include fatigue resistance, predictable failure modes, toughness, understanding of the microstructure evolution over time and satisfactory in-service environmental performance (temperature, vibration and humidity). Manufacturing demands include a reasonable liquidus temperature and percentage heat above liquidus to achieve satisfactory wetting, compatibility with current production equipment and product materials and a reasonable shelf life. This paper presents some of the results of an ongoing series of manufacturability trials at Loughborough which are assessing the solderability of various component termination finishes and styles with two candidate lead free solders under a number of different test regimes, these being representative of proposed manufacturing conditions (temperature and atmosphere inert).