The shift to lead-free solders - assessed through attributional and consequential life cycle inventory
Conference contribution, 2004
Electronics packaging is a research field that deals with everything in electronics, from the chip to the complete system, including the solder interconnection materials. As of July 1st of 2006, lead will not be allowed in solder pastes. This has called for evaluations of alternatives to tin-lead solders, and especially the environmental consequences of the shift from tin-lead solder paste (TL) to lead-free solder paste (LF). In 2003 a life cycle assessment (LCA) was initiated, having two aims: (i) to compare an TL (62% tin, 36% lead, 2% silver) to an LF (95.5% tin, 3.8% silver, 0.7% copper); both pastes assumed to include 10% flux, and (ii) to compare attributional and consequential LCA methodologies. The attributional LCA describes the environmental burdens of the solder life cycle. It describes, for example, the obvious fact that the shift from TL to LF means that lead is essentially eliminated from the solder life cycle. Our attributional LCA is largely based on literature data. Lacking environmental data for flux production, we used the economic input-output model from Carnegie Mellon to obtain approximate values . Preliminary results from the attributional LCA, indicate that LF contributes 10% more to the global warming potential (GWP) than TL. 60% of the difference, can be related to an increased reflow energy consumption, and 40% to an increased tin production. The production of flux contributed to about 5 % of the total GWP results for both solders. We have recently started the consequential LCA. It aims at describing how the environmental burdens of the technosphere are affected by a shift from TL to LF. It will describe, for example, to what extent the shift means that the total use of lead is reduced, and to what extent it means that the use of lead will increase in other life cycles. We do not expect the consequential LCA to include all inputs to the solder, because, for each input in the analysis, we need to investigate the supply curve as well as the demand curve, identifying price elasticities, marginal production, and marginal consumption.