A thermodynamic metric for process quality assessment in manufacturing: Pb vs. Pb-free solders spreading case study

Sustainability issues involving materials processing and manufacturing are still very poorly investigated. This is true in particular for non-energy parts of such systems. Thermodynamics approaches attract an increasing attention due to general applicability and a clear potential to include both quantity and quality aspects of resources utilization, process assessments and metrics selection. One of the main arguments in justifying development of thermodynamic metrics for sustainability is that irreversibility does indicate the level of imperfection of a process. However, traditional energy metrics cannot offer an assessment of the quality of resource utilization if the impact of entropy generation is not included. This can be done by shifting the analysis focus from the energy-only toward the energy and entropy generation and/or exergy balancing studies. In this paper, we consider a difficult problem of spreading of lead and/or lead-free solders over reactive surfaces important for manufacturing by soldering. We consider the level of entropy generation and/or entropy change associated with the process. Entropy is selected as a metric for analyzing contributions of surface tension and reaction driving/retarding forces. The study involves a eutectic Sn-Pb system and an Ag-Sn lead-free solder system.