The European Union’s Restriction of Hazardous Substances (RoHS) directive and other international and domestic mandates are intended to eliminate materials deemed hazardous. These mandates will force the electronics industry to convert from solders that have traditionally contained small amounts of lead (Pb) to alternatives that are Pb-free. While military electronics are currently exempt from these Pb-free imperatives, the consumer market drives the electronics industry, not the military, and what is permitted in consumer electronics will dictate the availability of parts and materials. Electronics for high reliability applications, such as in military equipment, rely heavily on commercial piece parts, circuit boards, and assemblies, the majority of which have transitioned or will transition to Pb-free.
Historically, Pb has been mixed with tin (Sn) into electronic solder materials to improve manufacturing processing and reduce the growth of Sn whiskers, which present reliability risks. The conversion to Pb-free solder in the commercial supply chain requires DoD to be diligent to ensure that the reliability and performance of military electronics throughout their long life cycle is maintained and not adversely impacted from the unanticipated introduction of Pb-free components.
DoD, with its unique environmental and qualification requirements, is impacted by Pb-free solders and finishes in the following key areas:
- Solder Joint Reliability – Currently no Pb-free solders have been qualified to military or aerospace standards. Mixing or improper selection of Sn-Pb and Pb-free materials can significantly decrease reliability.
- Tin Whisker Susceptibility – The use of pure Sn for surface finishes greatly increases the possibility of whisker growth, which can negatively impact performance.
- Logistics, Maintenance, and Repair – The incorporation of Pb-free finishes and solders will impact technical orders, material lists, consumable items, required equipment, and training.
- Configuration Control – For high-reliability systems for which the continued use of Sn-Pb solder and component finishes is necessary, procurement and inspection processes must be put in place to ensure that Pb-free materials do not enter these systems.
- Component/Module Availability – Global economic considerations will drive most suppliers to produce only Pb-free products, limiting the options of government procurement.
To address the issues associated with the introduction of Pb-free electronic components into military systems, SERDP is conducting research to (1) gain a scientific understanding of the function that Pb provides as a mechanism for mitigating the growth of whiskers, (2) exploit the understanding of the mechanisms associated with Sn whisker growth without the presence of Pb to develop methodologies to mitigate whisker growth, (3) understand the reliability implications associated with the use of multiple Pb-free alloys that are emerging, (4) understand the key mechanisms by which conformal coatings may provide long-term tin-whisker mitigation and growth inhibition, and (5) develop conformal coatings that can provide long-term tin-whisker mitigation.