LETTERSS · Lead-free Transition for the European Space Sector

Due to the overall transition of the Electronics industry worldwide to a Pb-free realm, the Space Industry is more and more confronted with a situation where they cannot avoid using EEE (Electrical, Electronic and Electromechanical) parts with Lead-free finishes and they need to manage the associated risks. The growing use of commercial components (COTS), notably for the expanding market sector of constellations, means that European Space Industry is already using large amount of components with lead-free finishes even when the equivalent leaded high-reliable version is available. Even though the Space Sector is exempted from RoHS restrictions (Restriction on the use of certain Hazardous Substances), market pressure may also result on potential future difficult availability of leaded solder paste. This project addresses the main challenges of the Pb-free transition for the European Space Sector that were described in the Roadmap delivered in 2020 by the ESCC Task Force created to that end. First, we will study the obstacles that hinder today the wider use of COTS components in space projects using existing qualified assembly processes based on leaded solders. Second, we will launch a comprehensive evaluation of two lead-free solders that show promise for the Space Sector including reliability model development. Sn-solders were alloyed with lead at the beginning of the electronics era mainly to inhibit the growth of whiskers, therefore going to lead-free electronics creates a serious risk for space projects that may result in catastrophic failure in the satellite due to whiskers growth. The Space sector has developed mitigation approaches but the real challenge is to obtain accelerated tests that will give confidence that, for a given mitigation used and for the duration of the project, the risk is managed and acceptable. For that we propose to perform basic research to advance the state-of-the-art on our knowledge of whisker growth, leading to the determination of the pertinent activation energies that can be used in the design of accelerated tests.