The European Space Sector can no longer avoid the need to plan and implement a managed transition to Pb-free electronics. This stimulus comes from two fronts: Regulatory and Market pressures.
In the Regulatory front while the Space Sector was out of scope of the RoHS Directive, a new front has opened with REACH. Lead (Pb, CAS 7439-92-1) has now been included in the ECHA Registry of SVHC Intentions and in 2018 it has been included in the REACH Candidate List of SVHC for Authorisation. While we cannot preclude the final outcome of the process, there is a clear risk for the Space Sector which may have to resort to future Requests for Authorisation to continue using lead.
The Sector is also subjected to increasing Market pressures. 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 parts with Pb-free finishes and they need to manage the associated risk of tin whisker growth. This is becoming more and more important due to the increased interest on COTS (Commercial Off-The-Self) for a wide range of projects.
The REACH regulatory pressure may also result on difficult market availability of leaded solder paste which means going to Pb-free soldering, an extensive and very expensive undertaking for the European Space Industry.These considerations have prompted, in 2019, the ESCC SCSB to launch a joint Task Force consisting of MPTB and CTB members to draw a consensual and detailed Pb-free Transition Roadmap which they delivered in 2020 after 18 months of work. Eight partners of LETTERSS were also in the Task Force and the proposed work is based on the Roadmap.
Lead is present in many subsystems of a spacecraft: Electronics; massive shielding with lead structures for X-Ray functions; partially shielding by lead containing tape; use in ceramics for sensors/actuators purposes; batteries; solid lubrication, etc. This proposal, in accordance with the content of the call, only addresses the Pb-free transition for Electronics Assemblies where lead is found today in finishes for parts and solder alloys. We propose to test and validate Assembly solutions for Pb-free electronics components as well as the evaluation of pb-free solders.
In this frame, LETTERSS project intends to achieve the following objectives:
• The WP1 goal is to determine the state of the art on the soldering process of COTS devices with lead-free finishes using classic tin lead alloys, the lead-free soldering process, including their relevant lead-free pastes and the whisker growth phenomena. The knowledge gathered will support the subsequent WPs, setting the starting point of the investigations and allowing the use of the collected data for establishing the right testing process, test candidates, conditions and flows.
• To contribute to the wide and speedy uptake of EEE COTs in Space Programmes by solving the issues related to the assembly of these components (that mostly have Pb-free finishes) using existing, lead based, assembly lines. This is the work proposed in WP2.
• To optimize and characterize assembly process for space use two Pb-free solder pastes. This is the work proposed in WP3.
• WP4 will be dedicated to the definition of acceleration factors and lead-free fatigue law, based on accelerated tests.
• To advance our understanding of the role of corrosion and other chemical factors as well as stresses in whisker formation and growth in the tin films in order to establish acceptable accelerated tests that will give confidence when applying existing or new mitigation techniques. This is the work proposed in WP5.
