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This Bulletin provides a brief description of tin whisker formation and describes various methods recommended by government and industry to reduce the risk of tin whisker-induced failures in electronic hardware. It is not a mandate nor does it contain any requirements. A tin whisker is a single crystal that emerges from tin-finished surfaces. Tin whiskers can pose a serious reliability risk to electronic assemblies that have pure tin finish. The general risks fall into several categories: [1, 2, 3, 8, 16] Short Circuits: The whisker can create a short circuit, either by 1) growing from an area at one potential to an area at another or 2) breaking free and later bridging these areas. In some cases, these shorts may be permanent and cause catastrophic system failures. A transient short may result if the available current exceeds the fusing current of the whisker, and the whisker can fuse open.

This standard defines the requirements for fully replacing undesirable surface finishes using robotic hot solder dip. Requirements for qualifying and testing the refinished piece parts are also included. This standard covers the replacement of pure tin and Pb-free tin alloy finishes with SnPb finishes with the intent of subsequent assembly with SnPb solder. This dipping is different from dipping to within some distance of the body for the purposes of solderability; solder dipping for purposes other than full replacement of pure tin and Pb-free tin alloy finishes are beyond the scope of this document. It covers process and testing requirements for robotic dipping process and does not cover semi-automatic or purely manual dipping processes. This standard does not apply to piece-part manufacturers who build piece parts with a hot solder dip finish.

This document is intended for use as technical guidance by Aerospace system suppliers, e.g., Aerospace system Original Equipment Manufacturers (OEMs) and Aerospace system maintenance facilities, in developing and implementing designs and processes to assure the continued performance, quality, reliability, safety, airworthiness, configuration control, affordability, maintainability, and supportability of high performance aerospace systems (subsequently referred to as AHP) both during and after the transition to Pb-Free electronics. This document is intended for application to aerospace products; however, it may also be applied, at the discretion of the user, to other products with similar characteristics, e.g., low-volume, rugged use environments, high reliability, long lifetime, and reparability. If other industries wish to use this document, they may substitute the name of their industry for the word “Aerospace” in this document.

This technical report identifies the requirements for an LFCP for ADHP soldered electronic products built fully or partially with Pb-free materials and assembly processes. An LFCP documents the specific Pb-free materials and assembly processes used to assure customers their ADHP soldered electronic products will meet the applicable reliability requirements of the customer. This standard specifically addresses LFCPs for: a Pb-free components and mixed assembly: Products originally designed and qualified with SnPb solder and assembly processes that incorporate components with Pb-free termination finishes and/or Pb-free BGAs, i.e., assembling Pb-free parts using eutectic/near-eutectic SnPb processes (also known as mixed metallurgy). b COTS products: COTS products likely built with Pb-free materials and assembly processes. c Pb-free design and assembly: Products designed and qualified with Pb-free solder and assembly processes.

This document provides technical background, procurement guidance, engineering procedures, and guidelines to assist organizations reworking/repairing aerospace and high performance electronic systems, whether they were assembled or previously reworked/repaired using traditional alloys such as SnPb or Pb-free alloys, or a combination of both solders and surface finishes. This document contains a review of known impacts and issues, processes for rework/repair, focused to provide the technical structure to allow the repair technician to execute the task. This document focuses on the removal and replacement of piece parts. For the purposes of this document, the term “Rework/Repair” is used as applicable. NOTE: The information contained within this document is based on the current knowledge of the industry at the time of publication. Due to the rapid changing knowledge base, this document should be used for guidance only.

This Standard establishes processes for documenting the mitigating steps taken to reduce the harmful effects of Pb-free tin finishes in electronic systems. This Standard is applicable to Aerospace, Defense, and High Performance (ADHP) electronic applications which procure equipment that may contain Pb-free tin finishes.

This standard defines the objectives of, and requirements for, documenting processes that assure customers and regulatory agencies that ADHP electronic systems containing Pb-free solder, piece parts, and PBs will satisfy the applicable requirements for performance, reliability, airworthiness, safety, and certifiability throughout the specified life of performance. It is intended to communicate requirements for a Pb-free Control Plan (LFCP), hereinafter referred to as the Plan, and to assist the Plan Owners in the development of their own Plans. The Plan documents the Plan Owner’s processes that assure their customers, and all other stakeholders that the Plan Owner’s products will continue to meet their requirements, given the risks stated in the Introduction. This standard does not contain detailed descriptions of the processes to be documented but lists high-level requirements for such processes, and areas of concern to the ADHP industries that must be addressed by the processes.