Process management for avionics—Aerospace and defence electronic systems containing lead-free solder—Part 23: Rework and repair guidance to address the implications of lead-free electronics and mixed assemblies
Process management for avionics - Aerospace and defence electronic systems containing lead-free solder - Part 23: Rework and repair guidance to address the implications of lead-free electronics and mixed assemblies
1 Scope
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 Sn-Pb 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 defined in 3.1.29 and 3.1.30.
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.
Note 1: For the purposes of this document, if the element “lead” is implied, it will be stated either as Pb, as lead (Pb), or as tin-lead. If a piece part terminal or termination “lead” is referred to, such as in a flat pack or a dual-inline package, the nomenclature lead/terminal or lead-terminal will be used.
Note 2: Processes identified in the document apply to either rework or repair.
This document may be used by other high-performance and high-reliability industries, at their discretion.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
IEC/TS 62647-1:2012, Process management for avionics - Aerospace and defence electronics systems containing lead free solder - Part 1: Preparation for a lead-free control plan
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
alloy composition
whole ingredients of an alloy whose weight is defined in percent
Note: For instance 63Sn-37Pb corresponds to a mixture of 63 % by weight of tin (Sn) and 37 % by weight of lead (Pb).
[SOURCE: GB/Z 41275.22-2023, 3.1.1]
3.1.2
assemblies
electronic items that require electrical attachments, including soldering of wires or component terminations
EXAMPLE: Circuit cards and wire harnesses.
[SOURCE: IEC/TS 62647-1:2012, 3.1]
3.1.3
backwards compatibility
Pb-free materials compatible with an Sn-Pb process
3.1.4
coefficient of thermal expansion; CTE
degree of expansion of a material divided by the change in temperature
Note: PCB/PWB CTE (x-y axis) is measured in the direction in the plane of the piece part mounting surface and is used to quantify the stresses in the solder joint arising from the differences in CTE between the piece parts and the PCB/PWB during thermal cycling. CTE (z axis) is measured in the “thickness” direction and is typically used to quantify plated through hole stress.
[SOURCE: GB/Z 41275.22-2023, 3.1.8]
3.1.5
conductive
use of a contact heat source such as a soldering iron, hot bar, or resistance to transfer heat to the assembly
3.1.6
convective
use of a non-contact heat source, usually heated air, nitrogen or infrared light to transfer heat to the assembly
3.1.7
copper dissolution
excessive loss of copper from plated through hole barrels and pads caused by wave or solder fountain processing primarily with high tin (Sn) content solders
3.1.8
critical
state of an item or function, which if defective, will result in the system’s inability to retain operational capability, meet primary objective, or affect safety
3.1.9
customer
entity or organization that
(a) integrates a piece part, soldered assembly, unit, or system into a higher control level system,
(b) operates the higher control level system, or
(c) certifies the system for use
EXAMPLE: This may include end item users, integrators, regulatory agencies, operators, original equipment manufacturers (OEMs), and subcontractors.
[SOURCE: IEC/TS 62647-1:2012, 3.5]
3.1.10
delamination
separation between plies within a base material, between a base material and a conductive foil, or any other planar separation with a printed board that may propagate under thermal stress
3.1.11
depot level maintenance
D
maintenance requiring major overhaul or a complete rebuilding of parts, assemblies, subassemblies, and end items, including the manufacture of parts, modifications, testing, and reclamation as required.
Note: Depot maintenance serves to support lower categories of maintenance by providing technical assistance and performing that maintenance beyond their responsibility.
3.1.12
dissolution
process in which one substance is dissolved in another by chemical action
3.1.13
eutectic
mixture of two or more metals at a composition that has the lowest melting point, and where the phases simultaneously crystallize from molten solution at this temperature
Note: A non-eutectic mixture will exhibit a pasty range during cooling where both liquid and solid phases are present prior to reaching the mixture’s solidus temperature.
[SOURCE: GB/Z 41275.22-2023, 3.1.12]
3.1.14
high performance
continued performance or performance on demand where an application (product, equipment, electronics, system, program) down time cannot be tolerated in an end-use environment which can be uncommonly harsh, and the application must function when required
EXAMPLE: Examples of high performance applications are life support or other critical systems.
[SOURCE: IEC/TS 62647-1:2012, 3.7]
