IEC PAS 62647-23:2011

IEC/PAS 62647-23
®

Edition 1.0 2011-07
PUBLICLY AVAILABLE
SPECIFICATION
PRE-STANDARD
colour
inside

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



IEC/PAS 62647-23:2011(E)

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IEC/PAS 62647-23
®

Edition 1.0 2011-07
PUBLICLY AVAILABLE
SPECIFICATION

PRE-STANDARD
colour
inside

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


INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
ICS 03.100.50; 31.020; 49.060 ISBN 978-2-88912-568-5
® Registered trademark of the International Electrotechnical Commission

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– 2 – PAS 62647-23  IEC:2011(E)
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 Symbols and abbreviated terms . 14
5 Pb-Free Concerns . 15
5.1 Reliability . 15
5.1.1 Mixed metallurgy reliability . 15
5.2 Configuration management . 16
5.3 Risk management . 17
5.4 Tin whiskers . 17
5.5 Copper dissolution (erosion) . 17
6 Materials . 17
6.1 Solder . 17
6.1.1 Solder alloys. 17
6.1.2 Solder forms . 18
6.2 Fluxes . 18
6.3 Piece parts . 19
6.3.1 Termination finishes . 19
6.3.2 Area arrays (BGA, CSP, etc.) . 19
6.4 Printed circuit boards . 19
6.4.1 Laminate material . 19
6.4.2 Surface finish . 20
6.5 Conformal coatings . 20
7 Soldering equipment . 20
7.1 Hand soldering equipment . 21
7.1.1 General hand soldering equipment considerations . 21
7.1.2 Tip selection . 21
7.1.3 Soldering iron tip life. 21
7.2 Fountain soldering . 22
7.3 Convective soldering equipment . 24
7.3.1 Thermal profile issues . 24
8 General rework/repair considerations . 24
8.1 Rework/repair procedure order of precedence . 25
8.2 Technician training . 25
8.3 Pb-Free rework/repair considerations . 25
8.3.1 General process considerations . 26
8.3.2 Solder processing considerations . 26
8.3.3 Flux considerations . 26
9 Pre-rework/repair processes . 27
9.1 Alloy identification . 27
9.1.1 IPC/JEDEC J-STD-609 . 27
9.1.2 X-Ray fluorescence (XRF) . 29
9.1.3 Pb swabs . 29

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PAS 62647-23  IEC:2011(E) – 3 –
9.2 Piece part and CCA preparation . 29
9.2.1 Piece part preparation . 29
9.2.2 CCA preparation . 30
10 Rework/repair processes . 30
10.1 Conductive Hand Soldering . 30
10.2 Convective soldering process . 32
10.2.1 Solder paste handling . 32
10.2.2 Paste printing . 32
10.2.3 Reflow process . 32
11 Post-Rework/Repair Processes . 34
11.1 Cleaning . 34
11.2 Inspection . 34
11.3 Reapplication of Conformal Coating . 34
Annex A (informative) Termination Finishes . 35
Annex B (informative) Tin whiskers . 37
Bibliography . 42

Figure 1 – Soldering iron tip construction . 22
Figure 2 – Worn soldering iron tip . 22
Figure 3 – Copper dissolution . 23

Table 1 – Assembly and piece part marking methods . 28
Table A.1 – Piece-part terminal and BGA ball metallization solder process compatibility
risk (see IEC/PAS 62647-22 (GEIA-HB-0005-2)) . 35
Table B.1 – Tin whisker information (see IEC/PAS 62647-22 (GEIA-HB-0005-2)) . 38
Table B.2 – Piece part termination tin whisker risk (see IEC/PAS 62647-22
(GEIA-HB-0005-2)) . 40

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– 4 – PAS 62647-23  IEC:2011(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

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


FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
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Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
A PAS is a technical specification not fulfilling the requirements for a standard, but made
available to the public.
IEC-PAS 62647-23 has been processed by IEC technical committee 107: Process
management for avionics.
The text of this PAS is based on the This PAS was approved for
following document: publication by the P-members of the
committee concerned as indicated in
the following document
Draft PAS Report on voting
107/132/PAS 107/140A/RVD
Following publication of this PAS, which is a pre-standard publication, the technical committee
or subcommittee concerned may transform it into an International Standard.

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PAS 62647-23  IEC:2011(E) – 5 –
This PAS shall remain valid for an initial maximum period of 3 years starting from the
publication date. The validity may be extended for a single 3-year period, following which it
shall be revised to become another type of normative document, or shall be withdrawn.
This PAS is based on GEIA-HB-0005-3 and is published as a double logo PAS. GEIA,
Government Electronics and Information Technology Association, has been transformed into
TechAmerica Association.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.

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– 6 – PAS 62647-23  IEC:2011(E)
INTRODUCTION
0.1 General
This PAS is intended to facilitate the development of procedures and processes for use when
undertaking the rework/repair of Aerospace and High Performance (AHP) electronics systems.
It is intended to contain sufficient information to support the processing of equipment that
incorporates either Tin-Lead (SnPb) or Lead-Free (Pb Free) solder alloy, SnPb or Pb-Free
piece parts and printed wiring board finishes, or a combination thereof.
This PAS may be used by Original Equipment Manufacturers (OEMs), contract manufacturers
(CMs) and commercial depots. This document may also be used by personnel performing
rework/repair at the Organizational (O) level, Intermediate (I) back shop level, and Depot (D)
overhaul level.
The purpose of this Working Group is to generate a series of industry standards and
documents intended to facilitate the maintenance of suitable equipment quality and reliability
standards within the AHP industries during the general industry migration to Pb-Free.
This PAS is intended to work in concert with IEC/PAS 62647-1 (GEIA-STD-0005-1), IEC/PAS
62647-2 (GEIA-STD-0005-2), and IEC/PAS 62647-21 (GEIA-HB-0005-1).
This PAS may be referenced in proposals, requests for proposals, work statements, contracts,
and other aerospace and high performance industry documents.
0.2 Pb-Free and Legislation
Recent Directives and Legislation by Nations around the world mandated elimination of Lead
and other hazardous material usage in sectors of the electronics industry by 2006. In
electronics, Lead (Pb) has been a primary component of Tin-Lead (SnPb) solder used in piece
part attachment and PWB finishes for over 50 years, and more recently in the solder spheres
for attachment of Ball-Grid-Array (BGA) packages. Since there is no “drop-in” replacement for
SnPb solder alloys, multiple Pb-Free alloys have emerged in the manufacturing industry as
replacements. These multiple replacement alloys are being used in Printed Wiring Boards
(PWB) / Printed Circuit Boards (PCB) finish, piece part termination finish and as solder alloys,
leaving the rework/repair technician with literally hundreds of possible combinations of
metallurgy in the finished repair.
The majority of the Pb-Free alloys being considered have melting temperatures 61 °F to 79°F
(34 °C to 44 °C) higher than that of SnPb eutectic solder. These higher Pb-Free processing
temperatures require significant changes to convective rework/repair procedures and minor
adjustments in conductive hand soldering procedures to ensure that quality products will be
produced.
Another major concern is the potential re-emergence of Tin Whiskers as an additional
equipment failure mechanism. Tin Whiskers are electrically conductive, crystalline structures
of Sn that grow under compressive force from surfaces where Sn [especially electroplated Sn]
is used as a final finish. Tin Whiskers have been observed to grow to lengths of several
millimeters (mm). Numerous electronic system failures have been attributed to short circuits
caused by Tin Whiskers that bridge closely-spaced circuit elements. Tin Whiskers have been
successfully suppressed for decades by the addition of Pb to Sn plating used in high reliability
applications. With the global shift to Pb-Free solders, Tin Whiskers have re-emerged as a
major concern to reliability. IEC/PAS 62647-2 (GEIA-STD-0005-02) further discusses Tin
Whisker issues and mitigation techniques.
This document will provide guidance to the organization performing rework/repair on various
combinations of SnPb, Pb-Free and mixed technology assemblies likely to be seen as the
global transition to Pb-Free solder continues. The organization typically consists of program

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PAS 62647-23  IEC:2011(E) – 7 –
management, procurement, process engineering, bench technician, and quality assurance
personnel.
Procedurally, conductive Pb-Free rework/repair is similar to that of SnPb. However,
adjustments must be made to accommodate the generally poorer wetting ability of Pb-Free
solders as well as differences in appearance and inspection criteria. Convective rework/repair
will require redevelopment of profiles to accommodate the higher melting temperature of Pb-
Free alloys. Also, Pb-Free rework/repair has a tighter process window leaving a smaller
margin for error in comparison to SnPb. With the proper materials, preparation, skill, and the
use of fundamentally sound procedures, Pb-Free rework/repair can be successfully and
1
reliably accomplished .

___________
1
 http://www.solder.net/leadfreerepair.asp

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– 8 – PAS 62647-23  IEC:2011(E)
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 PAS 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 PAS 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 PAS focuses on the removal and replacement of piece parts. For the purposes of this
PAS, the term “Rework/Repair” is used as applicable.
NOTE The information contained within this PAS is based on the current knowledge of the industry at the time of
publication. Due to the rapid changing knowledge base, this PAS should be used for guidance only.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC/PAS 62647-1, Process management for avionics – Aerospace and defence electronics
systems containing lead free solder – Part 1: Lead-free management
IEC/PAS 62647-2, Process management for avionics – Aerospace and defence electronics
systems containing lead-free solder – Part 2: Mitigation of the deleterious effects of tin
IEC/PAS 62647-21, Process management for avionics – Aerospace and defence electronic
systems containing lead-free solder – Part 21: Program management – System engineering
guidelines for managing the transition to lead-free electronics
IEC/PAS 62647-22, Process management for avionics – Aerospace and defence electronic
systems containing lead-free solder – Part 21: Technical guidelines
GEIA-STD-0005-1, Performance Standard for Aerospace and High Performance Electronic
Systems Containing Lead-free Solder
GEIA-STD-0005-2, Standard for mitigating the effects of tin in aerospace and high
performance electronic systems
GEIA-HB-0005-1, Program management / Systems engineering guidelines for managing the
transition to lead-free electronics
GEIA-HB-0005-2, Technical guidelines for aerospace and high performance electronic
systems containing lead-free solder

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PAS 62647-23  IEC:2011(E) – 9 –
3 Terms and definitions
For purposes of this PAS, the following terms and definitions apply:
3.1
alloy composition
is stated as weight in percent. For instance 63Sn-37Pb corresponds to a mixture of 63 % by
weight of Tin (Sn) and 37 % by weight of Lead (Pb)
3.2
assemblies
are electronic items that require electrical attachments, including soldering of wires or piece
part terminations; examples include circuit cards and wire harnesses
3.3
backwards compatibility
refers to Pb-Free materials compatible with a SnPb process
3.4
ball grid array
BGA
is a surface mount package type that uses a grid of solder balls arranged in an array to
provide direct electrical interconnection between the part substrate and the circuit board
3.5
coefficient of thermal expansion
CTE
is the linear dimensional change of a material per unit change in temperature
3.6
conductive
refers to the use of a contact heat source such as a soldering iron, hot bar, or resistance to
transfer heat to the assembly
3.7
convective
refers to the use of a non-contact heat source usually heated air, Nitrogen or infrared light to
transfer heat to the assembly
3.8
copper dissolution
is the 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
3.9
critical
item or function, if defective, will result in the system’s inability to retain operational capability,
meet primary objective, or affect safety
3.10
customer
refers to an entity or organization that (a) integrates a piece part, soldered assembly, unit, or
system into a higher level system, (b) operates the higher level system, or (c) certifies the
system for use. For example, this may include end item users, integrators, regulatory
agencies, operators, original equipment manufacturers (OEMs), and Subcontractors

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– 10 – PAS 62647-23  IEC:2011(E)
3.11
delamination
is a 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
3.12
depot level maintenance
D
is 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. Depot maintenance serves to support lower categories of
maintenance by providing technical assistance and performing that maintenance beyond their
responsibility
3.13
dissolution
is the process in which one substance is dissolved in another by chemical action
3.14
electroless nickel / immersion gold
ENIG
is a two technology process for the application of a desired finish where Nickel is applied
using Electroless plating, requiring the presence of a proper reducing agent in a plating bath
that converts the metal salts into metal and deposits them onto the substrate. The immersion
plating process deposits a new metal surface (Gold) by replacing the base metal; in this
process, plating stops when the surface of the base metal is completely covered, thus only a
limited coating thickness can be obtained through the immersion process. The control of the
kinetics associated with both processes is vital to plating results
3.15
eutectic (Solder)
is the alloy composition at which a solder alloy melts/freezes completely without going
through a pasty (partially solid) phase
3.16
high performance system
requires continued performance or performance on demand, or equipment down time cannot
be tolerated, or end-use environment may be uncommonly harsh, and the equipment must
function when required, such as life support or other critical systems
3.17
intermediate level maintenance
I
includes limited repair of commodity-orientated piece parts and end items, job shop, bay, and
production line operations for special mission requirements; repair of printed circuit boards,
software maintenance, and fabrication or manufacture of repair parts, assemblies, piece
parts. Intermediate maintenance consists of repair of aircraft and engine components, WRAs,
and LRUs forwarded to the Intermediate level by the organizational level flight-line activities.
WRA and LRU repair is accomplished by the removal, troubleshooting, and replacement of
faulty SRA and SRU, pieces, and parts within the WRA/LRU
3.18
lead
Pb
in this PAS, if the element “Lead” is implied, it will be stated as either Pb or as Lead (Pb)

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PAS 62647-23  IEC:2011(E) – 11 –
3.19
lead-free
Pb-Free
is defined as less than 0,1 % by weight of Pb in accordance with Waste Electrical and
Electronic Equipment (WEEE) guidelines
3.20
lead-free control plan
LFCP
refers to an aerospace or military system Supplier’s document that defines the processes that
assure the plan owners, their Customers, and all other stakeholders that aerospace and high
performance high-reliability electronics systems containing Pb-Free solder will continue to be
reliable, safe, producible, affordable, and supportable. Technical guidance for a LFCP can be
found in IEC/PAS 62647-21 (GEIA-HB-0005-1)
3.21
line replaceable unit
LRU
is a black box of electronics removed and replaced at the flight-line level
3.22
liquidus
is the minimum temperature at which all components of a mixture (such as an alloy) can be in
a
...