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
– 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

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

– 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
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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.

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.
– 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

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
reliably accomplished .
___________
http://www.solder.net/leadfreerepair.asp

– 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

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

– 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)

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 liquid state. Below liquidus, the mixture will be partly or entirely solid
3.23
measling
is a condition that occurs in laminated base material in which internal glass fibers are
separated from the resin at the weave intersection. This condition manifests itself in the form
of discrete white spots or “crosses” that are below the surface of the base material
3.24
organic solderability preservative
OSP
is a thin organic compound that selectively bonds with Copper (Cu) used to preserve the
solderability of bare Cu on printed wiring boards (PWB's)
3.25
organizational level maintenance
O
is maintenance normally performed by an operating unit on a day-to-day basis in support of its
own operations. Organizational-level maintenance typically includes "inspections," "servicing,"
"handling," and "preventive maintenance” and is limited to the replacement of electronics
assemblies at the WRA and LRU (black box) level of major aircraft and engine components.
There can be an exception is where troubleshooting and piece parts level repair are
accomplished at the Organizational level
3.26
Pb-Free tin
is any Tin alloy with <3 % Lead (Pb) content by weight. This means that some Pb-Free
finishes other than Pb-Free Tin, such as Tin-Bismuth and Tin-Copper, are considered to be
“Tin” for the purposes of this document. Many of these alloys have not been assessed for
whiskering behavior
3.27
Pb-Free tin finish
is Pb-Free Tin final finishes or underplating either external or internal to a device, PWB, or
other hardware. This includes all terminations and surfaces, even those coated,
encapsulated, or otherwise not exposed. It may include finishes on electrical piece parts,

– 12 – PAS 62647-23  IEC:2011(E)
mechanical piece parts, and PWBs. It does not include Pb-Free bulk solders, assembly
materials, solder balls, or those devices where the Pb-Free Tin finish has been completely
replaced
3.28
piece part
is an electronic component that is not normally disassembled without destruction and is
normally attached to a printed wiring board to perform an electrical function
3.29
procurement
is the process of obtaining services, supplies, and equipment
3.30
plated-through-hole
PTH
is a Cu-plated hole in a circuit board used to accommodate a through-hole piece part
termination
3.31
quality assurance
is a planned and systematic set of activities to ensure that requirements are clearly
established and that the defined process or product complies with these requirements
3.32
repair
is the act of restoring the functional capability of a defective article in a manner that precludes
compliance of the article with applicable drawings or specifications
3.33
rework
is the act of reprocessing non-complying articles, through the use of original or equivalent
processing in a manner that assures full compliance of the article with applicable drawings or
specifications
3.34
rework/repair
is the term used in this PAS where the processes identified apply to either rework or repair
3.35
SAC (Tin Silver Copper)
refers to the family Pb-Free alloys containing Tin (Sn), Silver (Ag), and Copper (Cu) used in
surface mount technology or sometimes in wave solder processes. The alloys typically have a
composition near the eutectic (Sn3.5Ag0.9Cu)
3.36
shop replaceable assembly
SRA
is a component assembly inside a black box (LRU or WRA) typically consisting of individually
replaceable circuit cards
3.37
shop replaceable unit
SRU
is a component assembly inside a black box (LRU or WRA) typically consisting of individually
replaceable circuit cards
PAS 62647-23  IEC:2011(E) – 13 –
3.38
should
indicates that, among several possibilities, one is recommended as particularly suitable,
without mentioning or excluding others; or that a certain course of action is preferred but not
necessarily required; or that (in the negative form) a certain course of action is deprecated but
not prohibited
3.39
SnCu (Tin Copper)
solder or alloy refers to Pb-Free alloys that are comprised of Tin-Copper (Sn-0.7Cu)
3.40
SnCuNi (Tin Copper Nickel)
solder or alloy refers to Pb-Free Tin-Copper with trace Nickel concentration alloy
(Sn0.7Cu0.05Ni). Some formulations also include other minor additions such as Germanium
(Ge)
3.41
SnPb (Tin Lead)
solder or alloy refers to Tin-Lead alloys at or near the eutectic composition (63Sn37Pb)
3.42
soldered assembly
is an assembly of two or more basic parts interconnected by a solder alloy. A Pb-based
soldered assembly is one in which the solder alloys are solely Pb-based. A Pb-Free soldered
assembly is one in which the solder alloys are solely Pb-Free
3.43
system
is one or more units that perform electrical function(s)
3.44
termination
is the term used in this document to identify the area to be soldered of the piece part
termination, castellations, or metallized surface(s) of an electronic device
3.45
ternary alloy
is a solder alloy containing three component metals
3.46
Tg
refers to the glass transition temperature of laminate material
3.47
High Tg
refers to the glass transition temperature of laminate material ≥ 338°F (170 °C)
3.48
tin whisker
is a spontaneous crystal growth that emanates from a Sn surface. They may be cylindrical,
kinked, or twisted. Typically they have an aspect ratio (length/width) greater than two, with
shorter growths referred to as nodules or odd-shaped eruptions. See IEC/PAS 62647-2
(GEIA-STD-0005-2) for further description of Tin Whiskers and their physical attributes

– 14 – PAS 62647-23  IEC:2011(E)
3.49
underplating
is the plating made as a base of a surface overplating usually required as a barrier to prevent
leeching of two dissimilar metals into one another
3.50
weapons replaceable assembly
WRA
is a black box of electronics, replaced at the flight-line level
3.51
X-ray fluorescence
XRF
is a form of metallurgical analysis that uses x-rays to identify composition of solder alloys and
termination finishes
4 Symbols and abbreviated terms
Ag Silver
AHP Aerospace and High Performance
Au Gold
Bi Bismuth
BGA Ball Grid Array
C4 Ball Controlled Collapse Component Connection Ball
CALCE Center for Advanced Life Cycle Engineering
CBGA Ceramic Ball Grid Array
CCA Circuit Card Assembly
CM Contract Manufacturer
CTE Coefficient of Thermal Expansion
Cu Copper
D Depot Maintenance Level
ENIG Electroless Nickel Immersion Gold
EU European Union
Fe Iron
I Intermediate Maintenance Level
ImAg Immersion Silver
In Indium
iNEMI International Electronics Manufacturing Initiative
JG-PP Joint Group on Pollution Prevention
GEIA Government Electronics and Information Technology Association
HASL Hot Air Solder Leveling
LFCP Lead-Free Control Plan
LRU Line Replaceable Unit
mm Millimeter
MSD Moisture Sensitive Devices
Ni Nickel
O Organizational Maintenance Level
OEM Original Equipment Manufacturer
OSP Organic Solderability Preservative
Pb Lead
Pb-Free Lead-Free
PCB Printed Circuit Board (also known as PWB)
Pd Palladium
PTH Plated-Through-Hole
PWB Printed Wiring Board (also known as PCB)
QFN Quad Flat No Leads package
RoHS 2002/95/EC Restriction of Hazardous Substances
SnAgCu Pb-Free solder alloy of Tin (Sn), Silver (Ag), and Copper (Cu)
SAC Pb-Free solder alloy of Tin (Sn), Silver (Ag), and Copper (Cu)
SACB Pb-Free solder alloy of Tin (Sn), Silver (Ag), Copper (Cu) and

PAS 62647-23  IEC:2011(E) – 15 –
Bismuth (Bi)
SMT Surface Mount Technology
SMTA Surface Mount Technology Association
Sn Tin
SnBi Pb-Free solder alloy of Tin (Sn) and Bismuth (Bi)
SnCu Pb-Free solder alloy of Tin (Sn) and Copper (Cu)
SnCuNi Pb-Free solder alloy of Tin (Sn), Copper (Cu), and Nickel (Ni)
SnPb Tin/Lead (normally 63 % Tin / 37 % Lead)
SRA Shop Replaceable Assembly
SRU Shop Replaceable Unit
WEEE 2002/96/EC Waste Electrical and Electronic Equipment
WRA Weapons Replaceable Assembly
XRF X-Ray Fluorescence
5 Pb-Free Concerns
The transition from SnPb to Pb-Free rework/repair has a variety of concerns.
IEC/PAS 62647-1 (GEIA-STD-0005-1) identifies five major areas that must be considered.
Those areas include reliability, configuration control, risk management, effects of Sn in the
system, and rework/repair. If the concerns in the first four areas are not properly identified,
planned for, assessed, managed, and documented, rework/repair of those assemblies
becomes extremely difficult. A quality Lead-Free Control Plan (LFCP) will identify and mitigate
potential concern areas and provide the technician with clear requirements for rework/repair.
5.1 Reliability
The program manager should understand how the transition to Pb-Free solder and piece part
termination finishes or mixing SnPb and Pb-Free solders may affect the reliability of the
assembly. Additionally, the effects on package types/geometry, piece part termination finish,
and laminate materials and finishes, must be clearly understood when authorizing and
introducing the use of alternate materials.
The reliability of the original solder joint is dependent upon the integrity of the solder in the
joint and the metallurgical interfaces to the terminations and PWB lands. The solder joint
reliability is influenced by the final solder alloy composition and microstructure, the shape of
the solder surface and the termination-to-solder interfacial strength. The initial composition of
the solder used to form the joint is typically modified to some extent during the soldering
process as the pad metallization and finish are dissolved into the solder joint. The amount of
dissolved piece part and pad metal typically does not significantly alter the initial alloy
composition. The exceptions to this rule are Ball Grid Array (BGA) type devices where the ball
solder volume represents a significant amount of the total solder volume, and pad interface
finish elements that have a tendency to segregate to either the piece part or the PWB pad
interfaces or grain boundaries such as Gold (Au) and Bismuth (Bi) alloys contaminated with
trace amounts of Pb.
5.1.1 Mixed metallurgy reliability
In a reworked/repaired solder joint, metallurgy mixing is a major reliability concern to
electronics equipment suppliers and users. As SnPb BGA ball metallurgy and SnPb finished
piece parts are being quickly replaced by Pb-Free alternatives, Pb-Free solders may be either
intentionally or unintentionally mixed with SnPb solder and/or Pb bearing finishes throughout
their service life and during repair activity. Annex A lists a number of the termination finishes
that potentially could be encountered. Annex B provides a summary of the Tin Whisker
propensity for the various elemental additions to Sn.
5.1.1.1 Pb-Free terminations in SnPb joints
One result of the WEEE/RoHS directives and the responding piece part fabricator initiative is
the introduction of piece parts with Pb-Free surface finish terminations into existing traditional
SnPb soldering processes. The variety and compositions of the Pb-Free surface finishes
being delivered into the electronics industry is extensive. Many of these piece parts materials

– 16 – PAS 62647-23  IEC:2011(E)
will find their way into the inventory of aerospace and Defence assembly processes under
government acquisition reform initiatives. Electronics assembly design teams must be
knowledgeable on the potential impact of the Pb-Free surface finish piece part and pad
interface on solder joint integrity. The impact is not universal—solder joint integrity
degradation can range from slight to severe depending upon the use environment.
5.1.1.2 SnPb terminations in Pb-free joints
The introduction of SnPb terminated piece parts in a Pb-Free solder system is likely during
the early stages of Pb-Free assembly processing while the piece part supply stream still
contains SnPb terminated piece parts.
5.1.1.3 Bismuth (Bi)
The addition of Bi to SAC has been shown to yield a solder joint that has improved durability.
However, the principal concern is that when Bi and Pb are intermixed, a low melting point
SnBiPb Ternary alloy can form, particularly at the grain boundaries. The melting point of the
ternary alloy is 205°F (96 °C) and the solder can lose strength during hot mission
environments.
5.1.1.3.1 SnPb finish in SnBi solder alloy
Trace amounts of Pb were found to have a detrimental effect (e.g., Kirkendall voiding,
embrittlement, etc.) on solder life of Bi containing solders (Sn91,8Ag3,4Bi4,8 and
Sn92,3Ag3,4Cu1,0Bi3,3) and resulted in catastrophic failure of Sn58Bi solder joints. Since
AHP products have a 20 year service life, a repair depot infrastructure will have both SnPb
and Pb-Free alloy configurations for a significant amount of time.
5.1.1.3.2 SnBi finish in SnPb solder alloy
Bismuth bearing solder alloys are noted as a concern in IEC/PAS 62647-1 (GEIA STD- 0005-
1). However, there are some piece parts that are only available with a SnBi termination finish.
Preliminary testing suggests that trace amounts of Bi in SnPb joints are not detrimental to
solder life. For further information see IEC/PAS 62647-22 (GEIA-HB-0005-2).
5.2 Configuration management
The need for configuration management is paramount to the Pb-Free transition. Studies have
shown that mixing SnPb and Pb-Free solders or the mixing of Pb-Free solders of different
alloys and/or piece parts (solders or finishes of different alloys) may have detrimental impact
on the long-term reliability under high stress (e.g., military, commercial aerospace, or space)
environments. All parties involved in the rework/repair process should understand the
appropriate configuration controls (e.g., traceability) that are necessary for the program’s
environment.
There are applications within AHP systems where acceptance of alternate materials may be
acceptable. Any deviation from the assembly drawings must be approved and promulgated by
the responsible engineering authority or the delegated representative.
Introduction of alternate solder alloys and piece part termination finishes that deviate from the
assembly drawing may or may not affect the user’s configuration management process. The
use of Pb-Free termination finishes in SnPb assemblies may not be considered a
configuration change. However, the use of alternate solder alloys on that assembly may result
in a configuration change. The authorized deviation to assembly drawing requirements should
be accompanied by clear, well documented rework/repair procedures.
NOTE Commercial part Suppliers may or may not modify part numbers when converting
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