IEC PAS 62647-2:2011

IEC/PAS 62647-2
®

Edition 1.0 2011-06
PUBLICLY AVAILABLE
SPECIFICATION
PRE-STANDARD

Process management for avionics – Aerospace and defence electronic systems
containing lead-free solder –
Part 2: Mitigation of the deleterious effects of tin



IEC/PAS 62647-2:2011(E)

---------------------- Page: 1 ----------------------
THIS PUBLICATION IS COPYRIGHT PROTECTED
Copyright © 2011 IEC, Geneva, Switzerland


All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester.
If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication,
please contact the address below or your local IEC member National Committee for further information.

IEC Central Office
3, rue de Varembé
CH-1211 Geneva 20
Switzerland
Email: inmail@iec.ch
Web: www.iec.ch

About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.
 Catalogue of IEC publications: www.iec.ch/searchpub
The IEC on-line Catalogue enables you to search by a variety of criteria (reference number, text, technical committee,…).
It also gives information on projects, withdrawn and replaced publications.
 IEC Just Published: www.iec.ch/online_news/justpub
Stay up to date on all new IEC publications. Just Published details twice a month all new publications released. Available
on-line and also by email.
 Electropedia: www.electropedia.org
The world's leading online dictionary of electronic and electrical terms containing more than 20 000 terms and definitions
in English and French, with equivalent terms in additional languages. Also known as the International Electrotechnical
Vocabulary online.
 Customer Service Centre: www.iec.ch/webstore/custserv
If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service
Centre FAQ or contact us:
Email: csc@iec.ch
Tel.: +41 22 919 02 11
Fax: +41 22 919 03 00

---------------------- Page: 2 ----------------------
IEC/PAS 62647-2
®

Edition 1.0 2011-06
PUBLICLY AVAILABLE
SPECIFICATION

PRE-STANDARD

Process management for avionics – Aerospace and defence electronic systems
containing lead-free solder –
Part 2: Mitigation of the deleterious effects of tin


INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
W
ICS 03.100.50; 31.020; 49.060 ISBN 978-2-88912-202-8
® Registered trademark of the International Electrotechnical Commission

---------------------- Page: 3 ----------------------
– 2 – PAS 62647-2  IEC:2011(E)
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 7
2 Terms and definitions . 7
3 Requirements . 9
3.1 Determination of levels . 9
3.2 Requirements for control levels . 9
3.2.1 General . 9
3.2.2 Control Level 1 requirements . 10
3.2.3 Control Level 2A requirements . 10
3.2.4 Control Level 2B requirements . 11
3.2.5 Control Level 2C requirements . 12
3.2.6 Control Level 3 requirements . 12
3.3 Implementation requirements . 13
3.3.1 Documentation of uses of Pb-free tin . 13
3.3.2 Detecting and controlling Pb-free tin finish introduction . 14
3.3.3 Methods for mitigating impact of Pb-free tin (applies to Level 2B,
Level 2C) . 14
3.3.4 Methods for analysis and evaluation of tests and mitigations for tin
whisker risk and mitigation effectiveness . 16
Annex A (informative)  Guidance on control levels, risk assessment, and mitigation
evaluation . 18
Annex B (informative) Technical guide on tin whiskers . 23
Annex C (informative) Technical guide on detection methods, mitigation methods, and

methods for limiting impact of tin . 26
Bibliography . 33

---------------------- Page: 4 ----------------------
PAS 62647-2  IEC:2011(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

PROCESS MANAGEMENT FOR AVIONICS –
AEROSPACE AND DEFENCE ELECTRONIC SYSTEMS
CONTAINING LEAD-FREE SOLDER –

Part 2: Mitigation of the deleterious effects of tin


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,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
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 62647-2 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
107/108/PAS 107/116A/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.

---------------------- Page: 5 ----------------------
– 4 – PAS 62647-2  IEC:2011(E)
This PAS is based on GEIA-STD-0005-2 and is published as a double logo PAS. GEIA,
Government Electronics and Information Technology Association, has been transformed into
TechAmerica Association.
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 period up to a maximum of
3 years, at the end of which it shall be published as another type of normative document, or
shall be withdrawn.
A bilingual version of this publication may be issued at a later date.

---------------------- Page: 6 ----------------------
PAS 62647-2  IEC:2011(E) – 5 –
INTRODUCTION
This PAS is intended for use by those procuring, designing, building or repairing electronic
assemblies that will use items with Pb-free tin finishes to document processes they use to
assure performance, reliability, airworthiness, safety, and certifiability of those assemblies. It
provides a framework to communicate and agree on the processes to be used to control and
mitigate the use of Pb-free tin in these applications.
The Aerospace Industries Association (AIA), the Avionics Maintenance Conference (AMC),
and Government Electronics and Information Technology Association (GEIA) formed a joint
working group with the express purpose of generating a series of industry standards
documents for the use and handling of Pb-free solder, piece parts, and boards in aerospace
and high performance applications. This PAS – originally published as GEIA-STD-0005-2 –
was prepared by that group. It was balloted and approved by GEIA G-12 (Solid State
Subcommittee) and GEIA Avionics Management Conference (AMC Subcommittee). According
agreements between GEIA and IEC, this PAS is extended at international level.
This PAS is intended to work in concert with IEC/PAS 62647-1 (based originally on GEIA-
1 2
STD-0005-1), GEIA-HB-0005-1 , GEIA-HB-0005-2 . This PAS may be referenced in
proposals, requests for proposals, work statements, contracts, and other documents. It may
be used as a stand-alone standard or as part of compliance with IEC/PAS 62647-1.
This PAS addresses the risk of tin whiskers. However, the state of research into tin whisker
risk still does not allow accurate quantitative estimates of the risk and reliability. It defines
three baseline control levels that detail the amount of attention that should be paid to the risk
of tin whiskers: no restrictions on tin use, some restrictions on tin use, and prohibition of tin
use.
There are three informative annexes in this PAS:
– Annex A provides guidance on selecting control levels and performing risk
assessments;
– Annex B describes mechanisms of formation, properties, and potential deleterious
effects of tin whiskers;
– Annex C provides some background on various mitigation methods.
Due to a variety of real and potential health issues, many constituent materials used in the
production of electronic products have come under scrutiny. The European Union (EU) has
enacted two directives; 2002/95/EC Restriction of Hazardous Substances (RoHS) and
2002/96/EC Waste Electrical and Electronic Equipment (WEEE) that restrict or eliminate the
use of various substances in a variety of products that are produced after July 2006. One of
the key materials restricted is lead (Pb), which is widely used in electronic solder and
electronic piece part terminations, and printed wiring boards. While these regulations may
appear to only affect products for sale in the EU, due to the reduced market share of the
Aerospace and High Performance Industry in electronics, many of the lower tier suppliers are
changing their products because their primary market is consumer electronics. Additionally,
several U.S. states have enacted similar “green” laws, and many Asian electronics
manufacturers have recently announced completely “green” product lines.
The restriction of Pb use has generated a transition by many piece part and board suppliers
from tin-lead (Sn-Pb) surface finishes to pure tin or other Pb-free finishes. Lead-free tin
finishes can be susceptible to the spontaneous growth of crystal structures known as “tin
whiskers” which can cause electrical failures, ranging from parametric deviations to
catastrophic short circuits, and may interfere with sensitive optical surfaces or the movement
___________
1
 A future IEC/PAS 62647-21, based on GEIA-HB-0005-1, is in preparation.
2
 A future IEC/PAS 62647-22, based on GEIA-HB-0005-2, is in preparation.

---------------------- Page: 7 ----------------------
– 6 – PAS 62647-2  IEC:2011(E)
of Micro-ElectroMechanical Systems (MEMS). Though studied and reported for decades, the
mechanism behind their growth is not well understood, and tin whiskers remain a potential
reliability hazard. Furthermore, the growing number of piece parts with pure tin finishes
means there are more opportunities for whiskers to grow and to produce failures.

---------------------- Page: 8 ----------------------
PAS 62647-2  IEC:2011(E) – 7 –
PROCESS MANAGEMENT FOR AVIONICS –
AEROSPACE AND DEFENCE ELECTRONIC SYSTEMS
CONTAINING LEAD-FREE SOLDER –

Part 2: Mitigation of the deleterious effects of tin



1 Scope
This PAS establishes processes for documenting the mitigating steps taken to reduce the
harmful effects of tin finishes in electronic systems.
This PAS is applicable to Aerospace and High Performance electronic applications which
procure equipment that may contain Pb-free tin finishes.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply:
2.1
assemblies
electronic items that require electrical attachments, including soldering of wires or component
terminations; examples include circuit cards and wire harnesses. This may include soldered
assemblies
2.2
bright tin
tin finish with higher internal stresses and smaller grain size of 0,5 µm to 0,8 µm and carbon
content of 0,2 % to 1,0 %
2.3
critical
item or function, if defective, will result in the system’s inability to retain operational capability,
meet primary objective, or affect safety
2.4
customer
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
2.5
energy dispersive (X-ray) spectroscopy
EDS
method for material composition analysis
2.6
high performance system or product
system or product which requires continued high performance or performance on-demand, or
equipment downtime 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

---------------------- Page: 9 ----------------------
– 8 – PAS 62647-2  IEC:2011(E)
2.7
lead-free
defined as less than 0,1 % by weight of lead in accordance with Waste Electrical and
Electronic Equipment (WEEE) guidelines
2.8
matte tin
tin finish with lower internal stresses and larger grain sizes typically of 1 µm or greater and
carbon content less than 0,050 %
2.9
Pb-free tin
tin defined to be pure tin or any tin alloy with <3 % lead (Pb) content by weight. This means
that some Pb-free finishes other than pure tin, such as tin-bismuth and tin-copper, are
considered to be “tin” for the purposes of this PAS. Many of these alloys have not been
assessed for whiskering behavior
2.10
Pb-free tin finish
Pb-free tin final finishes or underplates either external or internal to a device, board or other
hardware. This includes all leads and surfaces, even those coated, encapsulated, or
otherwise not exposed. It may include finishes on electrical piece parts, mechanical piece
parts, and boards. 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
2.11
piece part
electronic component that is not normally disassembled without destruction and is normally
attached to a printed wiring board to perform an electrical function
2.12
rework
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
2.13
repair
act of restoring the functional capability of a defective article in a manner that precludes
compliance of the article with applicable drawings or specifications
2.14
sub-contractor
organization, within the given high-reliability industry, that supplies, maintains, repairs, or
supports electronic systems, and is not the direct supplier to the customer or user of those
systems
2.15
supplier
entity or organization that designs, manufactures, repairs, or maintains a piece part, unit, or
system. For example, this includes original equipment manufacturers (OEMs), repair facilities,
subcontractors, and piece part manufacturers. In some cases, a single organization may be
both a customer and a supplier. They should follow the requirements for suppliers when
addressing their customer’s contracts and should follow the requirements for customers when
flowing down requirements to their lower tier suppliers
2.16
system
one or more units that perform electrical function(s)

---------------------- Page: 10 ----------------------
PAS 62647-2  IEC:2011(E) – 9 –
2.17
tin whisker
spontaneous crystal growth that emanates from a tin 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 (OSEs). See Annex B for further
description of tin whiskers and their physical attributes
2.18
unit
one or more assemblies within a chassis to perform electrical function(s)
2.19
X-ray fluorescence
XRF
method for material composition analysis
3 Requirements
3.1 Determination of levels
The customer is responsible for determining the control level they are seeking and identify it
in their request for proposal when this PAS is imposed. They should also determine the level
of oversight and review the program will require. For some programs, different control levels
may be required for different products. In these cases, the customer is responsible for
defining these different levels and their applications or define a process by which they and the
supplier will determine the levels.
The customer and supplier shall agree on the control levels and shall document this
agreement in appropriate control documents.
There will be cases where errors will be made in the finish determination or in the application
of mitigation methods. Customers and suppliers should have processes in place to document
and assess the impact of these errors. Already existing deviation or waiver processes may be
acceptable if technical experts on tin whiskers are consulted.
3.2 Requirements for control levels
3.2.1 General
Each program or system has the responsibility of determining the appropriate control level for
their product. This document is not intended to imply that any category of aerospace or high
performance application is more or less reliable or critical than any other category; nor is it
intended to imply that any aerospace or high performance system will be more or less
reliable, depending on the control level that is selected from the above list. Reliability is
assured by a wide range of design, production, use, and support decisions and activities, of
which tin whisker mitigation is only one. It is expected that, whatever level of mitigation
category is used, the system reliability will be assured by the totality of all the methods
available to the producer and user of the system.
There are many aspects to tin whisker control. For the purposes of this PAS, the activities
have been grouped into four categories:
– documentation of uses of Pb-free tin;
– detecting and controlling Pb-free tin introduction;
– tin whisker risk mitigation;
– tests and analyses of tin whisker risk and mitigation effectiveness.

---------------------- Page: 11 ----------------------
– 10 – PAS 62647-2  IEC:2011(E)
If only Level 2, with no sub-level, is identified in a control document, the default level shall be
assumed to be Level 2A.
3.2.2 Control Level 1 requirements
3.2.2.1 Requirements for documentation of uses of Pb-free tin
There are no requirements. The supplier should provide general information regarding types
of platings, finishes, and solder used and plans for process controls on those processes in
accordance with 3.3.1. If the supplier is unable to determine some materials, this shall be
stated.
3.2.2.2 Requirements for detecting and controlling Pb-free tin finish introduction
No requirements.
3.2.2.3 Requirements for tin whisker risk mitigation
No requirements.
3.2.2.4 Requirements for tests and analyses of tin whisker risk and mitigation
effectiveness
No requirements.
3.2.3 Control Level 2A requirements
3.2.3.1 Requirements for documentation of uses of Pb-free tin
There are no supplier requirements. The supplier should provide general information
regarding types of platings, finishes, and solder used and plans for process controls on those
processes in accordance with 3.3.1. If the supplier is unable to determine some materials,
this shall be stated.
The customer is responsible for listing any applications where Pb-free tin is not allowed.
3.2.3.2 Requirements for detecting and controlling Pb-free tin finish introduction
No requirements.
3.2.3.3 Requirements for tin whisker risk mitigation
The supplier shall provide descriptions of any mitigation methods assumed to be in use for the
tests and analyses in 3.2.3.4. The supplier shall provide descriptions of any mitigation
measures taken for hardware.
The customer is responsible for defining any mitigation measures that are required or
disallowed.
3.2.3.4 Requirements for tests and analyses of tin whisker risk and mitigation
effectiveness
The supplier shall provide an analysis addressing the risk of tin whiskers in accordance with
3.3.4. This analysis is expected regardless of whether mitigations are applied. If no
mitigations are applied, the analysis should demonstrate why they are not needed. If
mitigations are applied, the analysis should demonstrate that they are effective.
For Level 2A, these analyses may be performed at the process level. For example, the
analysis might address all devices with a particular mitigation technique employed.

---------------------- Page: 12 ----------------------
PAS 62647-2  IEC:2011(E) – 11 –
3.2.3.5 Exceptions
Specific piece parts, soldered assemblies, units, or applications may be required to meet a
higher level of control. These requirements shall be specified in contractual documents.
3.2.4 Control Level 2B requirements
3.2.4.1 General
For Level 2B hardware, these control plans may cover families of piece part types or
applications. Separate assessments and control plans for each individual item are not
required. For example, one assessment might allow use of all tin-plated capacitors in a variety
of applications.
3.2.4.2 Requirements for documentation of uses of Pb-free tin
The supplier shall provide lists of families of tin-finished piece parts and/or location and
material information for categories of applications where they would like to use Pb-free tin in
accordance with 3.3.1.2. If there are other uses of tin, the supplier shall provide a list of
additional specific applications of Pb-free tin that fall outside these families in accordance
with 3.3.1.3. If the supplier is unable to determine some materials, this shall be stated.
The customer is responsible for listing any applications where Pb-free tin is not allowed.
3.2.4.3 Requirements for detecting and controlling Pb-free tin finish introduction
The supplier should provide a plan for monitoring materials on a sample basis, including
method of test and sampling scheme, in their product in accordance with 3.3.2.1.
3.2.4.4 Requirements for tin whisker risk mitigation
The customer is responsible for defining any mitigation measures that are required or
disallowed.
The supplier shall implement the mitigating measures contractually required by the customer.
It is recommended that at least two mitigation measures in accordance with 3.3.3 be required
and performed.
3.2.4.5 Requirements for tests and analyses of tin whisker risk and mitigation
effectiveness
If a specific risk algorithm or other method for evaluation measure is required, the customer is
responsible for describing them in the request for proposal. The customer is also responsible
for communicating any documentation review or oversight requirements to the supplier.
The supplier shall have documentation covering the following elements:
– the mitigation measures taken for each family of piece parts or applications of Pb-free tin
finish in the product;
– the tests or analyses performed for each family of piece parts or applications using Pb-
free tin finishes, to determine risk of whisker growth in accordance with 3.3.4;
– if there are other uses of Pb-free tin outside the families, the mitigation measures taken
for each piece part or application of Pb-free tin finish in the product outside the families;
– if there are other uses of Pb-free tin outside the families, the tests and analyses performed
for each of these piece parts or applications to determine risk of whisker growth in
accordance with 3.3.4;

---------------------- Page: 13 ----------------------
– 12 – PAS 62647-2  IEC:2011(E)
– provide the risk assessment and mitigation measures to the customer for their review, as
requested or required by customer.
3.2.5 Control Level 2C requirements
3.2.5.1 General
For Level 2C hardware, separate assessments and mitigation plans are required for each
instance of Pb-free tin finish use. For example, instead of one assessment and mitigation plan
covering all tin-plated capacitors, each capacitor type and application must be reviewed and
approved, even if the same strategy is applied to each situation.
3.2.5.2 Requirements for documentation of uses of Pb-free tin
The supplier shall avoid use of Pb-free tin whenever possible. The supplier shall not allow use
of Pb-free tin finishes without prior written permission of the customer and shall provide the
customer with a list of all uses of Pb-free tin. Each individual use shall be reviewed and
approved or disapproved by the customer.
The supplier shall provide a plan for passing the requirement to lower level suppliers in
accordance with 3.3.1.4.
3.2.5.3 Requirements for detecting and controlling Pb-free tin finish introduction
The supplier shall provide a plan for monitoring materials in their product in accordance with
3.3.2.1. The supplier and customer shall reach an agreement regarding this plan.
For critical piece parts, assemblies or systems, the plan should include sampling at least one
part per lot of all piece parts not approved for tin.
3.2.5.4 Requirements for tin whisker risk mitigation
The customer is responsible for defining any mitigation measures that are required or
disallowed in their request for proposals and contractual documen
...