IEC TS 62647-2:2012

IEC/TS 62647-2 ®
Edition 1.0 2012-11
TECHNICAL
SPECIFICATION
colour
inside
Process management for avionics – Aerospace and defence electronic systems
containing lead-free solder –
Part 2: Mitigation of deleterious effects of tin

IEC/TS 62647-2:2012(E)
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IEC/TS 62647-2 ®
Edition 1.0 2012-11
TECHNICAL
SPECIFICATION
colour
inside
Process management for avionics – Aerospace and defence electronic systems

containing lead-free solder –
Part 2: Mitigation of deleterious effects of tin

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XB
ICS 03.100.50; 31.020; 49.060 ISBN 978-2-83220-519-8

– 2 – TS 62647-2 © IEC:2012(E)
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and abbreviations . 8
3.1 Terms and definitions . 8
3.2 Abbreviations . 11
4 Technical requirement . 12
4.1 Control level requirements . 12
4.1.1 General . 12
4.1.2 Control levels and levels of integration . 14
4.1.3 COTS and level selection . 14
4.1.4 Other level selection information. 14
4.2 Requirements for control levels . 15
4.2.1 Control level 1 requirements . 15
4.2.2 Control level 2A requirements . 15
4.2.3 Control level 2B requirements . 16
4.2.4 Control level 2C requirements . 17
4.2.5 Control level 3 requirements . 19
4.2.6 Requirements for mitigating tin whisker risk for solder joints . 19
4.3 Implementation methods . 20
4.3.1 Flowing requirements to lower level suppliers (applies to control level
2B, control level 2C, and control level 3) . 20
4.3.2 Detecting and controlling Pb-free tin finish introduction . 20
4.3.3 Sample monitoring plans (applies to control level 2B and control level
2C) . 20
4.3.4 Lot monitoring requirements (applies to control level 3) . 20
4.4 Methods for mitigating impact of Pb-free tin (applies to control level 2B,
control level 2C) . 21
4.4.1 General . 21
4.4.2 Hard potting and encapsulation . 21
4.4.3 Physical barriers . 21
4.4.4 Conformal and other coats . 21
4.4.5 SnPb soldering process with validated coverage . 22
4.4.6 Circuit and design analysis . 22
4.5 Part selection process . 23
4.6 Assessment and documentation of risk and mitigation effectiveness. 23
4.6.1 General . 23
4.6.2 Elements of assessment . 24
4.6.3 Other risk analysis issues . 24
Annex A (informative) Guidance on control levels, risk assessment, and mitigation
evaluation . 25
Annex B (informative) Technical guide on detection methods, mitigation methods, and
methods for limiting impact of tin . 33
Annex C (informative) Tin whisker inspection . 45
Annex D (informative) Analysis and risk assessment guidance . 52

TS 62647-2 © IEC:2012(E) – 3 –
Annex E (informative) Whiskers growing from solder joint fillets and bulk solder . 56
Bibliography . 63

Figure A.1 – Decision tree . 26
Figure A.2 – Decision tree, sub-tree 1 . 27
Figure A.3 – Decision tree, sub-tree 2 . 28
Figure B.1 – Insufficient solder flow . 39
Figure C.1 – Equipment setup for whisker examination . 46
Figure C.2 – Whiskers examination areas and direction . 47
Figure C.3 – Side-illumination by flexible light . 47
Figure C.4 – Coating residuals and dusts attached on lead-frame with conformal
coating . 47
Figure C.5 – Comparisons between whisker observations by microscope and SEM . 48
Figure C.6 – Limitation of microscope observation . 48
Figure C.7 – Preliminary whisker examination in non-coated test specimens . 51
Figure E.1 – Whiskers and hillocks formed after 500 hours of storage at 85 °C /
85 % RH followed by –55 °C to 85 °C air to air cycling, 1 000 cycles . 56
Figure E.2 – Long whisker growing from SAC405 no-clean assembly reported by Terry
Munson (Foresite) . 57
Figure E.3 – Whiskers and hillocks protruding through flux residue and growing from
solder free of the flux residue [87] . 58
Figure E.4 – Tin whisker length impact by ionic cleanliness . 59
Figure E.5 – Tin whisker density impact by ionic cleanliness . 59
Figure E.6 – Whisker length depending on component and assembly cleanliness . 60
Figure E.7 – Microstructures of solder fillet with 0,8 % HBr activated flux assembled in
air after 1 000 hours at 85 °C / 85 % RH . 61
Figure E.8 – The mechanism of Sn whisker formation on solder fillet induced by
oxidation . 61
Figure E.9 – SAC105 bulk solder at ambient T in nitrogen chamber [34] . 62

Table A.1 – Control level summary table (1 of 2) . 31
Table B.1 – Conformal coating material physical properties from S. Meschter [10] . 34
Table B.2 – Conformal coating physical properties from T. Woodrow [12] . 35
Table B.3 – Conformal coating physical properties from R. Kumar [13] . 36

– 4 – TS 62647-2 © IEC:2012(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PROCESS MANAGEMENT FOR AVIONICS – AEROSPACE AND DEFENCE
ELECTRONIC SYSTEMS CONTAINING LEAD-FREE SOLDER –

Part 2: Mitigation of 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
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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.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC/TS 62647-2, which is a technical specification, has been prepared by IEC technical
committee 107: Process management for avionics.

TS 62647-2 © IEC:2012(E) – 5 –
The text of this technical specification is based on the following documents: IEC/PAS 62647-2
and GEIA-STD-0005-2 Revision A.
This technical specification cancels and replaces IEC/PAS 62647-2.
A list of all the parts in the IEC 62647 series, published under the general title Process
management for avionics – Aerospace and defence electronic systems containing lead-free
solder, can be found on the IEC website.
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
107/160/DTS 107/193/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

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 – TS 62647-2 © IEC:2012(E)
INTRODUCTION
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 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,
defence, and high performance industry in electronics, many of the lower tier suppliers are
changing their products because their primary market is world-wide consumer electronics.
Additionally, several Asian countries and United States (U.S.) states have enacted similar
“green” laws. 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 (SnPb) 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
of micro-electro mechanical systems (MEMS) for example. 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.
It is important to state that that the nature and meaning of ‘risk’ posed by tin whiskers may
vary considerably across the range of users of this Specification. As in any assessment of
risk, the probability of occurrence and failure and consequence of occurrence and failure
should be considered in each application. Potential whisker failure modes for a particular
hardware/system application must be carefully considered when making the
choice/determination of which control level(s) to apply. For example, whisker-prone leaded
parts on circuit card used in a system that is under frequent/continual power may only incur
parametric deviations or interrupts as individual whiskers grow and short to an adjacent lead.
On the other hand, the same circuit card, employed in a missile subject to years of dormant
storage, could grow many long whiskers into potentially catastrophic shorting conditions but
the shorts will not occur until the missile is launched toward its target and results in mission
failure. For the purposes of this Specification, risk refers to the chance and consequence of a
failure due to a whisker, not just the chance of the presence of a whisker.

TS 62647-2 © IEC:2012(E) – 7 –
PROCESS MANAGEMENT FOR AVIONICS – AEROSPACE AND DEFENCE
ELECTRONIC SYSTEMS CONTAINING LEAD-FREE SOLDER –

Part 2: Mitigation of deleterious effects of tin

1 Scope
This Technical Specification establishes processes for documenting the mitigating steps taken
to reduce the harmful effects of Pb-free tin in electronic systems.
This Technical Specification is applicable to aerospace, defence, and high performance
(ADHP) electronic applications which procure equipment that may contain Pb-free tin finishes.
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 electronic
systems containing lead-free solder – Part 1: Preparation for a lead-free control plan
IEC/PAS 62647-3, Process management for avionics – Aerospace and defence electronic
systems containing lead-free solder – Part 3: Performance testing for systems containing
lead-free solder and finishes
IEC/PAS 62647-21, Process management for avionics – Aerospace and defence electronic
systems containing lead-free solder – Part 21: Program management – Systems 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 22: Technical guidelines
ANSI/GEIA-STD-0006, Requirements for using solder dip to replace the finish on electronic
piece parts
ANSI Z1.4, Sampling procedures and tables for inspection by attributes
IPC J-STD-001, Requirements for soldered electrical and electronic assemblies
___________
Previously known as GEIA-STD-0005-1.
Previously known as GEIA-STD-0005-3. IEC/PAS 62647-3 is in the process of being revised and will be issued
as IEC/TS 62647-3.
Previously known as GEIA-HB-0005-1. IEC/PAS 62647-21 is in the process of being revised and will be issued
as IEC/TS 62647-21.
Previously known as GEIA-HB-0005-2. IEC/PAS 62647-22 is in the process of being revised and will be issued
as IEC/TS 62647-22.
– 8 – TS 62647-2 © IEC:2012(E)
IPC-CC-830, Qualification and performance of electrical insulating compounds for printed
wiring assemblies
JESD201, Environmental acceptance requirements for tin whisker susceptibility of tin and tin
alloy surface finishes
JESD213, Standard test method utilizing X-ray fluorescence (XRF) for analyzing component
finishes and solder alloys to determine Tin (Sn) – Lead (Pb) content
MIL-STD-1580, Destructive physical analysis for electronic, electromagnetic, and
electromechanical parts
3 Terms, definitions and abbreviations
For the purposes of this document, the following terms, definitions and abbreviations apply.
3.1 Terms and definitions
3.1.1
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]
3.1.2
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
[SOURCE: IEC/TS 62647-1:2012, 3.2]
3.1.3
control level
amount of attention that should be paid to the risk of tin whiskers (i.e., no restrictions on tin
use, some restrictions on tin use, and prohibition of tin use)
3.1.4
conformal coat
insulating protective covering that conforms to the configuration of the objects coated (e.g.,
printed boards, printed board assembly) providing a protective barrier against deleterious
effects from environmental conditions
3.1.5
COTS
commercial-off-the-shelf
item whose design and configuration is controlled by the manufacturer and on which the user
has no control with regard to the design and configuration
Note 1 to entry: An item may be a component, a sub-assembly, an assembly, a system.
3.1.6
COTS assemblies or sub-assembly
assembly or sub-assembly developed by a supplier for multiple customers, whose design and
configuration is managed by the suppliers or an industry specification

TS 62647-2 © IEC:2012(E) – 9 –
[SOURCE: IEC/TS 62647-1:2012, 3.4]
3.1.7
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]
3.1.8
EDS
energy dispersive (X-ray) spectroscopy
method for material composition analysis
3.1.9
encapsulation
process which involves the surrounding of (a) component(s) or an assembly with a liquid resin
3.1.10
gap
minimum line of sight distance between tin surface and the nearest adjacent conductor at a
different potential.
Note 1 to entry: It refers to any conductors (leads, pads, connectors, contacts, or others).
3.1.11
high voltage
voltage level required to cause a plasma event
3.1.12
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]
3.1.13
lead-free
defined as less than 0,1 % by weight of lead in accordance with reduction of hazardous
substances(RoHS) guidelines guidelines
[SOURCE: IEC/TS 62647-1:2012, 3.8]
3.1.14
mitigation
method to reduce the risk or consequence of a whisker failure over a period of several years.
Note 1 to entry: This does not imply that the risk is driven to zero, simply that the risk or consequence is reduced in
some significant way.
3.1.15
Pb-free tin
pure tin or any tin alloy with < 3 % lead (Pb) content by weight

– 10 – TS 62647-2 © IEC:2012(E)
Note 1 to entry: 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 specification. Many of these alloys have not been assessed for whiskering
behaviour.
[SOURCE: IEC/TS 62647-1:2012, 3.11]
3.1.16
Pb-free tin finish
final finishes or underplates either external or internal to a device, board or other hardware,
including all leads and surfaces, even those coated, encapsulated, or otherwise not exposed
Note 1 to entry: 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 (consistent with GEIA-STD-0006).
[SOURCE: IEC/TS 62647-1:2012, 3.12]
3.1.17
plasma event
destructive arcing event that can occur at altitudes from sea level to space depending on
voltage and current levels
3.1.18
piece part
piece component
electronic component that is not normally disassembled without destruction and is normally
attached to a printed wiring board to perform an electrical function
[SOURCE: IEC/TS 62647-1:2012, 3.14]
3.1.19
potting
encapsulation process which involves the surrounding of a component(s) or an assembly in a
container with a liquid resin which is then cured in place
Note 1 to entry: The container usually becomes an integral part of the system such that the critical property that
needs to be maintained is the interfacial adhesion between the cured resin system and the container substrate and
critical components for an optimum long-lasting reliable package.
3.1.20
rework
action taken to return a unit (SRU/LRU/system) to a state meeting all requirements of the
engineering drawing, including both functionality and physical configuration by making repairs
Note 1 to entry: Also used to define 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.
[SOURCE: IEC/TS 62647-1:2012, 3.16]
3.1.21
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
[SOURCE: IEC/TS 62647-1:2012, 3.17]
3.1.22
risk
probability of a failure due to a tin whisker

TS 62647-2 © IEC:2012(E) – 11 –
Note 1 to entry: It is not used with regards to the risk of the presence of a whisker or nodule.
3.1.23
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
[SOURCE: IEC/TS 62647-1:2012, 3.22]
3.1.24
supplier
refers to an entity or organization that designs, manufactures, repairs, or maintains a piece
part, unit, or system
Note 1 to entry: This includes original equipment manufacturers (OEMs), repair facilities, subcontractors, and
piece part manufacturers.
[SOURCE: IEC/TS 62647-1:2012, 3.23]
3.1.25
system
one or more units that perform electrical function(s)
[SOURCE: IEC/TS 62647-1:2012, 3.24]
3.1.26
tin whisker
spontaneous crystal growth that emanates from a tin (Sn) surface and which may be
cylindrical, kinked, or twisted
Note 1 to entry: Typically tin whiskers have an aspect ratio (length/width) greater than two, with shorter growths
referred to as nodules or odd-shaped eruptions (OSEs).
[SOURCE: IEC/TS 62647-1:2012, 3.26]
3.1.27
unit
one or more assemblies within a chassis or higher level system to perform electrical function(s)
[SOURCE: IEC/TS 62647-1:2012, 3.27]
3.1.28
XRF
X-ray fluorescence
method for material composition analysis
3.2 Abbreviations
ADHP Aerospace, defence and high performance
COTS Commercial off the shelf
EDX Energy-dispersive X-ray spectroscopy
FMEA Failure mode effects analysis
FMECA Failure mode effects and criticality analysis
FOD Foreign object damage
IMC Intermetallic compound
iNEMI international Electronics Manufacturing Initiative

– 12 – TS 62647-2 © IEC:2012(E)
JEDEC Joint Electron Device Engineering Council
MEMS Micro-electro mechanical systems
OEM Original equipment manufacturer
OSD Odd-shaped eruptions
Pb Lead
PLCC Plastic leaded chip carrier
PQFP Plastic quad flat pack
QFP Quad flat pack
REE Rare earth elements
SEM Scanning electron microscope
Sn Tin
Sn-Pb Tin/lead
SOIC Small outline integrated circuit
TQFP Thin quad flat pack
TSOP Thin small outline package
XRF X-ray fluorescence
4 Technical requirement
This specification 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 bring credit of certification 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
This specification is intended to be used in concert with IEC/TS 62647-1, IEC/PAS 62647-21,
and IEC/PAS 62647-22. This specification may be referenced in proposals, requests for
proposals, work statements, contracts, and other documents. It may be used as a stand-alone
specification or as part of compliance with IEC/TS 62647-1.
This specification 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 five informative annexes in this specification:
– Annex A provides guidance on selecting control levels and performing risk assessments;
– Annex B provides some background on various mitigation methods;
– Annex C provides guidelines for performing tin whisker inspections;
– Annex D provides some additional guidance on tin whisker risk analyses;
– Annex E provides information on whiskers growing from bulk solder and joints.
4.1 Control level requirements
4.1.1 General
The supplier shall clearly state the control levels and shall document agreement by the
customer in appropriate requirement or lead-free control plan documents. Customers are
responsible for determining the control level they are seeking and identify it in their request
for proposal and contract when this specification is imposed.

TS 62647-2 © IEC:2012(E) – 13 –
Higher control levels impose tighter controls and thereby reduce exposure to tin whisker risk.
However, tin whisker risks are just one of many types of risks associated with component
selection and assembly design. Controls imposed on tin whiskers should be commensurate
with controls imposed to manage these other risks. 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 ADHP application is more or less reliable or critical
than any other category nor is it intended to imply that any ADHP system will be more or less
reliable, depending on the control level that is selected. 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 control 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.
In particular, it is recommended that the selection of control level involves consideration of the
following questions:
– What are the consequences of performance anomalies in your system?
– Do we antipate that the whiskers will produce a plasma event?
– Do local anomalies affect top-level system performance?
– Could a failure cause a critical failure or defeat redundancy?
– Are anomalies detectable and repairable?
More information on how these questions can be used to select an appropriate control level is
provided in Annex A.
Overall, there are three approaches to tin whisker control:
– tin part avoidance;
– whisker risk mitigation;
– whisker risk acceptance.
Different control levels represent different emphasis on each of these approaches.
Control level 1: Under control level 1 tin whisker risks are accepted. It is expected that this
control level will primarily apply to developmental models, test equipment,
and other units that will not be fielded.
Control level 2: Under control level 2, Pb-free tin is sometimes acceptable. Tin whisker risk
is managed primarily by a combination of design rules, mitigations, and
avoidance. The sub-control level under control level 2 determines the
emphasis given to each of these strategies. If only control level 2, with no
sub-control level, is identified in a control document, the default level shall
be assumed to be control level 2A.
Control level 2A: Under level 2A, tin whisker risks are managed primarily through the
acceptance of tin whisker risk, and to a lesser extent upon the use of
design rules. This control level was designed primarily for lower criticality
applications. Tin is permitted for use in all applications except where
specially restricted.
Control level 2B: Under control level 2B, tin whisker risks are managed primarily through the
use of design rules, and to a lesser extent upon tin avoidance. This control
level was primarily designed for non-critical boards or units or boards and
units with good redundancy used in systems with moderate to high failure
consequences.
Control level 2C: Under control level 2C, tin whisker risks are managed primarily by tin
avoidance, and in exceptional cases, by design rules. This control level
was primarily designed for critical boards with limited redundancy used in
systems with moderate to high failure consequences.

– 14 – TS 62647-2 © IEC:2012(E)
Control level 3: Tin whisker control is managed strictly by tin avoidance. This level was
designed for units and boards where failures cannot be tolerated.
For units or boards that apply a mix of design rules and individual Pb-free tin evaluations, the
unit or board shall be defined as control level 2B, with the rules defining the circumstances
requiring control level 2C-like evaluations clearly called out. Applications falling within the
control level 2C-like requirements shall be documented and mitigated per the requirements of
control level 2C.
Control levels are expected to be applied at the unit or board control level, consistent with the
overall risk strategy for that unit or board. However, an overall strategy for higher control
levels of integration may be appropriate and is discussed in 4.1.2 below.
4.1.2 Control levels and levels of integration
Control levels were designed to be applied at the unit or board control level, but customers
may want to have an approach to control levels and level selection at the subsystem, product,
or system control level. Some approaches at higher control levels of integration and in system
lead-free control plans:
• define the criteria that are to be used to evaluate unit control levels, preferably with some
general statements about what control levels are expected on most units and boards;
• define control levels based on unit criticality, function, or some other design rule;
• define the system level control level based on the expected control level of most units and
define when the program will require higher control levels. A discussion of this process for
requiring higher or allowing lower control levels should be included.
4.1.3 COTS and level selection
The imposition of control levels 2C and higher will generally preclude the use of COTS
assemblies and systems, unless directed or authorized by their customer. If COTS assemblies
are used in a program or system that is defined as control level 2C or 3, they shall be
identified and treated as exceptions or a comprehensive material control and analysis plan
shall be implemented or the material and mitigations requirements will be flowed down to and
accepted by the COTS supplier. In a control level 2B situation, the treatment of COTS shall be
addressed in the list of families where Pb-free tin alloys will be used or the materials and
mitigations requirements will be flowed down to and accepted by the COTS supplier.
COTS parts may be used under any level but need to be evaluated as any part or finish and
meet the requirements of the control level. This will likely involve at least one of the following:
• working with the part supplier to understand the material and mitigating as necessary;
• managing material identification for any lot or subset of parts with known uniformity of
finish and mitigating materials as necessary;
• treating all COTS material as Pb-free tin and performing mitigations on all as required.
4.1.4 Other level selection information
Annex A provides additional guidance on level selection.
Note that these levels are different than the IPC Product Classes described in IPC J-STD-
001E-2010 (IEC 61191). In general, it is expected that most users of this specification are IPC
Class 3 due to the types of final end applications their products support.
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.

TS 62647-2 © IEC:2012(E) – 15 –
4.2 Requirements for control levels
4.2.1 Control level 1 requirements
4.2.1.1 Control level 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.
4.2.1.2 Control level 1 requirements for detecting and controlling Pb-free tin finish
introduction
There are no requirements.
4.2.1.3 Control level 1 requirements for tin whisker risk mitigation
There are no requirements.
4.2.1.4 Control level 1 requirements for parts selection
There are no requirements.
4.2.1.5 Control level requirements for analysis and documentation of risk and
mitigation effectiveness
There are no requirements.
4.2.2 Control level 2A requirements
4.2.2.1 Control level 2A requirements for documentation of uses of Pb-free tin
The supplier shall document the design rules that are in place for determining when Pb-free
tin is not acceptable or when mitigations are required.
The customer is responsible for listing any applications where Pb-free tin is not allowed.
4.2.2.2 Control level 2A requirements for detecting and controlling Pb-free tin finish
introduction
There are no requirements.
4.2.2.3 Control level 2A requirements for tin whisker risk mitigation
The plan should indicate any mitigation that is applied as part of the general process at the
supplier.
The customer is responsible for defining any mitigation measures that are required.
4.2.2.4 Control level 2A requirements for parts selection
Unless the parts list or vendor list is provided by the customer, the supplier should have a part
selection process that encourages the use of parts that have lower tin whisker risk, consistent
with the requirements presented in 4.5.
4.2.2.5 Control level 2A requirements for analysis and documentation of risk and
mitigation effectiveness
This analysis is expected regardless of whether mitigations are applied.

– 16 – TS 62647-2 © IEC:2012(E)
For control level 2A, these analyses may be performed at the process control level. For
example, the analysis might address all devices with a particular mitigation technique
employed.
4.2.2.6 Control level 2A exceptions
Specific piece parts, soldered assemblies, units, or applications may be required to meet a
higher control level. These requirements shall be specified in contractual documents.
4.2.3 Control level 2B requirements
4.2.3.1 General
If the control level is defined at a system or assembly control level, this is the control level
that will most likely be
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