IEC PAS 62647-3:2011

IEC/PAS 62647-3 ®
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 3: Performance testing for systems containing lead-free solder and finishes

IEC/PAS 62647-3:2011(E)
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IEC/PAS 62647-3 ®
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 3: Performance testing for systems containing lead-free solder and finishes

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
W
ICS 03.100.50; 31.020; 49.060 ISBN 978-2-88912-599-9
– 2 – PAS 62647-3 © IEC:2011(E)
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 8
2 Normative references . 9
3 Terms and Definitions . 10
4 Default Test Methods . 11
4.1 Test Vehicles . 11
4.1.1 Test Vehicle type . 11
4.1.2 Sample size . 12
4.2 Pre-Conditioning by Thermal Aging Method . 12
4.2.1 Thermal Aging Acceleration Model . 12
4.2.2 Default Test Parameters . 13
4.3 Default Temperature Cycle Test Method . 13
4.3.1 Test Parameters . 13
4.3.2 Test Duration . 13
4.3.3 Failure Determination and Analysis . 13
4.3.4 Acceleration Model . 14
4.4 Vibration Test . 15
4.5 Mechanical Shock . 15
4.6 Combined Environments. 16
5 Protocol to Design and Conduct Performance Tests . 16
5.1 Test Vehicles . 16
5.2 Temperature Cycle Test Protocol . 16
5.2.1 Measure the recovery time . 17
5.2.2 Determine the high-temperature dwell times and temperatures . 18
5.2.3 Select other test parameters as appropriate for the application . 19
5.2.4 Conduct tests . 19
5.2.5 Determine the temperature versus cycles-to-failure relationship . 19
5.2.6 Estimate the cycles to failure . 20
5.3 Vibration Test . 20
5.4 Mechanical Shock . 21
5.5 Combined Environments Test Protocol . 21
5.5.1 Combined Environment Relation . 22
5.5.2 Additional Insight: NASA-DoD Lead-free (Pb-free) Project . 23
5.5.3 Additional Insight: Concept of Life Cycle per MIL-STD-810 . 23
5.6 Failure Determination and Analysis . 24
6 Final Remarks . 24
Annex A (informative) Test Sample Size . 25
Annex B (informative) Material Properties of Lead-free (Pb-free) Solder Materials . 27
Annex C (informative) NASA-DoD Lead-free (Pb-free) Electronics Project Test
Information (from the NASA-DoD Lead-free (Pb-free) Project Joint Test Protocol, 19
September 2007) . 30

Figure 1 – Notional method for determining the recovery time for a given solder alloy,

or combination of alloys. . 18

PAS 62647-3 © IEC:2011(E) – 3 –
Figure 2 – Notional method for determining the relationship between high temperature
dwell time, t , and recovery time, t . (This example assumes an idealized system but
hd r
the slope may differ depending on material, temperature range, and dwell.) . 19
Figure 3 – Notional method for determining the relationship between cycles to failure . 20
Figure C.1 – Vibration Spectrum . 31
Figure C.2 – Vibration Test Fixture (from JCAA/JGPP Lead-free (Pb-free) Solder
Project Team*) . 33
Figure C.3 – Vibration Table showing Y-axis (from JCAA/JGPP Lead-free (Pb-free)
Solder Project Team) . 34
Figure C.4 – Mechanical Shock Response Spectrum . 35
Figure C.5 – Mechanical Shock Test Set-Up (from JCAA/JGPP Lead-free (Pb-free)
Solder Project Team) . 37

Table B.1 – Test and Acceleration Model Parameters . 27
Table C.1 – Vibration Profile . 32
Table C.2 – Vibration Test Methodology . 33
Table C.3 – Mechanical Shock Test Methodology – Test Procedure. 37
Table C.4 – Combined Environments Test Methodology . 39

– 4 – PAS 62647-3 © IEC:2011(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
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
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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A PAS is a technical specification not fulfilling the requirements for a standard, but made
available to the public.
IEC-PAS 62647-3 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
107/124/PAS 107/135A/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 62647-3 © IEC:2011(E) – 5 –
This PAS is based on GEIA-STD-0005-3 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 3-year period, following which it
shall be revised to become another type of normative document, or shall be withdrawn.

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 62647-3 © IEC:2011(E)
INTRODUCTION
The implementation of Lead-free (Pb-free) interconnection technology into electronics has
resulted in a variety of reactions by designers, manufacturers, and users. While the prime
motivation for Lead-free (Pb-free) technology was to address the social concern of improving
the environment by limiting the amount of toxic and dangerous substances used in products,
the ramifications of this initiative have provided a state of uncertainty regarding the
performance – in this context, defined as operation and reliability, i.e. the expected life cycle
of a product – of aerospace and defence systems. For over fifty years, Tin-Lead solder was
the benchmark for electronics assembly and generations of research baselined its
performance under a variety of operating conditions including the harsh settings of aerospace
and defence equipment. However, with the integration of Lead-free (Pb-free) technology,
aerospace and defence companies are faced with questions as to whether these new
materials will provide, as a minimum, the same degree of confidence during the life cycle of
critical systems and products.
In evaluating performance, two approaches are used: analysis/modeling and test. This
document addresses the latter, providing guidance and direction in the development and
execution of performance tests for Lead-free (Pb-free) electronic interconnections. The user
of this document needs to be aware of the following: This document does not give answers as
to how to perform a specific test. Products and systems applications vary immensely, so
designers need to understand use conditions and the entire life cycle. Once this is
understood, then this document can be used to give designers an understanding of how to
develop a suitable test, e.g., ascertain the type of platform in which a product will be used,
comprehending all the environmental effects on the platform, and learning why material
characterization is key to deciding upon test parameters, etc.
Sound engineering knowledge and judgment will be required for the successful use of this
document.
The global transition to Lead-free (Pb-free) electronics has a significant impact on the
electronics industry; it is especially disruptive to aerospace and other industries that produce
electronic equipment for high performance applications. These applications, hereinafter
described as AHP (Aerospace and High Performance), are characterized by severe or harsh
operating environments, long service lifetimes, and high consequences of failure. In many
cases, AHP electronics must be repairable at the soldered assembly level. Typically, AHP
industry production volumes may be low and, due to low market share, may not be able to
resist the change to Lead-free (Pb-free). Furthermore, the reliability tests conducted by
suppliers of solder materials, components, and sub-assemblies cannot be assumed to assure
reliability in AHP applications. This document provides guidance (and in some cases
direction) to designers, manufacturers, and maintainers of AHP electronics in assessing
performance of Lead-free (Pb-free) interconnections.
Over the past several decades, electronics manufacturers have developed methods to
conduct and interpret results from reliability tests for lead-bearing solder alloys. Since these
alloys have been used almost universally in all segments of the electronics industry, and
since a large body of data, knowledge, and experience has been assembled, the reliability
tests for Pb-bearing solder alloys are well-understood and widely accepted.
When it became apparent that the use of Pb-bearing alloys would decline rapidly, programs
were implemented to evaluate the reliability of the Lead-free (Pb-free) replacement alloys.
Those programs have generated a considerable database. To date, however, there is no
reliability test method that is widely accepted in the AHP industries. Reasons for this include:
a) No single Lead-free (Pb-free) solder alloy has emerged as a replacement for lead-bearing
alloys; instead, a number of alloys are being used in various segments of the electronics
industry.
b) The physical, chemical, and metallurgical properties of the various Lead-free (Pb-free)
replacement alloys vary significantly.

PAS 62647-3 © IEC:2011(E) – 7 –
c) Due to the many sources of solder alloys used in electronic component termination
materials or finishes, assembly processes, and repair processes, the potential number of
combinations of alloy compositions is nearly unlimited. It is an enormous task to collect
data for all these combinations.
d) The test methods developed by other segments (References [1] and [2]) are directed
toward shorter service lives and more benign environments. Also, there is still a question
of suitable dwell times and acceleration factors. (However, the intent of this document is to
provide a mean of coordinating the information from References [1] and [2] into a basic
approach for AHP suppliers.)
e) The data from reliability tests that have been conducted are subject to a variety of
interpretations.
In view of the above facts, it would be desirable for high-reliability users of Lead-free (Pb-
free) solder alloys to wait until a larger body of data has been collected, and methods for
conducting reliability tests and interpreting the results have gained wide acceptance for high-
reliability products. In the long run, this will indeed occur. However, the transition to Lead-free
(Pb-free) solder is well under way and there is an urgent need for a reliability test method, or
set of methods, based on industry consensus. While acknowledging the uncertainties
mentioned above, this document provides necessary information for designing and conducting
performance tests for aerospace products. In addition, when developing test approaches, the
material in question needs to be suitably characterized. Such material properties as ultimate
tensile strength, yield strength, Poisson’s ratio, creep rate, and stress relaxation have been
shown to be key attributes in evaluating fatigue characteristics of Lead-free (Pb-free) solders.
Because of the dynamic nature of the transition to Lead-free (Pb-free) electronics, this and
other similar documents must be considered provisional. While this document is based on the
best information and expertise available, it must be updated as future knowledge and data are
obtained.
The intent of the document is not to prescribe a certain method, but to aid avionics/ defence
suppliers in satisfying the reliability and/or performance requirements of IEC/PAS 62647-1
(GEIA-STD-0005-1) [5] as well as support the expectations in GEIA-HB-0005-1 [6].
Accordingly, it includes
– a default method for those companies that require a pre-defined approach and
– a protocol for those companies that wish to develop their own test methods.
Also, this PAS will focus on testing the Lead-free (Pb-free) interconnections, i.e., the “system”
comprised of the solder alloy as well as the component and board finishes. While the bulk of
this introduction has discussed reliability testing of Lead-free (Pb-free) assemblies, this
document will direct attention to test guidelines to evaluate the performance of the Lead-free
(Pb-free) interconnection. The guidelines presented in this document do not suggest methods
for reliability testing of product. That is left to each individual user. The document provides
insight as to what approaches should be used as part of a performance test when Lead-free
(Pb-free) interconnection is of prime interest.
In summary, the purpose of this PAS is threefold:
1. It is meant to provide a means to acquire sound, accurate data regarding the performance
of a Lead-free (Pb-free) interconnection under harsh conditions (aerospace, military,
medical, etc.,)
2. It is usable for further design assessment and operation of a product, and
3. It is usable as part of a process development study.
Finally, any portion of this document may be used to develop a Lead-free (Pb-free) assembly
test program, i.e., this PAS is tailorable and provides room for flexibility. For those situations
in which results are used for reliability, verification, or qualification, it is strongly
recommended that stakeholder concurrence be sought and documented so that expectations
are understood and addressed.
– 8 – PAS 62647-3 © IEC:2011(E)
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
1 Scope
This PAS defines for circuit card assemblies (CCA)
– a default method for those companies that require a pre-defined approach and
– a protocol for those companies that wish to develop their own test methods.
The default method (Section 4 of the PAS) is intended for use by electronic equipment
manufacturers, repair facilities, or programs that, for a variety of reasons, may be unable to
develop methods specific to their own products and applications. It is to be used when little or
no other information is available to define, conduct, and interpret results from reliability,
qualification, or other tests for electronic equipment containing Lead-free (Pb-free) solder.
The default method is intended to be conservative, i.e., it is biased toward minimizing the risk
to users of AHP electronic equipment.
The protocol (Section 5 of the PAS) is intended for use by manufacturers or repair facilities
that have the necessary resources to design and conduct reliability, qualification, or process
development tests that are specific to their products, their operating conditions, and their
applications. Users of the protocol will have the necessary knowledge, experience, and data
to customize their own methods for designing, conducting, and interpreting results from the
data. Key to developing a protocol is a firm understanding of all material properties for the
Lead-free (Pb-free) material in question as well as knowledge of package- and board-level
attributes as described in Section 4.1.1. As an example, research has shown that the
mechanisms for creep can be different between Tin-Lead and Tin-Silver-Copper (SAC)
solders. Understanding these mechanisms is key to determining critical test parameters such
as dwell time for thermal cycling. The protocol portion of this document provides guidance on
performing sufficient characterization of new materials in order to accurately define test
parameters.
Use of the protocol is encouraged, since it is likely to yield more accurate results, and to be
less expensive than the default method. Reference [7] provides a comprehensive overview of
those technical considerations necessary in implementing a test protocol.
This PAS addresses the evaluation of failure mechanisms, thru performance testing, expected
in electronic products containing Lead-free (Pb-free) solder. One failure mode, fatigue-failure
thru the solder-joint, is considered a primary failure mode in AHP electronics and can be
understood in terms of physics of failure and life-projections. Understanding all of the
potential failure modes caused by Lead-free (Pb-free) solder of AHP electronics is a critical
element in defining early field-failures/reliability issues. Grouping of different failure modes
may result in incorrect and/or misleading test conclusions. Failure analysis efforts should be
conducted to insure that individual failure modes are identified, thus enabling the correct
application of reliability assessments and life-projection efforts.
When properly used, the methods or protocol defined in this PAS may be used along with the
processes documented in compliance to Reference [3], to satisfy, at least in part, the
reliability requirements of References [3] and [4].

PAS 62647-3 © IEC:2011(E) – 9 –
This PAS may be used for products in all stages of the transition to Lead-free (Pb-free)
solder, including:
• Products that have been designed and qualified with traditional Tin-Lead electronic
components, materials, and assembly processes, and are being re-qualified with use of
Lead-free (Pb-free) components
• Products with Tin-Lead designs transitioning to Lead-free (Pb-free) solder; and
• Products newly-designed with Lead-free (Pb-free) solder.
For programs that were designed with Tin-Lead solder, and are currently not using any Lead-
free (Pb-free) solder, the traditional methods may be used. It is important, however, for those
programs to have processes in place to maintain the Tin-Lead configuration including those
outsourced or manufactured by subcontractors.
With respect to products as mentioned above, the methods presented in this document are
intended to be applied at the level of assembly at which soldering occurs, i.e., circuit-card
assembly level.
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.
1) IPC-9701A, “Performance Test Methods and Qualification Requirements for Surface
Mount Solder Attachments”, IPC, February 2006
2) IPC/JEDEC-9703, “Testing Methodologies for Solder Joint Reliability in Shock
Conditions”, DATE TBD
3) IPC-SM-785, “Guidelines for Accelerated Reliability Testing of Surface Mount Solder
Attachments”, IPC, November 1992
4) JESD22-B110A, “JEDEC Standard Subassembly Mechanical Shock”, November 2004
5) IEC/PAS 62647-1, Program management for Avionics – Aerospace and defence electronic
systems containing lead-free solder – Part 1: Lead-free management
6) GEIA-STD-0005-1, Performance Standard for Aerospace and High Performance
Electronic Systems Containing Lead-free (Pb-free) Solder. Government Engineering and
Information Technology Association, 2006
7) IEC/PAS 62647-2, Process management for Avionics – Aerospace and defence electronic
systems containing lead-free solder – Part 2: Mitigation of the deleterious effects of tin
8) GEIA-STD-0005-2, Standard for Mitigating the Effects of Tin whiskers in Aerospace and
High Performance Electronic Systems. Government Engineering and Information
Technology Association, 2006
9) IEC/PAS 62647-21, Aerospace and defence electronic systems containing lead-free solder
– Part 21: Program management – Systems engineering guidelines for managing the
transition to lead-free electronics
10) GEIA-HB-0005-1, Program Management / Systems Engineering Guidelines For Managing
The Transition To Lead-free (Pb-free) Electronics, 2006
11) IEC/PAS 62647-22, Aerospace and defence electronic systems containing lead-free solder
– Part 22: Technical guidelines
12) GEIA-HB-0005-2, Technical Guidelines for Aerospace and High Performance Electronic
Systems Containing Lead-free (Pb-free) Solder, 2007
13) MIL-STD-810, “Department of Defence Test Method Standard for Environmental
Engineering Considerations and Laboratory Tests”, revision F, January 1, 2000.
14) MIL-HDBK-217F, “Military Handbook, Reliabilty of Electronic Equipment”, 2 December
1991.
– 10 – PAS 62647-3 © IEC:2011(E)
15) NASA-DoD LFE Test Protocol, 19 September 2007
16) Shigley, Joseph Edward, Mechancial Engineering Design, THIRD EDITION, McGraw-Hill
Book Company, New York, NY, 1977, pp. 185-188.
17) Collins, J.A., Failure of Materials in Mechanical Design, John Wiley and Sons, New York,
NY, 1981, pp. 240-269.
18) “Fatigue (Material)”, Wikipedia, http://en.wikipedia.org/wiki/Metal_fatigue
19) Joint Group on Pollution Prevention, “Lead-free (Pb-free) Solder Testing for High
Reliability”, Project Number S-01-EM-026, (A full report on the JG-PP effort can be found
at the JG-PP Web site).
20) NASA-DoD Lead-free (Pb-free) Project, http://www.teerm.nasa.gov/projects/NASA_DOD
LeadFreeElectronics_Proj2.html
21) Directive 2002/95/Ec of the European Parliament and of the Council of 27 January 2003
on the restriction of the use of certain hazardous substances in electrical and electronic
equipment (commonly known as the RoHS or Restriction of Hazardous Substances
Directive)
22) Communication with W. Engelmaier, January 7, 2006
23) Communication with W. Engelmaier, January 7, 2006 and Follow-up communication with
A. Dasgupta on September 28, 2007
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
AHP
Aerospace and High Performance, referring to a generalized level of equipment use in harsh
and stringent operating conditions.
3.2
coupon
a test sample representing a scaled-down or proportional version of an actual product or
higher level test vehicle.
3.3
CTE
Coefficient of Thermal Expansion
3.4
DSC
Differential Scanning Calorimeter.
3.5
JCAA
Joint Council on Aging Aircraft.
3.6
JG-PP
Joint Group on Pollution Prevention, referring to the Department of Defence initiative that
sponsored a project to obtain design data from testing Lead-free (Pb-free) assemblies under a
series of military environments.
3.7
lead
term associated with the termination of an electronic component, i.e., the structure that makes
electrical contact with a printed wiring board.

PAS 62647-3 © IEC:2011(E) – 11 –
3.8
lead-free (Pb-free)
meaning that the content of the element lead is < 0.1 % by weight. [The chemical symbol for
the element is used so as to not confuse the reader when the term “lead,” meaning the
electrical connection of a component, is used.]
3.9
PSD
Power Spectral Density; describes how the power of a signal or time series is distributed with
frequency.
3.10
RoHS
Restriction on Hazardous Substances (Directive 2002/95/EC of the European parliament and
of the Council of 27 January 2003 on the restriction of the use of certain hazardous
substances in electrical and electronic equipment).
3.11
tin-lead
solder bearing the elements tin and lead, respectively, in the by weight amounts of 63-37
unless otherwise specified.
3.12
vehicle
a test sample such as a populated circuit card assembly.
4 Default Test Methods
Use of the default method shall be limited to circuit-card assemblies (CCA). Also, the use of
test coupons may also be used provided the concerns listed in Section 4.1.1 are considered.
4.1 Test Vehicles
4.1.1 Test Vehicle type
Test vehicles used in testing of electronic systems containing Lead-free (Pb-free) solder shall
consist of soldered assemblies that are representative of the materials and processes used in
the assembly and/or repair procedures used by the AHP manufacturer or repair facility.
Characterization and documentation of the test vehicle attributes (both design and
manufacturing) is recommended. Test vehicle attribute documentation shall include, at a
minimum, the following data:
• Board type, material, size, finish, thickness, Copper content
• Piece-part material, package size, package type, termination finish
• Assembly solder alloy
• Assembly processes including fluxes and cleaners
• Thermal management materials
• Underfill and staking materials
• Other mechanically attached structures
• Environmental coatings
• Repair history/process (including solder alloys)
The utilization of electrically functional assemblies/units or representative test vehicles is
permitted provided full characterization of the electronic assembly materials, test vehicle
configuration, and assembly processes are documented. The IPC-9701A specification

– 12 – PAS 62647-3 © IEC:2011(E)
(Section 4.2) contains additional guidance on the characterization and documentation for test
vehicles [1].
The use of test coupons may be used but the user is cautioned that various attributes of
concern can be different at coupon level, i.e., cool down rates, metallurgy, pitch, others. If the
use of coupons is desired, the user shall perform an analysis to determine if such attribute
differences exist. If differences are determined, the user shall mitigate associated risks. Be
aware that results are based upon the processes used and that complete documentation of
the processes is necessary if this document is being used to evaluate the processes.
4.1.2 Sample size
The number of test vehicles shall be based on a statistically based sample size and analysis
plan. Accordingly, several options are available. IPC-9701A specifies a minimum number of
33 test samples. However, sample sizes can be smaller or larger dependent upon usage
conditions. Annex A provides additional insight into sample size selection.
4.2 Pre-Conditioning by Thermal Aging Method
Lead-free (Pb-free) solder properties tend to change over time even under typical storage
conditions, so test programs shall include some preconditioning exposure before the primary
environments (e.g., temperature cycling, vibration, mechanical shock) to replicate these
changes for the lifetime to be assessed [1]. Isothermal elevated temperature aging can
accelerate these changes, such as grain growth, intermetallic compound growth, diffusion-
driven voids, segregation, and oxidation. Such preconditioning can also help gain consistency
among test articles by driving the grain structures to similar characteristics. The isothermal
aging method may not cause changes representative of all particular application environments
and processing conditions (curing bake, burn-in, environmental stress screening, field use
and storage, etc.), so the test protocol and test result interpretation must account for this
effect, and different time/temperature combinations may be required for different programs. In
addition, the test protocol may need to include other preconditioning environments to assess
all the effects pertinent to a particular application.
4.2.1 Thermal Aging Acceleration Model
The default acceleration model to allow tailoring the basic isothermal aging preconditioning
exposure follows the Arrhenius formulation:
 
1 1 E
a
 
AF= exp − (1)
 
T T k
 2 1
where
AF is acceleration factor (dimensionless)
T is the test temperature in °K (in the default case, 100 °C, or 373.15 °K)
T is the application temperature
E is the activation energy (eV), and
a
–5
k is Boltzmann’s constant (8.620 × 10 eV/°K).
For most metallics, E typically is 0.9 to 1.0. However, use of measured results, i.e., actual
a
test data, is encouraged when available.
NOTE 1 E is based on specific material properties. (Each mechanism, i.e., grain growth, intermetallic compound
a
growth, etc., may have its own E and a summation of E should be used by either test or analysis.)
a a
NOTE 2 Isothermal aging may be used as a preconditioning process prior to mechanical vibration and shock
qualification testing. Specific details are beyond the scope of this document.
NOTE 3 Other models may be used as appropriate.

PAS 62647-3 © IEC:2011(E) – 13 –
4.2.2 Default Test Parameters
The isothermal aging of assembled test vehicles should consist of 100 °C for 24 hours. These
isothermal aging parameters will not represent all applications, so the preconditioning
exposure should be tailored as necessary to meet the goals of a particular test program.
4.3 Default Temperature Cycle Test Method
4.3.1 Test Parameters
The temperature cycle test parameters, test temperature ranges, and thermal cycle test
duration shall be in accordance with IPC-9701A sections 3.4.3, 5.1 and 5.2. Test monitoring
requirements shall be in accordance with IPC-9701A Table 4-4. The default test temperatures
shall be –55 °C to 125 °C and the duration shall be 1000 cycles. The ramp shall be less than
20°C /minute and the dwell shall be 15 minutes minimum. The PWB assembly must reach
temperature for the dwell time duration as defined in IPC-9701A. Ramp rates, other than
those specified here may be used but only if material characterization or data supports a
change. (Refer to Section 5.2 of this standard.)
NOTE 1 The –55 °C lower limit is selected based on defence requirements (e.g., performance, storage, etc.).
However, if the user is interested in determining acceleration factor at this temperature, behavioral factors must be
considered. Refer to NOTE 1 in Section 5.2. Accordingly, use of –55 °C readily accommodates a “go/no-go” type
test, i.e., straight performance test.
4.3.2 Test Duration
The number of temperature cycles (or duration) shall be sufficient enough to evaluate the
expected performance of the samples in the required applications. Continuing the test to
complete failure, or to > 75 % failure of all samples is recommended in order to obtain proper
statistical metrics.
NOTE 1 In most cases, 1000 cycles may be sufficient. 1000 cycles is considered a standard duration for many
companies/organizations. However, table 4-1 of IPC-9701A provides additional guidance for duration values.
NOTE 2 Section 4.3.4, of this document, provides further information about the number of temperature cycles and
their interpretation with respect to service life.
4.3.3 Failure Determination and Analysis
Failure determination can be performed by either of two methods.
One method is to define and monitor failure per the daisy-chain monitoring method as
described in IPC-9701A, Section 4.3.3. Implementation of this method requires the
manufacture of special-purpose assemblies constructed from special-purpose test
components and test boards. This method is therefore not generally applicable to standard
functional hardware.
The second method is to monitor electrical performance of functioning circuit card assemblies
continuously during test.
For each of these two methods, the test monitoring and failure criteria shall be fully
documented.
Traditionally, for Tin-Lead solder, a third method has occasionally been used, i.e., failure
analysis via optical criteria. For Lead-free (Pb-free) solders, this method is not recommended.
The failure modes of most Lead-free (Pb-free) solders, as known at this time, would render
the optical approach useless since the cracks tend to be extremely small and cannot be
reliably discerned against the naturally frosty and fissured surface of Lead-free (Pb-free)
solder.
– 14 – PAS 62647-3 © IEC:2011(E)
Failure analysis shall be performed in accordance with the test plan, on a minimum of three
components per test board type. Typical candidates for failure analysis include: early and
failures that fall near the statistical fit, and failures that deviate from the statistical fit.
Techniques for failure analysis may include methods such as "dye and pry" or cross-
sectioning, as appropriate for the components in question. Failure modes shall be
documented. The most important information to be obtained from the failure analysis is
whether or not the failure is associated with the solder interconnection, or whether it relates to
the package or board, or some other non-solder related failure. Beyond this, failure analysis
should also provide information on where solder joint failures occur (within the bulk solder or
at the intermetallic layer or interface). Results may also distinguish between fracture modes
within the solder. Grouping of different failure modes may result in incorrect and/or misleading
test conclusions. Failure analysis efforts should be conducted to insure that individual failure
modes are identified and characterized to avoid the confounding of statistical analyses.
Statistical analysis of the test sample failure data shall be completed in accordance with the
test sample and analysis plan. The completed statistical analysis shall be included in the test
documentation. A 2-parameter Weibull plot is preferred but only if this can provide a good fit
to the experimental data.
4.3.4 Acceleration Model
While this document is not meant for use exclusively for reliability testing, the following
section is presented for information.
The default general form of the acceleration model for temperature cycle testing is:
c
 
∆T
AF   (1a)
=
 
∆T
 2
Where;
AF = acceleration factor,
ΔT = the temperature cycle range in test (in the default case, 165 °C other values have
to be agreed),
ΔT = the application temperature range.
C = exponent, (fatigue ductility exponent) is material and package dependent; including
dependency leaded versus leadless configurations.
Additional possible dependencies are discussed in Note (1).
For many Lead-free materials, many parameters have not yet been characterized. Many
references are available which discuss the fatigue ductility exponent. It is the responsibility of
the user to choose the applicable value. Examples for presently documented values for the
fatigue ductility are in Annex B. It provides a short subset of such references. Annex B also
provides properties (e.g., acceleration test parameters, fatigue ductility exponents, etc.) for
presently known materials but the user should be aware that “C” is not yet known for many
Lead-free (Pb-free) materials.
This basic mod
...