IEC TR 63141:2020

IEC TR 63141 ®
Edition 1.0 2020-04
TECHNICAL
REPORT
colour
inside
Damp heat, steady state (unsaturated pressurized vapour with air)

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 Tel.: +41 22 919 02 11
3, rue de Varembé info@iec.ch
CH-1211 Geneva 20 www.iec.ch
Switzerland
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 corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform Electropedia - www.electropedia.org
The advanced search enables to find IEC publications by a The world's leading online dictionary on electrotechnology,
variety of criteria (reference number, text, technical containing more than 22 000 terminological entries in English
committee,…). It also gives information on projects, replaced and French, with equivalent terms in 16 additional languages.
and withdrawn publications. Also known as the International Electrotechnical Vocabulary

(IEV) online.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Glossary - std.iec.ch/glossary
details all new publications released. Available online and 67 000 electrotechnical terminology entries in English and
once a month by email. French extracted from the Terms and Definitions clause of
IEC publications issued since 2002. Some entries have been
IEC Customer Service Centre - webstore.iec.ch/csc collected from earlier publications of IEC TC 37, 77, 86 and
If you wish to give us your feedback on this publication or CISPR.

need further assistance, please contact the Customer Service

Centre: sales@iec.ch.
IEC TR 63141 ®
Edition 1.0 2020-04
TECHNICAL
REPORT
colour
inside
Damp heat, steady state (unsaturated pressurized vapour with air)

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 19.040 ISBN 978-2-8322-8090-4

– 2 – IEC TR 63141:2020 © IEC 2020
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
4 Overview of HAST and air-HAST . 9
4.1 Overview of HAST chamber . 9
4.1.1 Structure of HAST chamber . 9
4.1.2 Definition of humidity . 10
4.2 Structure of air-HAST equipment . 12
4.2.1 General . 12
4.2.2 Air concentration and relative humidity . 14
5 Evaluation of tin whisker growth from lead-free plating and solder-joints . 14
5.1 Whisker of lead-free solder (comb-type substrate) . 14
5.1.1 General . 14
5.1.2 Summary of evaluation results of solder-joint whisker growth [3] [4] . 15
5.1.3 Conclusion . 24
5.2 Lead-free whisker of plating (mounting substrate) . 25
5.2.1 General . 25
5.2.2 Test method . 25
5.2.3 Test results. 26
5.2.4 Observations . 27
5.2.5 Conclusion . 29
6 Applied case of JISSO using electrically-conductive adhesive and acceleration
test under humidity environments for joining parts . 29
6.1 General . 30
6.2 Experiment method . 30
6.2.1 Testing material . 30
6.2.2 Test conditions . 30
6.2.3 Measurement and evaluation method . 31
6.3 Test results . 31
6.3.1 Experimental result . 31
6.3.2 Test result (1608R/paste A) . 36
6.4 Points of attention . 38
6.5 Summary . 38
7 Applied air-HAST to c-Si PV modules evaluation tests . 39
7.1 Background and objective . 39
7.2 Photovoltaic module structure and deterioration factors . 39
7.3 Test methods . 40
7.3.1 Crystalline silicon photovoltaic module type-approval international
standard . 40
7.3.2 Air-HAST work . 41
7.3.3 Test samples . 41
7.3.4 Test conditions . 42
7.3.5 Measurement and analysis . 44
7.4 Test results . 44
7.4.1 DHT testing . 44

7.4.2 Saturated HAST. 46
7.4.3 Air-HAST . 47
7.4.4 External appearance comparison . 48
7.4.5 Use of dark I-V measurement to infer deterioration factors . 50
7.4.6 Use of ion chromatography to quantify residual acetic acid ions . 50
7.5 Discussion . 51
7.5.1 Environment test method comparisons . 51
7.5.2 Power-loss profiles by moisture permeation . 52
7.5.3 Comparisons by ion chromatography acetic acid quantification . 52
7.6 Conclusion . 53
8 Summary . 54
Bibliography . 55

Figure 1 – Two types of HAST equipment and their structures . 9
Figure 2 – Image of air vent process . 11
Figure 3 – Saturated test . 11
Figure 4 – Unsaturated test. 12
Figure 5 – Structure of two-vessel type air-HAST chamber . 13
Figure 6 – Structure of one-vessel type air-HAST chamber . 14
Figure 7 – Example of test vehicle with comb pattern . 15
Figure 8 – Process flow for sample build . 16
Figure 9 – Temperature/relative humidity profiles of HAST and air-HAST . 17
Figure 10 – Whisker generation situation in air-HAST . 19
Figure 11 – Mapping of the cross-section at the solder fillet in HAST . 20
Figure 12 – Mapping of the cross-section at the solder fillet in air-HAST . 20
Figure 13 – Arrhenius plot of the bromine-based flux . 22
Figure 14 – Reciprocal of relative humidity of whisker generation on solder . 22
Figure 15 – Humidity properties of whisker generation on solder (pt.2) . 23
Figure 16 – Evaluated sample . 25
Figure 17 – Whisker formation (Substrate: Cu) . 27
Figure 18 – Cross-section inspection results with electron-imaging (Substrate: Cu) . 28
Figure 19 – Elements analysis . 29
Figure 20 – Substrate for conductive resistance measurement and example of
component mounting . 30
Figure 21 – Humidity test conductive resistance monitor test status . 31
Figure 22 – Example of the conductive resistance value change . 32
Figure 23 – Weibull plot of temperature acceleration (under fixed humidity conditions) . 32
Figure 24 – Arrhenius plot (fixed humidity) . 33
Figure 25 – Weibull plot of humidity acceleration (under fixed temperature conditions) . 34
Figure 26 – Arrhenius plot (fixed temperature) . 35
Figure 27 – Eyring plot of all conditions . 35
Figure 28 – Comparison of paste (120 °C/85 % RH Air-HAST) . 36
Figure 29 – Cross-section analysis of 1608R after a humidity test (SEM image) . 37
Figure 30 – Magnified image of cross-section analysis of 1608R after a humidity test
(SEM image) . 37

– 4 – IEC TR 63141:2020 © IEC 2020
Figure 31 – Cross-section analysis of 1608R after a humidity test (SEM image) and
examples of componential analysis by EDX . 38
Figure 32 – Structure of c-Si PV module . 40
Figure 33 – Qualification test sequence in IEC 61215-1 [23] . 41
Figure 34 – Appearance of modules . 42
Figure 35 – EL images after DHT . 45
Figure 36 – Degradation profiles with DHT . 46
Figure 37 – EL images of HAST 105 °C/100 % RH . 46
o
Figure 38 – EL images after HAST 120 C/100 % RH . 47
Figure 39 – Degradation profiles with HAST . 47
Figure 40 – EL images after air-HAST . 48
Figure 41 – Degradation profiles with air-HAST . 48
Figure 42 – Appearance of modules after each test . 49
Figure 43 – Dark I-V . 50
Figure 44 – Residue of acetate ion and retention of P after each test . 51
max
Table 1 – Test conditions . 15
Table 2 – Influence of fluxes and circumstances to whisker growth . 18
Table 3 – Whisker generation in HAST. 18
Table 4 – Whisker generation in air-HAST . 19
Table 5 – Comparison of coefficients for Equations (5), (6) and (7) . 24
Table 6 – Details of evaluated samples . 26
Table 7 – Lead frames composition . 26
Table 8 – Environmental test conditions . 26
Table 9 – Electrically-conductive adhesives . 30
Table 10 – Testing material . 31
Table 11 – Test conditions . 36
Table 12 – Example of failure modes of PV module via materials . 40
Table 13 – Specifications of materials used in PV module . 42
Table 14 – Test conditions . 43
Table 15 – Test conditions and partial pressures . 43

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
DAMP HEAT, STEADY STATE
(UNSATURATED PRESSURIZED VAPOUR WITH AIR)

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.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a Technical Report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC TR 63141, which is a Technical Report, has been prepared by IEC technical committee
104: Environmental conditions, classification and methods of test.
The text of this Technical Report is based on the following documents:
Draft TR Report on voting
104/834/DTR 104/853A/RVDTR
Full information on the voting for the approval of this Technical Report can be found in the
report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 6 – IEC TR 63141:2020 © IEC 2020
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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.
INTRODUCTION
Highly accelerated stress test (HAST), is a high temperature (100 °C or more), high humidity
steady test of unsaturated pressurized steam of 85 % RH, and is the original test method that
was developed for the evaluation of corrosion of packaged semiconductor wiring. This test
method, often referred to as HAST, is applied to primarily non-hermetically sealed small
electronic components, and has been standardized as a standard test method for evaluating,
in an accelerated manner, the resistance to the deteriorative effect of high temperature and
high humidity (IEC 60068-2-66). The equipment used for this test method is a chamber, filled
with unsaturated water vapour, called a HAST chamber.
However, in life evaluation test conditions, acceleration cannot be obtained without air from
the environment being incorporated into the HAST chamber. This test method is referred to as
air-HAST.
Examples of the application of air-HAST are whiskers evaluation of lead-free solder,
deterioration life evaluation of conductive paste, and deterioration life evaluation of solar cells
and are given in this document in order to provide an understanding of air-HAST with the aim,
in future, to standardize air-HAST.
The International Electrotechnical Commission (IEC) draws attention to the fact that it is
claimed that compliance with this document may involve the use of a patent concerning
whisker evaluation given in Clause5.
IEC takes no position concerning the evidence, validity and scope of this patent right.
The holder of this patent right has assured the IEC that he/she is willing to negotiate licences
under reasonable and non-discriminatory terms and conditions with applicants throughout the
world. In this respect, the statement of the holder of this patent right is registered with IEC.
Information may be obtained from:
ESPEC CORP.
3-5-6,Tenjinbashi,Kita-ku
Osaka,530-8550
Japan
Attention is drawn to the possibility that some of the elements of this document may be the
subject of patent rights other than those identified above. IEC shall not be held responsible for
identifying any or all such patent rights.
ISO (www.iso.org/patents) and IEC (http://patents.iec.ch) maintain on-line data bases of
patents relevant to their standards. Users are encouraged to consult the data bases for the
most up to date information concerning patents.

– 8 – IEC TR 63141:2020 © IEC 2020
DAMP HEAT, STEADY STATE
(UNSATURATED PRESSURIZED VAPOUR WITH AIR)

1 Scope
This document describes a new test method to control the volume of air injected into a
conventional HAST chamber filled with water vapour. This document provides an overview of
the conventional HAST chamber, an overview of the air-HAST equipment where air is
incorporated into the HAST chamber, an example of an air-HAST test apparatus, and
application examples of air-HAST.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
galvanic corrosion
corrosion damage induced when two dissimilar materials are coupled in a corrosive electrolyte
3.2
Kirkendall effect
motion of the boundary layer between two metals that occurs as a consequence of the
difference in diffusion rates of the metal atoms
3.3
whisker
metallic protrusion which grows up naturally during storage or in use
3.4
HAST
highly accelerated stress test
original test method developed to evaluate the corrosion of the semiconductor wiring at a high
temperature of 100 °C or more
3.5
air-HAST
HAST test method with the addition of further air partial pressure in a HAST chamber

4 Overview of HAST and air-HAST
4.1 Overview of HAST chamber
4.1.1 Structure of HAST chamber
HAST is an evaluation test at a high-temperature and high-humidity unsaturated pressurized
steam atmosphere environment of more than 100 °C. The test apparatus is roughly divided
into a one-vessel type and a two-vessel type, as shown in Figure 1.

a) One-vessel type b) Two-vessel type
Key
1 pressure gauge
2 pressure vessel
2 temperature sensor for moisture
4 safety valve
5 door
6 working space
7 heater for humidifying water
8 humidifying water
9 temperature sensor for humidifying water
10 air-exhaust valve
11 fan
12 heater for moisture fan for air
13 magnetic coupling
14 pressure vessel 2
Figure 1 – Two types of HAST equipment and their structures
The configuration of the one-vessel type and the configuration of the two-vessel type are
explained as follows.
a) Configuration of the one-vessel type (See Figure 1 a))
This type of chamber is called a one-vessel type because it has only one pressure vessel.
The inner cylinder provided inside the pressure vessel is divided into a steam generator
for supplying humidifying water vapour and a working space to set the sample. A fan for
generating a flow of steam from the steam generator to the working space is provided in
the back of the inner cylinder. Heaters are arranged outside of this fan and in the steam
generator. Steam flow rate of this system is suppressed to about the flow rate of natural
convection.
b) Configuration of the two-vessel type (See Figure 1 b))

– 10 – IEC TR 63141:2020 © IEC 2020
This type of chamber is called a two-vessel type because it is composed of two different
pressure vessels: the test chamber which sets the sample and the steam generation chamber
which supplies humidifying water vapour. Heaters are respectively located in the test chamber
and the steam generation chamber. Water vapour is fed by boiling water vapour pressure to
the test chamber from the steam generation chamber holding the humidifying water, the
amount that was the condensed water goes back into the steam generation chamber. There is
an inner cylinder in the test chamber, and a heater is provided on the outside of this inner
cylinder. Heat from the heater is transmitted to the inner cylinder, keeping the temperature of
the entire working space at a constant level. This system is also referred to as a natural
convection because it does not require a fan for the circulation of water vapour.
4.1.2 Definition of humidity
HAST is carried out in a closed vessel which is isolated from the atmosphere of the
atmospheric pressure (pressure vessel), under the assumption that air is absent from the
filled water vapour atmosphere. Therefore during the start of HAST, steps to eliminate air
(Figure 2 air vent process) are always taken. The humidifying water is heated and boiled by
the heater, the exhaust valve is opened and the test vessel is filled with 100 % water vapour
until all air is discharged. Then the exhaust valve is closed to perform heating until the test
temperature in the vessel is reached again. The difference between the saturated test and
unsaturated test in the working space in the chamber is then recorded. The state of the
saturated test is shown in Figure 3. The state of the unsaturated test is shown in Figure 4.
The air vent process is executed in both the saturated test and unsaturated test, the chamber
needs to be filled with 100 % water vapour without air.
In saturation conditions, the working space is kept at a constant temperature by water vapour
generated from the humidifying water because the heating source is only humidifying the
water heater.
T : is the humidification water temperature;
T : is the test space temperature.
= T .
In this case the vessel temperature is T
1 2
In the case of the unsaturated test, a heater for heating the working space is installed in the
chamber. In the apparatus, water vapour generated from the humidifying water enters the
working space, it is re-heated by the heater to a higher temperature than the water vapour in
the surroundings. When the temperature in the vessel is controlled to T < T , the working
1 2
space is an unsaturated vapour atmosphere. At this stage, the relative humidity (RH) of the
working space is determined by the following equation:
H = P / P × 100
1 2
where
H: is the relative humidity, RH (%);
P : is the saturated water vapour pressure in the humidification water temperature T (MPa);
1 1
P : is the saturated water vapour pressure in the test space temperature T (MPa).
2 2
At this stage the vessel pressure, P , is the test pressure because it is determined by the
temperature of the humidification water (T ).
a) Air-exhaust valve open b) Air-exhaust valve close
Key
1 water vapour
2 humidifying water
3 heater
4 air-exhaust valve
Figure 2 – Image of air vent process

Key
1 working space
2 humidifying water
Figure 3 – Saturated test
– 12 – IEC TR 63141:2020 © IEC 2020

Key
1 working space
2 humidifying water
Figure 4 – Unsaturated test
4.2 Structure of air-HAST equipment
4.2.1 General
In the case of air-HAST, it is necessary to leave the air into a traditional HAST chamber.
Considering the possibility that a residual air volume greatly affects test results, it becomes
necessary to accurately control the amount of air. Using a conventional HAST chamber, to
ensure the air-HAST environment contains air, the following two methods are used:
a) keeping a certain amount of air during start-up, and
b) injecting a predetermined amount of air after discharging air to the outside of the chamber.
Technically, either method is possible. Method a) can be realized simply by omitting the vent
process, but it is difficult to control the amount of air to be discharged when adjusting the air
volume. Method b) injects air after discharging air, so that the entire process becomes
complicated but the control of the amount of air is easy. A dual-vessel type air-HAST chamber
is shown in Figure 5. This equipment, which is a wet bulb installed and provided with a pan
and wick temperature sensor in the working space of a conventional two-vessel type chamber,
has become a mechanism for controlling the humidification water heater (steam generator) at
the specified temperature. This air-HAST system is easily obtained from a dual-vessel type
HAST equipment and has the advantage of facilitating experimentation. The method consists
in injecting a predetermined amount of air from the air pressure port after the system has
reached a steady state and all air in the chamber has been evacuated. The air remaining in
the chamber is controlled by a pressure controller, so the constant partial pressure can be
held.
Key
1 pressure gauge 2 door 3 working space
4 pressure vessel 2 5 humidifying water 6 heater for humidifying water
7 solenoid valve for drain 8 heater for water vapour 9 wet bulb pan
10 cloth wick 11 sensor for humidifying water 12 sensor for water vapour
13 safety valve 14 pressure vessel 1 15 pressure sensor
16 pressure regulator 17 inlet 18 flow controller
19 check valve 20 solenoid valve
Figure 5 – Structure of two-vessel type air-HAST chamber
A one-vessel air-HAST chamber (Figure 6) is used for whiskers, electrically-conducting
adhesives and photovoltaic modules reliability tests. A one-vessel air-HAST chamber is of a
less complex constitution providing reproducible and compatible test results. At first, the
specimen is set in the vessel at room temperature, the door is closed, the test is started to
create heat and humidity. This way there is no pressure damage by a sudden change in
pressure and no condensation on the specimen. In addition, a forced steam of water-vapour is
normally generated by means of a fan installed in the chamber to create air velocity and
accurately detect humidity by a dry and wet bulb.

– 14 – IEC TR 63141:2020 © IEC 2020

Key
1 door 2 specimen 3 cloth wick
4 humidifying water 5 humidifying water temperature sensor 6 wet bulb temperature sensor
7 humidifying heater 8 air circulating fan motor 9 magnetic coupling
10 chamber temperature sensor 11 heater 12 air circulating fan
13 inner cylinder 14 pressure vessel
Figure 6 – Structure of one-vessel type air-HAST chamber
4.2.2 Air concentration and relative humidity
Initially the intention was to determine the exact concentration of oxygen using an oxygen
concentration meter. However, since the inside of the HAST equipment reaches a high
pressure up to 1 atm or more, a commercial oxygen concentration meter operating in such an
environment was not available.
Therefore, the amount of air is calculated based on the gauge pressure. Moreover, since it is
difficult to measure the correct relative humidity directly in an air-HAST chamber, relative
humidity is controlled by the temperature in the same way as for a conventional HAST
chamber.
5 Evaluation of tin whisker growth from lead-free plating and solder-joints
5.1 Whisker of lead-free solder (comb-type substrate)
5.1.1 General
Lead-free manufacturing of electronic products has now reached its implementation stage and
around 2 000, the focus was moved to finding a solution to suppress tin whisker growth.
Related studies are still on-going.

Clause 5 describes the results of the studies, and how the whiskers generated from the
corrosion of solder joints or plated surface are accelerated by high-temperature and high-
humidity conditions; conventional HAST with temperatures exceeding 100 °C does not give
the expected further acceleration and good acceleration is achieved only with air-HAST with
additional air partial pressure [1] to [11] .
5.1.2 Summary of evaluation results of solder-joint whisker growth [3] [4]
5.1.2.1 Test method
Figure 7 shows examples of the test vehicles with comb pattern conductors. The conductor
width and the conductor spacing in Figure 7 a) are both 0,318 mm. In Figure 7 b) the
conductor width and the conductor spacing are both 0,165 mm. These vehicles are submitted
to preconditioning as described in Figure 8 with Sn-3Ag-0,5Cu solder. The coated flux on the
comb pattern substrate consists of a mass fraction of 75 % of IPA (isopropyl alcohol) and a
mass fraction of 25 % of WW (water white) rosin with the addition of a varied amount of
diethylamine hydrobromide as an activator. Environmental test conditions are given in Table 1
and Figure 9 shows pressure, temperature and humidity profiles for both the HAST
(Figure 9 a)) and air-HAST test chambers (Figure 9 b)).

a) Large pitch (comb pattern 1) b) Small pitch (comb pattern 2)
Figure 7 – Example of test vehicle with comb pattern
Table 1 – Test conditions
Test type Test condition
55 °C/85 % RH
High temperature/high humidity 75 °C/85 % RH
85 °C/85 % RH
110 °C/85 % RH
HAST
(Air partial pressure 0 kPa)
110 °C/85 % RH
Air-HAST
a
(Air partial pressure 130 kPa)
a
Theoretical value.
___________
Numbers in square brackets refer to the bibliography.

– 16 – IEC TR 63141:2020 © IEC 2020

Figure 8 – Process flow for sample build
HAST (wet and dry bulb controlled) conditions are:
Total pressure: 0,121 8 MPa abs, 0,03 MPa G.
Air-HAST conditions are:
Total pressure: 0,251 8 MPa abs, 0,15 MPa G.

a) HAST temperature/relative humidity profiles

b) Air-HAST temperature/relative humidity profiles
NOTE 1 Both absolute pressure (abs) and gauge pressure (G) are shown.
NOTE 2 Total pressure of air-HAST is set at 0,251 8 MPa, as the sum of partial pressure of air (0,130 MPa) and
water vapour (0,121 8 MPa).
NOTE 3 Gauge pressure = Absolute pressure – 0,101 3 MPa (atmospheric pressure).
Figure 9 – Temperature/relative humidity profiles of HAST and air-HAST
5.1.2.2 Test results
The results of the temperature-humidity tests are shown in Table 2. Growth of whiskers was
observed in early stages with a bromine-based flux. The acceleration by temperature was also
observed from the test with varied temperatures. Air-HAST equipment with a single test
chamber as shown in Figure 6 was used for an acceleration property study. Although
conventional HAST in the region of 110 °C/85 % RH for test vehicles with a bromine-based
flux exhibited no whisker growth as shown in Table 3, air-HAST – with added air partial
pressure – exhibited whisker growth from an early stage as shown in Table 4 [3] [4].
Examples of such whiskers are shown in Figure 10.

– 18 – IEC TR 63141:2020 © IEC 2020
Table 2 – Influence of fluxes and circumstances to whisker growth
Activator Diethyl amine HBr salt
Content wt % 0,1 2 2 2 4
Temperature (°C) 85 85 70 55 85
Humidity (% RH) 85 85 85 85 85
500 h None 40 μm - - 45 μm
1 000 h None 67 μm None None 44 μm
1 500 h None 91 μm None None 63 μm
2 000 h None 83 μm 16 μm None 87 μm
3 000 h - 102 μm 35 μm None -
4 000 h - 125 μm 86 μm None -
5 000 h - 153 μm 64 μm None -
7 000 h - 160 μm 110 μm 20 μm -
10 000 h - 208 μm 112 μm 17 μm -

Table 3 – Whisker generation in HAST
No. Flux Solder Pattern HAST (110 °C /85 % RH)
composition
200 h 300 h 400 h 600 h
1 Flux none Sn-3Ag-0,5Cu Large None None None None
2 Small None None None None
3 Bromine Large None None None None
system flux
4 Small None None None None
Table 4 – Whisker generation in air-HAST
No. Flux Solder Pattern Air-HAST (110 °C 85 % RH)
composition
50 h 100 h 150 h 200 h 300 h 400 h
1 Flux Sn-3Ag- Large None None None None None None
None 0,5Cu
(A)
2 Small None None None None None None
(B)
3 Bromine Large None None 38 μm 15 μm 28 μm 46 μm
system
(A)
flux
4 Small None 30 μm 37μm 36 μm 53 μm 90 μm
(B)
Figure 10 – Whisker generation situation in air-HAST
Ohno et al reported that the whisker growth is accelerated by localized solder corrosion
enhanced by the residue of bromine-based activator [5].

– 20 – IEC TR 63141:2020 © IEC 2020

a) Reflected electron image b) Elementary analysis
Test conditions:
110 °C/85 % RH 200 h
Solder: Sn-3Ag-0,5Cu
Flux: Bromine system flux
Figure 11 – Mapping of the cross-section at the solder fillet in HAST

a) Reflected electron image b) Elementary analysis
Test conditions:
110 °C/85 % RH 200 h
Solder: Sn-3Ag-0,5Cu
Flux: Bromine system flux
Figure 12 – Mapping of the cross-section at the solder fillet in air-HAST

Cross-section observation of samples from these HAST and air-HAST tests are shown in
Figure 11 and Figure 12. Figure 11 shows no corrosion in the solder layer, even after 200 h of
HAST exposure with no apparent whisker growth, while in Figure 12, showing the result of the
air-HAST test, oxygen penetration into the solder layer was observed. These results
correspond to whisker growth [3].
5.1.2.3 Effect of oxygen on solder whisker generation [3]
The previous results indicate that, in addition to humidity, the presence of oxygen is
necessary for the generation of whisker. Electrochemical reactions of tin, with the effect of
oxygen included, were derived as follows. Tin transfers to oxide by way of hydroxide as these
formulae indicate.
2+ −
Sn ⇌ Sn + 2e (1)
− −
O + 2H O + 4e ⇌ 4OH (2)
2 2
2+ −
Sn + 2OH ⇌ Sn(OH) (3)
− −
Sn(OH) + 2OH ⇌ SnO + 2H O + 2e (4)
2 2 2
Tests to evaluate electrochemical migration (ECM) was also conducted, and ECM was
observed without any air partial pressure, thus indicating its mechanism is different from that
of whisker generation [7].
5.1.2.4 Acceleration property from varied humidity test [3]
5.1.2.4.1 General
Whisker generation evaluation was conducted on test boards with comb-pattern conductors,
with Sn-3Ag-0,5Cu solder and a mass fraction of 2 % flux with a bromine-based activator. The
environmental test conditions were based on standard conditions of 85 °C/85 % RH.
Temperatures ranging from 55 °C to 110 °C (typical air-HAST conditions) with a constant
humidity of 85 % RH were used. Humidity ranging from 65 % RH to 85 % RH with a constant
temperature of 85 °C was applied. The time needed for whisker growth of approximately
20 µm was defined as time-to-whisker L (hours) and used throughout the study.
5.1.2.4.2 Time-to-whisker versus temperature with constant humidity
The results of the test with a constant relative humidity of 85 % RH and varied temperatures
are shown in Figure 13. The figure shows good linearity on an Arrhenius plot (relationship
between reciprocal of absolute temperature and time-to-whisker on a logarithmic scale). Air-
HAST was employed at a temperature of 110 °C. Good linearity was obtained over a wide
range of test temperatures. Activation energy E was calculated from the slope of this plot as
a
0,84 eV.
– 22 – IEC TR 63141:2020 © IEC 2020

Figure 13 – Arrhenius plot of the bromine-based flux
5.1.2.5 Discussion on lifetime characteristic formulae
Various formulae were proposed for lifetime characteristics. The Arrhenius plot, among others,
is widely known for temperature changes, using the reciprocal of absolute temperature, and
exhibited good linearity as shown in Figure 13.

Conditions:
Solder: Sn-3Ag-0,5Cu
Temperature: 85 °C
Figure 14 – Reciprocal of relative humidity of whisker generation on solder
...