IEC PAS 62483:2006

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IEC
AVAILABLE
PAS 62483
SPECIFICATION
First edition
2006-09
Test method for measuring whisker growth
on tin and tin alloy surface finishes

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IEC/PAS 62483:2006(E)
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PUBLICLY
IEC
AVAILABLE
PAS 62483
SPECIFICATION
First edition
2006-09
Test method for measuring whisker growth
on tin and tin alloy surface finishes
 IEC 2006  Copyright - all rights reserved
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PAS 62483 © IEC:2006(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
TEST METHOD FOR MEASURING WHISKER GROWTH
ON TIN AND TIN ALLOY SURFACE FINISHES

FOREWORD
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all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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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 62483 was submitted by JEDEC and has been processed by IEC technical
committee 47: Semiconductor devices.
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
47/1842/NP 47/1876/RVN
Following publication of this PAS, the technical committee or subcommittee concerned will
investigate the possibility of transforming the PAS into an International Standard
An IEC-PAS licence of copyright and assignment of copyright has been signed by the IEC
and JEDEC and is recorded at the Central Office.
This PAS shall remain valid for an initial maximum period of three years starting from
2006-08. The validity may be extended for a single three-year period, following which it shall
be revised to become another type of normative document or shall be withdrawn.
Page i
Test Method for Measuring Whisker Growth on Tin
and Tin Alloy Surface Finishes

Introduction
This document contains a suite of recommended tin whisker growth tests. If these common
tests are adopted, then the industry can collect common and comparable data that may
improve the understanding of the fundamentals of whisker growth and allows comparisons
between technologies. Tests in this document may be changed in the future as a better
understanding of the mechanisms causing tin whisker growth is developed.

Based on a variety of testing and data review from around the globe, three test conditions
have been identified that appear to be suitable for monitoring tin whisker growth. The three
test conditions include two isothermal conditions with controlled humidity and a thermal
cycling condition. However, these test conditions have not been correlated with longer
environmental exposures of components in service. Thus, there is at present no way to
quantitatively predict whisker lengths over long time periods based on the lengths measured
in the short-term tests described in this document. At the time of writing, the fundamental
mechanisms of tin whisker growth are not fully understood and acceleration factors have not
been established. Certain applications, e.g., military or aerospace, may require additional
and/or different tin whisker tests or evaluations.

The predominant terminal finishes on electronic components have been Sn-Pb alloys. As
the industry moves toward Pb-free components and assembly processes, the predominant
terminal finish materials will be pure Sn and alloys of Sn, including Sn-Bi and Sn-Ag.

Pure Sn and Sn-based alloy electrodeposits and solder-dipped finishes may grow tin
whiskers, which could electrically short across component terminals or break off the
component and degrade the performance of electrical or mechanical parts.

Page 2 Copyright © 2005, JEDEC; 2006, IEC

Test Method for Measuring Whisker Growth on Tin
and Tin Alloy Surface Finishes
(TEST METHOD A121)
1 Scope
The methodology presented in this document, see Annex A for process flow, is applicable for
studying tin whisker growth from finishes containing a predominance of tin (Sn). This test
method may not be sufficient for applications with special requirements, e.g., military or
aerospace. Additional requirements may be specified in the appropriate requirements
document.
The purpose of this PAS is to:

• Provide an industry-standardized suite of tests for measurement and comparison of
whisker propensity for different plating or finish chemistries and processes.
• Provide a consistent inspection protocol for tin whisker examination.
• Provide a standard reporting format.

2 Normative references
JESD22-A104, Standard for Temperature Cycling

IPC 7530, Guidelines for Temperature Profiling for Mass Soldering (Reflow & Wave)
Processes
3 Terms and definitions
3.1 total axial whisker length: The distance between the finish surface and the tip of
the whisker that would exist if the whisker were straight and perpendicular to the surface.

NOTE For tin whiskers that bend and change directions, the total axial length can be estimated by
adding all of the straight subdivisions of the whisker. (See Figure 5.)

3 Terms and definitions (cont’d)

3.2 whisker: A spontaneous columnar or cylindrical filament, usually of monocrystalline
metal, emanating from the surface of a finish. (See Annex C for example pictures of tin
whiskers.)
NOTE 1 For the purpose of this document, whiskers have the following characteristics:
• An aspect ratio (length/width) greater than 2
• Can be kinked, bent, or twisted
• Usually have a uniform cross-sectional shape
• Typically consist of a single columnar filament that rarely branches
• May have striations along the length of the column and/or rings around the circumference
of the column
• Length of 10 microns or more. Features less than 10 microns may be deemed important
for research but are not considered significant for this test method.

NOTE 2 Whiskers are not to be confused with dendrites: fern-like growths on the surface of a
material which can be formed as a result of electromigration of an ionic species or produced during
solidification. (See Annex D for a picture of a typical solidification dendrite.)

3.3 whisker density: The number of whiskers per unit area on a single lead or coupon
area.
3.4 whisker growth: Measurable changes in whisker length and/or whisker density after
exposure to a whisker test condition for a certain duration or number of cycles.

3.5 whisker test coupon: A piece of metal of specified size and shape that is plated or
dipped with a tin finish for the purpose of measuring the propensity for whisker formation and
growth.
4 Apparatus
4.1 Temperature cycling chambers

Air to air temperature cycling chamber(s), capable of cycling from -55 (+0/-10) °C to
+85(+10/-0) °C or from -40(+0/-10) °C to +85(+10/-0) °C. The temperature cycling
chamber(s) must be able to satisfy the cycle conditions defined in Table 4.

Page 4 Copyright © 2005, JEDEC; 2006, IEC

4 Apparatus (cont’d)
4.2 Temperature humidity chambers

Temperature–humidity (T&H) chambers capable of non-condensing 60 ±5 °C, 87 +3/-2% RH
and 30 ±2 °C, 60 ±3% RH environment.

NOTE 1 The elevated temperature–humidity condition of 60 ±5 °C, 87 +3/-2% RH is close to the
condensation point. If water condenses on the tin finish during environmental exposure, the
condensed moisture and resulting corrosion may affect the final test results. To prevent condensation
in the T & H chamber, the chamber dry-bulb temperature must exceed the wet-bulb temperature at all
times by not less than 2.4 °C (or equivalent for electronic sensors). Before opening of the chamber
door for loading and unloading, the chamber temperature and humidity should be ramped down
sufficiently close to room ambient (recommended within 10 °C and 10% RH) to prevent condensation
on the test samples and chamber walls.

NOTE 2 During operation, condensation is most likely to occur on the T & H test chamber walls and
ceiling; therefore, it is recommended that the test samples be sufficiently shielded from any condensed
water that may drip from the chamber ceiling and/or walls onto the samples.

NOTE 3 When loading the test samples into the T & H test chamber, the sample temperature must
be sufficiently higher than the chamber ambient temperature to avoid condensation on the test
samples. It is recommended that the test samples and all sample trays or holders be preheated (to a
temperature equal to the test temperature of the T & H test chamber) in a dry-bake oven prior to
loading them into the T & H test chamber.

NOTE 4 Frequent wet-bulb maintenance is required for proper control of this test condition.

4.3 Optical stereomicroscope (Optional)

Optical stereomicroscope with adequate lighting capable of 50X to 150X magnification and
capable of detecting whiskers with a minimum axial length of 10 microns, per Annex B. If tin
whiskers are measured with an optical system, then the system must have a stage that is
able to move in three dimensions and rotate, such that whiskers can be positioned
perpendicular to the viewing direction for measurement.

4.4 Optical microscope (Optional)

Optical microscope with adequate lighting capable of 100X to 300X magnification and
capable of measuring whiskers with a minimum axial length of 10 microns, per Annex B. For
tin whisker measurements, the optical system must have a stage that is able to move in three
dimensions and rotate, such that whiskers can be positioned perpendicular to the viewing
direction for measurement.
4.5 Scanning electron microscope

Scanning electron microscope (SEM) capable of at least 250X magnification. An SEM fitted
with an X-ray detector is recommended for elemental identification.

4 Apparatus (cont’d)
4.6 Convection reflow oven (Optional)

A convection reflow system capable of achieving the reflow profiles of Table 3.

5 Sample requirements and optional preconditioning

For specific requirements of tin finishes, the relevant test conditions, read points, and
durations shall be described in a test plan agreed upon by the supplier and user. For
comparing various finishes for whisker propensity, it is recommended that all three conditions
defined in Table 4 be used and that sufficient test time be allocated to allow for the tin
whisker incubation period to expire (typically up to 3000 hours). In addition, each test
condition is to be performed independently on separate samples.

5.1 Test samples
Any test samples with tin-based finishes may be studied, including Sn-Pb finishes. Sample
types may include experimentally plated or tin-finished coupons or components, or
production-plated/finished electronic components. However, coupons may not be
representative of final product because of processes, such as lead trim and form.

5.1.1 Sample size
The measurement of maximum whisker length may be significantly influenced by the amount
of surface examined because whisker appearance and length are distributed over a range.
Examination of large areas may result in a larger maximum whisker length than would be
detected by examining a small area. In fact, whiskers may not occur on a particular sample
or termination even though other samples and terminations from the same plating or finish lot
exhibit significant whisker growth. Therefore, if the total area inspected is not held constant,
data will not be directly comparable among different experiments.

5.1.1.1 Electronic components with leads

For research and comparison of finished components, plating baths, processes, etc,
regarding propensity for whisker growth, a minimum of 96 terminations/leads on at least six
samples, for each test condition at each inspection read out, are required to attain a
meaningful detection level. The number of samples may need to be adjusted in order to
obtain a total of 96 terminations/leads. Components should have completed all
manufacturing operations. For consistency and traceability, if applicable to package type,
choosing corner leads is recommended. For finished components with large terminations,
Table 1 may be used to reduce the number of terminations that are recommended for
inspection.
Page 6 Copyright © 2005, JEDEC; 2006, IEC

5.1.1 Sample size (cont’d)
5.1.1.2 Test coupons
For comparison purposes, if using coupons, a total inspection area of at least 75 mm on at
least 3 coupons is required for each test condition. For small coupons, it is recommended
that there be sufficient coupons so that the total area inspected adds up to a minimum of 75
mm , as described in Table 1.
Table 1 — Details on the number of test samples and terminations required for
comparison of screening inspection data. The number of terminations required for
inspection depends on the tin-finished area of each termination.
Minimum Total
Minimum Minimum
Minimum Total Inspection Number of
Tin
Inspection
Sample Number Inspection Surface Area
Finished
Areas for
Type of Area for per Sample for
[1]
Area
Samples Screening Screening Screening
[2]
Inspection Inspection Inspection
2 2 2
Coupons 3 Top and two
< 25 mm 75 mm 75 mm ÷
sides of coupon
(Plated area on
top and 2 sides
of coupon)
2 2
Coupons 3 Top and two 3
≥ 25 mm 75 mm
sides up to a
total of 25 mm
2 2
Components 6 Top and 2-3 96
< 0.85 mm 75 mm
sides of
termination
2 2 2
Components 6 Top and 2-3
≥ 0.85 mm 75 mm 75 mm ÷
sides of
(Plated area on
termination
top and 2-3 sides
of termination)
NOTE 1 See Figures 2, 3, and 4 for detailed definition of the plated/finished area for inspection.

NOTE 2 For large terminations, more than one inspection area may exist on the same termination.

The same 6 components or 3 coupons for each test condition may be evaluated at all
sequential read outs, including the final readout. Hence, to study a single finish, 18
component or 9 coupon samples are required to complete the three test conditions.
Alternatively, the test may be started with sufficient test samples to inspect 6 different
component or 3 coupon samples at each read out. In this case, the number of test samples
required will be a minimum of 18 component or 9 coupon samples times the number of read
out points during the test. (For example, if a finish is studied in temperature cycling for 2000
cycles with read outs performed at 500, 1000, 1500, and 2000 cycles, then 24 component
samples are required just for this test condition.) If a more accurate determination of growth
kinetics is needed, it is recommended that the same test samples be used for each
sequential read out instead of using re-populated samples.

5.1 Test samples (cont’d)
5.1.2 Optional test sample preconditioning

Table 2 lists optional test sample preconditioning treatments that are recommended prior to
all subsequent Sn whisker growth tests. If the test method described in this standard is used
as part of a tin finish qualification, then the user and supplier must agree on the precondition
requirements before commencement of testing.

Table 2 — Optional Preconditioning Treatments for Tin Whisker Test Samples
Preconditioning
Thermal Profile
Condition Temperature Use Guidelines
Exposure
Exposure
Normal ambient Intended to test for whisker growth under
A None
exposure ambient temperature/humidity storage.
Room temperature Intended for samples without under-plating or
storage for a post bake mitigation before exposure to high
15 -30 °C
B minimum of 4 temperature/humidity storage, temperature
30 – 80% RH
weeks after the cycling or preconditioning per conditions C
finish is applied or D.
Sn-Pb Sn-Pb profile Intended to test for whisker growth after
Temperature per clause thermal exposure to Sn-Pb SMT assembly
C
Preconditioning  5.1.2.1 temperatures (backward compatibility).
Pb-free Pb-free profile Intended to test for whisker growth after
D Temperature per clause thermal exposure to Pb-free SMT assembly
Preconditioning 5.1.2.1 temperatures (Pb-free compatibility).

5.1.2.1 Optional test sample preconditioning profiles

Test sample preconditioning profile information is shown in Table 3 and Figure 1. All profile
criteria reference either the lead or solder joint temperature for components or the surface
temperature for coupons. For the profile and the preconditioning process itself, it is
recommended that non-metallized carriers or printed circuit boards are used to hold the
samples during the reflow process. For components with leads, the orientation of the
component shall be in the “live bug” configuration (i.e., leads down touching the carrier or
board).
Page 8 Copyright © 2005, JEDEC; 2006, IEC

5.1 Test samples (cont’d)
[1]
Table 3 — Optional Preconditioning Reflow Profiles
Profile Feature Sn-Pb Profile Pb-Free Profile
Average ramp-up rate
3 °C/second max. 3 °C/second max.
(Ts to T )
max peak
Preheat:
- Temperature Min (Ts )
min
100 °C 150 °C
- Temperature Max (Ts )
max
150 °C 200 °C
- Time (Ts to Ts ) (t )
60–120 seconds 60–120 seconds
min max s
Time maintained above:
- Temperature (T ) 183 °C 217 °C
L
- Time (t ) 60–120 seconds 60–120 seconds
L
[2] [3]
Lead or Solder Joint Temperature (T ) 200–220 °C 245–260 °C
peak
Average ramp-down Rate (T to Ts ) 6 °C/second max. 6 °C/second max.
peak max
6 minutes max. 8 minutes max.
Time 25°C to Peak Temperature
NOTE 1 All temperatures refer to lead or solder joint temperature for components or the surface
temperature for coupons.
NOTE 2 Maximum temperature of 220 °C ensures that the finish is not melted (i.e., melting point of
pure Sn is 232 °C).
NOTE 3 Minimum temperature of 245 °C ensures that the finish is melted.

T
peak
Ramp Range
T
L
t
L
Ts
max  Preheat Area
Ts min
t
S
o
Time 25  C to Peak
Time
Figure 1 — Optional Preconditioning Reflow Profile.

Temperature
6 Whisker inspection, length measurement and test conditions

The whisker inspection procedure includes three parts: (1) the initial pre-test inspection, (2)
the screening inspection, and (3) the detailed inspection. The initial inspection should be
performed once before the test samples are exposed to any test condition. The screening
inspection should be performed at each read out. If whiskers are detected in the screening
inspection, then the detailed inspection should be performed at that read-out. The whisker
inspections can be performed using either an SEM or a validated optical system meeting the
conditions as outlined in Annex B.

6.1 Handling
When handling test samples, care must be taken to avoid contact with the finish which may
result in the detachment of whiskers. For SEM inspection, a conductive material to attach
the test sample to the SEM work holder to prevent charging is recommended, however, if the
same test samples will be inspected at each read out and then returned to the test condition
for further exposure, conductive sputter coating, such as C, Pt, or Au, must not be deposited
to aid SEM inspection. If the test samples will not be returned to the test condition, then a
conductive coating may be used to reduce sample charging.

6.2 General inspection instructions

The screening (clause 7.5) and detailed inspections (clause 7.6) for whiskers shall include
inspection for whisker patterns and relationships (alignments) between whiskers and sample
features or between whiskers and irregularities. Irregularities are extrinsic (acquired)
features which deviate from the original, ideally (perfectly) plated surface, particularly those
features that occur as a result of post-plating mechanical operations or deterioration of the
plated surface.
During inspection, particular attention should be paid to the occurrence of corrosion, surface
scratches, tool/clamping marks, edges and surfaces created by punching or shearing
operations, heat affected zones or solder-to-plated surface boundaries (created during
assembly). The presence of special relations between whiskers and irregularities should be
recorded in Table E.2 of Annex E. In addition, it is strongly recommended that images are
taken to document any relationship observed between whiskers and features and/or
irregularities.
Annex F shows examples of corrosion irregularities. (In this instance the corrosion occurs in
areas adjacent to other irregularities created by shearing and punching operations that
expose copper base metal.)
6.3 Initial pretest inspection

Prior to any test condition exposure, an initial optical or SEM inspection should be conducted
and documented to determine if whiskers are present. The same procedure used for the
screening inspection, described in clause 7.5, shall be followed.

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