IEC TR 60068-3-82:2024
(Main)Environmental testing - Part 3-82: Supporting documentation and guidance - Confirmation of the performance of whisker test method
Environmental testing - Part 3-82: Supporting documentation and guidance - Confirmation of the performance of whisker test method
IEC TR 60068-3-82:2024, which is a Technical Report, provides technical background information on the whisker test methods from IEC 60068-2-82 and guidance on test selection.
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Standards Content (Sample)
IEC TR 60068-3-82 ®
Edition 1.0 2024-08
TECHNICAL
REPORT
colour
inside
Environmental testing –
Part 3-82: Supporting documentation and guidance – Confirmation of the
performance of whisker test method
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IEC TR 60068-3-82 ®
Edition 1.0 2024-08
TECHNICAL
REPORT
colour
inside
Environmental testing –
Part 3-82: Supporting documentation and guidance – Confirmation of the
performance of whisker test method
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 19.040 ISBN 978-2-8322-9494-9
– 2 – IEC TR 60068-3-82:2024 © IEC 2024
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Whisker growth mechanisms . 10
4.1 General . 10
4.1.1 Sn whiskers . 10
4.1.2 Sn surface finishes . 10
4.2 Basic Sn whisker mechanisms . 12
4.2.1 General remarks . 12
4.2.2 IMC growth . 13
4.2.3 Corrosion . 21
4.2.4 Coefficient of Thermal Expansion (CTE) mismatch – Temperature
cycling test . 26
4.2.5 Influential process factors . 31
5 Whisker testing . 44
5.1 Preconditioning . 44
5.1.1 Pre-aging before testing . 44
5.1.2 Preconditioning of test specimen intended for press-fit applications . 45
5.1.3 Preconditioning of test specimen intended for mechanical loads other
than press fit . 45
5.1.4 Preconditioning of test specimen intended for soldering / welding . 45
5.2 Ambient test . 46
5.2.1 General . 46
5.2.2 Test severity . 46
5.3 Damp heat test . 47
5.3.1 General . 47
5.3.2 Test severity . 47
5.4 Temperature cycling test . 47
5.4.1 General . 47
5.4.2 Test severity . 47
5.5 Ambient test for press-fit applications . 48
5.5.1 General . 48
5.5.2 Test severity . 48
6 Whisker inspection and measurement . 48
6.1 Inspection and detection methods . 48
6.2 Comparison of the methods . 48
6.2.1 Light optical inspection . 48
6.2.2 Scanning electron microscopy (SEM) inspection . 49
6.3 Verification of inspection methodology . 49
6.3.1 General remarks . 49
6.3.2 Overall criteria . 49
6.3.3 Capability of whisker detection . 50
6.3.4 Capability of whisker length measurement . 50
6.3.5 Capability of whisker density measurement . 51
6.4 Technological similarity . 51
Bibliography . 53
Figure 1 – Cross-sectional views of component termination surface finishes . 8
Figure 2 – Grain size and whisker growth on bright Sn and matte Sn finishes [10] . 11
Figure 3 – Example comparison of IMC formation between a Sn surface deposit and
Cu based substrate . 12
Figure 4 – Whisker formation in Sn layer [14] . 13
Figure 5 – Stress gradients in Sn layer [15] . 14
Figure 6 – An example of whisker growth (length) from approximately 2,5 µm matte Sn
plated on Cu aged at ambient conditions (RT/RH) . 14
Figure 7 – Microstructures of different Sn and SnPb surface finishes [5] . 15
Figure 8 – Stress states of different Sn and Sn/Pb surface finishes [5]. 16
Figure 9 – Effect of post-bake heat treatment on microstructure and stress gradients [16] . 17
Figure 10 – Stress states of different Sn surface finishes [16] . 18
Figure 11 – 2D-XRD analysis of Sn surface finishes [22]. 19
Figure 12 – IMC formation of Sn surface finishes . 19
Figure 13 – The compressive stress levels of matte Sn finishes without and with a Ni
barrier and the corresponding whisker growth [12] . 20
Figure 14 – Whisker growth with several factors and saturation with a Ni barrier [23],
[24] 21
Figure 15 – Schematic of corrosion stress in a Sn film and its redistribution capabilities . 21
Figure 16 – Grain orientation of different Sn surface finishes [32] . 23
Figure 17 – Percentage of corroded area after contamination and damp heat aging [32] . 24
Figure 18 – Whisker density with different humidity [27] . 25
Figure 19 – Frequency and length of whiskers after a thermal cycling test . 27
Figure 20 – Comparison max. whisker length with several base materials and
combining environment [25] . 28
Figure 21 – Comparison of whisker growth in an ambient experiment and a basic
experiment combining environmental stresses [25] . 29
Figure 22 – Distribution of whisker length grown on FeNi (Alloy42) base material after
300 cycles . 29
Figure 23 – Whisker growth on FeNi (Alloy42) base material for thermal cycling with ∆t
of 65 °C, 95 °C and 125 °C . 30
Figure 24 – A relationship of ∆ϑ and number of cycles for whisker growth on FeNi
(Alloy 42) base material to reach 100 μm . 31
Figure 25 – FIB and SEM images of the imprint in the Sn film due to a probe needle
[33] 32
Figure 26 – Whisker growing between to connector pins as a result of the externally
applied stressed from the plastic overmold [24]. 32
Figure 27 – Sn plating surfaces and IMC structures after bending by Trim and Form
and without bending [23] . 34
Figure 28 – Schematic representation of a press-fit connection [35] . 35
Figure 29 – A simulation of the stress distribution and corresponding stress gradients
in a press-fit zone [34] . 36
Figure 30 – Contact grooves in the PCB hole from press-in operation and cross-section
of a Sn plated pin with Ni underlayer [35] . 37
Figure 31 – Focused-ion beam investigations of different surface finishes [36] . 38
Figure 32 – Whisker growth from an iSn with Ag additive (for whisker mitigation) plated
via after 1 000 h at 85 °C / 85 % RH aging . 39
– 4 – IEC TR 60068-3-82:2024 © IEC 2024
Figure 33 – Pure Sn plated pin after Pb-free reflow process using solder paste under
serial production conditions . 40
Figure 34 – Sn plating after 3x reflow (40 s at 260 °C) [23] . 40
Figure 35 – Appearance of the Sn surface due to the various flux systems and their
corresponding residues after reflow (min. Profile) and 85 °C/85 % RH exposure . 41
Figure 36 – Representative whisker growth near areas where flux residue is located . 42
Figure 37 – Whisker density with no flux and several flux types . 42
Figure 38 – Sn whisker growth at the area with Al welding point . 43
Figure 39 – Feature of formation area of Sn whisker welding point .
...
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