IEC TS 62647-2:2012
(Main)Process management for avionics - Aerospace and defence electronic systems containing lead-free solder - Part 2: Mitigation of deleterious effects of tin
Process management for avionics - Aerospace and defence electronic systems containing lead-free solder - Part 2: Mitigation of deleterious effects of tin
IEC/TS 62647-2:2012(E) establishes processes for documenting the mitigating steps taken to reduce the harmful effects of Pb-free tin in electronic systems. This Technical Specification is applicable to aerospace, defence, and high performance (ADHP) electronic applications which procure equipment that may contain Pb-free tin finishes. It may be used by other high-performance and high-reliability industries, at their discretion.
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IEC/TS 62647-2 ®
Edition 1.0 2012-11
TECHNICAL
SPECIFICATION
colour
inside
Process management for avionics – Aerospace and defence electronic systems
containing lead-free solder –
Part 2: Mitigation of deleterious effects of tin
IEC/TS 62647-2:2012(E)
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IEC/TS 62647-2 ®
Edition 1.0 2012-11
TECHNICAL
SPECIFICATION
colour
inside
Process management for avionics – Aerospace and defence electronic systems
containing lead-free solder –
Part 2: Mitigation of deleterious effects of tin
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XB
ICS 03.100.50; 31.020; 49.060 ISBN 978-2-83220-519-8
– 2 – TS 62647-2 © IEC:2012(E)
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and abbreviations . 8
3.1 Terms and definitions . 8
3.2 Abbreviations . 11
4 Technical requirement . 12
4.1 Control level requirements . 12
4.1.1 General . 12
4.1.2 Control levels and levels of integration . 14
4.1.3 COTS and level selection . 14
4.1.4 Other level selection information. 14
4.2 Requirements for control levels . 15
4.2.1 Control level 1 requirements . 15
4.2.2 Control level 2A requirements . 15
4.2.3 Control level 2B requirements . 16
4.2.4 Control level 2C requirements . 17
4.2.5 Control level 3 requirements . 19
4.2.6 Requirements for mitigating tin whisker risk for solder joints . 19
4.3 Implementation methods . 20
4.3.1 Flowing requirements to lower level suppliers (applies to control level
2B, control level 2C, and control level 3) . 20
4.3.2 Detecting and controlling Pb-free tin finish introduction . 20
4.3.3 Sample monitoring plans (applies to control level 2B and control level
2C) . 20
4.3.4 Lot monitoring requirements (applies to control level 3) . 20
4.4 Methods for mitigating impact of Pb-free tin (applies to control level 2B,
control level 2C) . 21
4.4.1 General . 21
4.4.2 Hard potting and encapsulation . 21
4.4.3 Physical barriers . 21
4.4.4 Conformal and other coats . 21
4.4.5 SnPb soldering process with validated coverage . 22
4.4.6 Circuit and design analysis . 22
4.5 Part selection process . 23
4.6 Assessment and documentation of risk and mitigation effectiveness. 23
4.6.1 General . 23
4.6.2 Elements of assessment . 24
4.6.3 Other risk analysis issues . 24
Annex A (informative) Guidance on control levels, risk assessment, and mitigation
evaluation . 25
Annex B (informative) Technical guide on detection methods, mitigation methods, and
methods for limiting impact of tin . 33
Annex C (informative) Tin whisker inspection . 45
Annex D (informative) Analysis and risk assessment guidance . 52
TS 62647-2 © IEC:2012(E) – 3 –
Annex E (informative) Whiskers growing from solder joint fillets and bulk solder . 56
Bibliography . 63
Figure A.1 – Decision tree . 26
Figure A.2 – Decision tree, sub-tree 1 . 27
Figure A.3 – Decision tree, sub-tree 2 . 28
Figure B.1 – Insufficient solder flow . 39
Figure C.1 – Equipment setup for whisker examination . 46
Figure C.2 – Whiskers examination areas and direction . 47
Figure C.3 – Side-illumination by flexible light . 47
Figure C.4 – Coating residuals and dusts attached on lead-frame with conformal
coating . 47
Figure C.5 – Comparisons between whisker observations by microscope and SEM . 48
Figure C.6 – Limitation of microscope observation . 48
Figure C.7 – Preliminary whisker examination in non-coated test specimens . 51
Figure E.1 – Whiskers and hillocks formed after 500 hours of storage at 85 °C /
85 % RH followed by –55 °C to 85 °C air to air cycling, 1 000 cycles . 56
Figure E.2 – Long whisker growing from SAC405 no-clean assembly reported by Terry
Munson (Foresite) . 57
Figure E.3 – Whiskers and hillocks protruding through flux residue and growing from
solder free of the flux residue [87] . 58
Figure E.4 – Tin whisker length impact by ionic cleanliness . 59
Figure E.5 – Tin whisker density impact by ionic cleanliness . 59
Figure E.6 – Whisker length depending on component and assembly cleanliness . 60
Figure E.7 – Microstructures of solder fillet with 0,8 % HBr activated flux assembled in
air after 1 000 hours at 85 °C / 85 % RH . 61
Figure E.8 – The mechanism of Sn whisker formation on solder fillet induced by
oxidation . 61
Figure E.9 – SAC105 bulk solder at ambient T in nitrogen chamber [34] . 62
Table A.1 – Control level summary table (1 of 2) . 31
Table B.1 – Conformal coating material physical properties from S. Meschter [10] . 34
Table B.2 – Conformal coating physical properties from T. Woodrow [12] . 35
Table B.3 – Conformal coating physical properties from R. Kumar [13] . 36
– 4 – TS 62647-2 © IEC:2012(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PROCESS MANAGEMENT FOR AVIONICS – AEROSPACE AND DEFENCE
ELECTRONIC SYSTEMS CONTAINING LEAD-FREE SOLDER –
Part 2: Mitigation of deleterious effects of tin
FOREWORD
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