IEC TS 62647-2-2012 Process management for avionics - Aerospace and defence electronic systems containing lead-free solder - Part 2 Mitigation of the deleteriou.pdf

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1、 IEC/TS 62647-2 Edition 1.0 2012-11 TECHNICAL SPECIFICATION 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) colour inside THIS PUBLICATION IS COPYRIGHT PROTECTED Copyright 201

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9、0 2012-11 TECHNICAL SPECIFICATION Process management for avionics Aerospace and defence electronic systems containing lead-free solder Part 2: Mitigation of deleterious effects of tin INTERNATIONAL ELECTROTECHNICAL COMMISSION XB ICS 03.100.50; 31.020; 49.060 PRICE CODE ISBN 978-2-83220-519-8 Registe

10、red trademark of the International Electrotechnical Commission Warning! Make sure that you obtained this publication from an authorized distributor. colour inside 2 TS 62647-2 IEC:2012(E) CONTENTS FOREWORD . 4 INTRODUCTION . 6 1 Scope . 7 2 Normative references . 7 3 Terms, definitions and abbreviat

11、ions 8 Terms and definitions 8 3.1Abbreviations 11 3.2 4 Technical requirement 12 Control level requirements . 12 4.1General . 12 4.1.1Control levels and levels of integration 14 4.1.2COTS and level selection 14 4.1.3Other level selection information 14 4.1.4Requirements for control levels . 15 4.2C

12、ontrol level 1 requirements 15 4.2.1Control level 2A requirements 15 4.2.2Control level 2B requirements 16 4.2.3Control level 2C requirements . 17 4.2.4Control level 3 requirements 19 4.2.5Requirements for mitigating tin whisker risk for solder joints 19 4.2.6Implementation methods . 20 4.3Flowing r

13、equirements to lower level suppliers (applies to control level 4.3.1 2B, control level 2C, and control level 3) . 20 Detecting and controlling Pb-free tin finish introduction . 20 4.3.2Sample monitoring plans (applies to control level 2B and control level 4.3.3 2C) 20 Lot monitoring requirements (ap

14、plies to control level 3) . 20 4.3.4Methods for mitigating impact of Pb-free tin (applies to control level 2B, 4.4 control level 2C) 21 General . 21 4.4.1Hard potting and encapsulation . 21 4.4.2Physical barriers 21 4.4.3Conformal and other coats . 21 4.4.4SnPb soldering process with validated cover

15、age . 22 4.4.5Circuit and design analysis 22 4.4.6Part selection process . 23 4.5Assessment and documentation of risk and mitigation effectiveness 23 4.6General . 23 4.6.1Elements of assessment 24 4.6.2Other risk analysis issues 24 4.6.3 Annex A (informative) Guidance on control levels, risk assessm

16、ent, 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 Anne

17、x 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 .

18、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 o

19、f 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-clea

20、n 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 F

21、igure 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 . 6

22、1 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 coa

23、ting 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 1) The International Elec

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36、n an International Standard. Technical specifications are subject to review within three years of publication to decide whether they can be transformed into International Standards. IEC/TS 62647-2, which is a technical specification, has been prepared by IEC technical committee 107: Process manageme

37、nt for avionics. TS 62647-2 IEC:2012(E) 5 The text of this technical specification is based on the following documents: IEC/PAS 62647-2 and GEIA-STD-0005-2 Revision A. This technical specification cancels and replaces IEC/PAS 62647-2. A list of all the parts in the IEC 62647 series, published under

38、the general title Process management for avionics Aerospace and defence electronic systems containing lead-free solder, can be found on the IEC website. The text of this technical specification is based on the following documents: Enquiry draft Report on voting 107/160/DTS 107/193/RVC Full informati

39、on on the voting for the approval of this technical specification can be found in the report on voting indicated in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part 2. The committee has decided that the contents of this publication will remain unchan

40、ged until the stability date indicated on the IEC web site under “http:/webstore.iec.ch“ in the data related to the specific publication. At this date, the publication will be transformed into an International standard, reconfirmed, withdrawn, replaced by a revised edition, or amended. A bilingual v

41、ersion of this publication may be issued at a later date. 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 colo

42、ur printer. 6 TS 62647-2 IEC:2012(E) INTRODUCTION Due to a variety of real and potential health issues, many constituent materials used in the production of electronic products have come under scrutiny. The European Union (EU) has enacted two directives: 2002/95/EC Restriction of Hazardous Substance

43、s (RoHS) and 2002/96/EC Waste Electrical and Electronic Equipment (WEEE) that restrict or eliminate the use of various substances in a variety of products produced after July 2006. One of the key materials restricted is lead (Pb), which is widely used in electronic solder and electronic piece part t

44、erminations, and printed wiring boards. While these regulations may appear to only affect products for sale in the EU, due to the reduced market share of the aerospace, defence, and high performance industry in electronics, many of the lower tier suppliers are changing their products because their p

45、rimary market is world-wide consumer electronics. Additionally, several Asian countries and United States (U.S.) states have enacted similar “green” laws. Many Asian electronics manufacturers have recently announced completely “green” product lines. The restriction of Pb use has generated a transiti

46、on by many piece part and board suppliers from tin-lead (SnPb) surface finishes to pure tin or other Pb-free finishes. Lead-free tin finishes can be susceptible to the spontaneous growth of crystal structures known as “tin whiskers” which can cause electrical failures, ranging from parametric deviat

47、ions to catastrophic short circuits, and may interfere with sensitive optical surfaces or the movement of micro-electro mechanical systems (MEMS) for example. Though studied and reported for decades, the mechanism behind their growth is not well understood, and tin whiskers remain a potential reliab

48、ility hazard. Furthermore, the growing number of piece parts with pure tin finishes means there are more opportunities for whiskers to grow and to produce failures. It is important to state that that the nature and meaning of risk posed by tin whiskers may vary considerably across the range of users

49、 of this Specification. As in any assessment of risk, the probability of occurrence and failure and consequence of occurrence and failure should be considered in each application. Potential whisker failure modes for a particular hardware/system application must be carefully considered when making the choice/determination of which control level(s) to apply. For example, whisker-prone leaded parts on circuit card used in a system that is under fr