IEC TR 61191-9:2023
(Main)Printed board assemblies - Part 9: Electrochemical reliability and ionic contamination on printed circuit board assemblies for use in automotive applications - Best practices
Printed board assemblies - Part 9: Electrochemical reliability and ionic contamination on printed circuit board assemblies for use in automotive applications - Best practices
IEC TR 61191-9:2023, which is a Technical Report, applies to electronic and electromechanical automotive circuit board assemblies and describes current best practices for dealing with electrochemical reactions like migration or corrosion and ionic contamination on the surface of a circuit board as one failure mode under humidity load. This document deals with the evaluation of materials and manufacturing processes for the manufacturing of electronic assemblies with focus on their reliability under humidity loads. The electrical operation of a device in a humid environment can trigger electrochemical reactions that can lead to short circuits and malfunctions on the assembly. In this context, a large number of terms and methods are mentioned, such as CAF (conductive anodic filament), anodic migration phenomena, dendrite growth, cathodic migration, ROSE (resistivity of solvent extract), ionic contamination, SIR (surface insulation resistance), impedance spectroscopy, etc., which are used and interpreted differently. The aim of the document is to achieve a uniform use of language and to list the possibilities and limitations of common measurement methods. The focus of the document is on the error pattern of electrochemical migration on the surface of assemblies with cathodic formation of dendrites.
Evaluation of different test methods of control units under high humidity load are not part of this document.
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IEC TR 61191-9 ®
Edition 1.0 2023-06
TECHNICAL
REPORT
colour
inside
Printed board assemblies –
Part 9: Electrochemical reliability and ionic contamination on printed circuit
board assemblies for use in automotive applications – Best practices
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IEC TR 61191-9 ®
Edition 1.0 2023-06
TECHNICAL
REPORT
colour
inside
Printed board assemblies –
Part 9: Electrochemical reliability and ionic contamination on printed circuit
board assemblies for use in automotive applications – Best practices
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.180; 31.190 ISBN 978-2-8322-7028-8
– 2 – IEC TR 61191-9:2023 © IEC 2023
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms, definitions and abbreviated terms . 8
3.1 Terms and definitions related to management . 9
3.2 Technical terms and definitions . 9
3.3 Abbreviated terms . 10
4 Failure mode electrochemical migration . 10
4.1 Background of electrochemical migration . 10
4.2 Complexity of electrochemical migration . 12
4.3 Conductive anodic filament (CAF) and anodic migration phenomena (AMP) . 13
4.4 Creep corrosion . 14
5 Electrochemical migration and relevance of ionic contamination . 15
5.1 General aspects . 15
5.2 Background of ionic contamination measurement . 15
5.3 Restrictions and limitations of ionic contamination measurement for no-clean
assemblies . 17
5.4 Restrictions and limitations of Ionic contamination measurement for cleaned
products . 28
5.5 How to do – Guidance to use cases . 37
5.6 Examples for good practice . 40
6 Surface insulation resistance (SIR) . 43
6.1 SIR – An early stage method to identify critical material combinations and
faulty processing . 43
6.2 Fundamental parameters of influence on SIR . 43
6.3 Harmonization of SIR test conditions for characterization of materials for
automotive applications . 51
6.4 Different steps of SIR testing . 51
7 Comprehensive SIR testing – B52-approach . 55
7.1 General aspects . 55
7.2 The main B52 test board . 56
7.3 The test patterns . 57
7.4 Processing of B52 boards . 59
7.5 Sample size for SIR testing of B52 test coupons . 59
7.6 Preparation for SIR testing . 59
7.7 Sequence of SIR testing . 60
7.8 Evaluation . 62
8 Example for good practice . 62
8.1 Methodology for material and process qualification, process control . 62
8.2 Step 1 – Material qualification . 62
8.3 Step 2 – Product design verification and process validation . 64
8.4 Step 3 – Definition of process control limits . 65
Annex A (informative) SIR measurement for SMT solder paste – Representative
example . 67
A.1 Purpose . 67
A.2 Equipment . 67
A.3 Example of an instruction how to perform the test . 67
Bibliography . 70
Figure 1 – Principal reaction mechanism of ECM . 11
Figure 2 – Uncertainty in local conditions determines ECM failures . 11
Figure 3 – Occurrence of ECM failures during humidity tests . 12
Figure 4 – VENN diagram showing the factors influencing ECM . 13
Figure 5 – Occurrence of CAF and AMP . 14
Figure 6 – Creep corrosion caused by corrosive gases . 15
Figure 7 – Ionic contamination measurement . 16
Figure 8 – Principal operation mode (fluid flow) of ROSE . 17
Figure 9 – Effect of solvent composition on the obtained ROSE results . 18
Figure 10 – Effect of solvent composition on the obtained ion chromatography result . 18
Figure 11 – Comparison of ROSE values with different solvent mixtures and material
variations of the CBA . 21
Figure 12 – Variation in ROSE values depending on technology used . 22
Figure 13 – Destructive action of solvent on resin matrix . 23
Figure 14 – Comparison of the resin change . 23
Figure 15 – Destructive action of solvent on resin matrix and chipping effect . 24
Figure 16 – Assembly manufactured with 2x SMT and 1x THT process for the
connector . 28
Figure 17 – Comparison of SPC-charts from 1-year monitoring of different CB
suppliers and two different iSn final finish processes . 29
Figure 18 – Differences in ROSE values for unpopulated CBs depending on the
extraction method . 30
Figure 19 – Reduction of ionic contamination on bare CBs (state of delivery from CB
supplier) by leadfree reflow step without solder paste or components . 32
Figure 20 – Influence of components on the ionic contamination based on
B52‑standard . 33
Figure 21 – Formation of a white veil or residue on MLCCs during active humidity test . 34
Figure 22 – Chromatogram derived from ion chromatography measurement of a
cleaned CBA . 36
Figure 23 – Approach for achieving objective evidence for a qualified manufacturing
process in the automotive industry . 41
Figure 24 – ROSE as process control tool . 42
Figure 25 – View on SIR measurement . 44
Figure 26 – Principal course of SIR curves . 45
Figure 27 – Response graph concerning stabilized SIR-value after 168 h from a DoE
with B53-similar test coupons (bare CB) . 45
Figure 28 – SIR measurement with B24-CB, no-clean SMT solder paste . 46
Figure 29 – Increase in ECM propensity depending on voltage applied (U) and Cu-Cu
distances (d) of comb structures . 48
Figure 30 – Layout of B53 test coupon . 49
Figure 31 – B53 with solder mask, partially covered and fully covered comb structures . 53
Figure 32 – B52 CBA after SMT process, layout slightly adapted to fulfil company
internal layout rules . 56
– 4 – IEC TR 61191-9:2023 © IEC 2023
Figure 33 – Pattern of B52 CB, layout slightly adapted to fulfill company internal layout
rules . 57
Figure 34 – Positive example of comprehensive SIR tests obtained for qualification of
a SMT process . 61
Figure 35 – Negative example of a contaminated B52-sample, tested by the sequence
of constant climate and cyclic damp heat climate . 61
Figure 36 – SIR test coupon, similar to B53, for principal material qualification . 63
Figure 37 – SIR test with constant climate and cyclic damp heat condition . 63
Figure 38 – B52 test board and example o
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