IEC TR 61191-7:2020

IEC TR 61191-7 ®
Edition 1.0 2020-03
TECHNICAL
REPORT
colour
inside
Printed board assemblies –
Part 7: Technical cleanliness of components and printed board assemblies
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IEC TR 61191-7 ®
Edition 1.0 2020-03
TECHNICAL
REPORT
colour
inside
Printed board assemblies –
Part 7: Technical cleanliness of components and printed board assemblies

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.180; 31.190 ISBN 978-2-8322-7901-4

– 2 – IEC TR 61191-7:2020 © IEC 2020
CONTENTS
FOREWORD . 8
INTRODUCTION . 10
1 Scope . 11
2 Normative references . 11
3 Terms and definitions . 11
4 Technical cleanliness . 11
4.1 What is technical cleanliness? . 11
4.2 History – standardisation of technical cleanliness . 12
4.3 Technical cleanliness in the electronics industry . 12
4.4 Potential particle-related malfunctions . 12
5 Technical cleanliness as a challenge for the supply chain . 13
5.1 General . 13
5.2 Contamination . 14
5.2.1 Definition of particles . 14
5.2.2 Definition of fibres . 14
5.3 Test procedure to determine technical cleanliness . 15
5.3.1 Fundamentals . 15
5.3.2 Clarification form . 16
5.3.3 System technology . 18
5.3.4 Process parameters for pressure rinsing extraction . 19
5.3.5 Pressure rinsing process . 19
5.3.6 Preparing membrane filters for measurement analysis . 20
5.4 Measurement analysis . 22
5.5 Evaluating the results of cleanliness analyses. 22
5.5.1 Overview . 22
5.5.2 Particle count relative to component surface . 23
5.5.3 Procedure for violation of action control limits . 24
5.6 Extended risk assessment . 25
5.6.1 General . 25
5.6.2 Example . 25
5.7 Component cleanliness – Data management and visualization . 27
5.7.1 Component cleanliness analysis – flow diagram . 27
5.7.2 Explanation of SCI (Surface Cleanliness Index) . 28
5.7.3 Creating a database . 31
5.7.4 Summary . 34
6 State of the art – Technical cleanliness in the electronics industry . 35
6.1 Process flow (per cluster) . 35
6.1.1 General . 35
6.1.2 Electronics manufacturing cluster . 35
6.1.3 Passive components cluster (e.g. for inductors and aluminium
electrolytic capacitors) . 36
6.1.4 Electromechanical components cluster . 37
6.1.5 PCB cluster . 39
6.2 Technical cleanliness in the electronics industry – current situation . 39
6.2.1 General . 39
6.2.2 Electronics manufacturing . 40

6.2.3 Electronic components. 41
6.2.4 Electromechanical components. 44
6.2.5 Metal housings . 48
6.2.6 Packaging. 49
6.2.7 Printed circuit boards (PCBs) . 49
6.3 Determining potential particle sources in production areas . 52
6.3.1 General . 52
6.3.2 Particle generation . 52
6.3.3 Electronics manufacturing cluster . 52
6.3.4 Passive components cluster . 53
6.3.5 Electromechanical components cluster . 59
6.3.6 PCB cluster . 63
6.4 Cleanliness-controlled design and process selection . 72
6.4.1 Aspects of cleanliness-controlled design/production with regard to
metallic particles . 72
6.4.2 Environmental cleanliness and internal production processes . 74
6.5 Environmental cleanliness analysis and visualisation . 76
6.5.1 General . 76
6.5.2 Procedure for environmental analysis . 76
6.5.3 Conclusions: . 80
6.6 Cleaning tips . 81
6.6.1 General . 81
6.6.2 Washing . 81
6.6.3 Brushing . 81
6.6.4 Suction-cleaning . 82
6.6.5 Blowing. 83
6.6.6 Reducing carry-over and controlling cleanliness in workplace design . 83
6.6.7 Adhesive methods . 84
6.7 Packaging and logistics requirements . 84
7 Why do metallic particles in assemblies so rarely cause short circuits? . 84
7.1 General . 84
7.2 Probability of contact . 85
7.2.1 Introduction and theory . 85
7.2.2 Testing the probability of contact . 88
7.2.3 Results . 90
7.3 Rinsing extraction versus actual mobility . 92
7.4 Particle sinks . 92
7.5 Effect of short circuits on ICs . 93
7.6 Tool for estimating the risk of short circuit . 93
7.6.1 Overview . 93
7.6.2 Model hypotheses . 94
7.6.3 Calculation methods . 95
7.6.4 Orientation factor . 95
7.6.5 Critical area . 96
7.6.6 Number of particles per size class . 97
7.6.7 Weighting factors . 98
7.7 Example use of the risk assessment tool . 99
7.7.1 Example use of the risk assessment tool for calculating failure rate . 99
7.7.2 Example use of the risk assessment tool for design changes . 100

– 4 – IEC TR 61191-7:2020 © IEC 2020
7.7.3 Example use of the risk assessment tool for specification violations . 101
8 Summary . 102
9 Outlook . 102
10 Related topics . 103
10.1 Filmic contamination . 103
10.1.1 General . 103
10.1.2 Biological films . 103
10.1.3 Chemical films . 103
10.2 Whiskers . 103
Annex A (informative) Determining the surface area of components and assembled
circuit boards . 106
Annex B (informative) Examples of cleanliness clarification forms . 109
Bibliography . 114

Figure 1 – Test method as per VDA 19 Part 1 . 16
Figure 2 – Examples of extraction systems . 18
Figure 3 – Component holder during manual pressure rinsing . 20
Figure 4 – Examples of different options for drying membrane filters . 21
Figure 5 – Slide frame with membrane filter . 21
Figure 6 – Example procedure if specifications are exceeded . 24
Figure 7 – Particle size distribution and corresponding process capability. 26
Figure 8 – Flow diagram for component cleanliness analysis . 27
Figure 9 – Scope of analytical report . 27
Figure 10 – Derivation of Illig value . 28
Figure 11 – Derivation of SCI . 29
Figure 12 – Evaluation of 7-pin HV strip connector. 30
Figure 13 – Graph showing cleaning effect based on SCIs . 30
Figure 14 – Comparison of the three largest particles . 31
Figure 15 – Structural levels of a database . 32
Figure 16 – Option A – Evaluation of the largest particles by length and width . 32
Figure 17 – Option B – Extension to include the degree of contamination – SCI . 33
Figure 18 – Option C – Extension to include a separate data sheet "direct comparison
of test series" . 33
Figure 19 – Option D – Extension of the database "to include 'comparison with
customer standards'" . 34
Figure 20 – Flexible circuit board . 49
Figure 21 – Rigid circuit board . 50
Figure 22 – Burr formation on copper wire (D = 2,25 mm) after use of wire-cutter . 54
Figure 23 – Particles generated by wire cutting D = 1,8 mm (tinned copper) . 54
Figure 24 – Particles generated by wire cutting D = 1,8 mm (tinned copper) . 55
Figure 25 – Particle (tin) adhering to a tinned copper wire D = 2,25 mm. 55
Figure 26 – Hair-like particle (tin whiskers) chipped off a tinned wire (655 µm long) . 56
Figure 27 – Milled enamel wires . 56
Figure 28 – Molten solder balls fused to plastic housings . 57
Figure 29 – Ferrite particle, identified as metallic (419 µm) . 58

Figure 30 – Ferrite particle, identified as non-metallic (558 µm) . 58
Figure 31 – Non-metallic particle, probably burr or plastic residue (217 µm) . 59
Figure 32 – Non-metallic particle, probably pink polystyrene packaging material . 59
Figure 33 – Shielding plate . 60
Figure 34 – Stamped contacts . 61
Figure 35 – Connector pin . 61
Figure 36 – Connector housing . 62
Figure 37 – 58-pin connector housing . 62
Figure 38 – 12-pin connector with bridged contacts . 63
Figure 39 – Plastic particles + fibres . 64
Figure 40 – Plastic particles . 64
Figure 41 – Metallic particle . 64
Figure 42 – Milling crosses V-scoring line . 65
Figure 43 – V-scoring line on milling edge . 66
Figure 44 – Chip formation in milled hole . 66
Figure 45 – Edge plating . 67
Figure 46 – Connections for electroplated gold areas . 67
Figure 47 – Deep milling . 68
Figure 48 – Chip formation caused by stamping . 68
Figure 49 – Flexible circuit board with undercut . 69
Figure 50 – Punching burr in hole . 69
Figure 51 – Punching burr . 70
Figure 52 – Damaged metallic stiffener . 70
Figure 53 – Stamping residue along stamped edge . 71
Figure 54 – Stamping residue loosened by pickling bath . 71
Figure 55 – Plastic element with burr . 72
Figure 56 – Particles on externally supplied plastic elements . 72
Figure 57 – Process chain analysis as per VDA 19 Part 2 . 75
Figure 58 – Cleanroom production . 76
Figure 59 – Example particle trap . 77
Figure 60 – Position of particle trap . 77
Figure 61 – Database – Visualisation . 78
Figure 62 – Illustration of the Illig value with max. three particles . 78
Figure 63 – Airborne dispersion diagram . 79
Figure 64 – Analysis results in the cleanroom . 79
Figure 65 – Analysis results in the area not governed by VDA 19. 80
Figure 66 – Weighting of factors influencing technical cleanliness . 80
Figure 67 – Manual cleaning with brush and illuminated magnifier . 82
Figure 68 – ESD brush. 82
Figure 69 – Workstations designed for cleanliness control . 83
Figure 70 – Adhesive roller system for PCB contact cleaning . 84
Figure 71 – Diagram showing failure risks based on metallic particles on assemblies . 85

– 6 – IEC TR 61191-7:2020 © IEC 2020
Figure 72 – Sketch of electrical arrangement (particle forming "bridge" between two
conductors) . 86
Figure 73 – Diagram showing contact point of a particle on a conductor – nickel-gold
conductor and copper particle . 87
Figure 74 – SIR test circuit boards (interleaving comb pattern layout) . 89
Figure 75 – Voltage source that measures current with an analogue picoamperemeter . 89
Figure 76 – Automated current measurement with software . 90
Figure 77 – Comparison of CU particles in three conditions on SAC305 PCBs . 91
Figure 78 – Overview of all metals in the voltage classes, rounded . 91
Figure 79 – Functional structure of risk assessment tool . 94
Figure 80 – Geometric constraints at a contact pair . 96
Figure 81 – Clearance areas up to 400 µm (in white) . 97
Figure 82 – Clearance areas up to 600 µm (in white) . 97
Figure 83 – Clearance areas up to 1000 µm (in white) . 97
Figure 84 – Example calculation 1 – Calculating an absolute probability of failure . 99
Figure 85 – Example calculation 2 – Calculating probabilities of failure for layout
changes e.g. for a new generation component . 100
Figure 86 – Example calculation 3 – Optimising the main variables . 101
Figure 87 – Example calculation 3 – Calculating the changed probability of failure in
the event of specification violation . 101
Figure 88 – Whiskers growth of > 8 mm over a period of 10 years . 104
Figure 89 – Whiskers growth of > 2 mm over a period of 6 months . 105
Figure A.1 – Dimensions of cuboid components . 106
Figure A.2 – Dimensions of cylindrical components . 107
Figure B.1 – Ambient cleanliness clarification form . 109
Figure B.2 – Ambient cleanliness clarification form . 110
Figure B.3 – Component cleanliness clarification form . 111
Figure B.4 – Component cleanliness clarification form . 112
Figure B.5 – Component cleanliness clarification form . 113

Table 1 – Influence of the blank value on the measurement results for different
material surfaces (examples for a blank value fraction of 2,2 % and above) . 24
Table 2 – Electronics manufacturing cluster process flow . 35
Table 3 – Process flow for inductors . 36
Table 4 – Aluminium electrolytic capacitors . 37
Table 5 – Stamped contact production/plastic production (housing) process flow . 38
Table 6 – Housing assembly process flow . 38
Table 7 – PCB cluster process flow . 39
Table 8 – Empirical data from electronics manufacturing cluster . 40
Table 9 – Empirical data from inductors . 41
Table 10 – Empirical data from aluminium electrolytic capacitors . 41
Table 11 – Empirical data from tantalum capacitors . 42
Table 12 – Empirical data from chip components . 42
Table 13 – Empirical data from shunts . 43
Table 14 – Empirical data from quartz . 43

Table 15 – Empirical data from semiconductors . 44
Table 16 – Empirical data from metallic components – stamping from pre-treated strip
stock . 44
Table 17 – Empirical data from metallic components – stamping of contact from
untreated strip stock and subsequent electroplating process . 45
Table 18 – Empirical data from metallic components – turning of pins and subsequent
electroplating process . 45
Table 19 – Empirical data from pure plastic parts . 46
Table 20 – Empirical data from joined strip connectors . 46
Table 21 – Empirical data from high-voltage connectors (typically shielded) . 47
Table 22 – Empirical data from the assembly process of non-metallic components . 47
Table 23 – Empirical data from die-cast aluminium housing . 48
Table 24 – Empirical data from deep-drawn trays (new) . 49
Table 25 – Empirical data from flexible PCBs without cleaning step . 50
Table 26 – Empirical data from bare, flexible PCBs with cleaning step . 51
Table 27 – Empirical data from bare, rigid PCBs . 51
Table 28 – List of materials used in the test . 88
Table A.1 – Sample values of standard components to determine the component
surface area . 108

– 8 – IEC TR 61191-7:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PRINTED BOARD ASSEMBLIES –
Part 7: Technical cleanliness of components
and printed board assemblies
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as "IEC
Publication(s)"). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a Technical Report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC/TR 61191-7, which is a technical report, has been prepared by IEC technical committee
91: Electronics assembly technology.
The text of this Technical Report is based on the following documents –
Draft TR Report on voting
91/1583/DTR 91/1595/RVDTR
Full information on the voting for the approval of this Technical Report can be found in the
report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 61191 series, published under the general title Printed board
assemblies, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http//www.webstore.iec.ch" in the data
related to the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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
colour printer.
– 10 – IEC TR 61191-7:2020 © IEC 2020
INTRODUCTION
The Technical Report applies to electric, electronic and electromechanical components, circuit
boards and electronic assemblies and describes the resulting level of technical cleanliness
that can be expected for products that are manufactured with state-of-the-art standard
production methods and processes.
The Technical Report is an informative document which serves to illustrate the technically
feasible options and provide a basis for customer and supplier agreements. It is not intended
to be regarded as a specification or standard. It does not cover the production of electric
motors, batteries, cable harnesses and relays.
Its primary focus is on loose or easily detachable particles (labile particles). Film residues,
chemical and biological contamination are also briefly covered. It does not deal with the
cleanliness of functional fluids and/or gases.
This Technical Report provides information, how the requirements put down in VDA 19.1 and
VDA 19.2 could become reasonably applied in electronic industry It provides information
about particle generation considering processes and materials, illustrates their impact on
performance and reliability and describes suitable countermeasures as well as procedures for
risk assessments.
Related standards issued by the automotive industry and the electronic industry are gathered
in the bibliography.
The Technical Report has been prepared based on material provided by the working group on
component cleanliness of the ZVEI (Zentralverband Elektrotechnik- und Elektronikindustrie
e.V., Germany).
PRINTED BOARD ASSEMBLIES –
Part 7: Technical cleanliness of components
and printed board assemblies
1 Scope
This part of IEC 61191 serves as a Technical Report and provides information, how technical
cleanliness can be assessed within the electronics assembly industry. Technical cleanliness
concerns sources, analysis, reduction and control as well as associated risks of particulate
matter, so-called foreign-object debris, on components and electronic assemblies in the
electronics industry.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
4 Technical cleanliness
4.1 What is technical cleanliness?
The term 'technical cleanliness' was coined by the automotive industry to address particle-
related system interruptions in the automotive industry. In contrast to 'optical cleanliness',
which relates to the cosmetic or visual appearance, e.g. vehicle coating, technical cleanliness
always refers to the performance of components, assemblies and systems.
Particulate contamination in the automotive industry is often not limited to a certain area but
may migrate from a previously non-critical to a sensitive location and hence impair
performance. For instance, a particle on the lens of a traffic sign detection camera may cause
it to malfunction. Similarly, a conductive particle from the aluminum cover of an electronic
control unit may cause a short circuit on the circuit board and undermine its performance.
This is why the cleanliness requirements of the automotive industry often apply to complete
systems, whereby the most particle-sensitive component (weakest link in the chain)
determines the cleanliness level and admissible limiting values for the entire system and all
components within it. With regard to components, technical cleanliness refers to the
specification, observance and verification of limiting values, e.g. according to weight of
residual contamination, particle count, type and size. At the same time, the automotive
industry tolerates failures only in the ppm range. New stipulations are continuously being
added to the existing specifications. These are often tailored to suit the specific requirements
of a company or component and its performance. Their scope of application is limited, i.e.
they are valid in-house and/or for suppliers.

– 12 – IEC TR 61191-7:2020 © IEC 2020
Although the term 'technical cleanliness' was coined by the automotive industry, the
procedures relating to cleanliness inspections in accordance with VDA 19 (liquid extraction,
membrane filtration and subsequent analysis of the retained particles) have been increasingly
adopted by other industries such as medical technology, the optical industry, hydraulic and
mechanical engineering. Since there is no such thing as total cleanliness or purity, the focus
should be on the most practically feasible and economically viable solution for the designated
location and purpose.
4.2 History – standardisation of technical cleanliness
Contamination had been a growing problem for the automotive industry since the early 1990s
as systems became increasingly complex and installation spaces ever smaller. The anti-lock
braking systems in general or direct fuel injection systems for diesel engines were particularly
prone.
In some cases, customers and suppliers concluded individual agreements about technical
cleanliness to address the risk of potential damage.
As a result, the automotive industry called for the introduction of general standards regulating
the technical cleanliness of components. In summer 2001, TecSa was founded, an industrial
alliance for technical cleanliness. This panel published VDA 19 (Inspection of Technical
Cleanliness – Particulate Contamination of Functionally-Relevant Automotive Components) in
2004, which was revised in 2015 and republished as VDA 19 Part 1. These guidelines make
recommendations for inspecting the technical cleanliness of automotive products.
Its international counterpart is standard ISO 16232, which was published in 2007.
In 2010, VDA 19 Part 2 (Technical Cleanliness in Assembly) was published, detailing
cleanliness-related design aspects for assembly areas.
4.3 Technical cleanliness in the electronics industry
The industry increasingly uses the generally valid VDA 19 guidelines in addition to company-
specific standards.
This Technical Report outlines a system for designing and implementing component
cleanliness analyses to enable quantifiable comparisons of component cleanliness levels.
However, VDA 19 does not specify any limiting values for component cleanliness. These must
be defined according to component function, producibility and verifiability.
This Technical Report supplements VDA 19 and ISO 16232 by addressing outstanding
questions and providing practical solutions.
The producibility of a component as well as its performance must be considered in this
context, as is the case when defining dimensional tolerances. Production processes,
production environment and final packaging also influence component cleanliness. This often
calls for agreements concerning compliance with limiting values between customer and
supplier or product development and production. This is particularly relevant in instances
where limiting values are exceeded without necessarily impairing performance. A careful
review shall be carried out to ensure that efforts to comply with these values do not outweigh
the potential risk, thereby avoidi
...