Printed board assemblies - Part 10: Application and utilization of protective coatings for electronic assemblies

IEC PAS 61191-10:2022(E) provides guidelines which deal with the requirements for the protective coating,
its properties, as well as the application of liquid coating materials for electronic assemblies. These guidelines help control in practice the application of protective coatings from the layout to the functional test of the assembly after coating.

General Information

Status
Published
Publication Date
17-Jul-2022
Current Stage
PPUB - Publication issued
Completion Date
18-Jul-2022
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IEC PAS 61191-10
Edition 1.0 2022-07
PUBLICLY AVAILABLE
SPECIFICATION
colour
inside
Printed board assemblies –
Part 10: Application and utilization of protective coatings for electronic
assemblies
IEC PAS 61191-10:2022-07(en)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC PAS 61191-10
Edition 1.0 2022-07
PUBLICLY AVAILABLE
SPECIFICATION
colour
inside
Printed board assemblies –
Part 10: Application and utilization of protective coatings for electronic
assemblies
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.180; 31.190 ISBN 978-2-8322-3981-0

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC PAS 61191-10:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PRINTED BOARD ASSEMBLIES –
Part 10: Application and utilization of protective
coatings for electronic 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.

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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.

A PAS is an intermediate specification made available to the public and needing a lower level

of consensus than an International Standard to be approved by vote (simple majority).

IEC-PAS 61191-10, submitted by GfKORR – Gesellschaft für Korrosionsschutz e.V. was

processed by IEC technical committee 91: Electronics assembly technology. It is based on

Guidelines for the application and utilization of protective coatings for electronic assemblies –

Selection, fields of application, requirements and application recommendations – provided by

the working party “Corrosion protection in electronics and microcircuitry”. The structure and

editorial rules used in this PAS reflect the practice of the organization which submitted it.

---------------------- Page: 4 ----------------------
IEC PAS 61191-10:2022 © IEC 2022 – 3 –
The text of this PAS is based on the This PAS was approved for
following document: publication by the P-members of the
committee concerned as indicated in
the following document
Draft PAS Report on voting
91/1781/DPAS 91/1788/RVDPAS

This PAS shall remain valid for an initial maximum period of 2 years starting from

the publication date. The validity may be extended for a single period up to a
maximum of 2 years, at the end of which it shall be published as another type of
normative document, or shall be withdrawn.

IMPORTANT – The "colour inside" logo on the cover page of this document 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.
---------------------- Page: 5 ----------------------
– 4 – IEC PAS 61191-10:2022 © IEC 2022
G U I D E L I N E S
for the
APPLICATION AND UTILIZATION OF PROTECTIVE COATINGS
FOR ELECTRONIC ASSEMBLIES
Selection, fields of application,
requirements and application
recommendations
Provided by the working party
“Corrosion protection in electronics and microcircuitry”
GfKORR – Gesellschaft für Korrosionsschutz e.V.
---------------------- Page: 6 ----------------------
IEC PAS 61191-10:2022 © IEC 2022 – 5 –
CONTENT
Part A INTRODUCTION
Part B REQUIREMENTS FOR THE COATING OF ASSEMBLIES
1 General requirements
2 Climate impact requirements
3 Regulations for protective coating
3.1 Reference to the general requirements
3.2 Reference to climate impact
Part C CLASSIFICATION OF COATINGS
1 Subdivision according to binding agent
1.1 Acrylates
1.2 Alkyds
1.3 Epoxides
1.4 Polyesters
1.5 Polyurethanes
1.6 Silicones
1.7 UV acrylic hybrids
1.8 Thixotropic protective coatings
1.9 ORMOCER s
1.10 Parylenes
2 Subdivision according to solvent
3 Subdivision by drying and curing mechanism
3.1 Physically drying coating materials
3.2 Oxidatively drying coating materials
3.3 Chemically curing coating materials
3.4 (UV-)radiation-curing coating materials
4 Subdivision according to coating thickness
---------------------- Page: 7 ----------------------
– 6 – IEC PAS 61191-10:2022 © IEC 2022
Part D Film properties of protective coatings
1 Mechanical properties
1.1 Adhesion
1.2 Elasticity
1.3 Hardness
1.4 Further mechanical properties
2 Electrical properties
2.1 Insulation and moisture resistance
3 Thermal properties
3.1 Stress factors
3.2 Thermal mismatch
3.3 Fatigue - the Wöhler curve and its consequences
3.4 Thermal stress load
3.5 Thermal shock resistance
4 Condensation
5 Water absorption and water vapor permeability
5.1 Requirements
5.2 Transport of moisture
6 Thermal resistance
7 Flexibility (modulus of elasticity) and CTE
Part E INFLUENCE OF THE ASSEMBLY ON THE PROTECTIVE COATING
1 Base material
2 Component and circuit board layout
3 Solder resist
4 Soldering materials and soldering process
4.1 Flux types
4.2 Composition of NoClean fluxes
4.3 Residues from the soldering process
4.4 Detection of residues
5 Drying parameters
6 Keeping areas clear and exposing areas
---------------------- Page: 8 ----------------------
IEC PAS 61191-10:2022 © IEC 2022 – 7 –
Part F SUBSTRATE AND PRETREATMENT OF PROTECTIVE COATINGS
1 Requirements for the cleaning of assemblies
2 Decision on cleaning
3 Purity requirements
4 Minimum surface purity before protective coating
5 Measurement and analysis of ionic impurities
6 Detection of critical impurities
6.1 ZESTRON Flux Test
6.2 ZESTRON Resin Test
6.3 SIR measurement
6.4 Surface tension
6.5 Technical cleanliness
7 Implementation of the cleaning processes
7.1 Cleaning types
7.2 Cleaning systems
7.3 Microphase Cleaner
8 Optimization of the cleaning processes
Part G APPLICATION METHODS FOR PROTECTIVE COATINGS
1 Subdivision of the application procedures
2 Application by brush or brush method
3 Application by spray cans
4 Application by spraying
5 Application by dipping processes
5.1 Vertical dipping
5.2 Horizontal dipping
6 Flood method application
6.1 Form cup flooding
6.2 Form cup
7 Application by spray process
8 Automatic and selective coating in the casting process
8.1 How the SelectCoat process works
8.2 Closed and circulating coating supply
8.3 Software for the coating system
8.4 Process control
8.5 Coating system
8.6 Non-contact jetting with the PreciseCoat technology
---------------------- Page: 9 ----------------------
– 8 – IEC PAS 61191-10:2022 © IEC 2022
9 Application via dispensing procedure
10 Application via vacuum process
Part H HANDLING PROTECTIVE COATINGS DURING PROCESSING
1 Requirements for coating rooms and equipment
1.1 Overview and definition
1.2 Explosion-protected areas
1.3 Storage of coating materials
1.4 Mixing and staging areas
1.5 Coating equipment
1.6 Extraction and ventilation in rooms and areas
1.7 Evaporation and drying rooms or areas
1.8 Processing of UV-curing coating systems
1.9 Operation
1.10 Rules and regulations
2 Monitoring processing parameters
2.1 Viscosity and flow time
2.2 Flow time and temperature influences
2.3 Viscosity and temperature
3 Contamination
4 Maintenance of dipping systems
5 Aging of protective coatings
5.1 Coating aging
5.2 Dust and dirt absorption
5.3 Solulibizing substances not related to coating
5.4 Service life extension
6 Environmental protection with regard to protective coating
6.1 Regulations and laws for air pollution control
6.2 EU Solvents Directive (VOC Directive)
6.3 Technical instructions (TA) air
6.4 Hazardous substances in the workplace
6.5 Summary
6.6 Literature
---------------------- Page: 10 ----------------------
IEC PAS 61191-10:2022 © IEC 2022 – 9 –
Part I AVOIDANCE OF TYPICAL ERRORS DURING PROTECTIVE COATING
1 Application of too high coating thicknesses
2 Double coating
3 Early hermetic capsules of coated circuit boards
4 Avoidance of defects in the protective coating
5 Typical fault patterns in the protective coating
5.1 Chemical causes of error patterns
5.2 Process-related causes of error patterns
5.3 Flow defects
Part J TESTING METHODS FOR PROTECTIVE COATING
1 General verification of the protective coating
2 Methods for testing climate resistance
2.1 Water immersion test
2.2 Coating Reliability Test (CoRe Test)
2.3 Climate-cycle test
2.4 Condensation water test
3 Method for testing coating result
3.1 Coating adhesion
3.2 Coating thickness
3.3 Special features for surface modifications

4 Methods for testing and designing the drying of protective coatings by thermal

analysis
4.1 Problem definition
4.2 Procedure
4.3 Application examples
Part K REPAIR OF COATED ASSEMBLIES
1.1 Stripping of assemblies
1.1 Chemical coating stripping
1.2 Mechanical coating stripping
2 Soldering through of coatings
3 Repair coating
---------------------- Page: 11 ----------------------
– 10 – IEC PAS 61191-10:2022 © IEC 2022
PART L BIBLIOGRAPHY
PART M LIST OF AUTHORS
PART N COMPARISON OF THE GUIDELINE WITH THE IPC MANUAL
---------------------- Page: 12 ----------------------
IEC PAS 61191-10:2022 © IEC 2022 – 11 –
FOREWORD
GfKORR and its working group "Corrosion protection in electronics and microsys-
tems technology" as initiators of this guideline

GfKORR - Gesellschaft für Korrosionsschutz e.V., a non-profit technical-scientific associ-

ation, which was formed in 1995 from the merger of two predecessor organizations, has

set itself the goal of collecting, expanding and disseminating knowledge about corrosion,

corrosion mechanisms and corrosion protection possibilities to prevent corrosion damage

with the participation of all persons, institutes, companies and facilities involved in corro-

sion and corrosion protection. This project is to be realized on the one hand through joint

conferences, seminars and workshops and on the other hand through constructive work

in working groups with special orientation and topics. Further information about GfKORR

and its work can be found at http://www.gfkorr.de

The constantly increasing number of different electronic assemblies and miniaturized sys-

tems made of various materials and their use, especially in motor vehicles, telecommuni-

cations, aircraft, building services and even toys, is also associated with increasing ex-

pectations for the functional reliability and long-term stability of the products. In addition,

the progressive miniaturization of components places ever greater demands on purity

during manufacture and assembly. Furthermore, both electronics and the

microcomponents are increasingly exposed to changing climatic conditions such as hu-

midity, temperature changes and temperature shock. Based on long-term warranty re-

quirements and worldwide marketing, an effective assurance of the reliability of electronic

products is only conceivable with the help of in-depth knowledge of the mechanisms of

action of corrosion of electronic and microsystem components and corresponding corro-

sion protection measures.

In the spring of 1998, GfKORR founded the working group "Corrosion protection in elec-

tronics and microsystems technology" with a view to discussing such ever-increasing is-

sues and problems. It is currently headed by Dr. Helmut Schweigart, Dr. O.K. Wack

Chemie GmbH, Ingolstadt; his deputy is Dr. Michael Popall, Fraunhofer Institute for Sili-

cate Research, Würzburg. The working group meets twice a year in Würzburg in spring

and autumn (for further information and contact details, see the list of authors and the

Internet on the GfKORR homepage).

The working group includes representatives from industry (such as ALTANA Chemie AG,

CiS Institut für Mikrosensorik gGmbH, Continental AG, Dage Electronic Europa Vertriebs

GmbH, Dow Corning GmbH, GTL Knödel GmbH, Hella KGaA, ISO-ELEKTRA
Elektrochemische Fabrik GmbH, KC-Kunststoff-Chemische Produkte GmbH, Lackwerke
Peters GmbH & Co. KG, Nordson-Asymtek, Specialty Coating Systems, Stannol GmbH,

Wevo-Chemie GmbH, Würth Elektronik GmbH & Co. KG, Zollner Elektronik AG...) as well

as employees of various research institutions and service providers (such as the

Fraunhofer Institute for Applied Materials Research (IFAM), for Silicate Research (ISC)

and for Silicate Technology (ISiT) and the Karlsruhe Research Center GmbH).
---------------------- Page: 13 ----------------------
– 12 – IEC PAS 61191-10:2022 © IEC 2022
The goals of the working group are:

• the deepening of the understanding of the mechanisms leading to functional haz-

ards,

• the interdisciplinary exchange on the state of science and technology in the work-

ing fields of the working group in cooperation with industry and other scientific-

technical societies,
• damage assessment and prevention, and
• the provision of competent contact persons for acute questions.

An important point that the working group has already dealt with in the past and must con-

tinue to deal with is the current test methods for characterizing the protective coatings

applied to printed circuit boards and components. Here it is important to make further de-

velopments, which, however, can only be pursued jointly by coating manufacturers and

users.

The GfKORR working group "Corrosion protection in electronics and microsystems tech-

nology" has in recent years focused its work on the compilation of the present guideline

and discussed individual points controversially. This guideline, entitled "Application and

processing of protective coatings for electronic assemblies - selection criteria, areas of

application, requirement profiles and application notes", is based on the knowledge that a

comprehensive and fundamental understanding of the coating and its function on elec-

tronic assemblies is required. For this, it is necessary to analyze the entire process. This

guideline is intended to provide practical assistance in considering this process, starting

with the layout up to the functional test of the assembly after the coating.

In order to achieve optimum results in the application of protective coatings, it is also de-

sirable that both manufacturers and assemblers of electronic assemblies and users of

protective coatings discuss and implement the desired properties and the necessary and

possible process steps together with the manufacturers of protective coatings. Only with

such "round-table" discussions can successful solutions be developed for each individual

application. It is then also possible to update and improve this guideline at regular inter-

vals through such meetings and discussions.
September 2018
The authors of the guideline
---------------------- Page: 14 ----------------------
IEC PAS 61191-10:2022 © IEC 2022 – 13 –
INTRODUCTION

During their production and use in the field, electronic equipment and assemblies are ex-

posed to the influence of moisture and environmental conditions (air, weather, location of

the assembly, storage and cleaning) Air, humidity and water lead to an electrical conduc-

tive connection of adjacent metal surfaces, which may have different electrical potentials

and may thus cause disorder of the electrical insulation by developing additional electrical

pathes. Other influences like fluctuations of temperature or strain caused by harmful sub-

stances, vibrations and mechancial strain lead to changes in the electrical conduction

properties and changes and destruction of the conductor and insulation materials.

Disorder caused by water or moisture often disappears in a dry environment. Also

changes of the electrical conductivity caused by temperature disappear when used at

modereate ambient temperatures. However, the material, which was destroyed by thermal

or mechanical strain, remains in its destroyed condition. A disorder caused by moisture

may therefore disappear in favourable cases, however, in view of functional safety con-

siderations of electronic assemblies also such damages must be avoided.

An electronic assembly is only suitable if a safe performance is guaranteed for a specified

time. The majority of assemblies is installed in final equipment without any insulation and

operate throughout their lifetime without failure. However, the assembly is increasingly

used under more difficult conditions. In such cases, safe operation of an assembly is only

guaranteed by a protective coating.

Reliability of an electronic product and customer satisfaction are of utmost importance

for the success on the market. Product liability requires the manufacturers to take the

necessary steps in order to ensure safe operation of electronic equipment also under such

heavy conditions. This mainly applies to assemblies which are used in space technology

and aviation , defence technology, medicine and automotive industry.

Generally, the coating of the assembly is the last step in the value-added chain of the as-

sembly. Any fault during this step may become very cost intensive and in the worst case

may cause disastrous results in the field. Therefore, these guidelines represent a co-

operative effort by design engineers, producers, coating engineers and users of electronic

equipment. It was decided to establish these guidelines because of the fact that compre-

hensive and elementary knowledge of the coating and its performance on electronic as-

semblies is vital. For this purpose, it is necessary to analyse the entire process critically.

These guidelines shall help control in practice the application of protective coatings from

the layout to the functional test of the assembly after coating.

Nowadays, coating materials for electronic assemblies are nearly exclusively available in

liquid form. The application of powder to certain components as well as full body or partial

application of molten foils is limited to exceptional cases. Besides the complete sealing of

electronic assemblies, the protective coating offers a cost-effective and user-friendly alter-

native.
---------------------- Page: 15 ----------------------
– 14 – IEC PAS 61191-10:2022 © IEC 2022

Therefore, the present guidelines especially deal with the requirements for the protective coating,

its properties, as well as the application of liquid coating materials. .

The German terms „Lacke“ and „Anstrichstoff“ are generally and synonymously used for

pigmented and non-pigmented coating materials. The coatings for the protection of elec-

tric assemblies described herein are non-pigmented paints. However, a non-pigmented

paint should be called clear paint.

In order to stay as neutral as possible, the generic terms coating material and coating

process were used herein if further definitions were not expressly required. If more em-

phasis is placed on the properties of the protective coatings especially described herein,

then the term protective paint is used.

In order to set out the scope of these guidelines, the following limitations were made:

• The protective coatings described in these guidelines are protective paints (Conformal

2,3
Coatings, CC or Protective Coatings, PC).

• Protective coatings are polymer layers which protect assemblies against negative in-

fluences in service in order to extend their lifetime and operating time, resp.

• If the contours of the assembly are still visible, the polymer coating is defined as pro-

tective paint and protective coating resp.- conformal coating -.

• If the contours are entirely covered, then coating resins, casting resins and/or sealing

compounds are concerned.

• The entire sealing of an assembly and the processes to be used are not part of these

guidelines (see also [Kli05a, Ott05, Ott07 Pie07 HdT07]).

The coating of electronic assemblies is a part of the assembly production developing con-

tinuously and quickly. It is therefore planned to update the guidelines on a regular basis

and to add more chapters by the GfKORR study group. .

According to DIN EN 971-1 (1996-09; „Lacke und Anstrichstoffe – Fachausdrücke und Definitionen für

Beschichtungsstoffe – Teil 1: Allgemeine Begriffe“; in the meantime replaced by DIN EN ISO 4618 (2003-12)

„Beschichtungsstoffe – Begriffe“) coating material is defined as follows: „Coating material is either a liquid

product, or a paste or powder which, when applied to a surface, provides a coating with protective, ornamental

and/or other specific properties. “.

Note: The German term „Beschichtungsstoff“ acc. to this specification is the generic term for paints , coatings

and similar products. According to the supplement of the DIN EN 971-1 coating materials are also materials

for the production of synthetic resins, filler compounds, floor coating compounds, as well as similar materials.

The terms coating material, coatings and paint are used alternatively. This also applies to the term „An-

strichmittel“ [Zor98] which is not standardized and should hence be avoided. .

The term “conformal coating” is used in the English and American language and acc. to IPC-CC-830 is de-

fined as follows: “For the purpose of this specification (IPC-CC-830) the term conformal coating is used herein

when referring to a type of protective coating for use on printed board assemblies. The conformal coating is

intended to provide protection from moisture, contamination and provide electrical insulation; not as a sole

source of mechanical support.” The same applies to conformal coatings acc. to UL 746 C („Standard for safety

for polymeric materials – use in electrical equipment evaluations“).

The term „conformal coating“ was introduced and used for full body coatings, therefore the term shall be

used herein, allthough nowadays “conformal coating” is very often used by mistake in case of one-sided se-

lective coating of electronic assemblies.

The first edition of the guidelines is dated November 2005. This is the second edition dated June 2007, up-

dated and extended for the first time by 30 pages.
---------------------- Page: 16 ----------------------
IEC PAS 61191-10:2022 © IEC 2022 – 15 –
REQUIREMENTS FOR THE COATING OF ASSEMBLIES
1 General requirements
2 Climate impact requirements
3 Regulations for protective coating
3.1 Reference to the general requirements
3.2 Reference to climate impact
---------------------- Page: 17 ----------------------
– 16 – IEC PAS 61191-10:2022 © IEC 2022
1 General requirements

Due to the continuous miniaturization of printed circuit boards in recent years, live compo-

nents and conductors are moving ever closer together, increasing the risk of leakage cur-

rent formation under moisture. Due to the good dielectric properties of protective coatings,

minimum distances between live conductors can be reduced.
In addition, depending on the coating system used, protection against
• mechanical abrasion, vibration and impact,
• atmospheric humidity and hand perspiration,
• chemicals and environmental gases,
• mold infestation in tropical conditions,
• metal splinters/particles.

can be achieved. The surfaces to be coated on assemblies can be of very different types,

e.g.
• metal surfaces (tin, tin lead, gold, nickel, copper etc.),

• plastic surfaces (solder resist, PCB base material, component housing, etc.) or

• residues from various soldering processes (HAL = Hot Air Levelling, reflow sol-

dering, solder paste residues, etc.), welding, gluing and other processes.
Very different surface topographies must be taken into account:
• plane surfaces (horizontal, inclined and partly vertical),
• inner edges, outer edges and corners,
• tips and pods,
• wires, curved terminal frames (component connections),
• shadow areas that are not accessible in a straight line, and
• narrow gap (expansion gap).
In general, very high demands are placed on optimum protective coatings, e.g.

• protection against moisture by forming an electrically insulating material barrier,

• avoidance of corrosion phenome
...

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