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2021-07-28
Reference Book: Conformal Coatings for Electronics Applications
2021-07-28
Reference Book: Conformal Coatings for Electronics Applications

A reference book that packs a punch: "Conformal Coatings for Electronics Applications" by Dr. Manfred Suppa is 527 pages long and describes in great detail with 329 illustrations and in 112 tables the areas of application, requirement profiles, characteristics as well as the processing of conformal coatings for electronics. It was published in 2010 by company founder Werner Peters. On the occasion of last year's anniversary, the 50 years of Lackwerke Peters, we would like to delve deeper into this comprehensive work for practitioners and experts and summarise what can be found in terms of content.

Have you ever asked yourself what electronics, conformal coatings, chemistry and physics have to do with each other? Or have you ever thought about why electronic assemblies need special protection? And why this might be interesting? We have asked the author Dr Manfred Suppa; he was Head of Research and Development at the Peters Group for many years.

“Conformal coatings have not been on the market that long," says Dr Suppa, looking back at the history. The driving force was the military: Vehicles with much electronics on board, such as tanks or jeeps, failed to perform under extreme climatic conditions in the tropics.  "That was life-threatening." At that point, at the latest, it was clear: electronics need special protection. It was the time when the first inks for protecting electronics were developed. A blessing because electronic assemblies are increasingly incorporated in more and more applications in ever smaller spaces and must be protected from moisture and dirt. Moreover, in today’s PCB production, the knowledge of yesteryear that a conformal coating has to dry, for example, is no longer sufficient. "The customer wants to know in more detail what exactly happens physically and chemically within this period of time, in view of optimising and accelerating processes," says Dr Suppa.

Electronic assemblies in the smallest space

Dr. Suppa explains why these conformal coatings are becoming more and more important, using the example of a power socket: "The electrical poles are, for example, one centimetre apart, so a drop of water doesn't make any difference. But if the two poles are less than a millimetre apart, a drop of water may be the end of the line."

The electronics industry, including electric mobility, LEDs and sensors, is facing the challenge of protecting electronic assemblies from heat generation, short circuits and corrosion in the smallest possible space, in order to ensure durability, among other things. 

A book that provides detailed insights into the highly complex physical and chemical background of electronic assemblies and their loads and that answers various interdisciplinary questions.

Conformal coating helps to preserve and improve

The conformal coating of electronic assemblies helps to maintain or improve electrical mass production. Among the important aspects for selecting conformal coatings or insulating coatings, there are operating temperature range, barrier effect against water or water vapour, gas permeability, electrical properties, coating properties and adhesion as well as reparability, transparency and abrasion resistance. "The large number of conformal coatings of different chemical compositions available today shows the flexibility and variety of possibilities for producing functional electronic assemblies by means of conformal coating," writes Professor Dr.- Ing. Wolfgang Scheel (until 2008 head of the Department of Assembly Technology and Interconnection Techniques at the Fraunhofer Institute for Reliability and Microintegration, IZM, Berlin) in the foreword of the book. Together with his team, he has done ground-breaking work for a new generation of circuit carriers and has had a great influence on the assembly and interconnection technologies chosen.

The reference book, for both the practitioner and the expert, presents the current state of knowledge on conformal coatings and points to future developments. Complex interactions between the coatings used, manufacturing processes applied, quality testing and reliability considerations are the main content of the book. "The requirements of the last 10 years in assembly coating have changed or become more stringent, in some cases drastically. This is true for both the area of application and the technical performance of the actual coating. As to the application, one can give as examples the shortening application and drying times and the control and documentation possibilities in the various phases. With regard to the technical performance of a coating, the electrical properties under the highest humidity conditions on the one hand and the thermal resistance and thermal shock resistance of the coated assembly on the other should be mentioned," adds the author Dr. Manfred Suppa.

Why coating materials are necessary

This book includes detailed descriptions of basic knowledge. For example, why electronic assemblies have to be coated and what requirements are being placed on them to a growing extent. Coatings provide mechanical protection against mechanical abrasion, vibration or light impact loads, among other things. They provide corrosion protection, e.g. against moisture, chemicals or mould. In addition, they improve the electrical insulation between two potentials for requirements in explosion protection or high-voltage stress, especially at great heights. "Due to this variety of applications and the high sensitivity, optimally adapted protective and insulating materials are also becoming increasingly important for sensors. Only by protecting against environmental influences and interfering electrical currents, a wide use of these products is possible even under extreme conditions," one can read in the section on why electronic assemblies need to be coated.

Manufacture and application of conformal coatings

Much space is devoted to the detailed description of conformal coatings. Here, the author describes the basics and the composition of coating materials. Among other things, classifications according to the chemical binder base, properties of conformal coatings, drying and curing mechanisms, coating thicknesses, pre-cleaning and pre-treatment of the assemblies of a conformal coating are discussed. In addition, the question is discussed whether rather liquid, plastic, ionic or powdery states play a role in the manufacturing process and application.

If these materials with all their properties are applied and processed, sophisticated tests are performed. It is distinguished between the examination of the coating process, the functional test of the assemblies and the quality test of a coating. Here, the uniformity of coating, uniformity in colour and layer thickness of the surface, plus hardening or the absence of bubbles are important factors. In addition, the coating film must be free from harmful substances, bubbles, wrinkles and cracks. 

Find and fix faults

After all, errors and can also occur in such complex technical and chemical processes as the processing of conformal coatings. There are many chapters on this topic, which are described in the context of "Troubleshooting". One will find central descriptions of error analysis and repair here. Which types of errors can occur, how can they be detected and how can they be repaired? For example, the processing of the coatings is relatively unspectacular - but a number of errors can occur during the coating process. Several causes can be significant, which does not exactly make the entire process of error detection and possible repair any easier.

Content grown over years

In the 40-page appendix, the reader will find conversion factors, physical parameters, environmental testing standards and an extensive index of key words, figures, tables and literature. The content of this comprehensive work has grown over many years, initially in the form of lectures and various articles in specialist journals. "Until I was approached more and more frequently by colleagues in the field who expressed the wish that all of this should be summarised," says author Dr Suppa, recalling the beginnings. An extensive work that certainly took almost six years.

A special topic that is of great consequence. Before electrical circuits based on printed circuit boards found their way into industrial use, wires as electrical conductors were protected against short circuits by organic resin-based coatings. With the use of printed circuit boards as circuit carriers and the rapid development of circuit technology, even under increasingly extreme operating conditions such as in tropical, military, space and automotive applications, the demand for protective properties for electronic circuits has increased and continues to increase. Parts are being installed in increasingly confined spaces and are therefore far more sensitive to moisture, corrosion and the loss of function that often accompanies this.

This makes it all the more important that there are full-range suppliers like the Peters Group, which carries out research and development at the highest level for the further development and processing of conformal coatings. Operating as a high-tech provider of holistic solutions in the assembly of printed circuit boards, this group specialises in this way and sells its products worldwide, passing on its expertise in the form of consulting services worldwide. This is achieved through such an extensive and detailed reference book, in seminars and workshops, in the transparency of production and manufacturing processes and very soon, by the possibility for external parties to have their products subjected to a test procedure at Peters. We will describe shortly in one of our next blog articles what are the options in this respect and who may consider this testing procedure.

If you are interested in the Peters reference book by Dr. Manfred Suppa, you can order it here. Anyone who would like to find out more about the Peters family business operating worldwide, or is interested in news and developments within the Peters Group, is welcome to subscribe to our newsletter or visit the website www.peters.de where extensive material is available.

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