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Sensible Design: When Coatings Go WrongAugust 23, 2016 | Phil Kinner, Electrolube
Estimated reading time: 2 minutes
This month, I consider some of the more common, and often very frustrating, problems that may be encountered when coating electronic circuit boards and components. I also discuss some practical solutions.
As we all know, nothing in life is straightforward. In any engineering discipline, if there is the slightest chance that something might go wrong, you can bet your bottom dollar that it will. The secret is to be prepared for it. For the purposes of this column, I’m going to concentrate on the use of conformal coatings for the protection of electronic assemblies, highlighting some of the potential pitfalls associated with the choice of coating and the method of application. In each case, I will suggest an approach that should mitigate the majority of problems you are likely to encounter.
Problem: The quality and performance of a conformal coating material could be compromised according to the method of application.
This issue is commonly encountered when a product is transferred from one circuit manufacturer to another; for example, a product may be dip-coated in one country but selectively coated in another, with the specification requiring that the same material be used at both sites. The problem that arises here, however, is that using a material formulated for dip-coating in selective coating equipment can result in poor yield due to excessively fast drying and bubble entrapment.
One of my customers spent six months trying to solve a bubble issue internally, without realising that the root cause of this problem lay in the material formulation. After working with the customer, we found that by changing the solvent blend, the bubble entrapment issue could easily be resolved. Moreover, this solution simplified the process and reduced the cycle time. And since the non-volatile formulation remained the same, there was no need to re-qualify.
Problem: Achieving incorrect coating thickness, especially with acrylics.
The IPC specification allows a dry film thickness of between 30 and 130 microns, with the greater thickness being achieved by the application of multiple coating layers. Trying to achieve a 130-micron dry film thickness from a single selective-coating process with a solvent-based acrylic material is a recipe for a disaster, likely to result in excessive bubble formation, film shrinkage, coating delamination and additional stress on components. The result is poorer protection, rather than an improved overall level of circuit protection. Aiming for a uniform 30-50 microns and focusing on achieving perfect coverage at each application is a much better approach to improving the protection of electronic circuits.
Achieving the correct coating thickness is important; bear in mind that if the coating is too thick it can lead to entrapment of solvents in areas where the coating does not fully cure. Similarly, it can cause the coating to crack as it cures or as the result of changes in temperature, or due to mechanical shock and vibration.
To read this entire article, which appeared in the July 2016 issue of The PCB Design Magazine, click here.
The practical question around CHIPS Act development and electronics assembly is, “Will this change how we do business?” Indium Corporation’s Dr. Andy Mackie sat down with Nolan Johnson to share what he sees as emerging answers to that question from his perspective as an expert in electronics assembly and packaging, and as a participant in standards development through IPC, JEDEC, and SEMI.
IPC continues to collaborate with the electronics manufacturing industry to meet their current and future workforce training needs.
Though product demand weakened this month with Orders and Backlog Indexes slipping, overall electronics industry operations remain healthy per IPC’s September 2023 Global Sentiment of the Electronics Supply Chain Report.
Rigid-flex circuits are unique structures; part rigid board and part flex, they’re increasingly working their way into many of the electronic devices we use every day. There have been many advances in rigid-flex lately as more companies find themselves exploring this technology. So, before I started writing this article about rigid-flex design, I double-checked a few things. Fortunately, there is plenty of rigid-flex information available on a variety of great websites that we all know and trust.
IPC Day France: Aerospace Electronics is an aerospace-focused networking event featuring key industry experts from NASA and Airbus and will take place on October 2, 2023 .