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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.
This week’s news items taught me a few things I didn’t know. For instance, there’s news about the new equipment for THT work, governmental support for advanced packaging technologies, an upcoming webinar from iNEMI on counterfeits, an interview with U.S. Rep. Blake Moore, one of the sponsors of the bipartisan Protecting Circuit Boards and Substrates Act, and columnist Tim Haag, using Star Trek to illustrate why simplicity is, ahem, paramount.
VPT, Inc., a HEICO company, VPT, Inc., a trusted provider of power conversion solutions for aerospace and defense, proudly announces its latest achievement of obtaining SAE AS9100 Revision D certification. SAE AS9100 Revision D enhances VPT's existing suite of certifications, including MIL-PRF-38534, MIL-STD-883, J-STD-001 (Space), IPC-A-610, and IPC-A-600, further cementing our commitment to excellence in quality and reliability.
Test Research, Inc. (TRI), the industry's leading provider of Test and Inspection systems for the electronics manufacturing industry, is pleased to announce the expansion of its Malaysian office, which opened in 2010.
November’s issue of Design007 Magazine had an excellent theme that evolved around design simplification. There were exceptionally good articles about how to reduce over-constrained or needlessly complex designs. One significant time-consuming category is the creation of many design files and drawings which lead to lengthy creation and interpretation time along with the considerable time to resolve conflicting or erroneous information.
Statement of Support from IPC for New Actions to Strengthen America’s Supply Chains, Lower Costs for Families, and Secure Key Sectors11/27/2023 | IPC
IPC welcomes the actions outlined today by the U.S. Government “to strengthen supply chains critical to America’s economic and national security.”