In my last few columns, I’ve covered quite a bit of ground regarding the important considerations for conformal coating selection and performance, and the suitability of conformal coatings for LEDs and protecting circuitry from the harshest environments. I hope these columns have provided plenty of food for thought as well as given you a basic understanding of coatings and their benefits and limitations. In this column, I’m going to look at the different angles that design engineers and purchasing professionals come from and explore how these can sometimes conflict when selecting conformal coatings.
It is an area we are often confronted with at Electrolube. However, if experienced production personnel are reviewing the designer’s suggestions at an early enough stage, they could potentially prevent the perpetuation of some common problems. Thoughtful design will always pay huge dividends down the line, and designers will have friends for life among your production colleagues if you make their jobs just that little bit easier!
In an ideal world, the design engineer would work closely with either production engineers or the industrial engineers who oversee the coating process in the factory. Identifying potential production problems at the design stage will always be preferable and far easier than trying to fix problems or concerns following finalization of the engineering drawings. Here are four factors to consider when designing out production issues with coatings:
1. Simplify the Board Layout
By the simple act of placing connectors and components that must not be coated along one edge of the assembly, the conformal coating application process will be simplified. This might allow dip coating to be explored as a potential alternative methodology, speeding up application times, and reducing costs. Also, avoid large arrays of discrete components, which can pose a huge coating challenge due to the high levels of capillary forces present. The net result is often areas of no coverage/protection on the board as well as areas of excessive thickness prone to stress-cracking, delamination, and other coating defects. Similarly, tall components present challenges of their own by the creation of shadowed or hard-to-reach areas. Splashing is another associated problem. The trick is to avoid placing tall components next to must-coat components to avoid this eventuality.
2. Be Mindful of the Processes That Can Impact the Coating
The designer should ideally be aware of what kinds of manufacturing practices may occur following the application and cure of the coating because other materials, such as thermal greases/putties and rework/repair chemicals, can all have an impact on the integrity and overall performance of a coating. Also, when selecting adhesives for assemblies, care should always be taken to ensure that they are compatible with the selected coating materials and processes. Adhesives that are not compatible can have a detrimental effect on the overall performance of the coating.
To see the rest of this column, which appeared in the July 2019 issue of Design007 Magazine, click here.