Manual brushing is just one of many methods commonly used for applying conformal coating materials to PCBs and other components. It is a hand-applied method that requires little investment into automation or equipment. With practice, it can be one of the simplest methods available, especially for small-batch production or isolated applications.
While its simplicity is apparent, there are essential considerations required for effective manual brushing that can lead to dire consequences when ignored. This guide will review everything you need to know to ensure you get the best results when applying coating with manual brushing.
Manual Brushing Benefits
Out of all the methods for applying conformal coatings, manual brushing has the least overhead. Most standard paint brushes work just fine for this purpose. As such, any 6-12 mm, horse-hair brush can be used. These are quite common, and typically cost no more than $12 at the highest.
Application can be time-consuming, as you must delicately coat the surface in a consistent stroke of coating. For companies mass-producing components, this is not a viable choice. Instead, brushing is used for validation and testing before it’s time to invest in production. The proper machinery costs anywhere between $40,000 and $1,000,000. Additionally, assembly lines can take up to 120 feet of machinery. Before you’re ready to make that level of investment, it’s critical to ensure that the process, design, and materials function to expectations.
This is where manual brushing excels. As a cheap method of application, manual brushing empowers engineers to create prototypes and other pre-production designs for validation.
How to Brush Conformal Coatings
When brushing conformal coating material, the idea is to spread the coating as cleanly and consistently as possible. To do this, a fresh, well-cared-for brush is essential. We have suggestions for proper brush maintenance and storage below. Additionally, conformal coating material should be poured into a small jar or container, with enough material that the brush head may be fully submerged.
We never recommend applying material directly out of its original container for multiple reasons. This runs the risk of contaminating the supply and makes application far more difficult. For the best results, use a small sized glass or chemically resistant container and ensure the tip of the brush is immersed evenly in the material, wiping off any excess materials on the side of the container to prevent drips.
The brush should be held at a gentle angle. Please refer to the diagram below for reference. Brush lightly, with small brush strokes over the desired area. Too much pressure causes an uneven spread of material. Drag the brush gently across the surface; flip the brush to use both sides of the head; recoat the brush in material liberally.
Additionally, we recommend a few other considerations:
- We find it’s best to use a 5:1 – 2:1 coating to thinner ratio
- We use medium to high evaporation solvents when manually coating in our lab (521EU, 503, 905, etc)
- Check the viscosity of the solution before application. Ideally, these tests are run daily or weekly. Add more thinner or coating as needed. (See our guide on measuring viscosity for more information)
Related Article: The Ultimate Guide to Viscosity Part 1
Brush Maintenance and Care
Proper brush care is essential. Ideally, you should always use a relatively fresh brush. We recommend changing out brushes every 30-90 days. This range may be shorter if the brush is heavily employed. Over-used brushes run the risk of damaged or matted bristles, both negatively affecting the brush’s capacity for smooth, consistent strokes.
Matted bristles occur when the conformal coating material dries and sets on the hairs. The hairs then clump up with hardened compounds. To avoid this, we recommend storing the brushes in their pour jars with the liquid conformal coating fully submerging the hairs (at a level even with the metal band as submerging to the wood causes other problems). This ensures the bristles do not dry out, thus leaving a clean brush head.
This has another benefit too. Storing the brush semi-submerged in a small size container filled with HumiSeal Thinner prevents debris and other contaminants from adhering to the brush hairs. Whether it be dust or other particles, it’s incredibly difficult to keep the exposed hairs free from particles when the brush is left in the open. These foreign contaminants are some of the last things you want mixing into the conformal coating or scraping against the PCB during application.
For these reasons, it’s absolutely critical to store the brush head in excess thinner.
Manual brushing is a tremendously effective solution for many operations. For its low cost and easy application, it’s perfect for small batches and process testing. We have plenty of resources available on our site for additional information on manual brushing techniques, materials, and troubleshooting.
If you have any questions on conformal coatings and their application, please reach out. We are happy to assist you with any needs you may have.