Last updated: October 28, 2026
Conformal coating protects a finished board from moisture, dust, and corrosion — but only if it’s applied evenly. The three defects we get called about most often are voids, bridging, and thin or starved edges. Almost every one of them traces back to the application method rather than the coating chemistry. Here’s how to get a clean, repeatable coat.
Why selective coating beats the brush
Hand-brushing and aerosol cans can’t hold a consistent film thickness, and they coat areas that should stay clean — connectors, test points, and gold fingers. A precision spray or film-coat valve lays down a controlled, even layer exactly where you want it. Pairing that valve with a controller gives you repeatable cycle timing, so board number 1,000 looks like board number 1.
Fixing the three common defects
Voids and bubbles
Voids usually come from trapped air or coating that’s pulled away from a component edge before it cures. Controlling flow rate and atomization pressure at the valve — rather than relying on a steady hand — keeps the film continuous. Dialing back fluid pressure slightly and slowing the pass often clears up micro-bubbles.
Bridging between leads
Bridging happens when too much coating pools between closely spaced leads. The fix is deposit control: a valve that shuts off cleanly, without drooling, plus the right tip or nozzle for the gap. Drip-free cutoff is the single biggest factor here.
Starved or thin edges
Edges get starved when coverage isn’t uniform across the pass. Consistent standoff distance and overlap — easy to hold with an automated dispensing system, hard to hold by hand — give you an even build across the whole board.
Process controls that pay off
- Fluid pressure and valve timing: document them and they become repeatable.
- Atomization air: too much causes overspray and bridging; too little causes orange-peel.
- Coating viscosity and temperature: small shifts change film thickness.
- Masking: the right valve reduces how much you have to mask in the first place.
When volume justifies automation
If you’re coating boards in any quantity, moving from a handheld process to a programmed valve on a 3-axis robot pays for itself fast in reduced rework and material savings. It also gives you the documented, repeatable process that high-reliability electronics customers increasingly require.
Prove it on your boards first
Coating behavior depends on your specific material and board layout. We’ll run your coating in our local lab and recommend the valve, nozzle, and settings that fix the defects you’re seeing. Talk to a specialist or browse our online store to get started.
J.A. CRAWFORD CO. is an authorized Nordson EFD Solutions Experts partner serving Southern California, Arizona, and Baja Mexico, supporting electronics manufacturers with on-site application help and same-day shipping since 1967.
Frequently Asked Questions
What causes bridging in conformal coating?
Bridging happens when too much coating pools between closely spaced leads. The fix is deposit control: a valve with clean, drip-free cutoff and the right nozzle for the gap.
What causes voids and bubbles in conformal coating?
Usually trapped air, or coating pulling away from a component edge before it cures. Controlling flow rate and atomization pressure at the valve, and slowing the pass, keeps the film continuous.
What dispensing tip works for conformal coating?
Nordson EFD’s component selection guide rates tapered tips as recommended for conformal coatings, stainless and flexible tips as satisfactory, and PTFE-lined tips as not recommended. See dispensing by fluid type.