Ask the Experts
January 31, 2024 - Updated
October 5, 2021 - Originally Posted

Conformal Coating Bubbles

Conformal Coating Bubbles
We use a conformal coating house whose workmanship is beginning to display a ton of bubbles around the leads of the IC's. Per IPC-A-610 Rev G, section 10.8.2, one of the conformal coat defects for Class 1, 2, and 3 is "Bridging of adjacent lands or exposed conductive surfaces caused by: voids or bubbles."

Is this a true IPC-A-610 defect? I just want to be sure I'm not misinterpreting the standard.


Expert Panel Responses

Based on the IPC-a-610 Rev G section 10.8.2. Per IPC-A-610 Rev G, section 10.8.2, one of the conformal coat defects for Class 1, 2, and 3 is "Bridging of adjacent lands or exposed conductive surfaces caused by: voids or bubbles." I am not exactly sure of the intent of the above, however this is my interpretation.

I am assuming the void in the coating creates an open area to the atmosphere that would allow moisture to collect and become a conductive bridge. The picture that was posted shows voids on top of chip components. I am assuming that if moisture came to rest in this location, it would cause a direct short. Therefore, it would be a defect that could cause detrimental failure.

Karl Seelig

Deck Street Consultants
In his 32 years of industry experience, Mr. Seelig has authored over 30 published articles on topics including lead-free assembly, no-clean technology, and process optimization. Karl holds numerous patents, including four for lead-free solder alloys, and was a key developer of no-clean technology.

If the bubbles bridge adjacent leads, then absolutely it is a defect. If adjacent leads are exposed, then the purpose of the coating has been compromised. It may well be that the bubbles don’t really expose adjacent leads, but how is one to determine this? If we see bubbles of sufficient size that they seem to bridge the gap between leads, then we have to assume there is no protection between said leads.

The usual cause of bubbles like this is laying down too thick a coating, then heating it too quickly during cure. This can happen with both solvent-based and water-based coatings. It’s not the only reason you can get bubbling, but in my experience it is the most common one. They do tend to appear often between leads, because capillary action can result in thicker coating there.

Fritz Byle
Process Engineer
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.

Yes the IPC mention that is a Defect – Class 1,2,3 if have: Bridging of adjacent lands or exposed conductive surfaces caused by: Loss of adhesion, Voids or bubbles, De wetting, Cracks, Ripples, Fisheyes, Orange peel, Flaking.

If you have a lot of bobbles or voids probably you have materials incompatibility (Flux vs conformal, Conformal vs Solder Mask) or have flux residues that activates once the conformal is curing, that generates outgassing and remain trapped on the conformal.

Andres Rojas
Engineering Director / Master IPC Trainer (MIT)
AMMSA Solutions
More than 20 years of technical experience in the electronics industry in roles ranging from Process & Project Engineer to engineering manager and Technical Applications Engineer for Latin Americas. IPC Master Trainer, International speaker and consultant.

Just from reading your supplied information related to the bubbles being present & the clear language of the IPC spec, my answer would be, Yes your vendor is providing you with out of spec material.

Jerry Karp
JSK Associates
Based in. Northern California since 1971. Founded JSK Associates in 1979. Actively involved in soldering, cleaning, chemistries. 30 years experience in EOS/ESD control.

Fun times! Yes, bubbles are a defect. Bubbles in your conformal coating is a result of one of two things. First, it could be that the two-part coating was mixed well, but not degassed. After mixing a two part system, you need to degas it by putting the mixture in a vacuum oven and pull a slight vacuum for about 15 minutes, I think for 20 mm Hg, more or less.

This will remove the bubbles in the liquid. If that is not the problem, then more than likely you are using conformal coating that has gone bad... possibly it is a 2 part urethane system and somehow you got water in it. The coatings do not like water to get into them, so throw it out, remix, degass, and apply.

Be sure that you are storing your coatings in a low humidity environment. And purchase in the correct size of container so that you are not opening and closing a container and allowing moisture to affect the two ingredients. Now, if you need any solvents or equipment to help you with rework, or cleaning the boards before conformal coating, please give me a call.

Rick Perkins
Chem Logic
Rick Perkins is a chemical engineer with more than 33 years of Materials & Processes experience. He has worked with Honeywell Aerospace in high-reliability manufacturing, as well as with several oil-field manufacturing companies. He also has a good understanding of environmental, health, and safety regulations.

Conformal coating is applied on electronics to improve reliability. It does this by protecting conductive surfaces from external and internal factors. External factors can include moisture and dust; the internal factors include electrical shorts and corrosion.

The coating isolates the conductive surfaces from one another to protect from internal failures. Not all bubbles are defects and IPC specifications state limits around acceptable bubble sizes. Bubbles that bridge leads are gaps in the coating coverage and are considered defects.

Mark Norris
Vice President Asia
Nordson Advanced Technologies
Responsible for Nordson Advanced Technology Electronic Systems throughout Asia including China, Taiwan, Korea, Japan & SE Asia. Nordson Advanced Electronic Systems includes the world leading technology companies Asymtek Dispensing, Dage X-Ray, Dage Bond Test, March Plasma, Matrix AXI & Yestech AOI.

From your description, yes – this is an IPC-A-610 defect. These bubbles bridge the gap between the adjacent leads – it means the area is open to the atmosphere and no longer protected.

If you get moisture in that open area it can bridge the area and create an electrical short. So yes it is defect and your supplier doesn't provide you with an approved and sufficient quality.

Anki Forsberg
Senior Quality Engineer - PCB Assembly
Axis Communications
Over 27 years of experience within the PCB assembly area. Hands on experience troubleshooting SMT on a global basis as well as implementing and setting up new processes/technology/equipment. ESD questions is also a key area.

Air bubbles generated After Conformal coating on circuit card, that main reason has, make the circuit board pre heat up 60 to 80 Degree temperature into oven that purpose entire circuit board Moisture has been viporised. Then do the çonformal coating, and Again post heat for curing heat up to 80 to 120 degree temperature the circuit board Full cured and there is no air bubbles observed.

Raju Wagh
Senior Engineer SMT
Advance Power Display system Ltd Mumbai
Mr. Raju Wagh has worked in the electronics industries for the past 20 years focused in TV manufacturing, mother boards, mobile, LED lighting, power supply manufacturing and more. His specialty is in SMT production and processes
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