Selective PCB conformal coat options - Page 1
Forum section: electronics / general

author: Psi
author_rank: Super Contributor
timestamp: October 26, 2022, 03:43:13 am
content: So I've had a few boards made over the years with conformal coating. Usually done by pcbway as a PCBA project.They use some sort of UV set coating but it's not very thick and touching the PCB pads with multimeter probes will usually break through the coating.If I want to get something a big thicker/better what should I ask for?Or alternative is there any substances I can buy a big container of for low cost and just apply to PCB areas myself selectively?I'm thinking like $0.5 per board sort of cost. I know some of the silicone coatings can get really expensive.Mainly i'm looking for some resistance to water/humidity in sensitive areas.

author: tomgat
author_rank: Regular Contributor
timestamp: October 27, 2022, 12:50:17 am
content: Quote from: Psi on October 26, 2022, 03:43:13 amJust a thought, but you can always conformal coat it yourself.For all my conformal boards I just spray MG Chemicals 419D Acrylic Conformal Coating. Its easy to get, cheap, and dries in about 5 mins. If you want a thicker layer, you can just spray it as many times as you like. Just tape off any connectors you really care about first. Also, the advantage of using acrylic is that you can always take it off later with acetone which is also cheap and easy to get.

author: Psi
author_rank: Super Contributor
timestamp: October 30, 2022, 05:29:36 am
content: Do you know if you can apply MG Chemicals 419D with a brush?

author: jpanhalt
author_rank: Super Contributor
timestamp: October 30, 2022, 06:02:25 am
content: From the datasheet:QuoteIt is basically a flexible lacquer. I would use a soft hair artist brush, like camel hair.

author: Psi
author_rank: Super Contributor
timestamp: October 30, 2022, 10:31:57 am
content: Cool.Are there any options for off-brand equivalents to 419d ?$1700 NZD for 20 Liters is a bit pricy.

author: jpanhalt
author_rank: Super Contributor
timestamp: October 30, 2022, 11:06:07 am
content: Some people, including myself, have used Krylon brand clear spray acrylic. I have not seen it it in a bottle or can. If all you want is a clear one-part lacquer you might try airplane dope (still available in some places), which is a plasticized lacquer. Nitrate version sticks better but is not as durable as the butyrate version. Clear brushing lacquer or fingernail polish are lacquers and might work. Old time automotive clear might also work. It was used for "candied apple" finishes in my school days. Today, it is probably replaced with clear coat because of VOC restrictions.Automotive clear coat is probably two-part. I am not sure of its chemistry. Plasticized polyurethanes in clear are also available for fabric aircraft. The latter might be available in non-two part (i.e., moisture curing). (I haven't checked. Search on Ceconite finishing.) Of course, there are clear polyurethane varnishes at every home store. Polyurethanes meet VOC requirements, but are not as easily removed*, adherent, or flexible as lacquers, unless specifically stated to be flexible. Surfaces must be very clean for them to stick.*They generally require mechanical scraping or harsh chemicals to remove them.

author: Psi
author_rank: Super Contributor
timestamp: October 30, 2022, 11:58:45 am
content: I wouldn't use any unless it has PCB coating as one of its intended uses.I would be too scared it contains some chemical that might corrode the PCB after a while.

author: jpanhalt
author_rank: Super Contributor
timestamp: October 30, 2022, 12:29:56 pm
content: I doubt you will find such notices in alternative products, but reviewing the MSDS/SDS for them might tell you. Here's the SDS for Krylon clear:https://www.paintdocs.com/docs/webPDF.jsp?SITEID=KRI&doctype=SDS&cntry=US&prodno=075577000548Nothing in that is considered as corrosive to metals. Although the word, "corrosive" is used relative to skin irritation, it does not cause corrosion of metals. Compare that to the SDS for the expensive MG product:https://www.mgchemicals.com/downloads/msds/01%20English%20Can-USA%20SDS/sds-419d-l.pdfIf you want the PCB specification, then you will likely need to pay a higher price.

author: tomgat
author_rank: Regular Contributor
timestamp: October 31, 2022, 01:49:08 pm
content: Quote from: Psi on October 30, 2022, 05:29:36 amI do. However, I work with 100/250/500 boards, and found it is faster to spray. Ive been tempted to convert one of my solder robots to a conformal coater machine, but havent had allot of free time to spend on the project. I saw some used conformal coating machines, but they look pretty messy.

author: Psi
author_rank: Super Contributor
timestamp: November 01, 2022, 06:54:02 am
content: Quote from: tomgat on October 31, 2022, 01:49:08 pmYes, Spraying would be better for me too, I'm just looking at options.If I spray them I need to sort out a vented spray booth and it will have to be huge as I cant have them fuming up the house. Ideally I would get the PCB fab to do it, but if I do that it makes any rework very messy.Maybe the solution is sending a test jig to the pcbfab so they can try repair any bad ones before they get coated.