mg chemicals silicone conformal coating... dry blistering - Page 1
Forum section: electronics / general

author: coppercone2
author_rank: Super Contributor
timestamp: August 30, 2025, 03:15:16 am
content: So I got back to the old project I abandoned a while back, which got coated with MG chemicals silicone conformal coating.It was dormant for about 8 months, with PCB mounted in the chassis. I pulled it out today... the underside totally dried out and started flaking off. There is a bunch of flakes that fell to the bottom of the chassis and glued themselves to it. If I run a wooden stick across the PCB, it basically snow glitter. Its like it has terrible dandruff. I would say the coating is 85% compromised.What the hell caused this? Also, this was from the bottle, painted on with a brush, and it was cleaned with alcohol and baked before coating.Like... its beyond terrible. I renember it was kind of crappy to begin with, but it looks like it just had a major malfunction. I actually got 'glitter' in my eye from about 1.5 feet away when I gently ran a wooden stick through the coated pins, it cracks off like spring loaded super stale dry breadLike, this stuff... has the same material properties as like, failed kiln coating. It basically reminds me of ceramic, or maybe molten sugar. It's like if you made a planko cutlet or some kinda cupcake sugar glitter.Why did it get so much 'strain' just siting out in the open for months??and I don't understand how it glued itself to the bottom of the chassis, because it was dry on the pcb when it was put in there.

author: Rat_Patrol
author_rank: Frequent Contributor
timestamp: August 30, 2025, 04:57:58 am
content: Sounds like contamination on the boards when you applied it.

author: coppercone2
author_rank: Super Contributor
timestamp: August 30, 2025, 07:59:14 am
content: what could contaminate it so bad that approx 1 square foot of material all dries up and flakes off ?

author: Whales
author_rank: Super Contributor
timestamp: August 30, 2025, 08:55:19 am
content: Do you know the SKU? 422B? That looks like a single-part silicone, so it requires humidity to cure.QuoteCould the case have been kept very dry after the board was installed? Can you give us more info about the application & environment?

author: tooki
author_rank: Super Contributor
timestamp: August 30, 2025, 10:06:02 am
content: Quote from: Whales on August 30, 2025, 08:55:19 amThis is the second time coppercone2 has posted about this exact problem, and the last time, he adamantly refused to share the SKU, even after repeated requests for it, and me calling him out for the idiocy of refusing to share key information:https://www.eevblog.com/forum/manufacture/brittle-silicone-conformal-coating/So I’d be very surprised if he actually does anything that could be considered “active participation in solving his problem”.

author: jpanhalt
author_rank: Super Contributor
timestamp: August 30, 2025, 10:42:27 am
content: Without positive photographic evidence, there is no foul. The calling on the field stands.

author: coppercone2
author_rank: Super Contributor
timestamp: August 30, 2025, 06:13:07 pm
content: I forgot about the first time, the problem must not have been so bad. Maybe a few patches had to be touched up, and the problem was different with the spray. This actually looked OK for a while.This time I got the entire PCB to clean just by rubbing it with nylon ESD PCB brushits not hard to find based on the entire name that I wrote......https://mgchemicals.com/products/conformal-coatings/silicone-conformal-coatings/silicone-modified-conformal-coating/and I probobly cleaned the ever living shit out of it, because when I did this, the other failure must have been in my mind already last yearthe sugar on a greasy doughnut is more robust then this coating lol. i should have just put carpenters polyurethane in itand it was stored in a regular garage

author: coppercone2
author_rank: Super Contributor
timestamp: August 30, 2025, 06:26:33 pm
content: and the flakes that stuck on the insulator on the chassis bottom, maybe its some kind of polyethylene sheet, are adhered better then the PCB

author: tooki
author_rank: Super Contributor
timestamp: August 30, 2025, 09:33:45 pm
content: Quote from: coppercone2 on August 30, 2025, 06:13:07 pmAs I told you the first time, but you just ignored, MG Chemicals has TWO “silicone-modified” conformal coatings, 422B and 422C. So no, your description was not sufficient to conclusively identify the item. It boggles the mind that you plain and simply refused to write down the 4 characters that would have identified the product without ambiguity.

author: coppercone2
author_rank: Super Contributor
timestamp: August 30, 2025, 09:35:24 pm
content: I probobly tried both of them at this point and the spray with bad results lolthey are not flexible or durable

author: tooki
author_rank: Super Contributor
timestamp: August 30, 2025, 09:50:59 pm
content: Similar question to last year: if you can’t tell us with certainty what product you used (whether it’s because you are just being difficult, or because you no longer know what you used), how can you expect anyone to give useful advice?And did you ever reach out to MG? The last time I asked, you just replied with some preemptive rant about how they’ll brush you off, without even having given them the chance to help.

author: coppercone2
author_rank: Super Contributor
timestamp: August 30, 2025, 09:53:47 pm
content: Its highly possible someone on this forum stumbled on the problem, which can be discussed in a public space, rather then trying to bust through clankers

author: Matt-Brown
author_rank: Regular Contributor
timestamp: September 03, 2025, 03:15:35 pm
content: More data is needed1) board completely coated, or just certain areas?2) You state applied with a brush and cleaned with alcohol, what alcohol? Was the brush new?3) Were the boards clean and dry before applying coating?4) How old is the bottle? It has a 5 year shelf life5) From the datasheethttps://mgchemicals.com/downloads/tds/tds-422B-l.pdfI dont think the cured glass transition temperature looks right. 29C is not good, but it does state service life of -40 to 200c

author: coppercone2
author_rank: Super Contributor
timestamp: September 03, 2025, 08:34:32 pm
content: yesmg chemicals brand alcohol and fresh acid brush from home depot packboards were ultrasoniced, rinse in distilled bottled water (I put boards in a big ziplock with distilled water and ultrasonic clean them more then rinse with bottle) and baked @90C in PID oven before application and left to dry in garage after applicationbottle <1 month old at time of application

author: coppercone2
author_rank: Super Contributor
timestamp: September 03, 2025, 08:46:24 pm
content: I found the bottle in back of my garage mini fridge now, its 1 year old or so. I can put it on a blank PCB fiberglass substrate (no copper) to see what happens. It got lost in a pile of thread locker tubes