Author Topic: conformal coating with rework ability?  (Read 824 times)

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Online coppercone2Topic starter

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conformal coating with rework ability?
« on: May 30, 2023, 11:09:58 pm »
When I tried to do the conformal coating on the miller dynasty welder, I noticed that the one I had (spray on MG chemicals silicone) caused the old coating to peel off. I thought I could do a touch up but it all went to hell in a hand basket, looked like some napalm burn victim

I notice this is the case with some uncured spray paint, but the thing is, that is usually the 1-24 hour rule, that is recoat within 1 hour or after 24 hours, or you get peeling. But this conformal coating is... 15? years old.

Are all conformal coatings like this ? Is it because i used the spray can?


Like, its fucking super lame that I need to clean this entire PCB to recoat like 1 IC. Just wow, what a bad technology. Scrub a dub dub time to sit over a pool of fumes with a paint brush again  >:( >:( >:(


Is there like a safe coating that is designed for touch ups vs total recoats? Are the pens any better? It makes it blister like CRAZY. Any contact between the two makes the old one just fall off. It works about 5x better then the conformal coating remover liquid. In fact if you spray on new coating, then use the liquid, it comes off MUCH easier then just using the remover liquid. If I had to do another board, I would first spray it down with the conformal coating, then let it blister, then just brush it off with the remover (WOW!)
« Last Edit: May 30, 2023, 11:13:50 pm by coppercone2 »
 

Online coppercone2Topic starter

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Re: conformal coating with rework ability?
« Reply #1 on: May 31, 2023, 02:14:12 am »
well I put it on the cleaned PCB again, this time it went on better but it looks pretty ass. And its WAY thinner what they put on. Miller must have gooed that board. I can live with it though I won't be running the angle grinder into the exhaust vent
 

Offline Solder_Junkie

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Re: conformal coating with rework ability?
« Reply #2 on: May 31, 2023, 06:55:50 am »
It is many years since I worked on coated print boards. Back then I repaired intrinsically safe hand held radios that were used in the chemical, mining and oil industries. The coating was to prevent any stray wire strands, or similar metal debris, causing a spark or components to heat up.

The older radios, from the late 1960s, had two part epoxy resin coating. That took some removing… usually with heat from a soldering iron.

Later radios had a Dow Corning silicon rubber coating that was fairly easy to peel off and re-coat. It was semi transparent and came in a “toothpaste” size tube and flowed quite easily. I expect it was originally brushed on during manufacturing.

More recently I have protected connections,  and the rear of sockets from moisture within enclosures used outdoors, with “704 high temperature” white silicon from eBay vendors in China. This stuff resembles pouring cream and easily coats connections, coax braid, etc. Both this and the Dow Corning silicon are the type that doesn’t produce acid when curing.

Many boards are sprayed with a lacquer that resembles polyurethane varnish, although this  is primarily to protect them from tarnishing, or the effects of condensation in outdoor enclosures. I spray most of my home made projects with this stuff.

I would expect that Dow Corning can advise on a suitable coating.

SJ
 

Online coppercone2Topic starter

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Re: conformal coating with rework ability?
« Reply #3 on: May 31, 2023, 01:27:42 pm »
Hmm I do have flowable silicone. Since I just need to brush up 1 IC on this board, I suppose I can brush that on, its not reactive. I don't like it because it will be hard to remove but I can't complain for like a single 74 series package. Its like a thinner version of the electronics silicone, I suppose I can remove it with rubber abraisves later, I have a feeling it would not be cheap to buy a new product..  I was hoping for like a 20$ pen lol
 

Offline thm_w

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Re: conformal coating with rework ability?
« Reply #4 on: May 31, 2023, 09:35:20 pm »
You buy the little glass jars with a brush, its about $20 yeah.
I can't guarantee its less aggressive than the spray but it would have way lower solvent content.
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Online coppercone2Topic starter

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Re: conformal coating with rework ability?
« Reply #5 on: June 01, 2023, 02:09:02 am »
yeah I just got it in the mail today I will give it a shot on the bare PCB area. I definatley don't want to clean the optics board, the fucking optics boards (display) are always the one that break on me. Especially old HP 7 segment displays but still

I was really hoping the low solvent content thing ur talking about is the case

otherwise my suggestion is if you want to do a full miller PCB board recoat, first spray it with conformal coating, then add the remover. Whatever solvent is in the spray just... denatures the miller coating
 

Online coppercone2Topic starter

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Re: conformal coating with rework ability?
« Reply #6 on: June 01, 2023, 02:30:52 am »
ok yeah it does not react. And its thicker like the original.

The spray coated (totally cleaned PCB) looks kinda shitty and its very thin, the brush applicator stuff is fairly thick and looks like the stuff miller had on their originally. Go figure :o
 
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Online coppercone2Topic starter

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Re: conformal coating with rework ability?
« Reply #7 on: June 02, 2023, 05:33:41 am »
I coated two boards with the bottle, and it only took 20 ml (knocked it over unfortunately so I am almost out!).

Tedious process to brush it on, and it does not look great, but its OK. The solution would be to use a bigger brush for such a large PCB.


very tedious, I hope it works :-DD
 


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