Clear resin or epoxy coating

General Electronics
#1

Hey y’all!

I made a small PCB with some RGB Leds (everybody loves those). The pcb is 19x19mm or so with a 2 row, 12 pin (0.1inch) connector on one end, on the opposite the SMD leds (with SMD passives).

I’d like to coat/surround this thing in clear resin/epoxy/silicone something so that 1. the LEDs are still visible 2. the pcb will be inserted/removed and otherwise exposed to an indoor, somewhat clean environment. So it’d be nice to protect the electronics mainly from normal indoor use and human interaction.

Conformally coating the PCBA would have been smart, but I missed that boat, and I already have them.

Options I considered:

  1. Heat shrink tubing the thing. Either clear or black with a cutout for the leds.
  2. I can dip the PCBA into something (held by the connector on the opposite end) but what that is, I’m not sure.
  3. 3D printing with translucent filament an enclosure. The normal trick here of course is just getting the top/bottom half to snap somehow. Although, I did leave myself two cutouts in the PCB for standoffs.

Clear heat shrink will probably be acceptable, but yeah, curious as to what y’all think.

Thanks for the help,

Josh

#2

This immediately reminds me of a video (I think) that Mike Harrison made about board failures he had on his boards following potting. Unfortunately, I cannot find the video, but I found the related tweet. It’s probably buried in one of his many videos. I think it may be related to the snowflake display.

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#3

Hmm, heatshrink I have used a lot, and it works well (you might lightly file sharp corners of the PCB if you have them, and check no electrolytics or other packages standing in the air will get smushed by the heatshrink).

Epoxy was unusually challenging due to unexpected heat generation in my application, mainly it was terrible for insulating the circuit causing the LDO to die a death (or rather stop working after 20 minutes, cool down for 10 minutes, and then start working again!). May be a problem for you.

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#4

Never to late to coat! I’ve used MG 422B with good success, you can also use a soldermask (pink stuff) to block anything you don’t want coated. There is spray-on & dip versions of that. Get a good respirator though, and you can get a tabletop spray booth that helps contain overspray.

EDIT: There is some other ones (including epoxy) conformal coatings on MG chemicals site too. In my experience they all smell like cancer so you know they are good.

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#5

kafuter k-705
Don’t know if it would be too soft not to pick up finger prints but great stuff in many ways.

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#6

I use normal ClearCoat for hobby projects. Works great. Any non water based laquer will work. This also works well for waterproofing 3D prints (to prevent water from leaking through the layer seams).

For customer projects, I’ve used various polurethane based products, but they typically come in huge cans, so not relevant for personal use.

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#7

Thank y’all for the comments! I’ve got a few things to try now!

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#8

How many boards Josh?

Silicone is thixotropic enough that it doesn’t move much once you’ve tooled it into shape, but it’s sticky and nasty.

The trouble with how I use epoxy for certain situations is the constant 3D rotation of the assembly during cuing to keep the epoxy from sagging and running due to gravity.

#9

Have you ever seen those beautiful wood table tops with 1/8 inch of perfectly clear epoxy on the top. Well maybe that type of product is just what the doctor ordered.

You said you had 0.1 headers on one end of the boards. So tie a string to one of the male header metal posts…I’m assuming they are male.

Then mix up a very batch, but instead of pouring, suspend your boards in it, like making candles. Don’t let any of the liquid get near the headers. Tie the free end of the string to a clothes line and let the wet boards set thoroughly.

I would assume the product is thick enough to put on a nice even coat.

Let the first coat dry…and repeat the whole process as many times as necessary to get the thickness you want.

I wouldn’t think it would have any adverse electrical consequences…but I don’t know.

OK…here is the product…EnviroTex Lite Epoxy Resin. It is…very highly rated at Dick Blicks Art Supplies. You can get a 8 oz. size for about $9 at Dick’s online. I’m sure it is probably very clear…and very workable.

I tried to post a picture…and link to Dicks…but the forum software says “I can’t post links or pictures”.
I just registered for the forum an hour ago…so maybe I’m not allowed.

Anyway, if you try it…please report back as to the results.
I think it is something a lot of people may like to do with their board projects.

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#10

On rereading my last post, it was a little confusing in one part.

Mix up a small batch of the epoxy…and dip the board into the liquid up and down a few times. Then remove it from the liquid and tie the free end of the string somewhere…and let the board air-dry until the epoxy is fully set. If you need more thickness repeat the process.

As I said…the forum software is not letting me post pictures or links.
I know I’ve seen other threads with pictures and links.
Help…

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#11

I found the same! It turns out due to the number of bad folks abusing the internet the forum doesn’t trust us when we first join for links or pictures. Give it a day or so.

Like the advice, I would add a comment that check the conductivity of hardened epoxy, superglue for example gets progressively more conductive over time (don’t ask how I know!). Also beware if the epoxy twists/crushes things as that does tend to mess with the electronics. But it sounds well worth doing anyway to see.

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#12

Wait what, how conductive over how long? Didn’t know that!

I had picked up an insulation meter a while back and it’s pretty nice for a lot of stuff like this. Also you can use it to test ESD claims… I’ve been both pleasantly surprised (cheap aliexpress stuff that has claimed resistance) & shocked (figuratively, about how stuff sold by more major stores had no useful ESD properties).

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#13

I’ve been advised that all epoxies are not the same and anything containing a radio may or may not suffer from the coating. The simplest way to know is to try. For one of my products I’m using “ELECTROLUBE UR 5048K5K” as waterproofing. The entire product is filled with this product. It’s really messy, but the result holds up to quite some abuse. It works great, but is overkill for hobby stuff.

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#14

Here’s a pretty good article on the difference between “Epoxy Coating” and “Casting Resin”:

https://epoxycountertopdiy.com/epoxy-vs-resin-the-difference-explained/

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#15

I few hundred. :slight_smile: Not all at once though. Yeah, good point on the rotation though.

#16

To contextualize my comment on conductive superglue.

It was told me by the product engineer -> manager -> engineer for about 18 medical systems, mostly electrochemistry.
They spotted over time it becoming more conductive (6mo +) leading to field failures after using it to secure chips for soldering.
However for them pA were major issues for their systems, so PCB leakage was a very serious challenge.

All the other research I have done (10mins websearch) suggests it is not conductive, but spreads rapidly and unexpectedly leading to coating pads etc. - think the while bloom - making it unhelpful on electronics in most cases. There seem to be electronic variants: https://www.henkel-adhesives.com/us/en/product/instant-adhesives/loctite_444.html

From datasheet:
Electrical Properties:VolumeResistivity,IEC60093,Ω·cm 7.2e15
SurfaceResistivity,IEC60093, Ω 66e15