Non-conductive/corrosive coating material

I have designed a device that uses a couple of off-the-shelf sensor modules. All works great, except that some of these modules have metal parts that occasionally touch each other. The result is usually that one or more parts temporarily stop working, which has a big impact on the functionality of my device.

There's no simple placement fix to this (due to space constraints of my device, parts have to be placed very close to each other) and as I don't have any design files of these modules I can't reproduce the boards with a different component layout either. Therefore I was hoping anyone here could recommend a non-conductive and non-corrosive coating that I can apply on the metal parts instead.

As a temporary solution I've been using a hot glue gun, but obviously I don't want my modules to stick together either...

Why do you care if the stick together? Seems like a perfectly good solution.

Paul

Paul_KD7HB: Why do you care if the stick together? Seems like a perfectly good solution.

Paul

You're right in that it does the job, but ideally I'd want a non-sticky solution so I can still take individual components out of my PCB, without ripping off components in the process. So I'm just wondering if anyone here has a better suggestion than regular glue.

Vitesze: You're right in that it does the job, but ideally I'd want a non-sticky solution so I can still take individual components out of my PCB, without ripping off components in the process. So I'm just wondering if anyone here has a better suggestion than regular glue.

Then I guess you need to show us a drawing of how your boards are actually oriented. I assumed one on top of the other with hot glue going from the edge of one board to another. Perhaps on two sides of the boards.

Are you thinking of gluing the components of one board to the bottom of another board?

Paul

Paul_KD7HB: Then I guess you need to show us a drawing of how your boards are actually oriented. I assumed one on top of the other with hot glue going from the edge of one board to another. Perhaps on two sides of the boards.

Are you thinking of gluing the components of one board to the bottom of another board?

Paul

It looks something like this (Paint FTW): |500x108

Green - The ''base'' PCB the modules are soldered onto Blue - Soldermask of the modules Grey - components, leads, etc. Yes, the boards are identical.

The components are a mix of SMD and through-hole - everything is mounted on one side of the board. The through-hole components are what's causing the issues, as the leads protrude through the board, where it can freely touch the components of the board behind it.

Note that there is NO way for me to avoid placing the boards in this setup - there's simply no space elsewhere on the PCB, and upgrading to a larger PCB to separate them is not an option as the full device can't exceed certain dimensions. If I can coat the leads of the boards with something, then the issues should be permanently fixed.

Vitesze: I have designed a device that uses a couple of off-the-shelf sensor modules. All works great, except that some of these modules have metal parts that occasionally touch each other.

Um well ....... why exactly do the 'modules' 'occasionally' touch each other ?

Normal construction would have 'modules' fixed in place.

Vitesze: It looks something like this (Paint FTW): |500x108

Green - The ''base'' PCB the modules are soldered onto Blue - Soldermask of the modules Grey - components, leads, etc.

The components are a mix of SMD and through-hole - everything is mounted on one side of the board. The through-hole components are what's causing the issues, as the leads protrude through the board, where it can freely touch the components of the board behind it.

Note that there is NO way for me to avoid placing the boards in this setup - there's simply no space elsewhere on the PCB, and upgrading to a larger PCB to separate them is not an option as the full device can't exceed certain dimensions. If I can coat the leads of the boards with something, then the issues should be permanently fixed.

Then fasten a piece of paper between the boards. Thin card board might work. Think "insulator".

Paul

srnet: Um well ....... why exactly do the 'modules' 'occasionally' touch each other ?

Normal construction would have 'modules' fixed in place.

The distance between one board and the leads of the other is probably a few mm at most... but the modules are pretty large (2.5" x 1.5" or so) so there's actually sufficient wiggle room for them to touch one another. It's not possible to absolutely fix them into place unfortunately.

The devices also experience a lot of motion for their application, so it increases the likelihood further.

A dab of hot glue cools Then is not sticky Put on the dab them le cool then assemble

It’s not possible to absolutely fix them into place unfortunately.

Sounds like you have a bunch of boards connected by wires in a bag.

The devices also experience a lot of motion for their application

Expect the connecting wires to fail then.

srnet:
Sounds like you have a bunch of boards connected by wires in a bag.

Expect the connecting wires to fail then.

Of course they’re not loose pieces flopping around. They’re attached to male header pins which get soldered onto the PCB. What I meant is that with sufficient motion there’s still a couple mm of wiggle room. I’ve been working on several iterations of this device over the last year, and so far the failure-rate for components (besides the issue mentioned in this post) has been 0.

The entire device only has 2 wires, which won’t even experience much stress

Anyway, I’ll probably stick with hot glue.

Not the requested coating, but they make paper specifically for this purpose. Called "fish paper": https://www.ebay.com/itm/122330119683

Just need to put a few dots of glue on one board, let it cool, then those dots would be a long lasting spacer that would be easy to pop off if needed since they are only one side.

Duct tape folded onto itself also makes a good spacer, just keep adding layers as needed...

Vitesze: ... The through-hole components are what's causing the issues, as the leads protrude through the board, where it can freely touch the components of the board behind it. ...

Cut them off before you solder the components in. Then put tape on the bottom of the board.

ChrisTenone: Cut them off before you solder the components in. Then put tape on the bottom of the board.

When we made lots of thru-hole boards, we always trimmed the leads quite short after soldering. Probably less than 1/16 inch. Many times that included trimming the solder aro0und the lead.

How long are you leaving the component leads? That is probably the source of the trouble.

Paul

Paul_KD7HB: When we made lots of thru-hole boards, we always trimmed the leads quite short after soldering. Probably less than 1/16 inch. Many times that included trimming the solder aro0und the lead.

How long are you leaving the component leads? That is probably the source of the trouble.

Paul

I've got some very sharp, well angled nippers. I can get the underside of a board nearly flat with those.

ChrisTenone:
I’ve got some very sharp, well angled nippers. I can get the underside of a board nearly flat with those.

The very thin cutters seem so sharp as to cut the solder right off the trace!

Paul

Paul_KD7HB: The very thin cutters seem so sharp as to cut the solder right off the trace!

Paul

:(

Yes, I have done that. So now I have a 16x8 LED matrix that I have to wrap wire around, and fill in the hole with solder so it'll work. Learned my lesson, and now wear double glasses when cutting. I also try to leave a quarter millimeter or so of nub.