How to keep liquids out of PCB mounted switches? - Page 1
Forum section: electronics / general

author: e100
author_rank: Frequent Contributor
timestamp: March 03, 2025, 02:47:47 pm
content: As in this style of push button used in consumer gadgetshttps://core-electronics.com.au/media/catalog/product/cache/d5cf359726a1656c2b36f3682d3bbc67/m/i/mini_push_button_switch__com-00097__01.jpgI would like to put a thin film of silicone potting compound across the whole PCB, but obviously don't want it to get inside switches and contaminate the contacts. Will a blob of Blu-Tack (mounting putty) over the top keep the liquid out for the 30 minutes or so that it takes to cure, or do I have to build a dam around the thing using hot melt glue?

author: wraper
author_rank: Unknown
timestamp: March 03, 2025, 03:03:43 pm
content: Unless you coat in a way that compound will get on the top side of these switches, nothing will happen to them. If you cover all over them, you'll block the plunger even if compound does not get onto the contacts anyway. If you want it to be moisture resistant, do not use these switches to begin with. They grow silver dendrites over the plastic surface between the contacts in presence of moisture.

author: thm_w
author_rank: Super Contributor
timestamp: March 03, 2025, 10:16:28 pm
content: You can get higher IP rated switches that are better suited to the task, as wraper says.Though I've seen these last a while outdoors, from quality brands.Some boards will either be manually coated, or selectively coated via programmed conformal coating machine, often only in areas with very fine pitch ICs (more sensitive to corrosion).For DIY coating purposes blutack would work.Or maybe custom 3D printed shields.

author: Kasper
author_rank: Frequent Contributor
timestamp: March 04, 2025, 12:02:18 am
content: You can make caps for them. Heat shrink may work well. Cut pieces an inch long and pinch the top. When you're done, pull them off and save them for next timeI used to do that almost 20 years ago, can't remember what we were covering, maybe LEDs.

author: e100
author_rank: Frequent Contributor
timestamp: March 05, 2025, 05:24:10 am
content: Update:The sticky glue used on moth traps seems like the ideal stuff. It's semi-transparent, always sticky, doesn't have a shape memory, and once done you can remove it by using a larger blob like a sponge. Chemically it appears to be polyisobutylene which is related to butyl rubber.

author: coppercone2
author_rank: Super Contributor
timestamp: March 06, 2025, 08:24:30 am
content: the best way to keep liquids out of pcb mounted switches is to mount the switches on a panel and connect them with wires

author: Kean
author_rank: Unknown
timestamp: March 06, 2025, 05:54:09 pm
content: The OP mentioned "a thin film", and I suspect if it is just that then I doubt there would be much if any if the compound able to enter the switch. Just make sure it is allowed to dry before actuating the buttons, and the film isn't thick enough to prevent actuation. Solder a bunch of these switches to a piece of protoboard and apply the compound as you plan to see the effect. Maybe try double or triple coating and see how that changes operation.That said, such a thin layer isn't going to provide an industrial level of protection, but it may add some longevity to a consumer product used in a kitchen or similar. Personally, I'd suggest looking at sealing your enclosure by using a stick on membrane keypad decal, or maybe a custom molded silicone keypad.