Another Potting Question - Page 1
Forum section: electronics / projects

author: Sierra
author_rank: Contributor
timestamp: January 30, 2017, 06:14:59 pm
content: Sorry to bring up another potting question and I hope this is in the right place. Most of the potting questions I found in my search were in this subforum.Complete newbie here so I suspect I don't actually know the proper term for what I'm looking to do. For now, it's "potting" but in my search "potting" was generally used for completely covering (often in a mold) an entire PCB and it's components.I have a handful of PCBs that I solder 24-26 AWG leads to (most but not all are through hole connections). I'm looking for a material that I can apply on top of these solder joints. Strain relief on the thin wires as well as a layer of insurance that it does not short if a lead breaks. Have been using standard hot melt glue to date.What I'm hoping for in a compound:1) Easy to apply (no mixing, no messy cleanup, etc.)2) Inexpensive3) Does not conduct electricity4) Has a bit of give (staring relief)5) Reasonable cure time6) Bonds well to PCB and PVC insulated wireThings like color and temperature rating are not a concern.Any help would be appreciated.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: January 30, 2017, 06:39:33 pm
content: This could be used:http://www.usplastic.com/catalog/item.aspx?sku=38058&gclid=CLjmyvHB6tECFdQ6gQodELQOvQPEACE===>T

author: DTJ
author_rank: Super Contributor
timestamp: January 31, 2017, 10:35:01 am
content: Clear neutral cure RTV silicone - down side is the ~12 hour cure

author: steaky1212
author_rank: Regular Contributor
timestamp: January 31, 2017, 10:57:29 am
content: Quote from: DTJ on January 31, 2017, 10:35:01 amThere are UV-curable RTV silicones

author: james_s
author_rank: Super Contributor
timestamp: February 01, 2017, 12:29:12 am
content: Mixing epoxy is pretty easy, disposable plastic party cups work well and make cleanup easy. I save popsicle sticks and by the end of summer I usually have plenty of them on hand for mixing. Silicone is nice but it's harder to clean up and a lot of it is thicker than ideal for potting.

author: Sierra
author_rank: Contributor
timestamp: February 01, 2017, 02:04:20 pm
content: Thanks for the feedback guys. I'll take a look at the RTV silicones, although I was hoping for something for a faster cure.Any inexpensive epoxies that would do the trick?

author: drussell
author_rank: Super Contributor
timestamp: February 01, 2017, 04:18:37 pm
content: For silicone, one of the typical industry standard products designed for electronic use (compared to the hardware store variety) is the RTV100 line by Momentive Performance Materials. It is sold under many brands like Momentive, MG Chemicals and GE. The general purpose ones like RTV102 are about $20 for a 300 mL caulking-gun type tube, though RTV102 is still an acetic acid cure type which is fine unless the stuff you are glooping it on is very delicate. 20 mins to tack free, 3 days at room temp for complete cure. They have other formulas that are totally corrosion free but are more expensive.For faster cure, you usually need a two part system like an epoxy, though they are generally physically harder once cured and don't provide as much of a strain relief property compared to a silicone. Something like MG chemicals 832 is available in clear or black and intended for electronics potting. The 375 mL size is about $40 around here or the 3L kit about $120.You could also consider a quality hot melt glue. Good quality formula sticks are available that have good adhesion yet have a bit of flexibility. Very fast set time, no mixing, etc.

author: Jeroen3
author_rank: Super Contributor
timestamp: February 01, 2017, 04:33:23 pm
content: An epoxy meeting your specification and an applicator with mixing nozzle.https://www.google.nl/search?q=3m+mix+nozzle

author: kb0thn
author_rank: Contributor
timestamp: February 02, 2017, 12:27:17 pm
content: We use DOW 748 extensively for these type of applications. It is non-acetic acid curing. So no odor and no turning your electronics green. Available from McMaster for about $20 per tube.

author: Sierra
author_rank: Contributor
timestamp: February 06, 2017, 06:46:53 pm
content: Quote from: drussell on February 01, 2017, 04:18:37 pmDrussel - when you say quality hot melt, is there any type or brand you'd recommend?Thanks everyone for the additional input. RTV silicone seems to be a recurring item.

author: mmagin
author_rank: Frequent Contributor
timestamp: February 06, 2017, 08:07:16 pm
content: Some of the high temperature 3M hot melt adhesives will bond to nearly anything, including polyolefins. They may be too much for some heat-sensitive items, but if you're talking about putting some goop around wires, FR4 board and non-critical components, you might be fine.http://multimedia.3m.com/mws/media/44021O/hot-melt-bonding-systems-guide.pdfhttp://multimedia.3m.com/mws/media/764981O/iatd-product-info.pdf3748 is the one I've made some casual hobby use of.There have been some past threads on strain relief of wires connecting to PC boards that might be interesting to look up. Certainly proper use of purpose-designed connectors might be the best way to solve the problem, if not the cheapest/easiest.