Dielectric silicon grease for corrosion protection - Page 1
Forum section: electronics / projects

author: nukie
author_rank: Frequent Contributor
timestamp: April 06, 2017, 03:34:51 am
content: Hi,I am building a solar garden irrigation controller where I need to protect the pin headers. I can't use conformal coating on the pins because I may be reprogramming the microcontroller, I need to access the pins later. So silicon dielectric grease is first that comes to my mind because 100% silicone is inert but I am aware of a few things for eg. it may mess with high impedance circuits. Also grease migration could be a problem if cleanliness is priority.I have use dielectric grease to protect many remotes controls and clocks that runs on leakable alkaline batteries and it works very well.So what are there any downsides of using dielectric grease on a low voltage electronic project?ThanksVincent.

author: tautech
author_rank: Super Contributor
timestamp: April 06, 2017, 03:40:32 am
content: Should work OK but for less mess this is what I'd use:https://www.jaycar.co.nz/circuit-board-lacquer-spray-can/p/NA1002

author: BravoV
author_rank: Super Contributor
timestamp: April 06, 2017, 03:54:04 am
content: I use this CRC Plasticote 70 alot, though its old product, CRC should have newer similar to this one.Its a clear coating with high break down voltage and really high surface resistance that is suitable for PCB.One thing I like about this is, as advertised, the thin layer of coating can be soldered through for circuit repair or probing, and then just re-apply again on that spots.https://www.crcindustries.com.au/products/corrosion-protection-and-inhibitors/plasticote-70

author: eliocor
author_rank: Unknown
timestamp: April 06, 2017, 04:10:00 am
content: I use this one:http://au.rs-online.com/web/p/electronics-varnishes-lacquers/0569313/(here in Europe is immediately available)It works very well and PCB can be soldered without removing coating.I treat PCB/components which can be subjected to condensation/harsh environment (lots of humidity) with this spray. I forgot to mention: I use it also for protecting homemade PCBs from copper oxidation (they have no soldermask!).Board was solderedaftercoating it with spray - hence the small drops of flux on it:

author: coppice
author_rank: Super Contributor
timestamp: April 06, 2017, 05:25:46 am
content: Quote from: nukie on April 06, 2017, 03:34:51 amWhile silicone greases and oils are chemically inert, they are rather hygroscopic. When used as a high grade insulator they need to be combined with dessication and/or a regular replenishment schedule. This means water does slowly pass through them. Oxygen must get through too, and corrosion does occur.If you want something cheap and readily available that really keeps moisture out, and corrosion at bay, almost indefinitely use vaseline.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: April 06, 2017, 06:33:20 am
content: Quote from: coppice on April 06, 2017, 05:25:46 amCan you please provide a citation for this? I honestly am curious. Incredulous too but willing to have my opinions changed.(Google-fu is failing me).

author: coppice
author_rank: Super Contributor
timestamp: April 06, 2017, 07:36:58 am
content: Quote from: Paul Moir on April 06, 2017, 06:33:20 amWell, its why things like thishttp://www.chemicaldesign.com/systems/silicone-oil-drying.htmlexist.I used to work with a lot of high voltage equipment which sat in tanks of silicone oil. After a few months the tank was start to glow pink, as leakage through the silicone built up. The silicone was drained and replace as the glow became obvious, and the old stuff was run through a drying machine for later reuse. I haven't heard of anything changing since then. Silicone greases and gels are similar.I couldn't find a good overview of this issue from a quick Google search.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: April 06, 2017, 08:23:45 am
content: Thank you. And I'll keep looking.(I've had very good results with it in many applications, and out here on the ocean we live and die by the stuff. But my experience has been wholly unscientific.)

author: Gyro
author_rank: Super Contributor
timestamp: April 06, 2017, 08:46:37 am
content: If it's just the pin headers that you want to protect then I'd go for Vaseline. Silicone will be a pain to get out of your patch leads, you can was Vaseline out with some meths. Excellent corrosion protection.

author: Ian.M
author_rank: Super Contributor
timestamp: April 06, 2017, 09:03:43 am
content: Personally, I'd choose to mask off the headers etc. and lacquer the rest of the board then applyLear Chemicals Corrosion Blocksparingly to the header pins. A 1 Oz liquid bottle (sample size) will last you for years if you don't slop it everywhere! It leaves an oily film that wont interfere with JTAG or ISP connector contacts, and a gold plated pin protected with it should be serviceable for years.A far more likely cause of failure will be spider sh-t and other contamination. If possible use a gasketed sealed enclosure, with glands for all cables and a Goretex vent for pressure equalisation to keep the bugs out. If that's not possible, you'll need to protect the board with a heavy coat of a tropicalising PCB lacquer, and after lightly wiping the pins with silicone grease, (to act as a release film), paint the headers withLiquid Electrical Tapeto form a peelable protective coating.

author: nukie
author_rank: Frequent Contributor
timestamp: April 06, 2017, 10:19:04 am
content: I specifically mentioned I want to protect the pin headers and I want to be able to use them regulary so I won't be able to use those spray on conformal coating.I looked at silicone because 3M sells Scotchlok wire connectors filled with silicone grease.IanM solution on the pin headers seems better than my silicone grease, I will look into it. There are a few pin headers I may use Vaseline, Silicone and the mentioned Lear Corrosion Block put them to the test and report back again in a many months time just for future reference.I also have Boeshield T9, Inox MX3 and the super smelly super migrating FluidFilm all these claim to protect metal I will put them to test too. Very unkeen on the later.

author: Ian.M
author_rank: Super Contributor
timestamp: April 06, 2017, 11:25:10 am
content: I see FluidFilm is Lanolin based. If you apply it using a Q tip so it doesn't go everywhere, it should be good enough. Whatever you use you should probably make up some JTAG or ISP extender cables so you don't contaminate your programmer socket or cable.If they do corrode, header pins will be a PITA to clean. Have you considered using an edge connector for programming? If you spec HASL finish, or tin and wipe the board edge contacts if you are using any other PCB pad finish other than hard gold, and smear a little Vaselene over them, any corrosion/oxidisation that doesn't just wipe off can be removed easily by re-tinning the pad.