Conductive filler for copper to copper connection - Page 1
Forum section: electronics / general

author: Deku Tree
author_rank: Contributor
timestamp: September 15, 2022, 04:19:07 pm
content: I'm working on a battery design with a high current connection from a unmasked copper pour on the PCB to a copper terminal block. The pours are 4oz on each side, stitched with copper-filled vias. The unmasked copper pour is bolted to a block of copper bus bar.I'm wondering if it might be a good idea to fill in any imperfections in the contact with a conductive grease of some sort? This connection needs to pass up to 150A so it needs to be solid. Any recommendations for a conductive grease, or if it's a good idea?

author: jwet
author_rank: Frequent Contributor
timestamp: September 16, 2022, 06:35:20 pm
content: i don't think so and I don't know of such a product- have you found something for copper? (they do exist for Al). There are copper anti seize greases but they don't have low conductivity, they just keep corrosion out and are mainly for keeping dissimilar metals from galling. I would get both copper surfaces very clean and flat (mill the copper bar face if possible) and bolt them together with some strong hardware with large washers and star type lock washers, torque them down and use loctite. Clean brass or bronze hardware would be good if you can find it. (its used in marine applications). You also want to immobilize the connection from vibration and stress- if things are flat, you'll get a good connection and if things are tight, it will be gas free, having things immobilized will make sure it doesn't work loose. You could seal it with conformal coat or grease/vaseline over the top after. This is how battery banks are bonded together. When you're all done, you could measure drop across the connection- you would want to have tenths of milliohms so at 150A, this would be a drop less than .01 volt. What's amazing is that at 150 amps, .1 mOhm dissipates a couple of watts!

author: coppercone2
author_rank: Super Contributor
timestamp: September 18, 2022, 10:21:34 pm
content: this exists for electrical purposeshttps://caig.com/product/new-deoxit-l260dcp-plus-grease-l260-dc1/yes its a good idea, grease never really impedes the connection, it gets rid of air so there is better thermal transfer. Even if your connection is poor, it will be better if heat is going to both sides. If the small thing on the PCB is getting hot, you have a problem and potential for PCB damage and de lamination. If you have it effectively transfering heat to a bus bars, thats like putting a heat sink on your PCB! Think about it more like thermal compound with a heatsink and corrosion inhibitor(and reverser for deoxit). The copper in this grease has the added benefit of improving surface contact, unlike normal grease, and improving thermal transfer more, unlike normal grease. Silver grease also exists... but just about any material is superior to air (which is a great insulator) by like a order of magnitude if you go by thermal transfer materials cosntants.Think about it, copper gets worse with temperature. If you lower the temperature, even if the contact is relatively dubious, it might work better then a bigger contact that gets hot (ignoring the corrosion which knocks this all out of the park).If you add copper particles to the grease it further improves things.I suggest you lap your bus bars

author: jpanhalt
author_rank: Super Contributor
timestamp: September 18, 2022, 10:39:19 pm
content: There's a silver "ink" that is basically a modified Tollens reagent for silver plating.https://pubs.acs.org/doi/abs/10.1021/ja209267cI believe it is sold commercially and is claimed to have conductivity similar to pure silver. I don't believe you need it. Just do the experiment.

author: TERRA Operative
author_rank: Super Contributor
timestamp: September 19, 2022, 04:38:49 am
content: I second the use of jointing compound or grease.Look for the stuff used by electricians in mains voltage connections, it's designed exactly for this purpose.Something like Gardner Bender OX-100B Ox-Gard is available on Amazon and is cheap.It is zinc loaded to provide a conforming conductive layer that fills the gaps and excludes air and water.When I was fixing welders for a job, I suggested that we start using jointing compound on busbar joints in the welders we repaired. The number of burnt out joints dropped significantly.This is valid for little pocket welders in the 100A range all the way up to 1500A power sources and gensets etc.Grease everything, it's cheap. Replacement parts and labour to repair is not.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 19, 2022, 10:53:18 am
content: We used copper-loaded anti-seize for mounting induction heating coils.Probably didn't actually do anything for electrical conductivity. Heat transfer, a bit. Those were water-cooled blocks of copper, or busbar or tubing, of course. We might not've noticed anyway...Proper electrical grease is probably a good idea. Like the Ox-Gard above.Tight fitting joints and consistent pressure are mandatory. Note that PCBs vary in thickness due to inner copper, if applicable; keep the copper density consistent in the area. PCB material also smooshes over time (creep), especially with heat. Use spring (Belleville) washers to maintain pressure. Maximize contact area: multiple small screws and relatively thin busbar is probably better than big thick busbar and few screws.Tin plated contacts are fine; PCB is normally tin or solder coated which is fine, and busbar can be plated as well, which will tarnish less than bare copper. HASL is a little uneven but that might be acceptable here. ENIG would be fine too, but mind that it wears away rapidly with reclamping. Probably avoid silver plating because of tarnishing.Tim

author: coppercone2
author_rank: Super Contributor
timestamp: September 19, 2022, 05:03:11 pm
content: Oxguard has abrasives in it that break up aluminum oxide, I think it’s a quartz abrasive media. I am not sure if that is the best thing to use for copper to copper connections since the cu oxide is not as bad as Al oxide , different filler focused on conductivity might be better then one meant for aluminum

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 19, 2022, 05:51:04 pm
content: Aluminum has a different system, grease (the correct formula -- the above grease doesn't mention aluminum, I doubt it's recommended*) and proper bolting is pretty much mandatory.*Though its zinc content is metallurgically compatible, so it might not be bad. But if you're desperate enough to use aluminum (mainly power transmission), definitely look up best practices and find the materials recommended for it.Tim

author: coppercone2
author_rank: Super Contributor
timestamp: September 19, 2022, 08:51:24 pm
content: I was thinking of al-nox, maybe ox-guard is something different, I think I saw it at home depot, maybe I got the labels confused.So it is ox guard I was thinking about, what got me thinking is the talc powder in the mixture. I think I read about why thats there before, and its for breaking surface oxides on aluminum, I think. Maybe it transfers heat too, but you can buy talc products meant to be a polishing type abrasive (just watch out for that, it appears its not great for your body). I figured if its clean, and not prone to making non conductive oxides (since the grease prevents it anyway) it would better off to put more metals in there instead of oxides because conductivity is better. I think the talcum cleans the contact as it expands and contracts or something, maybe.