MGChemicals liquid tin - risk of tin whiskers? - Page 1
Forum section: electronics / general

author: matthuszagh
author_rank: Frequent Contributor
timestamp: January 20, 2023, 04:56:40 pm
content: MGChemicals liquid tin is a commonly used way of adding a protective coating to the exposed copper of DIY PCBs. However, tin platings are subject to the tin whisker effect. Apparently, pure tin plating is more subject to this than non-pure platings (seehttps://nepp.nasa.gov/whisker/background/index.htm). Does this mean that the result of using liquid tin is very subject to tin whiskers?If so, what are good alternatives to liquid tin plating of DIY PCBs?

author: matthuszagh
author_rank: Frequent Contributor
timestamp: January 20, 2023, 05:05:52 pm
content: One thought I've had is to use a soldering iron with a blade tip to apply a flat solder layer on top of the copper. I haven't actually tried this yet, but it sounds like it would be relatively easy to do.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 20, 2023, 07:32:33 pm
content: This seems relevant:https://ieeexplore.ieee.org/document/6066954/similar#similarYou'll have to find a source / buy if it really matters.AFAIK, annealing (bringing it up to soldering temperature) helps.Mind that electroless tin is extremely thin, so it may oxidize through and/or diffuse into the copper (forming Sn-Cu intermetallics), leaving an unsolderable mess. (On the upside, with no metallic tin left, it won't whisker.) Coating with soldermask, or solder or electroplated tin (heavier than electroless), is best.I don't have a problem leaving bare copper on proto PCBs, as long as it's not exposed to a corrosive environment.Regarding NEPP, mind that much of the information is fairly old (circa when RoHS was introduced). Not to say it's outdated or irrelevant -- it is good work, and very much applicable to the materials and processes that were around at the time, and have been for a long time. That's the catch: RoHS processes have improved since then, so the risk with modern commercial components and processes may not be as severe.(To be clear, at-home electroless tin is probably old tech, not really anything they can refine in the formula I think, so it will still be applicable to that.)Also, keep in mind, NASA's in the business ofspaceships; if you're just making one-offs, well, that's a very different thing.Tim

author: Bud
author_rank: Super Contributor
timestamp: January 20, 2023, 08:51:51 pm
content: Quote from: matthuszagh on January 20, 2023, 05:05:52 pmIt can be done but the board will not look as neat and nice as if liquid tin solution was used.

author: rancor
author_rank: Contributor
timestamp: January 23, 2023, 04:51:36 pm
content: Solder covering the plating will mitigate any risk so if you are not letting the tin plated board sit around before building it shouldn't be a problem. You'd also want to make sure all pads had solder on them. My only other through would be to attempt ENIG plating the boards.

author: bdunham7
author_rank: Super Contributor
timestamp: January 23, 2023, 05:47:35 pm
content: Quote from: matthuszagh on January 20, 2023, 04:56:40 pmThin some SnPb solder paste with liquid flux to make it like thick paint. Brush it on and toast to perfection. If it gets lumpy, use a hot air gun to blow the excess around or off. Homemade HASL!Don't laugh too hard, it makes a nice solderable board, although you may have to vacuum out any through holes with a solder vac tool. If you get the amount right you can just tap the board a few times when you take it out of your toaster oven. And I've never tried it with large or fine-pitch boards, this is more for the DIY PCBs you make from a laser printer transfer or resist marker and an etchant tray. I imagine it will also work for the ones you make with the little CNC mill machines.

author: matthuszagh
author_rank: Frequent Contributor
timestamp: January 23, 2023, 11:23:30 pm
content: Quote from: rancor on January 23, 2023, 04:51:36 pmTrue, although with DIY boards I'll still have a lot of area without solder (I probably won't add a soldermask, though I may eventually start doing that).Quote from: rancor on January 23, 2023, 04:51:36 pmThat sounds hard...

author: matthuszagh
author_rank: Frequent Contributor
timestamp: January 23, 2023, 11:26:41 pm
content: Quote from: bdunham7 on January 23, 2023, 05:47:35 pmNot laughing - this is a great idea! Should have thought of it. I considered getting a soldering pot to DIY HASL, but I'm not sure that would come out level and I'm not sure how easy it would be to level. Your method sounds better.