Post B5Zz5SRBb8pimpkVsm by azonenberg@ioc.exchange
(DIR) More posts by azonenberg@ioc.exchange
(DIR) Post #B5ZeTVrARJknIrWya8 by azonenberg@ioc.exchange
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OK so... Silver nitrate, sodium chloride, and potassium bitartrate are all here.First step will be conversion of silver nitrate to chloride. I have 25 grams but don't want to use too much at a time so I'll do 500 mg for the first run.That's 2.95 mmol of silver nitrate so I need 172 mg of sodium chloride to be stoichiometric. But to ensure a 100% conversion of the expensive silver salt I'll add an excess, aiming for around 250 mg.The reaction is 1:1 so a perfect yield would be 2.95 mmol of silver chloride or 422 mg. Let's see how close I can get.
(DIR) Post #B5ZeYPmOSeZBu5dSLY by azonenberg@ioc.exchange
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The big challenge here will be minimizing container losses, when working at these scales the amount of residue that sticks to pipettes and glassware will be a nontrivial fraction of the total reaction volume.And I need to figure out how I'm going to separate the precipitated silver chloride from the aqueous sodium nitrate solution without losing too much or exposing it to too much light.
(DIR) Post #B5ZfCgqeQ4e6QNpc9Y by azonenberg@ioc.exchange
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Oh right, I should figure out solvent volumes too.Silver nitrate has a solubility of 256 g/100ml at 25C so 500mg should dissolve fully in 195 μl of water.Sodium chloride has a solubility of 360 g/l at 25C so 250 mg should dissolve fully in 70 μl of water.I want to add a slight excess to ensure full dissolution, plus my lab is more like 22C or so. So I'm figuring maybe target 225 μl for the silver nitrate solution and 90 μl for the sodium chloride solution would be good to start.My micropipette only goes to 100 μl and I don't need to be super exact so I'm thinking I'll just use a 1ml syringe, I get about 20 μl resolution on the tick marks which should be more than enough.
(DIR) Post #B5ZfSdojSLl1epXXyC by xeno@hexokina.se
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@azonenberg@ioc.exchange ooh what’s this for? make sure to cover especially the AgCl from light and be careful with the nitrate (goggles are a must tiny amounts can blind you)
(DIR) Post #B5ZfSe0Qkr7CF70tCi by azonenberg@ioc.exchange
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@xeno I'm going to turn out the lab lights and work quickly keeping stuff in amber glass vials as much as possible between steps, and see if I can maybe unscrew one of the fume hood light bulbs to reduce exposure further.I'll be wearing normal lab PPE and working in the fume hood. I can't imagine it's more dangerous to your eyes than boiling nitric acid and other things I work with routinely here.
(DIR) Post #B5ZfYUTL77KkPbK5WS by azonenberg@ioc.exchange
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@xeno I also have some amber lighting gels I was going to mount over the fume hood lights to minimize blue/UV content
(DIR) Post #B5ZgHFhorUlxe6RKrI by azonenberg@ioc.exchange
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Ok here's the setup. The gels were a little too small so there's light leakage at the back of the hood but not much, if i keep my work towards the front it should be OK.If not, I'm only using 2% of my silver nitrate stock for this run so i can afford to try again.
(DIR) Post #B5ZgW1U01ZzNsV1EUS by azonenberg@ioc.exchange
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The lab is pretty in the dark
(DIR) Post #B5Zj8EFBEApQMsQu9Y by azonenberg@ioc.exchange
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I expected a really fine milky clay like powder instead i got big goopy clumps. This looks a lot bigger than i thought 422 mg of a heavy metal compound would be especially considering how small the 500mg of silver nitrate was when I started. Maybe it'll shrink down when it dries?Turned off all the lights including the fume hood (there's no vapor hazard here it's just my only bench space designated for wet chemistry) and will let it dry in darkness for a few hours on the filter paper, then scrape off into an amber glass vial and maybe pull vacuum for a bit to let it desiccate more completely so I can calculate yield. I think I got most but definitely saw some precipitate sticking to pipettes etc
(DIR) Post #B5ZjiwxATaNFSOWAhk by azonenberg@ioc.exchange
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The product is super insoluble in water and all of the starting material and side products (sodium nitrate) are extremely soluble, so i did three or four cycles of stirring it in fresh water to mix and break up clumps then pipetting it off to try to wash as best I could. Not sure how well I got into the clumps though.
(DIR) Post #B5ZjoNDmExIyNCsBF2 by azonenberg@ioc.exchange
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The first washing had a kind of milky color to it and likely contains a bit more product that was really fine and didn't join the clumps. I saved all the washings and will see if anything settles out that might be worth trying to save in a second work-up pass later on.But first step will be seeing what my dry yield on the filter paper is.
(DIR) Post #B5ZlCNWaraXODcgUq0 by r@glauca.space
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@azonenberg oh what's the end goal here?iirc silver halide preparation is basically almost-100%-stoichiometric because of that insolubility, it's almost all going to be in handling losses
(DIR) Post #B5ZlCNybBSwHcTmrUO by azonenberg@ioc.exchange
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@r yeah i expected a perfect conversion but with small volume a lot of handling losses due to very large surface-to-volume ratio on containers and filters etc.End goal is experimenting with several different electroless plating recipes to try and develop something i can put on bare copper after milling into a PCB that is solderable and wire bondable and won't oxidize too readily
(DIR) Post #B5ZlKZXu3LQhonCiPI by azonenberg@ioc.exchange
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@r I have 25 grams of silver nitrate to start with and not all of the plating recipes use the chloride, plus I wasn't sure how much the light sensitivity would be a problem, so I did 500 mg for my first batch
(DIR) Post #B5ZpEfdCuiLslt7taK by sudo200@layer8.space
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@azonenberg I think you made one thing clear for me:I need more monitors
(DIR) Post #B5Zw4lIRhBBB7ndakK by azonenberg@ioc.exchange
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538 milligrams, lol. Either I had an excess of silver nitrate somehow (weighing quantities this small in a fume hood with airflow is tricky) or it's not fully dry.Anyway, plenty to run the next test.
(DIR) Post #B5ZwulwIYChaB14wT2 by azonenberg@ioc.exchange
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The first formula I'm trying uses a 1:2:3 weight ratio of silver chloride, potassium bitartrate, and sodium chloride. I used 100, 200, 300 mg for a total of 600 mg in the mix.The recipe calls for grinding in a mortar and pestle which i don't have yet (although one is on order) so I'll see what i can improvise in the meantime. Plenty of material for another few runs if needed without having to repeat the chloride synthesis.
(DIR) Post #B5Zz5SRBb8pimpkVsm by azonenberg@ioc.exchange
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Took 50 milligrams of the silvering powder plus a few drops of water, let it sit for a while to dissolve, and pipetted it onto a small copper disk to see what would do.Basically nothing, a very slight darkening of the surface where some of the silver chloride granules were sitting but not much.This recipe seems to rely on scrubbing/agitation to force the nearly insoluble silver chloride to react with the copper surface.After aggressively rubbing a kimwipe over the surface with the silvering powder and water, I got this. Probably could have gone a bit longer to get better coverage, but it's a first attempt.Next step will be to see what I can do with a lint-free swab or wooden stick to get in smaller spaces. One of the things I was afraid of with this formula was that it might not work well in tight spaces due to the process calling for rubbing (you can't just soak the surface)
(DIR) Post #B5Zz9o9omnMzJ9hSIS by azonenberg@ioc.exchange
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But the main use case for this was stuff I'm going to wire bond to. For something I plan to solder, I have another idea using an off-the-shelf tin plating solution that I'll try later. It's not wire bondable but should just be "warm the part, soak in the solution for a few minutes, suction excess, rinse"
(DIR) Post #B5a1d9qPQvKcsJkD5M by andreas@mstdn.dk
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@azonenberg experimenting with several different electroless plating recipesAs someone who has worked in a plating shop: That's some fucking side quest to take on! God speed 🫡If you get tired of it (or you get to the point where the problem is the silver plating starting to tarnish), you might want to look into organic silver passivation dips...
(DIR) Post #B5a1dovSh2jcHrQK9Y by roos@tooting.ch
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@azonenberg I want to move here.
(DIR) Post #B5a1dpBliPmL6R3LZQ by azonenberg@ioc.exchange
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@roos Who doesn't, lol.
(DIR) Post #B5a1nZmrpiLAEP3VFg by azonenberg@ioc.exchange
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@andreas The good news is I don't need visual quality or longevity or large area uniformity or lots of other things people care about.What I need is something that I can plate onto a bare copper surface that is compatible with gold ball bonding and will handle being at ~150C in atmosphere for at least five minutes without corroding bad enough to render it un-bondable.Once bonded, the bonds need to stay attached long enough for me to dump firmware or whatever I was trying to do to the device.
(DIR) Post #B5a1sE3q2R2YIRD7gm by azonenberg@ioc.exchange
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@andreas I've managed to make bare copper work, although I had to scrape oxidation off after every 1-2 connections to get a clean copper surface the next one would stick to.So any plating (edit: of a wire bondable metal) that even *slightly* improves the oxidation resistance will be good enough.
(DIR) Post #B5a1vlDJEXk3zEKHM8 by azonenberg@ioc.exchange
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@andreas oh and the area being plated is <1 mm^2
(DIR) Post #B5a3WlUvEwvHXJm0ye by andreas@mstdn.dk
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@azonenberg The common cyanide-based silver electroplating solution might work if you're just going for a very thin layer of silver. It's not autocatalytic, but it'll plate out a thin layer onto copper (through redox IIRC). Plus, being chuck full of KOH and KCN, it might let you skip a bunch of cleaning steps. And it works at room temp, and should have a pretty long shelf life if you keep it cold.See if you have a plating shop nearby that does silver plating. Maybe you can talk someone at the shop floor into letting you have a bit from their tank.
(DIR) Post #B5a3awNQjXp6R5GBl2 by azonenberg@ioc.exchange
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@andreas I'm specifically trying to go cyanide-free to avoid the obvious toxicity hazard if at all possible.
(DIR) Post #B5a4x7pYvgMgHfYqga by andreas@mstdn.dk
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@azonenberg Haven't I seen you post stuff about decapping with conc. nitric acid? I could go into detail about how I much prefer working with cyanide solutions, but I'd rather not come off as some guy who recommends random people on the internet to work with cyanide.
(DIR) Post #B5a5JGicZ3coDjsBzE by azonenberg@ioc.exchange
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@andreas I don't mind corrosives as much as toxics, tbh.Although the highest "nope" on my list is things like dimethylmercury where an extremely small exposure will have serious or fatal long term effects but you don't realize until way too late.
(DIR) Post #B5a5VH4J5d2kmRk156 by azonenberg@ioc.exchange
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@andreas Like, yes I probably *could* work safely with cyanide if I needed to.But if there are alternatives that are less nasty, I'm gonna take that approach first. Same reason I decap with concentrated nitric instead of RFNA and don't stock 49% HF like work does.
(DIR) Post #B5aEa4PiSxykZH7JJY by chrisgj198@mastodon.social
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@azonenberg Would this stuff do what you want? https://www.cool-amp.com/products/cool-amp-silver-plating-powder-partBack in th 90s a radio amateur suggested to me that spent photographic fixer was also usable but I never tried it.