Using Wood's metal as a low melt alloy? - Page 1
Forum section: electronics / general

author: JGAN
author_rank: Contributor
timestamp: December 07, 2015, 03:37:08 am
content: I found some stuff called Wood's metal on ebay for dirt cheap.Wikipediasays it contains bismuth and tin -- similar to Chipquik low melt -- and it is eutectic. The melting point is extremely low, 70c, although not as low as Chipquik low melt. However, it is considerably cheaper than Chipquik.How well would it work as a low melt alloy for soldering and desoldering? The only thing I am really worried about is it apparently expands when it cools, although I guess the point is to not let it cool. Any thoughts?

author: sleemanj
author_rank: Super Contributor
timestamp: December 07, 2015, 04:52:21 am
content: Quote from: JGAN on December 07, 2015, 03:37:08 amDid you read the toxicity section of that wikipedia article? I like being able to smell stuff (and not having cancer).

author: amyk
author_rank: Super Contributor
timestamp: December 07, 2015, 05:01:52 am
content: Lead is toxic and yet we use it all the time.As long as you're not breathing the stuff in any quantity and have good ventilation you should be OK... no guarantees though.

author: BravoV
author_rank: Super Contributor
timestamp: December 07, 2015, 05:12:46 am
content: As with it's quite low melting point, wonder if normal solder tip temperature will evaporate some of the metal/alloy, even at minuscule amount.

author: KE5FX
author_rank: Super Contributor
timestamp: December 07, 2015, 06:21:45 am
content: 10% cadmium? What could possibly go right?!

author: Ian.M
author_rank: Super Contributor
timestamp: December 07, 2015, 06:58:23 am
content: You certainly don't want to use real Wood's metal as it contains cadmium.ChipQuick's lead free alloy contains Bismuth, Tin and Indium. They are very unlikely to manufacture it themselves, so its probably a known low melting point solder composition. Indalloy #27 is a likely candidate. *ALL* Indium alloys are $expensive$. If you want to depress the melting point below 125 deg C to avoid chip and board damage there aren't really any affordable low toxicity alternatives.As pure Bismuth is hard and brittle, you cant simply use that. You could try 58Bi/42Sn solder (138 deg C) but getting small quantities isn't going to be cheap.

author: JGAN
author_rank: Contributor
timestamp: December 07, 2015, 08:22:04 am
content: Quote from: BravoV on December 07, 2015, 05:12:46 amNo, it doesn't got hot enough to evaporate unless you are soldering with butane. Cadmium requires thousands of degrees farenheit to boil.Quote from: Ian.M on December 07, 2015, 06:58:23 amChipquik looks to be the same as Cerrolow 136.Maybe Rose's metal would be another option? No cadmium or indium but it isn't eutectic.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 07, 2015, 12:15:59 pm
content: Quote from: JGAN on December 07, 2015, 08:22:04 amNot plural, only 1000 K. That's below Zn and Mg boiling points, and means the vapor pressure at modest temperatures (like soldering temperatures) will be significant.I wouldn't suggest soldering with it. I like my kidneys too much...Tim

author: Ian.M
author_rank: Super Contributor
timestamp: December 07, 2015, 12:38:42 pm
content: If you need a lead free chipquick replacement, its not easy.There was a discussion here about 2 1/2 years ago:https://www.eevblog.com/forum/blog/eevblog-437-removing-smd-parts-with-chipquick/Someone tried pure Bismuth and got nowhere.

author: G7PSK
author_rank: Super Contributor
timestamp: December 07, 2015, 10:06:06 pm
content: Quote from: JGAN on December 07, 2015, 03:37:08 amLead expands when it solidifies, why it used to be used to fix railings into masonry, pour it into hole around rail and it expands to hold tight.

author: vk6zgo
author_rank: Super Contributor
timestamp: December 08, 2015, 03:28:58 am
content: Quote from: Ian.M on December 07, 2015, 12:38:42 pmThere's a joke about catching Polar Bears with bismuth,,,,,,,,

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 08, 2015, 03:31:33 am
content: Quote from: vk6zgo on December 08, 2015, 03:28:58 amI just dissolve them in water. No worries.Tim

author: calexanian
author_rank: Super Contributor
timestamp: December 08, 2015, 06:03:11 am
content: The lead is not so much an issue unless you decide to nibble on it, but the cadnium is a real concern especially if you get it too hot.

author: JGAN
author_rank: Contributor
timestamp: December 08, 2015, 06:07:45 am
content: I'm tempted to try Rose's metal but it is in a sort of pebble form, not sticks like solder. Any ideas on if there are any molds I could use and maybe my hot air station to melt them into sticks or rods?

author: Ian.M
author_rank: Super Contributor
timestamp: December 08, 2015, 08:04:29 am
content: Its melting point is sub 100 deg C, so try using a fluxed sheet of coarse corrugated cardboard as the mould with a masking tape dam at the edges. Melt it in a beaker or a well oxidized steel tin.

author: JGAN
author_rank: Contributor
timestamp: December 09, 2015, 04:25:52 am
content: Roll the cardboard into a tube or use the corrugations?

author: Ian.M
author_rank: Super Contributor
timestamp: December 09, 2015, 08:46:02 am
content: I'd go for use the corrugations. It may not work if surface tension pulls it together too much.