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Tacky lead-free flux? Tacky low-temp lead-free paste?
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Tacky lead-free flux? Tacky low-temp lead-free paste?

by magpie_lark on Fri Aug 03, 2018 2:11 am

Hi folks! I'm wondering if there's a good tacky flux for lead-free solder. Ideally one that cleans up with alcohol, since these are FR-1 boards without a solder mask. I'm currently using a rosin flux pen with mediocre results. I'd love to be able to tack down SMD components in place when I solder.

Alternatively, is there a reasonably tacky low-temp lead-free solder paste? I bought some bismuth solder paste and I'm having a hard time using it because it's not the least bit tacky

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Re: Tacky lead-free flux? Tacky low-temp lead-free paste?

by adafruit_support_mike on Sat Aug 04, 2018 12:30 am

You won't find anything in the fluxes.. they have to float on top of the solder when that melts, so when you heat them up the parts will float away.

The chemical for the job is single-component thermoset epoxy:

https://www.masterbond.com/industries/s ... ve-systems

but the stuff is crazy expensive:

https://www.ellsworth.com/products/adhe ... cartridge/

An alternative is that old Victorian wonder material: shellac. It's cheap, very sticky, dissolves in alcohol and is thermoplastic up to about 150C, but at soldering temperatures becomes a thermoset.. it becomes hard and somewhat brittle, and its solubility in alcohol decreases. Its properties are impressively convenient even by today's standards.

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