A while back, I bought a syringe of tin-bismuth-silver solder paste: lead-free, no-clean flux, and I had a suspicion that it would have good reflow (and re-reflow, for rework) characteristics, unlike the usual tin-silver-copper alloy.
Comes time to use some of it, it won't come out of its syringe. Did the flux coagulate in the weeks it was sitting on my workbench?
I got out the snippers and nibbled away the back of the syringe down to the plunger tip. Whaddya know: said rubber item was immovably glued to the wall of the tube. The paste itself was still good & pasty.
So I scooped it out and repotted it in a small snap-lid plastic container - OK, a plastic film can.
Applying the stuff with the pointy end of a toothpick doesn't work very well. Surprise! Needs either a gluing-resistant syringe or a paste mask; I don't have a suitable clean syringe handy, nor did I have a paste mask made for this board.
Still: aside from the nonuniform application and the resulting blobbiness, the stuff does indeed reflow quite nicely. Seems even better behaved than the straight tin-bismuth alloy. And the wetting is so good that cleaning up the excess with slightly-tarnished desoldering braid goes smoothly.
Just needs a more suitable storage/application system.
Comments