Recently I found . It is a low-temp alloy with Bismuth (and Silver.) When using hot air to solder parts, or during re-work, it makes the process go so much faster. It melts around 140C. It also does not appear to need refrigeration and has a long shelf-life. With all of those positives, I'm wondering what the downsides to using it are compared to more "traditional" solder alloys.