Eric Bastow: Gold is very useful as a soldering material when it's used with alloys. They have very high melting points, and, for that reason, sometimes the gold-based alloys are referred to as braising alloys, because braising alloys are the next step above solder alloys in terms of their melting point. The most common alloys of gold are: One, for example, is 80% gold, 20% tin, which melts at 280 degrees C; there's another one called 88 gold, 12 germanium, that melts at 356 degrees C; and there's also some gold-silicon alloys that are used for soldering to bare silicon die.
Gold is very noble, and part of that nobility is that it resists oxidation, which lends itself to fluxless soldering. If you're not a soldering person, that may not mean much to you, but if you are, you'll appreciate the ability to do soldering without the use of a flux. It is also, again, due to the nobility of gold, it resists corrosion. That makes it useful for harsh environments, like if there's an acid involved or something like that.
Gold forms very hard, strong, alloys. That may be counter-intuitive, because pure gold itself is so soft, but when you alloy it, it becomes much stronger. For example, 80% gold, 20% tin has a tensile and shear strength of 40,000 psi. It also has very high electrical and thermal conductivity, so gold is extremely useful, especially in solder and soldering alloys. We have these alloys. If you'd like to know more about them, please contact us at AskUs@indium.com.