What Do We Need From Low-Temperature Solder?

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So is coffee hot or not?

The more I work with customers on projects using Durafuse® LT, the more I to define what a process really needs in regards to "Low-Temperature".

I know when we think of low-temperature solder, we aren't generally comparing solder to the melting point of copper and gold. But it is worth remember that, relative to other metals and other solder alloys such as high-Pb, that even SAC can play the role of a low-temperature material.

But taking it down another level, are there times when our "goal posts" are around the melting point of eutectic SnPb? That's lower than SAC305 - so low-temperature right?

Or maybe we are trying to accommodate the temperature limit of plastics. There is a wide range of melting points in plastics, but cups used to contain "hot" liquids melt at 170°C - there are are other plastics in components and plastics as part of substrates.

Or to go to the extreme definition of low-temperature - how about cryogenics? Indium metal stays ductile below -150°C - that's cold. There are even electronic applications such as those facilitating quantum computers that might need to withstand ultra cold temperatures. 

PS: Fun fact someone pointed out to me recently - if ice is a rock, wouldn't that make water magma? 'Till next time!