Unlocking the Mystery: What Supercooling Is and Why It Matters
/SAFI-Tech is using supercooling to develop supercooled solder pastes for the next generation of electronics assembly, but what is supercooling exactly? Supercooling is a phenomenon where a liquid is cooled below its standard freezing point but remains in a liquid state without solidification. Many people’s first experience with supercooling is with water. Very pure water in a clean container can supercool easily in your freezer, and all it takes is one flick of your finger to trigger the water to freeze. My first experience was with freezer pops. I would throw them in the freezer; the next day, some would be frozen, and some would not. Turns out the liquid ones were supercooled. This somewhat common phenomenon can be seen in other materials besides water and is a crucial consideration in applications involving precise temperature control and solid-to-liquid phase transitions, like in solder paste reflow.
Engineers can induce supercooling and initiate solidification at precise moments by carefully controlling the materials and the cooling process. An example is the pharmaceutical industry, where supercooling is used to solidify drugs without crystallizing them, which makes them more soluble and bioavailable. Supercooling can also be used in materials science to make specific crystal structures with desirable properties. SAFI-Tech uses supercooling to make a paste of solder particles, putting the solder particles in a supercooled liquid state. The tailored properties of the solder particle shell in the paste keep the metal alloy in a supercooled liquid state until after soldering. The metal does not need to be heated above the melting point to make the metal liquid because it is already liquid. The solidification occurs after soldering, resulting in a joint made at a temperature lower than the melting point of the solder alloy.
Supercooled solder pastes are under development for practical use at dramatically lower temperatures than typical, opening the door to the future of electronics. In our next post, we will explain why supercooling is useful in electronics assembly.
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