The thermal response setup used a Fluke 7340 oil bath, heated to 75°C (ambient temp is 25°C) with the lid off. A metal stand is placed inside the oil, but does not exceed the height of the oil so it stays fully submerged.

A graphite crucible is placed on top of the metal stand, with a 3D-printed ABS insert designed to fit the test PCB. Then the crucible is filled with liquid gallium. The working principle is that the crucible can be surrounded by the hot oil, so it can heat the liquid gallium very quickly. The top of the crucible is exposed to the air, so that the test PCB can be inserted without contacting the oil.

Liquid gallium is used because it has a thermal conductivity of 29W/mK and it can be liquid at room temperature. The oil bath uses Galden HT-200 oil, which has a thermal conductivity of 0.065W/mK, so it isn’t viable on its own for this test. Furthermore, the oil moves around while the bath is running, so it is impossible to control the submersion depth. The gallium inside the crucible is then heated to 75°C, and verified with a thermometer.