Eutectic solder explained

Eutectic solders take advantage of an interesting bit of physical chemistry that lower the melting point of metals by carefully mixing them.

Every integrated circuit, passive component, wire, connector, and copper pad is cleaned with an acid called flux and attached to printed circuit boards with a carefully engineered combination of metals called 'solder.'

Have you ever heard the term 'eutectic' used to describe solder but were afraid to ask what it meant? That is a shame, because eutectic describes a very interesting bit of physical chemistry, and unfortunately, is not always covered in undergrad electrical engineering classes!

As the temperature of a pure substance increases, it will undergo phase transitions at specific temperature. The entire body of the substance absorbs any heat delivered to it during the transition and uses all of the thermal energy to change the phase of the material while maintaining a constant temperature.

While phase transition temperatures vary between elemental metals, that concise temperature blurs as alloys are used. In alloys, the discrete transition temperatures that exist between the solid-phase and liquid-phase morph into transition temperature ranges as a new intermediate phase of matter appears that is part liquid and part solid. The transition temperature range depends on the ration of substances in the mixture and how thoroughly the substances are mixed.

The eutectic temperature is a discrete transition temperature that is lower than the transition temperature of either substance in pure form. This is important for microelectronics because it reduces the exposure of integrated circuits to high temperatures.

Check out this video to take a deeper dive into the subject of eutectic solder!