SCHOTT Group Home

Solder Glasses

Solder glasses, also referred to as frit glasses, are special glasses with a particularly low softening point (below 550°C). They are used to join glass to other glasses, ceramics, or metals without thermally damaging the materials to be joined. To ensure stress-free sealing, the coefficient of thermal expansion (CTE) needs to be closely matched to the sealing partners.

Three kinds of solder glasses can be distinguished according to their behavior during the soldering process: Vitreous solder glasses, devitrifying solder glasses, and composite solder glasses.

Vitreous solder glasses preserve their material properties during soldering and remain in the so-called “glassy” state. When reheated, they show the same softening behavior as prior to the sealing process.

Devitrifying solder glasses crystallize at least partially during the sealing process. Since this results in an increase of softening temperature, they are especially used in applications with high operating temperatures. The crystallization may lead to a change of CTE.

Composite solder glasses were developed to achieve a very low CTE while assuring low soldering temperatures at the same time. This is done by adding inert (non-reactive) fillers with low or negative coefficients of thermal expansion.