An important parameter for thick-film resistors is the maximum permissible power dissipation density that may be applied across the resistor. It is measured in watts per unit area. Above the permissible power dissipation density, the thick-film resistor is irreversibly damaged.
The IKTS group "System Integration and AVT" calculates the power dissipation density of thick-film resistors and other components of high-power electronics via "Short Term Overload (STOL)".
In the measurement, the samples are sufficiently electrically and thermally contacted on a test set-up and selectively subjected to an electrical power dissipation: The sample is heated, and the heating is documented. After a specified time, the power dissipation is switched off. The sample cools down. The electrical cold resistances of the sample before and after heating are compared.
This procedure is repeated with a power dissipation increased by a factor of X until the cold resistance only changes by a defined value (usually 0.1 %). This value signals the damage limit. Due to the sample geometry, the electrical parameters are linked to the geometrical parameters and the maximum permissible power loss density can be calculated at this point.