Fundamentals of Thermal Transient Measurements

Abstract

In this chapter the fundamentals of thermal transient measurements are expounded, with a focus on the practical procedures such as calibration and implementation of cooling and heating transients in a test environment.

The chapter starts with the definition of tester instrumentation and the environment, including the semiconductor device under test, which is used as heater and sensor during measurement, power switching unit to provide the exact powering, measurement or data acquisition unit to detect the temperature-dependent electric signal, temperature-controlled environment (cold plate, still-air chamber, etc.), and the data processing unit.

Further on, the interaction of the components in a complete test system is investigated.

The electrical arrangement in a test is defined for such categories as devices with separate heaters and sensors; two-pin devices, diodes; discrete devices with three or more pins (transistors, integrated circuits); and modules with multiple active devices.

The main testing mode treated is current jump measurement, switching between a higher heating current and a low measurement current on the device under test. Also, the voltage jump method on three-pin devices is explained, which is rarely used despite its obvious advantages.

The voltage to temperature calibration process, indispensable for a precise and valid thermal measurement, is then elaborated, with preferred procedures and possible pitfalls. The concept of temperature-sensitive parameters (TSP) is introduced in a generalized form. The differences between calibration on cold plate and in a closed chamber or bath are shown.

Finally, noise and interference immunity in the thermal testing is discussed, a vital aspect of the measurements due to tiny temperature-induced electric signal levels.