Development of a standard for transient measurement of junction-to-case thermal resistance

The paper summarizes the development of a standard method to measure the thermal resistance “junction-to-case” θJC of semiconductor devices with heat flow through a single path. Power switches or amplifiers are typical examples. θJC is a key performance metric to decide whether a device can be used in thermally critical applications. Hence an accurate and reproducible method to measure θJC is required. This is not easy, especially for low θJC, which is reflected by the fact that no JEDEC industry standard existed then to measure θJC. During the last 4 years we have evaluated approaches and developed a new method called Transient Dual Interface (TDI) method. It uses two measurements of the thermal impedance Zth or more specific ZθJC(t) of the device with different cooling conditions at the interface of device case and a heat sink. To evaluate these measurements two methods are applied. Method 1 determines θJC directly from the separation of Zth-curves. θJC is the thermal impedance ZθJC(ts) at the time ts where the two ZθJC(t)-curves separate. Method 2 first calculates cumulative structure functions and uses their separation point to determine θJC. Both data evaluation methods complement each other, because method 1 is most accurate for low θJC in the range of 1 K/W or below, while method 2 is more accurate for higher θJC > 1 K/W. The TDI method allows to measure θJC with higher accuracy and better reproducibility than the steady state method used in industrial practice up to now. The TDI method was published as JEDEC standard JESD51-14 in November 2010. Problems of the traditional steady state measurement and main steps of the development of the TDI method are discussed.