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

The paper summarizes the development of a standard to measure the thermal resistance “junction-to-case” θ_JC of semiconductor devices with heat flow through a single path. Power switches or amplifiers are typical examples. θ_JC 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 θ_JC is required. This is not easy, especially for low θ_JC, which is reflected by the fact that no JEDEC industry standard existed to measure θ_JC. During the last four 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 Z_θJC(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 θ_JC directly from the separation of Zth-curves. θ_JC is the thermal impedance Z_θJC(ts) at the time ts where the two Z_θJC(t)-curves separate. Method 2 first calculates cumulative structure functions and uses their separation point to determine θ_JC. Both data evaluation methods complement each other, because method 1 is most accurate for low θ_JC in the range of 1K/W or below, while method 2 is more accurate for higher θ_JC >; 1 K/W. The TDI method allows to measure θ_JC 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.