METHOD AND APPARATUS FOR TWO-PARAMETER THERMAL RESISTANCE MEASUREMENTS
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2002-Mar-21
A new experimental technique, including both hardware and data-reduction methodology, has been developed for thermal characterization of semicon- ductor packages. This technique allows direct meas- urement of the two primary thermal resistances corresponding to a two-parameter thermal model of a package mounted on a board, namely junction-to- case and junction-to-board (or junction-to-ambient through the board). The hardware consists ofa "ther- mal chuck:' which allows the package case temper- ature to be fixed at a specific temperature, and a "heat shield" which allows active control of the ambi- ent temperature around the board itself(thereby iso- lating the board from undesired thermal interactions with the chuck). Depending on the measured junction-to-case thermal resistance, a variety of "ther- mal resistors" may be introduced between the chuck and the package in order to ensure that the junction- to-board measurements are statistically significant. The data reduction is a two-parameter least squares Figure 1 shows the experimental test setup used to characterize the packages. The test setup consists of a temperature controlled "thermal chuck" against which the package upper casing is placed (using ther- mal grease). The central area of the thermal chuck which contacts the package upper casing is of a size suitable for contacting the entire upper casing with little to no overhang. In addition, a temperature con- trolled "heat shield" is interposed between the main structure of the chuck and the thermal test board to which the package is mounted. The heat shield allows for the active control of the ambient temperature around the thermal test board, thereby isolating the board from undesired thermal interactions with the chuck. Both the thermal chuck and the heat shield contain heating elements, coolant recirculating tubes, and sensors, which together allow an automatic con- troller to fix the temperature of each structure to desired values.