THERMAL ANALYSIS OF HIGH POWER HYBRID ELECTRONIC CIRCUITS FOR MOTORBIKE REGULATORS. 2001-01-1872
This paper deals with the experimental characterization of the thermal properties of a power hybrid electronic circuit used for motorbike electrical power regulation. The main power devices were MOS transistors mounted in “naked chip” configuration. These devices suffered for an abnormal over-heating, causing the system failure, due to unsuitable heat dissipation capabilities of the assembling structure. The thermal characterization was carried out by means of the TRAIT (Thermal Resistance Analysis by Induced Transient) method based on the careful analysis of the device temperature cooling transients. This technique is able to measure the thermal resistance as a sum of several contributions due to the various parts of the system, so that it possible to localize within the assembling structure the sources of heat conduction impediments. Several measurements, carried out on samples mounted on allumina and insulated aluminium substrates, clearly indicated the thin Sn-Pb soldering layer, between the die and the top metal pads, as the main responsible for the thermal resistance high values. Unsuitable solder deposition and annealing methods probably caused the incomplete removal of the organic matrix and the formation of a mixed metallic-dielectric layer with bad thermal conductivity.