This study introduced the SiC micro-heater chip as a novel thermal evaluation device for next-generation power modules and to evaluate the heat resistant performance of direct bonded copper (DBC) substrate with aluminum nitride (AlN-DBC), aluminum oxide (DBC-Al2O3) and silicon nitride (Si3N4-DBC) ceramics middle layer. The SiC micro-heater chips were structurally sound bonded on the two types of DBC substrates by Ag sinter paste and Au wire was used to interconnect the SiC and DBC substrate. The SiC micro-heater chip power modules were fixed on a water-cooling plate by a thermal interface material (TIM), a steady-state thermal resistance measurement and a power cycling test were successfully conducted. As a result, the thermal resistance of the SiC micro-heater chip power modules on the DBC-Al2O3 substrate at power over 200 W was about twice higher than DBC-Si3N4 and also higher than DBC-AlN. In addition, during the power cycle test, DBC-Al2O3 was stopped after 1000 cycles due to Pt heater pattern line was partially broken induced by the excessive rise in thermal resistance, but DBC-Si3N4 and DBC-AlN specimens were subjected to more than 20,000 cycles and not noticeable physical failure was found in both of the SiC chip and DBC substrates by a x-ray observation. The results indicated that AlN-DBC can be as an optimization substrate for the best heat dissipation/durability in wide band-gap (WBG) power devices. Our results provide an important index for industries demanding higher power and temperature power electronics.

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Wide bandgap (WBG) semiconductors such as SiC and GaN have opened their market as the next generation of high power modules. As advanced electronic power modules must deal with increasing power density, power modules with an insulating ceramic substrate are subjected to extremely high temperature due to high current and voltage. Currently, the junction temperature of Si power devices is kept low enough, around 150 ℃ , to maintain the module durability. Nevertheless, the temperature will be soon beyond 200 ℃ for WBG devices. Thus thermal dissipation performance has one of the key technologies in designing modules. Directly bonded copper (DBC) or aluminum (DBA) substrates have been widely used as two of the typical ceramic insulating substrates for high power modules. If the extensive heat from a junction is kept inside a module, the module will be easily damage due to the increasing temperature resulting in severe thermal stress inside. Designing a proper module structure requires not only each material property but also complex component shape/structure/layout including each interface heat transfer. An accurate measurement method of precise thermal properties for such a complex metallized ceramic substrates is currently still missing. To meet the urgent requests for the next generation of high power modules, a new and simple measurement method of the thermal properties has been proposed for complex metallized ceramic substrates. First we have designed a micro heater SiC chip as an accurate and controllable heat source instead of a SiC active die. The heater chip was die-attached on metallized ceramic substrate mimicking real module packaging structure. The thermal resistance of the metallized ceramic substrate was evaluated. Due to the high power of the chip, i.e. 1 kW/cm 2 , the obtained thermal resistance has an excellent accuracy within a few percent error, when adequate cooling system is used. The thermal resistance includes those of dieattach material and thermal interface materials (TIM). The developed method thus enables precise comparison in thermal properties of high power modules, which was proposed as an ISO standard.

Next generation power semiconductors, e.g. SiC and GaN, are emerging for the further minimization and high current/voltage of power devices with high reliability covering wider operating environments than those based on Si. To implement high reliability operation, the key technology is the control of the temperature distribution in the module, and thermal stress caused by the heat generated by power loss. In the present study, we have developed SiC micro-heater chip with temperature probe to evaluate thermal characteristics of an assembled system of Ag sinter die-attach on metalized ceramic substrate (Cu/Si3N4/Cu) during the repetitive power cycling. The test specimens were fixed on a water cooling system, and steady-state heat resistance of the system was measured during the power cycling. For comparison, Pb-Sn, Sn-Cu-Ni-P, Sn-Ag-Sb-Cu solders were used as die-attach material bonded on the same metalized ceramic substrates. The maximum applied power exceeds 200 W with cycles of 2 seconds of heating and 5 seconds of cooling, and the test cycles was over 5000 cycles. The power cycle number dependence on the temperature swing and thermal resistance characteristics would be discussed, in connected with the power cycle testing for real power devices.

In the present study, we introduce a heater dummy chip equipped with temperature sensor, with extremely high capability of high heat-density using SiC wafer. As often used in high voltage/temperature SiC devices exhibit their advantage of high thermal stability and heat conductivity. Our testing heater chip (thermal test engineering group, TEG) consist of insulated SiC and Pt thin-film heater and temperature sensor realizes extreme heat density of 250 W/mm2 with reliability above 300°C of high temperature. The TEG chip was the n-doped 4H SiC chip, which is used generally for SiC devices, coated with an alumina insulation film and molded the Pt heater and sensor by lithography technique. Using the TEG chip, we demonstrate simple but accurate heat resistant measurements of several types of metal bonded ceramic substrates. The combination of SiC TEG chip and heat resistance measurement system is also applied to power cycle testing, avoiding numerous problems arising from using actual working device chips. Therefore, this study systematically was carried out the thermal measurement technology of SiC with repetitive power cycle by TEG chip as new concept heat system. Through this progress, the technologies developed in the study may have further applications in evaluation and testing of various packaging materials targeted for high temperature/wattage power modules.