The next generation of switches for power electronic will be based on white band gap (WBG) semiconductor GaN or SiC. This materials supports higher switching current and high frequency. White band gap semiconductors enables higher application temperature. Certainly, high temperature capability is also to discuss in combination with high number of thermal cycles. For a frame module concept shows these paper a comparison of different joining techniques with the focus on the reliability issue on wire and ribbon bonding. Beside to the 1000 passive thermal cycles from −40°C to +125°C there are active thermals cycles for technology qualification required [3]. Depending on the application and mission profile a high thermal cycling capability is necessary. For this reason, new high temperature joining techniques for die attach, e.g. Silver sintering or diffusion soldering, were developed in the recent past [4]. All of this new joining techniques focusing on higher electrical, thermal and thermo-mechanical performance of power modules. By using an optimized metallization system for the WBG the numbers of thermal cycles can be increased and the maximum operating temperature advanced up to 300°C. In these new temperature regions silicon semiconductors will be substituted by WBG semiconductors. The present work shows an active power cycling capability of different wire and ribbon bonds and the failure mechanism will be discussed. A calculation model explained the reliability for the different wire diameter and the impact of bonding materials. This reliability calculation explain the thermo-mechanical effects and based on materials and geometry data and is not optimized for evidence. Through these physical background understanding more than 1.000.000 thermal cycles with a 150 K temperature swing from +30°C to +180°C are now possible. These is a the basic knowledge for a design for reliability based on current, mission profile and reliability optimization for future high end applications with wire or ribbon bonding technique.
Two-phase, capillary-fed cooling devices are appealing thermal management technologies due to their potential for high heat transfer performance and ease of system-level integration. While existing evaporative wicking structures such as copper inverse opals (CIOs) and copper wire meshes (CWMs) have shown promise for achieving target heat dissipation rates of 100 Wcm−2 or greater, the reliability of these structures for long-term device operation and optimal capillary-driven boiling performance has not received much attention. To ensure proper functionality of the evaporator wick, the microporous copper structures must retain a hydrophilic contact angle during device operation. Surface oxidation of the copper is a critical degradation mechanism that must be addressed to preserve the integrity of the wick. In this study, we systematically investigate the contact angle change of untreated copper and various copper oxides under different conditions. To avoid the formation of hydrophobic Cu2O, we pre-oxidize the copper micro porous wick to form hydrophilic cupric oxide CuO and study the effect of various thermal and chemical oxidation recipes on the hydrophilicity and morphology of the resulting structures. A chemical oxidation formula is implemented for the creation of a stable superhydrophilic surface at a low temperature (70°C) for copper inverse opals (CIOs) (5 μm pore size) and copper wire meshes (CWMs) (76 μm pore opening). The recipe has been optimized to create nano CuO needles with a length of < 100 nm and keep the necks (∼1 μm diameter) open for better capillary wicking of the working fluid. The findings of this study potentially benefit the development of copper-based capillary-fed cooling devices.
Phase change thermal management devices including heat pipes and ultra-thin vapor chambers can remove and spread the excess heat from microprocessors more efficiently compared with the conventional heat sinks. However, the capillary and CHF limits of the evaporator section remained a challenge for high heat flux (> 100 Wcm−2) large area (> 5 × 5 mm2) applications. In this study, a hybrid microporous structure consists of copper wire meshes (CWMs) as the liquid delivery routing and copper inverse opals (CIOs) film as the boiling/evaporation platform is proposed. The feasibility of the approach and the design optimization were studied with extensive modeling and CFD simulations. For the experiment setup, the heater and the RTD sensors are fabricated over a Silicon chip using the conventional micro fabrication processes and the micro porous copper film is deposited based on template-assisted electrodeposition, resulting in CIOs structure with average 5 μm pore size, 1 μm neck, and 15 μm thickness. A copper wire mesh structure (500 μm thickness, 0.5 porosity, 71 μm wire diameter) with 4 × 4 tile openings (1 × 1 mm2 area per tile) was fixed over the CIOs film with mechanical constraints. A flow loop and vapor chamber are designed and fabricated to perform capillary boiling experiments in a saturated environment (liquid water and vapor at ∼100°C). The hybrid microporous structure was able to remove over 75 W from the 5 × 5 mm2 heater area (over 300 W cm−2 heat flux) with 9°C super heat resulting in thermal resistance of 0.03 cm2°CW−1 at the CHF. The findings of this study are largely beneficial for the design and fabrication of high performance evaporator wicks and next-generation heat routing technologies.
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