Inverter Unit Non-Parallel Conductor Cooling
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Solution Overview
Problem
Conventional inverter units for electric vehicles face challenges in achieving high cooling efficiency and reliability due to non-uniform heat transfer and thin insulating substrates, leading to increased thermal resistance and manufacturing complexities.
Innovation Solution
The inverter unit design features semiconductor chips with conductors disposed on a cooler such that their joint surfaces are not parallel to the cooler's surface, bonded with an insulating resin sheet containing ceramics, and connected through both positive and negative surfaces for enhanced heat dissipation, reducing thermal resistance and manufacturing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the radiating metal plate is pressed into contact with the inverter unit case using attachment screws, then the power semiconductor device can be cooled by the refrigerant flowing through the flow passage, but the pressing force is applied only around the attachment screws and not uniformly to the entire radiating metal plate, resulting in non-uniform heat transfer and increased contact thermal resistance
Solution Approach 1:
A heat transfer sheet is introduced as an intermediary between the radiating metal plate and the inverter unit case. This heat transfer sheet has a larger contact area with the inverter unit case than the radiating metal plate, allowing it to distribute the pressing force uniformly across the entire contact surface. The sheet material is selected to have appropriate thermal conductivity to facilitate uniform heat transfer from the radiating metal plate to the flow passage, thereby reducing contact thermal resistance and improving cooling efficiency.
2Volume of moving object
If the insulating substrate thickness is reduced to decrease the power semiconductor device size, then the device can be miniaturized, but the heat generated in the IGBT cannot be sufficiently diffused within the insulating substrate, leading to increased thermal resistance
Solution Approach 1:
The insulating substrate is constructed as a composite material structure combining resin and ceramic materials. The resin portion provides electrical insulation while the ceramic portion, which has higher thermal conductivity, forms a heat diffusion path that extends in the thickness direction. This composite structure enables effective heat diffusion from the IGBT even in thin substrates, reducing thermal resistance while maintaining the miniaturized device size.
3Ease of manufacture
If wire bonding is used to electrically connect the IGBT and diode chips, then the semiconductor device can be manufactured, but the manufacturing time is significantly increased
Solution Approach 1:
The wire bonding process is completely eliminated by extracting this step from the manufacturing sequence. Instead, the IGBT and diode chips are directly mounted on their respective conductors using chip mounting technology, establishing electrical connections through the conductor structures themselves. This direct mounting approach removes the time-consuming wire bonding process while maintaining electrical connectivity and simplifying the manufacturing process.
4Volume of moving object
If the inverter unit is miniaturized to meet electric vehicle requirements, then the overall size is reduced, but the cooling efficiency of the power semiconductor devices deteriorates
Solution Approach 1:
The cooling system is optimized with local quality enhancements where heat transfer is most critical. The heat transfer sheet is positioned to provide uniform heat distribution across the radiating metal plate surface, and the ceramic-containing insulating substrate creates localized high-conductivity heat paths directly under the IGBT. These localized improvements in heat transfer quality enable effective cooling in the miniaturized inverter unit without requiring proportional increases in cooling system size.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design significantly improves cooling efficiency, reduces thermal resistance, and increases the current carrying capacity while enhancing manufacturing yield and reliability, allowing for a smaller and more reliable inverter unit.
Implementation Method 1
the power semiconductor device 2 is cooled by a refrigerant 12 flowing within the flow passage 13
Implementation Method 2
heat generated in the IGBT 171 and diode 181 is released by the refrigerant 12
Implementation Method 3
heat transfer grease 19 is applied. The heat transfer grease 19 reduces contact thermal resistance generated when the power semiconductor device 2 is attached to the bottom face of the inverter unit case 1
Data Source
AI summary
To provide an inverter unit with excellent manufacturing performance and with current carrying capacity increased and size reduced by further increasing the cooling efficiency of a power efficiency device.The inverter unit includes: a semiconductor chip constituting an arm of an inverter; a first conductor 33 joined to a positive side of the semiconductor chip; and a second conductor 35 joined to a negative side of the semiconductor chip. The first and second conductors are disposed above a cooler 22 cooling the semiconductor chip so that a joint surface of the first conductor 33 which is joined to a positive electrode of the semiconductor chip and a joint surface of the second conductor 35 which is joined to a negative electrode of the semiconductor chip are not in parallel to a surface of the cooler 22.