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Applicable Business AreasxEV Tier1 (inverter makers) and Tier2 (power module makers)
Target ApplicationsxEV inverter cooling devices
Effective solution to inverter cooling system problems!
The non-plated Al/Cu composite heatsink
Electric vehicles use various heat sources such as motors, inverters and batteries, making heat release and cooling systems crucial to preventing the deterioration or breakdown of components or thermal runaway due to high temperatures. Thermal management for efficient gathering and reuse of released heat and weight reduction of car-mount parts for energy conservation are becoming key issues, not only for the driving range (electric mileage) of EVs but also from a sustainability perspective.
Among EV heat sources, efficient heat release is particularly important for inverters, whose power semiconductors cause localized temperature increases.
For this reason, liquid cooling systems are commonly used for inverters. To reduce their weight, inverter circulative cooling systems use aluminum pipes and radiators, while devices to dissipate heat from inverters conventionally contain copper heatsinks to reduce thermal resistance. In such structures, copper heatsinks require metal plating to prevent the copper from ionizing and dissolving in the coolant, causing the aluminum pipes and radiators to corrode.
As a superior solution, Resonac proposes its heatsink with low thermal resistance. Using the Al/Cu composite material for the base, its non-plated aluminum fins exposed to the coolant will not cause radiators to corrode. With the combined effect of the fins, which fully utilize Resonac’s processing techniques, and sintered copper paste, the Al/Cu composite heatsink demonstrates almost equivalent thermal resistance to cooling devices with copper heatsinks.
Conventional copper heatsink
with electroless Ni-P plating for inverters
The above heatsink is 200mm x 130mm.
Forged pin fins can be used for small heatsinks like this.
Innovative Solution
Reducing thermal resistance through the combination of Resonac’s Al/Cu composite heatsink and sintered copper paste
Conventional copper heatsinks used for inverter cooling require plating to prevent the dissolution of copper ions in the coolant, but the complicated forms of the heat dissipation fins and other parts mean that the plating thickness can easily become uneven. Copper ions eluting in the coolant can cause aluminum parts such as radiators to corrode as the coolant circulates.
Another problem is the inadequate thermal conductivity (at around 30W/(m･K)) of the high-lead solder conventionally used to connect power semiconductors and heatsinks thermally and physically with an insulating plate in between.
Resonac’s Al/Cu composite heatsink with its Al/Cu composite base and small-pitch aluminum fins can reduce thermal resistance by approximately 10% compared with all-aluminum heatsinks. The aluminum parts exposed to the coolant do not require plating, which eliminates the risk of radiator corrosion. Thermal resistance can be reduced further by making the fin pitch smaller.
If the insulating plate between the power semiconductor and the heatsink is DCB (Direct Copper Bonding: heat-conductive electric insulating substrate with copper bonded on either side of the Si3N4 insulating ceramic), thermal resistance can be lowered another 10% by adopting Resonac’s sintered copper paste (thermal conductivity: 180W/(m･K)), instead of conventional high-lead solder, to connect the Al/Cu composite base explained above. By combining Resonac’s technologies and materials, thermal resistance equivalent to cooling devices with copper heatsinks can be achieved.
Al/Cu composite heatsink
The above heatsink is 300mm x 150mm.
Using pin fins for a large heatsink like this slows
the coolant’s flow due to the large pressure drop,
but extruded fins can reduce the pressure drop.
Product Features
Combination of the Al/Cu composite base and small-pitch Al fins contributes to lower thermal resistance and reduced weight
The chart below shows the heatsink thermal resistance values obtained by simulation. Compared with the benchmark value of the copper heatsink, thermal resistance increased by about 30% with the same shaped aluminum heatsink. By using the Al/Cu composite material for the base, thermal resistance was approximately 10% lower than the all-aluminum type, and by making the fin pitch smaller, thermal resistance can be reduced further by some 10%.
Resonac’s Al/Cu composite heatsink can also be produced about 50% lighter than conventional copper heatsinks.
Comparison of heatsink thermal resistance
Comparison of heatsink weight
- ※ The data shown are representative values that represent examples of the results of measurements, calculations, etc., and are not guaranteed values.
Lower thermal resistance when paired with sintered copper paste
The chart below shows the result of another thermal resistance simulation. By using the Al/Cu composite heatsink described above, while replacing the solder between the power semiconductor and DCB, and between DCB and the heatsink with Resonac’s sintered copper paste, thermal resistance equivalent to a cooling device with a copper heatsink is expected to be achieved.For further details, please refer to the technical documents
.
Total thermal resistance using sintered copper paste
| Simulation | Benchmark Cu Fin pitch 0.9mm |
③ Al/Cu Fin pitch 0.7mm |
Sintered copper* replaces solder in ③ |
|
|---|---|---|---|---|
| Chip | Chip | Si | Si | Si |
| Between chip and DCB | Solder | Solder | Sintered copper | |
| DCB | Upper wire layer | Cu | Cu | Cu |
| Insulated substrate | Si3N4 | Si3N4 | Si3N4 | |
| Lower wire layer | Cu | Cu | Cu | |
| Between DCB and base | Solder | Solder | Sintered copper | |
| Heatsink | Material | Cu | Al/Cu | Al/Cu |
| Fin pitch (mm) | 0.9 | 0.7 | 0.7 | |
| Thermal resistance | K/W | 0.156 | 0.171 | 0.156 |
| Percentage(％) | 100 | 109.3 | 100.3 |
- ※ Sintered copper paste between DCB and base (for large area) is currently under development. ※ The data shown are representative values that represent examples of the results of measurements, calculations, etc., and are not guaranteed values.
Total thermal resistance model between power semiconductor chip and cooling device
For Resonac’s sintered copper paste, please refer to the article below.
Resonac’s technologies for cooling systems
Resonac uses various aluminum processing technologies, such as extrusion, forging and pressing, and its bonding methods include vacuum brazing and laser welding. We can provide an optimal cooling system that meets our customers’ design and specification requirements.
As shown above, Resonac also excels in thermal management simulation and assessment technologies. The development process we provide requires minimum do-overs or reworks to achieve the designs and specifications required by customers.
Resonance’s technologies for cooling devices
Update date: 22th November, 2023
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Click here for detailed data including simulations comparing thermal resistance.
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