“Imagine a copper block with the same surface area but different thicknesses in cross-section,” says project leader Woo-Sik Chung from the Microjoining Group at the Fraunhofer ILT, breaking down the principle of the newly developed manufacturing process to its essence. “The thicker the block, the greater the current-carrying capability. Where the most current is needed, we reinforce the circuit board. Where little current needs to flow through, we save material.” With standardised manufacturing processes, it has so far been very costly to selectively thicken individual areas so that a welded connection can be applied. In the CLAPE project (Innovative Cold spray deposition and Laser joining for PCB based Power Electronics), experts from the Fraunhofer ILT, PCB manufacturer ILFA GmbH and the French SME Ouest Coating successfully tackled this challenge.
“Until now, the rule was: you use a PCB with thin metallisation or one with thick. Either-or. Depending on the application,” explains Chung. “A current transformer to charge batteries in e-cars, for example, needs a lot of current within a short period of time to transfer power. In contrast, to transmit a current signal to an LED light, only a few milliamperes are needed. “Our new manufacturing process makes it possible to realise both on just one PCB at the same time: Signal and current transmission.”
This was made possible by the successful combination of two proven processes. For this, the researchers used specially adapted circuit boards. They were thickened locally by cold gas spraying according to the specific requirements so that conductor tracks of different thicknesses could be welded to the circuit board by laser beam microwelding without thermal damage. The advantage of the process: thanks to their specific structure for signal and current transmission, the resulting hybrid circuit boards not only require less space, but also distribute the energy much more efficiently.
In the future, these hybrid circuit boards could combine several functions within one component. The Fraunhofer scientists see the potential for a significantly cheaper production of corresponding circuit boards; at the same time, the technology can also be used more flexibly than classic ceramic substrates.
And another advantage: this process could significantly reduce both the installation space for the power electronics and the overall weight of e-cars, which would result in both a longer range and lower CO2 emissions in the long term.
The fact that the higher efficiency is also accompanied by greater cost-effectiveness makes the Fraunhofer ILT’s new development particularly interesting for industry, especially when one thinks of the stricter climate targets.
“We have only recently completed the project,” says Chung. “The technology is not yet ready for the market and some adjustments are still necessary before it can be used in practice. But we’ve already been able to show that there are promising technological alternatives to the status quo.” The next research goal is now to optimise the selectivity in the cold gas spray process and to further reduce costs. “Here we still have room for improvement. But this also shows us what great potential lies in the technology as soon as it can be used in an economically viable way.”
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