"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