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Micro-welded hybrid PCBs could lead to lighter electric vehicles

Scientists have produced hybrid printed circuit boards (PCBs) using laser micro-welding that are both more versatile and 20-times cheaper than conventional power electronics made of ceramics.

The new PCBs could significantly reduce the installation space required for power electronics and thus the overall weight of electric vehicles, resulting in longer driving range and ultimately lower CO2 emissions.

They are also an extremely important development due to the resources needed to manufacture chips currently being in short supply, according to the scientists.

To produce the PCBs, the scientists developed a new manufacturing process that makes it possible to use low-cost FR4 circuit board substrates in power electronics, for example in electric motors.

Woo-Sik Chung from the Micro Joining Group at Fraunhofer ILT, explained: ‘Imagine two copper blocks with the same surface area, but different thicknesses in cross section. The thicker the block, the greater the current flow. Where the most current is needed, we reinforce the circuit board. Where little current needs to flow through, we save on material.’

With standardised manufacturing processes, it was previously very costly to selectively thicken individual areas so that a welded connection could be applied. In the CLAPE project however (Innovative Cold-spray deposition and Laser joining for PCB-based Power Electronics), experts from Fraunhofer ILT, ILFA GmbH and Ouest Coating have successfully tackled this challenge over the past three years.

‘Until now, the rule was: you use a PCB with a thin metallisation layer or one with a thick layer – either-or – depending on the application,’ Chung explained. A current transformer to charge batteries in electric cars, for example, requires a great deal of current within a short period of time for the charging process, whereas only a few milliamperes are needed to transmit a current signal to an LED light. ‘Our new manufacturing process enables us to realise both simultaneously on just one circuit board: signal and current transmission,’ said Chung.

The researchers achieved this using specially adapted circuit boards that were thickened selectively by cold gas spraying according to specific requirements. Conductor tracks of different thicknesses could then be micro-welded to the printed circuit board using lasers without causing thermal damage.

Optimised design

Thanks to their specific structure for signal and current transmission, the resulting hybrid PCBs not only require less space, but also distribute the energy much more efficiently.

'In the future, our hybrid PCBs could combine several functions within one component,' said Chung. 'If the [manufacturing] process becomes established in practice, both the installation space for power electronics and the overall weight of electric cars could be significantly reduced, resulting in both a longer range and lower CO2 emissions in the long term. This is also an extremely important finding as the resources needed to manufacture chips for power electronics are in short supply.’

With the project only recently being completed, the technology is not yet ready for the market, and some adjustments still need to be made 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.’ said Chung. 

The next research goal is to now optimise how selective the cold gas spray process works and further reduce costs. ‘Here we still have room for improvement. But this also shows us what great potential there is in the technology once it can be used in a commercially viable way,’ Chung concluded.

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