PCB Requirements for E-Mobility

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Nolan Johnson, Barry Matties, and Happy Holden speak with Christian Klein, section manager for PCBs in the automotive electronics division, about Bosch’s recent presentation on PCB requirements of the future in regard to automotive and electro mobility trends and challenges.

Nolan Johnson: We’ve been looking through the presentation from Bosch on requirements for PCBs going on in the future, and there are quite a lot of requirements. How do you see the requirements for printed circuit board manufacturing for automotive playing out? What do you see as the future landscape?

Christian Klein: That depends on the area or on the use case. We have two big megatrends. One is electro mobility and the other one is connected cars. These megatrends require different technologies. For example, electro mobility needs substrates on which we can integrate power components at temperatures up to 160°C, perhaps even higher, as well as currents up to several hundred amps. Those are difficult requirements for these kinds of PCBs. On the other side, we have PCBs for computers. They are more like graphic cards or servers and are already used in the consumer industry, but not in the automotive environment. Therefore, we have to distinguish between these two use cases and with different requirements for the PCB. What is common is that they all need to survive the automotive environment.

Barry Matties: Since the presentation at the World Conference was looking at future requirements, are the requirements currently being met?

Klein: At the moment the requirements are being met. But today, electrical cars often still use power electronics based on ceramic substrates. For autonomous driving the requirements will increase. The new components need even more sophisticated HDI technology than before. Computers need a higher data rate; it is increasing every year. Therefore, we will be forced to use other materials in the future for the high-speed electronics: very low loss or ultra-low loss materials with suitable Dk and Df values. These materials are normally a bit more brittle and not that robust regarding micro-cracks like the traditional materials. Taking into account the known failure modes like CAF or micro-cracks, this could be challenging.

In the automotive environment, temperature cycling and temperature storage are important parameters. But it is the humidity for which we have to be really careful. Vehicles have subsystems that are always on with low power consumption. There could be electrochemical migration in these systems. If you have to use these new materials due to the high-speed electronic requirements, then we have to be very careful. Therefore—at the moment—we have solutions, but for the next generation with bigger bandwidth and higher frequency, we have to go to other materials, and these have to be qualified.

Matties: Are you looking at the cleaning standards and changing the requirements as you talk about the electrochemical migration?

Klein: Cleaning is always discussed because cleaning is quite difficult. The problem is that up to now nobody can offer the perfect cleaning solution. After assembly, some of the solder paste residuals could stay in small gaps below the QFPs and other components. That is very difficult to clean perfectly. Regarding the bare PCB itself we do not really see a problem. What is still on the board after the PCB production will evaporate during first reflow. Thereafter, it depends on the use case. If a designer makes the housing of the PCB quite tight and uses a pressure compensation element, the warm and humid air does not get directly onto the PCB itself, and dewing can be avoided. Therefore, we must be really careful in designing our units that dewing of water will not happen. Cleaning has not been a big topic because we use a specific design of our control units to avoid this dewing.

To read this entire interview, which appeared in the March 2021 issue of PCB007 Magazine, click here.


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