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26 PCB007 MAGAZINE I APRIL 2018 al load over lifetime. The diversity of require- ments will increase, depending on the applica- tions. On the one hand, electronics are getting smaller, coming closer to the actuators, and will see higher temperatures like power elec- tronics. On the other hand, electronics such as vehicle computers can be better protected against external stress, but have longer life- times due to charging times and 24/7 services. Some of the requirements for PCBs and sub- strates are shown in Figure 7. The functional requirements are manifold as well. Using PCBs in the electric power train can be a cost-effective solution, but PCBs must cover several hundred amps and up to 1000 volts over lifetimes of greater than 100,000 hours in the automotive environment. To cover the signal processing requirements of autonomous driving and connected cars, the automotive HDI technology must make a big step forward to enable the use of proces- sors and memories with several thousand I/Os and BGA pitches of <0.8 mm. High-speed re- quirements need new materials, which must cope with the environmental requirements, es- pecially humidity and temperature. Figure 8 shows a summary of important functional re- quirements. Failure Modes Due to Humidity and Temperature in the Automotive Environment In automotive electronics, the industry has been focused for a long time on failures in- Automotive Electronics | AE/EAI1 | 12/10/2017 © Robert Bosch GmbH 2017. All rights reserved, also regarding any disposal, exploitation, reproduction, editing, distribution, as well as in the event of applications for industrial property rights. 8 Trend to plastic housings or even open housing and Asian market Trend to longer operational time (charging) and always- on mode Trend to hotter applications and hotspots on PCB due to higher currents Increase of humidity load on and in PCB and short dewing periods on PCB Increase of temperature load and temperature cycle load (160 – 175 °C) over whole PCB or at hotspots Longer Temperature/Humidity/Bias (THB) impact (up to 130.000 h instead of 8000 h) Trend to higher operation voltage at small box volume Trend to devices with smaller pitch (~ 0,4 mm) and higher I/O (~ 3000) Power electronics on organic substrates Trend to high speed applications (vehicle computer, radar) Increase of voltages up to 800 V (battery systems) Reduction of isolation distance < 100 µm (for signals) Impedance controlled and high-speed materials up to 10 Gbps (today 100 Mbps – 1 Gbps) and 77 GHz Increase of necessary layer count (~ 20) and reduction of line/space and via ∅ (~70 µm, 80 – 90 µm µvias) Increase of Cu in substrates (e.g. busbar) and local anisotropic heating around power lines Figure 7: Increasing environmental loads require adaptions of materials and concepts for automotive electronics. A very good understanding of cause and effect relationships is essential. (Source: Bosch) Figure 8: New functional requirements necessitate new PCB concepts such as power PCB and highly integrated logic PCBs. (Source: Bosch)