Our Journey in Designing ECAD for ADAS-Enabled ECUs

The trend of shifting towards the miniaturization poses substantial challenges to the design, specifically in hybrid technology that includes high-voltage circuits.

With miniaturization it is possible to merge multiple boards, which also allows the designer to utilize mixed technologies including analog, digital and RF circuits.

PCB line spacing adhering to IPC standards is required to implement precise circuit formation and reducing overall product size.

Increasing the Clearance Challenge

In PCB design, the copper-to-copper area distance is known as clearance. If the clearance is less, manufacturing can become challenging.

The project we handled where the client requested an increase in clearance to 4 mils, while the existing PCB had a clearance of less than 3 mils.

Why it is required to increase the clearance?

High speed design needs to have this clearance in order to have suppressed crosstalk in order to ensure a perfect signal integrity.

Also, the clearance was preferred based on the IPC 2221 voltage and spacing standards for preventing ESD between conductors. While preferring the spacing, have to balance both PCB clearance layout and manufacturability.

It is required to check the traces be wide enough to carry sufficient current without becoming too hot.

It is also important to maintain clearance from the bounding surface and through-hole connection points present on the board.

Lower clearance may lead to over-voltage, resulting in instantaneous fault between neighbouring conductive traces.

Non-Impedance-Controlled Signal Width

Our client expected an increase in the width of all non-impedance-controlled signals to 4 mils.

This is the width through which high-speed signals flow. It’s essential to maintain a constant impedance from the start to the end.

However, the existing PCB had widths less than 3 mils.

A targeted impedance on a PCB trace can be attained by varying its width.

Why the impedance needs to be controlled across the line?

If the impedance varies, the voltage also may vary significantly as it is propagated along the trace.

A major issue with boards that don’t have impedance matching is the presence of reflections. So, some of the energy of the signal will reflect toward the driver and the remaining signal will continue onward. When you look at the waveform for this, a pure square wave will not be seen. Rather, a distorted waveform with overshoots and undershoots and some ringing will be observed.

Any unmatched impedances on the PCB will result in some electromagnetic interference (EMI). As a result, the mis-match of the impedance will cause some electromagnetic radiation in that localized area where this transition occurs, and where these reflections appear.

The radiation can couple its energy to neighbouring traces or, affect some susceptible components on the board.

The power is transmitted uniformly across the length of the trace across the PCB only when there is uniform impedance.

Impedance control in PCB design helps products perform better for longer periods of time, improving value and controlled reliability.

Controlled impedance is also essential during transition from a lower ohm to a higher ohm environment where impedance is present. These kinds of transitions can lead to energy reflection in the form of powerful pulses capable of disrupting energy flow.