PCB layout optimization

I’m designing a PCB featuring a CAN transceiver, I2C sensor, microcontroller, and linear regulator. I’m considering using both sides of a two-layer stack-up to optimize space. However, I’ve never attempted this before, usually using only one side of the board for components.
My main concern is understanding what components I should avoid placing back-to-back. For instance, I assume it might be unwise to position the linear regulator directly behind the microcontroller. Should I also be cautious about crossing communication lines (I2C, UART, CAN) over each other?

A linear regulator underneath a microcontroller probably wouldn’t be a problem. A switching regulator should definitely not be placed there. As to the other mentioned signals, crossovers aren’t too much of a problem. The problems really arise when you run the CAN bus and the I2C parallel to each other. Same with any clocks or repetitive signals. Switching regulators are probably the worst because of the high currents circulating thru it. Consider ground pours around unused areas.


There are a few items to consider.

First is heat. Placing a heat generator such as a linear regulator directly below other objects will likley transfer heat to nearby components including the opposite side of the board. So the questions are: how much heat will be generated, where is that heat going, and will the destination be able to handle it?

Second is EMC/EMI and similar, related to nets with high amounts of signal energy being radiated into nearby circuits that may not be accepting to unexpected noise.

Third is manufacturing. There are situations where certain components should not have any, or certain types of components placed under them for various performance or assembly reasons.

Some of these concerns can be minimized by changing from a 2 layer to 4 layer PCB. Layout of a double sided PCBA on a two layer stackup is possible but can be challenging to achieve optimal performance in comparison to the same circuits on a 4 layer stackup.

When it comes to crossing communication lines, it is ideal to cross them at 90 degrees from each other in order to minimiize the abilty of one signal to affect the other. You should always consider signal return paths which is much harder to maintain under a double sided, two layer stackup.

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Thank you both.