Details on PCB layout for microcontroller

  1. No, you should not. And get rid of the so called "local ground". What do you think is happening with all the digital signals when you implement this local ground? You should find the answer in Henry Ott's article that you linked, Figure 1.

    Sure, you do have a connection between local ground and the ground plane, but all you do is increase the loop area, essentially turning your trances into small antennae.

  2. That sounds fine.

  3. The reference manual says that VREF- must be connected to VSSA which in turn must be connected to VSS. I suggest that you just connect the VREF- directly to ground and try to keep digital currents out of the way using clever placement.

As for the suggestions, if 1uF caps are the only components you plan to place on the bottom, I recommend that you place them on top. When you have components on both sides, the manufacturer either has to run the board through the oven twice, or solder the components by hand. Both of which will increase the manufacturing cost.

You may find this answer useful.

There are a very few times I use truly separate planes (such applications still exist), but not for a circuit such as yours.

Careful placement of components and a bit of thought on the power / ground should help you achieve a good layout.

You don't necessarily need a local ground plane for the micro. The local ground can be a star with the central point under the micro, which is where this star is connected back to the main ground, for example.

If you have at least 4 layers, then it can make sense to dedicate one of the layers in the immediate vicinity of the micro to a local ground. If this makes routing too hard or this is a two layer board, just use the star configuration. The main point is to keep the high frequency power current drawn by the micro off the main ground plane. If you don't do that, you have a center-fed patch antenna instead of a ground plane.

The loop from micro power pin, to bypass cap, to micro ground pin should not cross the main ground plane. This is where the high frequency power currents will run. Connect the ground pin to the main ground in one place, but do not connect the ground side of the bypass cap to the main ground separately. The ground side of the bypass cap should have its own connection back to the micro's ground pin.

Digital signals going between the micro and other parts of the board will still have small loop area because the micro will be connected to the main ground close to its ground pin.