Electronic – Crystal PCB Layout Design on Re spin Board

crystallayoutoscillatorpcb-design

I'm trying to redesign the layout with a 8 MHz crystal(XT1) for atmega328p micro controller. Since this micro controller uses internal oscillator,UART Communication does not work reliably on current design.So I decided to go with external crystal for the production.

Since this board works fine with all the other functionalities except UART,we need to re spin the board with minimal changes.The red represents the top PCB layer and blue is the bottom PCB layer (it's a 2-layer design).Due to the placement constraints on the bottom side of the PCB,I placed the Crystal and its Load capacitance on the Top side whereas the micro-controller sits on the bottom side.

I've been reading through several recommendations specifically for crystals layout design.I am sure that design does not meet most of them(ex.Avoid vias). I am concerned about the functionality of the PCB, especially from EMC problems.There are really no high frequency signals on this board except 8 MHzenter image description here. Can anybody give some suggestions on how the PCB can be improved?

Best Answer

Things which I would change:

  • do not use right angle tracks;
  • consider usage of generator instead of oscillator of respective frequency;
  • do not put components too close to dimensions (in your case I see a hole);
  • put GND plane near and behind the crystal;
  • wiring between SMD capacitor pads IMHO may not be a good idea.

Sometime you have to put some extra effort and make things right from the start. I think it is this case.