Printed Circuit Board Power Bus Decoupling Questions

3. What is the best method for connecting decoupling capacitors if my PCB has closely spaced power planes?

The short answer to this question is to connect the capacitors directly to the power planes using vias mounted in or adjacent to the mounting pads. Never use traces between the vias and the mounting pads and don't be too concerned about the capacitor's location on the board.

More information can be found in the LearnEMC Tutorial: Power Bus Decoupling Guidelines for Printed Circuit Boards with Closely Spaced Power Distribution Planes.

References

[1] T. H. Hubing, J. L. Drewniak, T. P. Van Doren, and D. Hockanson, "Power Bus Decoupling on Multilayer Printed Circuit Boards," IEEE Trans. on Electromagnetic Compatibility, vol. 37, no. 2, May 1995, pp. 155-166.