Printed Circuit Board Power Bus Decoupling Questions

6. How effective is embedded capacitance for power bus decoupling?

Boards with embedded capacitance have power planes that are very close to each other (generally 0.05 mm or less). The capacitance between these planes is capable of supplying high frequency current to active devices without developing a significant voltage between the planes. Some of the newer embedded capacitance materials with plane spacings on the order of 0.01 mm or less are also immune to power bus resonances.

The new embedded capacitance materials are extremely effective. If your PCB design employs embedded capacitance with a plane spacing of 0.01 mm or less, and a bulk decoupling capacitor to meet low-frequency current needs, then power bus noise is not likely to be a problem. However, these materials are relatively expensive and not all board fabricators can work with them. Embedded capacitance may not be a good option unless your design requirements demand it.

References

[1] M. Xu, T. Hubing, J. Chen, T. Van Doren, J. Drewniak and R. DuBroff, "Power bus decoupling with embedded capacitance in printed circuit board design," IEEE Transactions on Electromagnetic Compatibility, vol. 45, no. 1, Feb. 2003, pp. 22-30.

[2] M. Xu and T. Hubing, "Estimating the power bus impedance of printed circuit boards with embedded capacitance," IEEE Transactions on Advanced Packaging, vol. 25, no. 3, Aug. 2002, pp. 424-432.

[3] T. Hubing, M. Xu and J. Chen, "Electrical Model and Test Results for Embedded Capacitance Boards," UMR EMC Laboratory Technical Report, TR00-2-042, March 27, 2000.