Design tips about PCB Backdrill-Controlled Depth Drilling (CDD)

The backdrill process removes stubs from plated-through-holes (vias). Stubs are the unnecessary / unused portions of vias, which extend further than the 

last connected inner layer.Stubs can lead to reflections, as well as disturbances of capacity, inductivity and impedance. This discontinuity errors become critical with increasing propagation speed.

Backplanes and thick Printed Circuit Boards in particular, can endure significant signal integrity disturbances through stubs. For High Frequency PCBs (e.g. with Impedance control), the application of backdrilling, as well as the application of blind and buried vias, can be part of the solution.

Backdrill can be applied to any type of circuit board where stubs cause signal integrity degradation, with minimal design and layout considerations. In contrast, when using blind vias, the aspect ratio has to be kept in mind.

1.Advantages of Backdrill:

1.Less signal attenuation with improved impedance matching
2.Reduced deterministic jitter

3.Lower bit error rate (BER)

4.Increased data rates

5.Increased channel bandwidth

6.Reduced excitation of resonance modes

7.Reduced EMI radiation from the stubs

8.Reduced via-to-via crosstalk

9.Aspect ratio can be neglected (in contrast to blind vias)

Send us an additional info layer in your production data, identifying the vias intended for backdrilling. Different backdrill depths can, for example, be identified through different symbols in the info layer.

2.Design Parameters for Backdrill