Signal Integrity

Signal layers should always be adjacent to ground or power planes.

Signal layers should be tightly coupled to their adjacent planes.

Route traces orthogonally (at right angles) on adjacent layers.

Power and ground planes should be closely coupled together. Drilled Holes will effect the actual plane capacitance value.

Multiple-ground planes are very advantageous.

High speed signals should be routed on buried layers and located between planes.

When critical signals are routed on more than one layer they should be confined to the two layers adjacent to the same plane. If the two routing layers are not adjacent to the same plane, you should drop return path vias at each signal via in the routed path.

To Minimize Crosstalk in Single-Ended Traces (Not Diff Pairs):

Digital circuits with internal traces (Stripline Traces) should be separated by at least the distance to the nearest ground or power plane. For example if H=0.006" (0.15mm) then the traces should be separated by at least 0.006" (0.15mm).

Digital circuits with external traces (Microstrip Traces) should be separated by at least twice the distance to the nearest ground or power plane. For example if H=0.006" (0.15mm) then the traces should be separated by at least 0.012"(0.3mm).

The general rule of thumb to minimize crosstalk to 10% or less is as follows: 50 Ohm traces should be spaced as suggested in the stripline and microstrip examples shown above.

Basically, on FR4 keep 50 ohm lines separated at least one line width.

Use the 20H Power Plane Rule to Minimize Radiated EMI from the PCB edges:

The power plane should be pulled back from the edge of GND planes by a factor of 20 x the dielectric thickness between the power and ground planes. For example with a dielectric thickness of 4mils the power plane would be pulled in on all sides of the GND plane by 80mils (4x20). 

Signal Integrity Links:

Signal Consulting Inc. (Dr. Howard Johnson)

Right the First Time by Lee Ritchey.

Speeding Edge (Lee Ritchey's Home Page).

Henry Ott Consultants

Eric Bogatin's Blog

Terry Fox and Associates
Istan Novak - Electrical Integrity

Common Mode Ground Currents:

Common Mode Ground Currents  Dr. Howard Johnson

Crosstalk:

Crosstalk Modes   Power Point Slides - Intel

Crosstalk Explained  PDF - Douglas Brooks

Crosstalk Calculator  Web Calculator - EEWeb

Power Distribution Networks Design:

Power Distribution Networks Design Tools  Altera

Advanced Power Delivery  IPBLOX

Power and Ground App Note 4992  Maxim

Discrete Components:

SRF & PRF for RF Capacitors  Johanson

Phase Shifts:

Source of Phase Shift  ECE 209 - Wikipedia

Phase Difference Simulator  Jave Applet - Wikipedia

Thumb Rules:

• To Maintain Cross Sectional area of a Controlled Impedance Route the VIA Diameter should Equal 1/3 Trace Width.
• Via stitching of 1/10th wave length can suppress radiated signals approximatley 25dB.