User manual

Advantech SOM-Express Design Guide
50 Chapter 5 Carrier Board Design Guidelines
5.2.3.3 Crossing a plane split
The mistake shown here is where the data lines cross a plane split. This causes
unpredictable return path currents and would likely cause a signal quality failure as
well as creating EMI problems.
Figure 5-10 Violation of Proper Routing Techniques
5.2.3.4 Stubs
A very common routing mistake is shown in Figure 5-11. Here the designer could
have avoided creating unnecessary stubs by proper placement of the pull down
resistors over the path of the data traces. Once again, if a stub is unavoidable in the
design, no stub should be greater than 200 mils. Here is another example where a
stub is created that could have been avoided. Stubs typically cause degradation of
signal quality and can also affect EMI.
Figure 5-11 Creating Unnecessary Stubs