User manual

Advantech SOM-Express Design Guide
Chapter 4 General Design Recommendations 37
4.1.1 Four layer board stack-up
Figure 4-1 illustrates an example of a four-layer stack-up with 2 signal layers and 2
power planes. The two power planes are the power layer and the ground layer. The
layer sequence of component-ground-power-solder is the most common stack-up
arrangement from top to bottom.
L1 Signal Layer
Prepreg
L2 Ground Layer
Core
L3 Power Layer
Prepreg
L4 Signal Layer
Total
Thickness
62 mils
62 mils
Figure 4-1 Four-Layer Stack-up
Table 4.1: Recommended Four-Layer Stack-Up Dimensions
Layer Layer Signal-End Signals Differential Signals
USB differential
Signals
Dielectric
Thickness
(mil)
No Type
Width
(mil)
Impedance
(ohm)
Width
(mil)
Impedance
(ohm)
Width
(mil)
Impedance
(ohm)
0.7 L1 Signals 6/6 55+/-10% 6/7/6 100+/-10% 6/5/6 90+/-10%
5 Prepreg
1.4 L2 Ground
47 Core
1.4 L3 Power
5 Prepreg
0.7 L4 Signals 6/6 55+/-10% 6/7/6 100+/-10% 6/5/6 90+/-10%
Notes:
Target PCB Thickness totals 62mil+/-10%