
Advantech SOM-Express Design Guide
38 Chapter 4 General Design Recommendations
4.1.2 Six layer board stack-up
Figure 4-2 illustrates an example of a six-layer stack-up with 4 signal layers and 2
power planes. The two power planes are the power layer and the ground layer. The
layer sequence of component-ground-IN1-IN2-power-solder is the most common
stack-up arrangement from top to bottom.
L6 Signal Layer
Prepreg
L1 Signal Layer
Prepreg
L2 Ground Layer
Total
Thickness
62 mils
62 mils
Core
L3 IN1
Prepreg
L4 IN2
L5 Power Layer
Core
Figure 4-2 Six-Layer Stack-up
Table 4.2 Recommended Six-Layer Stack-Up Dimensions
Layer Layer Single-End Signals Differential Signals USB differential Signals Dielectric
Thickness
(mil)
No Type
Width
(mil)
Impedance
(ohm)
Width
(mil)
Impedance
(ohm)
Width
(mil)
Impedance(ohm)
1.7 L1 Signals 5/5 55+/-10% 5/6/5 100+/-10% 5/4/5 90+/-10%
4 Prepreg
1.4 L2 Ground
5 Core
1.4 L3 IN1 5/5 55+/-10% 4/8/4 100+/-10% 4/5/4 90+/-10%
35 Prepreg
1.4 L4 IN2
5 Core 5/5 55+/-10% 4/8/4 100+/-10% 4/5/4 90+/-10%
1.4 L5 Power
4 Prepreg
1.7 L6 Signals 5/5 55+/-10% 5/6/5 100+/-10% 5/4/5 90+/-10%
Notes:
Target PCB Thickness totals 62mil+/-10%
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