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42 Design Guide
Intel
®
31244 PCI-X to Serial ATA Controller
Printed Circuit Board (PCB) Methodology
6.2.2 Motherboard Stackup for Backplane Designs
The motherboard is supporting components in addition to GD31244, so an assumption is, desktop
PC requirements are dominate to assure the processor and memory subsystem may be implemented
with normal 60 ohm guidelines.
When possible, it is recommended that the designer use stripline for the following reasons:
• Reduced skin effect relative to microstrip
• Reduced forward cross talk
• Reduced jitter through differential stackup and isolated power delivery
Table 12. Motherboard Stackup, Microstrip
Variable Nominal (mil) Tolerance Min (mil) Max (mil)
Mask Thickness 0.8 +/- 0.2 0.6 1.0
Mask Er 3.6 3.6 3.6
Trace Height 4.0 +/- 0.3 3.7 4.3
Preg Er 4.15 +/- 0.55 3.6 4.7
Plane Thickness 1.4 +/- 0.2 1.2 1.6
Trace Thickness 1.4 +/- 0.4 1.0 1.8
Trace Width 5 mil +/- 1.5 3.5 6.5
Total Thickness 62.0 +/- 6.0 56.0 68.0
Table 13. Motherboard Microstrip Parameters
Parameter Routing Guideline Notes
Motherboard Layout Microstrip
Single Ended Trace Impedance 55 +/- 12%
Differential Trace Impedance 100 ohms +/- 15%
Reference Plane ground
Trace Thickness 1.4 mil
Trace Width 5 mil
Intra Pair Trace Spacing 15 mil intra-pair to pair center-to-center
Pair-to-Pair Trace Spacing 55 mil pair to pair center-to-center
Trace Length 2” to 6”
Trace Length Matching 10 mil Intra-pair matching
Vias 0
Minimize number of vias (none preferred). Each
channel in the pair has an equal number of vias.