Intel® Quartus® Prime Standard Edition User Guide: PCB Design Tools

ID 683619
Date 9/24/2018
Document Table of Contents

1.7.3. Defining PCB Layers and PCB Layer Thickness

Every PCB is fabricated using a number of layers. To remove some of the pessimism from your SSN results, Altera recommends that you create assignments describing your PCB layers in the Intel® Quartus® Prime software.

You can specify the number of layers on you PCB, and their thickness. The PCB layer information is used only during SSN analysis and is not used in other processes run by the Intel® Quartus® Prime software. If a custom PCB breakout region is not described you can select the default thickness, which directs the SSN Analyzer to use a single-layer PCB breakout region during SSN analysis.

All the assignments you create for the PCB layers are saved to the .qsf. You can also use Tcl commands to create PCB layer assignments. You can create any number of PCB layers, however, the layers must be consecutive.

 Tcl Commands for Specifying PCB Layer Assignments

set_global_assignment -name PCB_LAYER_THICKNESS 0.00099822M -section_id 1
set_global_assignment -name PCB_LAYER_THICKNESS 0.00034036M -section_id 2
set_global_assignment -name PCB_LAYER_THICKNESS 0.00034036M -section_id 3

The cross-section shows the stackup information of a PCB, which tells you the number of layers used in your PCB. The PCB shown in this example consists of various signal and circuit layers on which FPGA pins are routed, as well as the power and ground layers.

Figure 9. Snapshot of Stackup of a PCB Shown in the Allegro Board Design Environment

In this example, each of the four signal layers are a different thickness, with the depths shown in the Thickness (MIL) column. The layer thickness for each signal layer is computed as follows:

  • Signal Layer 1 is the L4-SIGNAL, at thickness (1.9+3.6+1.2+3+1.2+4=) 14.9 mils
  • Signal Layer 2 is the L5-SIGNAL, at thickness (0.6+6=) 6.6 mils
  • Signal Layer 3 is the L8-SIGNAL, at thickness (0.6+4+1.2+3+1.2+4=) 14 mils
  • Signal Layer 4 is the L9-SIGNAL, at thickness (0.6+6=) 6.6 mils
    Figure 10. PCB Layers and Thickness Assignments Specified in the Intel® Quartus® Prime Software