AN 766: Intel® Stratix® 10 Devices, High Speed Signal Interface Layout Design Guideline

ID 683132
Date 3/12/2019
Public
Document Table of Contents

PCB AC Capacitor Placement Layout Recommendation

Figure 47. Recommended 0402 AC Capacitor LayoutFor this layout, there is no dependency on the stackup.

Follow these guidelines for 0402 AC capacitor layout:

  • AC capacitors are mounted on either the top or bottom layers for RX lanes (for some specific interfaces)
  • If the AC capacitor is mounted on the top layer, RX routing must be stripline with back-drill as close to the top layer as possible to reduce the AC capacitor signal via height
  • If the AC capacitor is mounted on the bottom layer, RX routing must be stripline as close as possible to the bottom layer with a back-drill of the via from the top
  • A x B GND cutout under the AC capacitor (only one layer GND cutout)
  • Signal-to-signal via pitch P = 40 mil
  • Signal-to-GND via pitch C = 30 mil
  • Signal/GND via drill diameter = 10 mil
  • Signal/GND via pad diameter = 20 mil
  • Signal anti-pad diameter = 45 mil
Figure 48. Recommended 0201 AC Capacitor LayoutFor this layout, there is no dependency on the stackup.

Follow these guidelines for 0201 AC capacitor layout:

  • A x B GND cutout under the AC capacitor (only one layer GND cutout)
  • Signal-to-signal via pitch P = 40 mil
  • Signal-to-GND via pitch C = 30 mil
  • Signal/GND via drill diameter = 10 mil
  • Signal/GND via pad diameter = 20 mil
  • Signal anti-pad diameter = 45 mil

Where possible, Intel recommends using the 0201 AC capacitor rather than the 0402 AC capacitor for improved differential return loss and TDR performance.

Figure 49. Differential Return Loss and TDR Comparison Between the 0402 and 0201 AC Capacitor LayoutsFigure shows results after optimization of the GND cutout and signal via anti-pad. Both structures use a 22 mil signal via anti-pad radius. The 0201 AC capacitor has a 55 mil GND cutout width and the 0402 AC capacitor has a 90-mil GND cutout width on the first GND layer under the capacitors.

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