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

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

The Impact of Via Height and Via Anti-pad Over Insertion Loss

This section demonstrates how much via length and anti-pad size change the insertion loss. The results of this examination are based on the following criteria:

  • A 24-layer stackup
  • A via-in-pad with a 10 mil drill (finished size) hole
  • 18 mil pad
Figure 34. 24-Layer Stack-up Information for investigations on insertion loss impact using various via lengths and anti-pad sizes.
Figure 35. Differential Via and Anti-pad Configuration
Table 3.  Impact of Via Length on Insertion LossIn this case, the anti-pad (GND cutout for each GND layer up to the backdrill) is fixed at 95 mil x 28 mil.
Case Insertion Loss @ 14 GHz Return Loss @14 GHz, ~ dB
Via length from top to L3 (7.4 mil) -0.1730 dB -29
Via length from top to L5 (16.6 mil) -0.1768 dB -28
Via length from top to L7 (25.8 mil) -0.1828 dB -27
Figure 36. Impact on Differential Insertion Loss by Via Length (SDD21)
Figure 37. Impact on Differential Return Loss by Via Length (SDD11)
Table 4.  Impact of Via Anti-pad Length on Insertion LossThe via length from the top to layer 3 is 7.4 mil.
Case GND02 Cutout Size GND04 Cutout Size IL 14 GHz
1A 68 mil x 28 mil 68 mil x 28 mil -0.1988 dB
2A 95 mil x 28 mil 95 mil x 28 mil -0.1730 dB
Table 5.  Impact of Via Anti-pad Width on Insertion LossFor various GND cutouts or (or anti-pad), the via length from the top to layer 5 is 16.6 mil.
Case/Cutout GND02 GND04 GND06 IL @14 GHz
1B 95 mil x 28 mil 95 mil x 28 mil 95 mil x 28 mil -0.1768 dB
2B 95 mil x 50 mil 95 mil x 50 mil 95 mil x 50 mil -0.1741 dB

The signal anti-pad size results in these tables demonstrates that the larger the anti-pad, the less insertion and return loss results. Because space is always a consideration, you must balance the signal anti-pad size with the need for proper break-out routing.

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