[Hardware design] Stitching via的重要性

Poor stitching via could lead to significant margin loss, so it is essential to stitch reference planes for signal transition, where the reference plane change took in place.

在Intel的design guide內提到這段話，可以解釋為什麼在高速訊號換層的時候需要加上兩個Ground Via在旁邊，為的就是減小邊界雜訊，但為什麼可以減小，如何減小，可能還需要更多的理論證實，甚至是SI的證明。

 In case signal transition to another routing layer, but the referencing plane still kept the same, no stitching via is required.

如果換層之後還是reference同一層，那可以把stitching via給省略。

Placing GND stitching via according current guidelines maintains optimal current return path and minimize crosstalk effect.

• Stitching vias should be placed with this spacing: — 30-mils (0.762-mm) pitch between differential clock via and closest stitching GND-via.
• Every differential clock via must have at least one GND stitching via with a maximum spacing of 30 mils (0.762 mm).
• Placement of additional stitching vias, where possible, is recommended.