Vladimir Duvanenko, Manager for Signal Integrity, PCB Fabrication Operations, Sanmina-SCI
Dr. Nicholas Biunno, Principal Engineer, Sanmina-SCI
George Dudnikov, Senior Vice President, CTO, Sanmina-SCI

In line cards and backplanes the inherent impedance mismatch of a via stub is a significant impediment to obtaining higher transmission bandwidth. This investigation examines short and long via stubs for 22 and 44 layer backplanes. Data analysis shows long stubs gives significant reflection losses and corruption of the S21 characteristics. These obstacles have been circumvented by using back drilling production methods resulting in higher product cost for backplanes. In line cards, the tighter dimensions on vias and pads make back drilling difficult to impossible.

A matched terminated stub (MTS) via technology is presented as an alternative approach to the high cost of stub back drilling and can be applied to lines cards and backplanes.