SPI Proceedings: Impact of Motherboard High Density Interconnect on High Speed Signaling

As notebook designs move to smaller form factors and more aggressive package designs, motherboard density increases and package pin pitches decrease. These changes require more advanced motherboard PCB technologies for effective design. High density interconnect (HDI) is a manufacturing process where additional build up layers are included on a PCB. These build up layers allow for the implementation of microvias and buried vias, which aid in the routing of denser platforms. As the industry moves to more advanced via structures and finer geometries, while at the same time increasing bandwidth and frequency, it is important to consider the impact on signal integrity. Designers need to look for ways to increase the routing density without decreasing margins or solution space. This paper compares via structures, transmission lines, and obstacles such as routing over voids and their impact on signal integrity as we move to bus frequencies of 5 GT/s and above.