The excerpt below does a great job explaining some key notes on Signal Integrity
“The way materials are selected and used can help create products that really stand out against the competition by offering great performance and value. At a high level, choosing low-loss materials can ensure you meet signal-integrity targets, but can add cost to the end-product. On the other hand, if the design know-how is there, it may be possible to meet the same targets with a lower-cost material and remove the burden of those extra dollars from the BoM.
Typically, engineers will look at dissipation factor as their key parameter determining the impact the substrate material will have on signal integrity. It’s not the only relevant metric, however. At Ventec, we see the dielectric constant, or Dk, as having a large impact on the mechanical and electrical properties of the printed circuit board. For example, it can determine the overall Z height of the PCB, and this can affect the overall enclosure size and whether the electronic assembly will allow the finished product to meet the specified dimensions. Simply put, both the dissipation factor and the Dk describe the substrate’s energy-release properties, and the mathematics bears this out. The importance of the Dk, however, is often neglected.”