TABLE OF CONTENTS As we know, there are known knowns we also know there are known unknowns But there are also unknown unknowns the ones we don't know we don't know.
Donald Rumsfeld
Printed circuit boards (PCBs) using Fire Resistant #4 (FR-4) material constitute one of the most prevalent mediums for electrical interconnects. Despite their widespread use, however, fundamental characteristics of the PCB are often overlooked or misunderstood.
To build a successful PCI Express interconnect, you must address certain PCB design considerations. For example, you must decide which layers of the PCB to route the signals on, determine how wide and how long to make the traces, and understand the impact of your routing choices on the product's performance to electrical specifications. You must also understand the physical properties and limitations of the materials that make up the PCB and influence its performance.
Each printed circuit board is composed of various materials arranged in a defined manner. The ordering and combination of these materials is often referred to as the PCB stackup. For PCI Express interconnects, you can use a wide variety of stackups. For any given design, you must consider such stackup-related factors as overall cost, routing density, power delivery, signal integrity requirements, and reference plane requirements.
Desktop and mobile system implementations are often more cost-constrained than server-type platforms and tend to generally use four-layer stackups, since more layers typically cost more money. For server or workstation system implementations, multi-layer stackups...
