Selecting Dielectric Substrates for High Speed Multilayer Stackup Design
Selecting dielectric substrates requires balancing dissipation factor, glass weave uniformity, foil roughness, and panel yields to meet high-speed impedance targets.
Style 1078 Glass
Uniform Weave
Flat fiberglass yarns crossing each other in a spread pattern create a smooth and consistent reinforcement for high speed laminates. The style 1078 glass is designed to eliminate the large gaps of resin found in traditional weaves which can interfere with electrical signals. This fabric is a popular choice for boards that carry very fast data where signal timing is critical.
Resin Distribution
Spreading the glass fibers evenly across the surface ensures that the electrical properties of the board are the same everywhere. A style 1078 glass layer prevents the signal from seeing alternating patches of high-dk glass and low-dk resin. This uniformity reduces the jitter and data errors that can occur when signals travel at different speeds on the two lines of a differential pair.
The flat nature of the yarns also makes the material easier to drill and plate because the surface is more level.
Signal Delay
Timing variations are minimized when the dielectric environment is perfectly consistent along the entire path of the trace. The style 1078 glass is specifically used to combat fiber weave effect in designs operating above ten gigahertz. While the material cost is higher than standard glass, it provides the performance needed for high-end networking and server applications where signal integrity is the top priority.
Using this style ensures that high speed links operate without the interference caused by physical non-uniformity in the substrate.