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APRIL 2021 I DESIGN007 MAGAZINE 83 traditional open weave glass can yield signal integrity benefits as the transmission line runs in a "more" homogeneous medium. But you need to keep in mind the mechanical and fluid flow considerations, as the flat glass—while better for laser drilling and signal integrity— provides a barrier to resin flow across the reinforcement, so you need to ensure adequate resin content to avoid glass stop, or delamination. Copper Characteristics Moving from the dielectric medium to the copper plane and signal layers, new designers will oen think they can use datasheet values for copper roughness. is is an understand- able position if they don't have a knowledge of the PCB fabrication process, but a glance at Figure 4 shows that the PCB fabrication process adds plated copper to the surfaces Figure 4: Traditional glass cloth/epoxy resin weave. (Source: Ventec International Group) Figure 6: Flattened glass cloth/epoxy resin weave. (Courtesy of Ventec International Group) Figure 5: Traditional glass cloth/epoxy resin weave. (Courtesy of Ventec International Group)