I was reviewing an FR4 laminate datasheet and noticed options for different glass cloth types, specifically 106 and 1067 glass. Could you explain the key differences between these two types of glass cloth used in FR4 laminates? Additionally, I encountered the term “spreading” in the datasheet. Please explain what “spreading” refers to in this context?
Type 106
Weave Warp Fill Thickness Weight Hor/Vert Fiber Width Hor/Vert Fiber Pitch
Plain 56 56 0.0013” 25g/m^2 10.2mils/4.8mils 20.6mils/18.5mils
Type 1067
Weave Warp Fill Thickness Weight Hor/Vert Fiber Width Hor/Vert Fiber Pitch
Plain 70 70 0.0014” 31g/m^2 12.4mils/8.85mils 13.7mils/14.3mils
So, as you can see, the 1067 cloth is getting wider fibers on a smaller pitch, increasing the number of fibers by 25%, while keeping almost the same thickness. That means there will be less gaps and a more consistent base for the epoxy resin to infuse into. The net result is a more consistent dielectric constant and better HF operation. Given one particular weave type there are two ways to vary it to improve performance. The base weave is called the “standard” then mfgs. offer an “expanded” weave, which amounts to having them “fluffed up” a little, and a “spread” weave where the fibers bundle is flatted out; greatly reducing the amount and size of any gaps.
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