Variations in dielectric constant, Er, across a glass-resin printed circuit board can have a significant effect on signals on the board. Depending on the proportion of time they spend traversing the glass weave and resin, signals will experience changes in average values of Er.

Using a spread weave reduces the gaps between glass fibres, averaging the Er value across the signal path.

One alternative to 1080 glass is single-ply or dual ply 1078. Another alternative,is the thicker, single or dual ply 1086 glass. Alternatives to 106 glass include 1067, similar in thickness, but with higher fabric count and 1065, thicker but with similar fabric count.

Glass spread in PCBs

In response to Application Note AP554 Speedstack library values and why they may differ from published vendor data sheet values Michael Gay of Advanced Chip & Circuit Materials (ACCM), Inc commented:

"Almost all glass is spread using various methods by the major fabric suppliers. In fact, in order to purchase 106 or 1080 glass that is not spread, you must order it as a special order.

The change began to happen around 2015–2020 as each of the glass weavers found that glass to resin silane treatments were more consistent on spread weaves because they reduced the potential for CAF failure mechanisms such as triple point voids and excess silane coating defects.

It should be noted that although spreading is performed on all glass styles, the process is most effective on thin weave like 1035, 1078 and others.

Users should also be aware that during the treating process, the weave of thin and ultra thin weaves can be stretched by the tension needed to pull the glass fabric through the treater during processing. This tends to result in less spread yarns in the machine direction compared to the cross grain or fill direction across the weave."

Michael J Gay
Vice President, Marketing
Advanced Chip & Circuit Materials (ACCM), Inc

https://adv-ccm.com/