Structural Backbone
Heavyweight fiberglass fabric provides mechanical rigidity and thickness in multi-layer printed circuit board cores. Fabricators select 7628 coarse weave to build thick, stable laminate layers that resist warpage during thermal cycling. This heavy fabric uses thick glass yarns woven together, which creates a durable structure that withstands high mechanical loads.
The thick bundles create larger resin-filled windows between the woven fibers, establishing a stable structural foundation for double-sided boards.
Resin Absorption
Capillary action within the large fiber bundles of heavy glass styles influences the flow of epoxy during laminate pressing. When prepreg layers melt under heat and pressure, the resin must fully fill the open regions between the warp and fill yarns. The wide spacing of 7628 coarse weave demands careful resin volume control to prevent internal voids.
If the resin fails to penetrate the bundles, entrapment of moisture or air can occur, leading to conductive anodic filament growth or delamination during assembly. Insufficient resin flow also increases the risk of measling where the fibers cross, appearing as white spots after solder exposure.
Drill Wear
Mechanical drilling of dense glass reinforced laminates increases the temperature at the tool tip. Thick fiber bundles in 7628 coarse weave present high physical resistance to the drill bit, resulting in faster tool wear than thinner glass styles. This friction generates localized heat that can smear epoxy along the hole wall.
