Fiber Wash

Lamination Cause

Excessive press pressure applied while the resin is at its lowest viscosity drives this fiber movement during the lamination cycle. As the resin melts, it behaves like a pressurized fluid, flowing toward the low-pressure margins of the panel and dragging the loosely woven glass fibers along with it. This defect is common in thick multilayers with heavy copper patterns that require large volumes of resin to flow and fill the empty spaces.

Incorrect laminate layup or improper venting of the press plates can also accelerate this fluid velocity, worsening the fiber displacement.

Quality Impact

Automated optical inspection and cross-sectional analysis readily identify the uneven glass distribution caused by this defect. Since the displaced fibers create areas of high and low permittivity, the impedance of traces routed through these regions becomes unpredictable. Fabricators prevent this issue by optimizing the temperature ramp rate to keep the resin viscosity within a safe, controlled range.