Substrate Defect Attributable Scrap Clawback Formulas in High Density Interconnect Quoting
HDI scrap clawback formulas isolate raw substrate flaws from process loss to recoup unrecovered value-add costs across sequential lamination steps.
Glass Weave Resin Recession
Structural Failure
Internal separation of epoxy from glass bundles occurs when thermal stress overcomes the bond at the resin interface. If glass weave resin recession develops during reflow, the resulting gap creates a path for moisture or conductive anodic filament growth. The condition is usually identified at the intersections of the weave where mechanical or thermal stress is highest.
Voids Formation
Microscopic air pockets appear along the filaments of the reinforcement fabric after the board undergoes high temperature processing. Once glass weave resin recession occurs, the local dielectric strength of the laminate decreases. Heat from soldering causes the resin to shrink away from the glass surface, leaving a vacuum or gas-filled space that disrupts the uniform thermal expansion of the composite.
Inspection Criterion
Microsection analysis provides the primary method for identifying and measuring the depth of these internal separations. Although a small amount of glass weave resin recession is often permissible under specific workmanship standards, any separation that bridges more than a fixed percentage of the dielectric thickness triggers a rejection. The measurement starts from the glass filament edge and extends to the nearest boundary of the surrounding cured epoxy.
This evaluation requires high magnification and precise grinding to ensure the plane of the cut passes through the center of the bundle. The analysis confirms the extent of the damage.