Cross Hatched Ground Plane Geometry Optimization for High Frequency Signal Integrity
Cross-hatched ground plane geometry requires balancing mesh pitch, line width, and trace bias angle to prevent impedance elevation and slow-wave phase delay.
Resin Filling Voids
Material Discontinuity
Cavities within a blind or buried via result from the incomplete displacement of air during the lamination or plugging process. These resin filling voids represent a measurable reliability risk in high density circuit boards. Small pockets of trapped gas can expand during assembly soldering and cause internal delamination.
Encapsulation Failure
Air entrapment occurs most frequently in high aspect ratio holes where the resin cannot flow freely. Viscosity of the prepreg or plug material must be low enough to reach the bottom of the cavity. Vacuum lamination helps to remove air before the resin cures.
Failures in this process create weak points that are susceptible to thermomechanical stress. Proper venting and board orientation during the filling stage reduce the likelihood of these pockets forming.
Thermal Risk
Expansion of trapped gas during reflow exerts pressure on the surrounding copper barrel. This stress often leads to circumferential cracks in the via wall or separation of the inner layer junctions. Thermal cycling during the life of the product makes these defects grow until a permanent open circuit occurs.
Microsectioning is the standard method for verifying that all vias are completely filled and solid. Reliability of a multilayer board depends on the absence of resin filling voids.