Process Variation
Inconsistency in the distribution of mechanical force across the surface of a multilayer board leads to uneven thickness and resin distribution. This lamination pressure variance can occur because of worn press plates or incorrect loading of the build stack into the press. If the edges receive less force than the center, the board might not achieve proper dielectric targets.
This results in unpredictable electrical properties in the finished substrate. Monitoring sensors help ensure that hydraulic force remains uniform during the curing stage.
Force Distribution
Hydraulic cylinders must exert equal downward energy over the entirety of the pressing area to prevent thickness taper. When lamination pressure variance becomes excessive, the liquid resin flows differently depending on its position relative to the heat source. This creates areas with more glass and less resin near high pressure zones.
Uniformity is hard to maintain when processing multiple small boards in a single large panel. Thinning at the center of the press is a common symptom of plate warping.
Dimensional Accuracy
Final board height depends on the resin being forced into all copper air gaps without being squeezed entirely out of the assembly. If lamination pressure variance is poorly controlled, the finished height will deviate from the design specification. Impedance on signal lines will change because the distance to the ground plane is not stable.
High quality presses use compensation pads to normalize the force. Stable pressure ensures repeatable performance across large production runs.
