Positional Accuracy
Precise alignment of copper patterns across the different levels of a multilayer printed circuit board ensures that drilled holes accurately connect the intended traces. Reliable inter-layer registration prevents unintended electrical shorts or open circuits.
Manufacturing Constraint
Lamination of pre-preg and core materials requires pins or optical targets to maintain the stackup position within tight tolerances. Factors such as material shrinkage during the heat and pressure of the press cycle can degrade inter-layer registration if not compensated for in the original design. Advanced fabricators use X-ray systems to measure the offset of inner layers before the drilling process begins.
This data allows the drill bits to adjust their path to hit the center of internal pads even when slight shifting has occurred.
Inspection Methodology
Excessive deviation in the stackup leads to breakout where the drill bit exits the copper pad area. When inter-layer registration falls outside of the allowable limits defined by standards like IPC-6012, the structural integrity of the annular ring is compromised. High density interconnect designs with small features are particularly sensitive to these alignment errors.
Corrective actions often involve adjusting the artwork scaling to match the measured dimensional changes of the specific material lot.
