Internal Alignment
Imaging of buried features using high energy radiation allows the manufacturing system to synchronize the drilling process with the actual position of internal copper pads. This x-ray target registration is necessary because the lamination process causes the inner layers of a multilayer board to shift and shrink in ways that external mechanical stops cannot predict. The system finds the specific center of the targets to adjust the drill coordinates.
Compensation Mechanism
Sensors detect the contrast between the copper targets and the surrounding laminate to determine the exact degree of panel distortion. Once the offsets are calculated, the x-ray target registration data is sent to the drilling machine to scale the drill program in real time. This adjustment ensures that every hole lands within the center of its corresponding internal pad.
Modern systems can compensate for linear scaling, rotation, shear and even trapezoidal distortion across the panel.
Quality Acceptance
Failure to achieve proper alignment results in annular ring breakout which compromises the reliability of the vias. Using x-ray target registration is the standard method for producing boards with more than four layers or those with very small pad diameters. It eliminates the guesswork associated with blind scaling based on historical averages.
