Dimensional Adjustment
Compensation multipliers applied to PCB photolithography master patterns counteract the predictable shrinkage and expansion that occurs during lamination. Fabricators utilize artwork scaling factors to ensure that copper features on different layers line up precisely when heated and pressed together. These numerical values modify the master photoplots, altering the physical dimensions in the X and Y dimensions before exposure.
Without this step, multi-layer registration fails.
Calculation Method
Mathematical ratios derived from historical production runs dictate the percentage of enlargement applied to the film or laser direct imaging files. To establish reliable artwork scaling factors, engineers measure test patterns before and after laminate pressing. The shrinkage typically remains proportional to the glass weave style and the percentage of retained copper on each circuit layer.
Fabricators adjust the scaling coefficients continuously to match the specific lamination parameters. This systematic calculation minimizes pad-to-drill offsets on inner layers. Furthermore, modern laser direct imaging machines apply these factors in real time, executing minute adjustments for individual panels to match the distorted copper targets perfectly.
Calibration Practice
Production variations require regular verification runs to sustain yield. Frequent measurements of processed panels guide the adjustment of artwork scaling factors for subsequent batches. When a new lot of copper-clad laminate arrives, technicians process a pilot panel to confirm that dimensional changes fall within the expected tolerance band.
This continuous feedback loop prevents breakout defects during the via drilling stage.
