Coordinate Mapping
Linear mappings preserve points and lines during the adjustment of digital artwork to physical board dimensions. Board fabrication processes apply affine transformation to compensate for material shrinkage or expansion that occurs during lamination. This method allows the imaging system to stretch or rotate the circuit pattern to match the actual position of drilled holes.
It relies on a matrix that maintains the parallelism of lines even as it alters the spacing between them. Calculations involve six parameters that define how the coordinate system is skewed or translated. The system applies these changes in real time as the laser direct imaging head moves across the panel.
Scaling Correction
Software routines compare the measured locations of fiducial marks against the nominal CAD data to determine the required offset. This affine transformation handles non-uniform movement across the panel surface by calculating separate scaling factors for the horizontal and vertical axes. If the material has shrunk by 0.1 percent, the mapping expands the image to ensure the pads remain centered on the vias.
High density interconnect designs depend on these adjustments to maintain electrical connectivity between layers.
Alignment Calculation
Automated optical inspection tools use these mathematical corrections to distinguish between actual defects and simple positional shifts. Precise alignment is verified by checking the annular ring width on the final product.
