In-process verification of MLC substrates
Abstract Circuit features on multi-layered ceramic (MLC) substrates used in microwave applications, such as wireless handheld devices, are decreasing in size and pose significant challenges to manufacturers. Features of 50 μm lines and spaces on MLC substrates are now common and the circuits on the substrates are more complex. These trends towards miniaturization and circuit density emphasis the changing requirements of the verification and monitoring of registration tolerances throughout the manufacturing process. To effectively manage yields, manufacturers must verify that punching and printing is consistent and uniform while maintaining careful process controls to avoid substrate shrinkage and print screen stretch. The common method of visual inspection cannot achieve the precision or consistency that is necessary to assure the precise registration of dense multi-layer circuitry. Automated Optical Inspection (AOI) addresses the shortcomings of visual inspection and provides additional process improvements. This method of inspection verifies print integrity against a digitized standard, confirms print registration and detects common print defects such as voids, shorts, mouse bites, and other print process defects. Employing AOI during critical stages of the manufacturing proves to be instrumental in providing critical feedback necessary to correct in-process errors. This feedback is essential for manufacturers specializing in shorter productions runs that must identify and understand process abnormalities immediately.