Metrological Step Height Verification for Cluster Processed Amorphous Substrates
Step height verification on cluster-processed amorphous substrates requires guardbanded metrology and tip-force or dispersion compensation to prevent yield loss.
Coherence Scanning Interferometry
Optical Profiling
Optical instrumentation of high precision represents the primary means for non-contact three-dimensional measurement of board surfaces. Coherence scanning interferometry uses a broad-band light source to produce interference fringes that vary with the surface height of the sample. The system splits a single light beam into a reference path and a measurement path, then recombines them at the camera detector to form high-contrast patterns.
By scanning the optical head vertically, the system localizes the point of maximum fringe contrast for every pixel to construct a high-resolution topographical map of the entire region. This technique resolves sub-nanometer height variations.
Surface Characterization
Surface topography measurement provides critical information on the roughness and planarity of fine-pitch copper pads. Through coherence scanning interferometry, the localized micro-topography of printed circuit boards is mapped without causing mechanical damage to delicate traces. The resulting height maps help detect issues like pad cratering or coplanarity defects before final component placement.
Process Integration
Quality control protocols rely on automated optical tools to verify board finish parameters before solder masking. Advanced assembly lines use automated interferometers to confirm that micro-via depths and solder pad heights remain within specified tolerances. Continuous monitoring ensures high yields for subsequent ball grid array attachment.