Metrology Application
High-resolution imaging instruments provide non-destructive three-dimensional analysis of microelectronic features. For fine-pitch surface mount assemblies, laser scanning confocal microscopy delivers precise surface topography measurements of solder joints and printed circuit board pads. This technique maps height variations across sub-micron intervals to evaluate the quality of printed solder paste deposits.
Optical Mechanism
Spatial filtering of out-of-focus light allows this imaging method to isolate a single thin plane of a specimen. The instrument uses a focused laser beam to scan the sample sequentially point by point through a pinhole aperture that blocks out-of-focus signal. Computer software assembles these individual optical sections into a sharp three-dimensional render of the circuit trace or solder joint.
Because the pinhole eliminates scattered light, the resulting image exhibits superior contrast and vertical resolution compared to conventional optical microscopes. This detailed profiling reveals subtle defects like micro-voids in solder and microscopic fractures in trace copper.
Precision Boundary
Resolution limits are defined by the wavelength of the light source and the numerical aperture of the objective lens. When analyzing very deep or highly reflective vias, the steep angle of the sidewalls can scatter the laser light away from the collector, reducing measurement accuracy. This metrological boundary requires careful calibration and sometimes the use of supplementary contact profiling methods.
