Topographic Metrology
Optical surface profilers measure the three-dimensional geometry of microelectronic structures without making physical contact with the delicate components. Through white light interferometry, engineers extract precise height maps of printed circuit board features with sub-nanometer vertical resolution. This measurement approach is particularly useful for verifying the planar uniformity of modern high-density ball grid array pads.
Wave Interference
The instrument divides a broadband light beam into a reference path and a measurement path that reflects off the sample surface. When these two paths recombine, they produce interference fringes only where the optical path lengths are nearly equal, which occurs within a very narrow region along the vertical axis of the scan. By scanning the sensor vertically relative to the circuit board, the system detects the point of maximum fringe contrast for each pixel across the field of view.
These detected points are translated into a highly detailed elevation map of the surface, revealing microscopic variations in trace thickness or pad flatness. This method provides rapid surface measurements over a wider area than can be achieved with conventional laser scanning systems.
Assembly Verification
Quality control teams use this three-dimensional data to inspect solder paste deposits after printing and to evaluate pad coplanarity before component assembly. Ensuring that all pads are flat and uniform prevents defective joint formation during the solder reflow process. This non-contact metrology steps up the reliability of the finished assembly by identifying surface defects early.
