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In today's manufacturing of PCBs (Printed Circuit Boards), there is an increasing demand on 3-D inspection of mesoscale
objects for quality assurance. Two representative examples are the solder pastes on printed circuit board and bumps
on FC-BGA (Flip Chip - Ball Grid Array) substrates, of which heights and volumes are precisely controlled to avoid
defects in direct surface mounting of semiconductor chips. Despite the demand, no suitable 3-D inspection techniques
are available yet, especially for high speed real time quality control of FC-BGA bump heights. Well-established
monochromatic or white light interferometry is not easy to produce large measuring ranges up to a few millimeters and
become robust to the vibrations on factory floor, while widely-used optical triangulation techniques with structured light
illumination fail to provide the measurement precision usually required down to a few micrometers. Moire
interferometry may be considered as a hybrid approach that combines the two distinct principles of the monochromatic
light interferometry and optical triangulation. Thus, when appropriately configured, moire interferometry is capable of
filling the gap between the two principles in terms of measurement range and precision. In this paper we propose a new
method of 3-D inspection of meso-scale objects, which is in fact based upon the principle of grating projection moiré
interferometry. This method projects a series of line patterns with predetermined phase shifts onto the target object and
detects phase information leading to construction of 3-D profiles. Making the most of modern computer vision and
digital signal processing technology allows for high speed measurement of 0.6 sec per 15mm×15mm field of view, with
a resolution of 1μm for all three (x,y,z) axis.
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