Abstract
A new IC chip selection system with the use of laser beam has been developed. Compared with conventional systems which use microscopes, ITV's and signal processors for detection, the new system facilitates determination of the exact chip position and identification of a bad mark, beveled edge or surface defect with laser beams.
To detect the exact chip position, Fraunhofer diffraction patterns generated by laser at the scribed edges of chips are utilized. For detection of a bad mark and beveled edge, on the other hand, differences of reflecting power are made use of.
This system consists only of two He-Ne laser tubes and three photo-Darlington sensors, outputs of which are led to stepping motors control circuits that drive the X-Y shift table on a chip bonding machine.
The developed system is of simple construction and low cost; it can detect a bad mark instantaneously in contrast to the usual systems which cost considerably more and are less reliable. The reason for this is that optical magnification of the chip surface image by microscopes brings reduced contrast of the image and TV image scanning and A/D signal conversion requires several hundreds of milliseconds.
The correct detection rate by this system was 99.6% as to marks of 600μm diameter on 1.7mm×1.8mm chips and 99.8% as to marks of 300μm diameter on 1.5mm×1.3mm chips. In either case, about 1, 000 chips were tested.
