Nobuyuki Akiyama

Automatic Inspection System for Printed Circuit Boards

The purpose of this correspondence is to present problems and methods in automating visual inspection of printed circuit boards (PCBs). Vertical and diagonal illumination are useful in detecting PCB patterns correctly. An algorithm comparing local features of the patterns to be inspected with those of the pattern to be referenced is proposed. An inspection system using developed technologies is also described.

Study on Automatic Visual Inspection of Shadow-Mask Master Patterns

Abstract An automatic appearance inspection technique for C.P.T. shadow-mask master patterns has been developed. The system structure of the automatic inspection machine, characteristics on the pattern detection, algorithm of judgment and the experimental results are reported.

Particle Detection for Patterned Wafers Using Hybrid Optical-Digital Image Processing

A particle detection method for patterned wafers has been developed. This method achieves much better sensitivity by using hybrid optical-digital image processing. Optical image processing employs newly developed 45° diagonal illumination combined with spatial frequency filtering, to reveal the presence of particles with minimal loss of light energy. Digital image processing is characterized by a two-chip comparison procedure insensitive to positional mismatching between the two chips, and eliminates residual pattern information which could not be completely eliminated by optical image processing alone. This method is performed so as to detect 0.5 µm particles on patterned wafers.

Study on Automatic Inspection of Defects on Contact Parts

Publisher Summary This chapter discusses the study on the automatic inspection of defects that occur on contact parts. It reports on the mechanism of detective parts and its algorithm. Automation for the appearance inspection process has been so far the following two reasons, while automation for the production process has been made a great progress. It appears difficult first to mechanize the excellent function of the eyes of human being and second to indicate the appearance inspection criteria in terms of quantity. In addition, it seems almost impossible for the purpose of automation of inspection to change the design of products and to alter the existing criteria that are carried out through visual inspection, from the stand point that the first priority is given to production. The chapter presents an example of having defects in appearance, which will give bad effects of electrical contact when the switch is turned on and to insulation when the switch is turned off. These defects are caused while contact points are welded on the spring.

Experimental Analysis of Measurement Error due to Optical System in Profile-Measuring Machine for Inner Groove

The measurement error due to the optical system in a profile-measuring machine is evaluated experimentally for an inner groove fabricated in a circular hole. In this report, the method for measuring the groove fabricated on a plane surface is used, because it is difficult to produce a precise groove inside the circular hole. Even in this case, it is difficult to fabricate a groove within an error of±0.1μm. Then, a groove composed of a middle plate and two knife-edge plates set on both sides of the middle plate is developed. The groove depth can be changed from 0 to 300μm by moving the knife-edge plates back and forth using the developed groove. Furthermore, the groove width can be changed from 0.5 to 3.0mm by changing the middle plate. The measurement error of the optical profile-measuring machine can be evaluated within an error of±0.1μm using the developed groove.

Improvement of Measuring Equipment Using Pattern Projection Methods for Small Hole Diameter (2nd Report.) Experimental Results and Comparison with Theoretical Results for Parallel Plate Specimen.

In this equipment, the inner diameter of the specimen is measured by detecting an image of a small spot reflected at the wall of the specimen. In this report, the width of the gap between parallel plates is measured instead of measuring the diameter of the hole, and the factors that cause measurement errors are analyzed experimentally. The results obtained in the experiment are compared with the theoretical results discussed in the 1st report of this work. Since it is very difficult to make a specimen with a narrow gap, a special specimen with which the width measurement errors are evaluated without measuring the gap is developed in this work. The following results are obtained. (1) The measurement errors depend on the degree of defocus of the objective lens used for detection. (2) The inner diameters measured in the middle, or the inlet or outlet of the specimen are different. The difference is small when the gap is large and the numerical aperture of the lens is large. (3) The measurement errors are influenced significantly by the degree of defocus of the objective lens used for detection when its numerical aperture is large.In this equipment, the inner diameter of the specimen is measured by detecting an image of a small spot reflected at the wall of the specimen. In this report, the width of the gap between parallel plates is measured instead of measuring the diameter of the hole, and the factors that cause measurement errors are analyzed experimentally. The results obtained in the experiment are compared with the theoretical results discussed in the 1st report of this work. Since it is very difficult to make a specimen with a narrow gap, a special specimen with which the width measurement errors are evaluated without measuring the gap is developed in this work. The following results are obtained. (1) The measurement errors depend on the degree of defocus of the objective lens used for detection. (2) The inner diameters measured in the middle, or the inlet or outlet of the specimen are different. The difference is small when the gap is large and the numerical aperture of the lens is large. (3) The measurement errors are influenced significantly by the degree of defocus of the objective lens used for detection when its numerical aperture is large.

Development of Automatic Detection Method for Cracks Originating at Side Face of Ceramic Parts. (1st Report). Detection of Diffused Light near Cracks and Development of Detection Method.

Both surfaces of fine ceramics used for electric parts are covered with, for example, a resin, a ceramic alumina or a solder. An automatic optical method for detecting cracks originating at the side faces of ceramic parts, the surfaces of which are covered with the above-mentioned materials, has been developed and is reported in this work. A laser beam is diffused into the specimen by illumination onto the side faces through an objective lens. When the specimen has a crack near the laser spot, the diffused laser light is reflected by the crack and the amount of radiant exitance near the crack is increased. The image of the side face is enlarged by the objective lens and detected by a CCD camera. It is clarified experimentally that it is possible to recognize the region surrounded by a close-ended crack wider than 20μm and longer than 351im, or an open-ended crack longer than 50μm, by detecting signals higher than the average level with the CCD camera.Both surfaces of fine ceramics used for electric parts are covered with, for example, a resin, a ceramic alumina or a solder. An automatic optical method for detecting cracks originating at the side faces of ceramic parts, the surfaces of which are covered with the above-mentioned materials, has been developed and is reported in this work. A laser beam is diffused into the specimen by illumination onto the side faces through an objective lens. When the specimen has a crack near the laser spot, the diffused laser light is reflected by the crack and the amount of radiant exitance near the crack is increased. The image of the side face is enlarged by the objective lens and detected by a CCD camera. It is clarified experimentally that it is possible to recognize the region surrounded by a close-ended crack wider than 20μm and longer than 351im, or an open-ended crack longer than 50μm, by detecting signals higher than the average level with the CCD camera.

In-process Automatic Detection for Cracks in Dark PZT Plates Using Diffusion of Laser Light.

An automatic in-process detection system for narrow and short cracks in dark PZT plates used for piezoelectric parts has been developed. A crack in a dark PZT plate is difficult to detect because the diffuse reflectance of PZT is very low compared with that of an alumina plate. With this system, the contrast and SN ratio in the crack detection signal are improved. The former is improved by using a polarized beam splitter for separating the incident light beam from the reflected light beam. The latter is improved by illuminating the PZT plate with the optimum radiant flux of a laser and by setting the detection window at an optimum position. The 0.2 mm-long cracks with 1 μm and 3 μ m in width, are detected at 50% detection reliability and 100% detection reliability, respectively, using the laser scanning system developed for the in-process inspection.

Particle detection technology opn wafer using spatial filter

An automated particle detection system for patterned wafers has been developed. A specific area of the wafer is illuminated with a laser at 45° diagonal in reference to an orientation-flat shaped on the wafer. The diffracted light is detected by an objective lens. The signal obtained by the memory-mat on a wafer is reduced to 1/8-1/15 by setting the printed spatial filter on the conjugate image plane of a Fourier transformed plane in an objective lens. By using the subtracted image signal with the spatial filter, 0.5μm standard particles on a multi-layer pattern can be detected.

Precision position detecting technique for alignment mark applied in a step-and -repeat projection aligner. (3rd report). 2-wavelength2-inclination illumination, diffraction light detection system.

An alignment mark illumination and detection technique is described in which the alignment error caused by the alignment pattern depth and the resist thickness asymmetry is reduced. For the alignment mark, a diffraction pattern which gives a high contrast signal is used. 2-wavelength laser (488, 543 nm) is diverged in 2 directions by a double refraction prism and illuminates the alignment mark vertically and with 26.2 degree inclination. The first order diffraction light is detected. The variation in the detected signal is 30% in the range of 0.6-2.5 pm of pattern depth and resist thickness, compared with the signal detected by the single wavelength light illumination. The experimental result gives a detection error of ± 0.045 μm (3σ) for a wafer in the worst condition.