Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2000-05-05
2002-08-20
Cariaso, Alan (Department: 2875)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S208100, C250S559400, C250S559450, C356S237500, C356S429000, C356S430000
Reexamination Certificate
active
06437312
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to visual inspection of surfaces of articles, and more particularly to an illuminator for the automated optical inspection of ball grid array substrates, lead frames and printed circuit boards.
BACKGROUND OF THE INVENTION
Apparatus and methods useful for illuminating substantially flat patterned surfaces of articles, such as electrical circuits on printed circuit boards (PCBs), ball grid array substrates (BGAs) reticles, semiconductors and other similar articles, during the automated optical inspection thereof are well known in the art.
During automatic optical inspection of flat patterned surfaces of articles, such as electrical circuits on PCBs and BGAs, the surface is illuminated by intense broad spectrum illumination while the article is transported beneath a sensor, such as a CCD or TDI camera. Conventionally, the sensors acquire scanned gray level images of the surface. Various materials which appear on the surface of an article each have different reflective properties and reflect illumination at a different level of intensity. For example, copper which defines conductors, various metal platings on the conductors, and the substrate itself each have different reflective properties. The reflected intensities in the image are sensed and automatically processed and analyzed to determine the presence of defects in the patterns on the surfaces.
The surfaces of electrical circuits being inspected, although substantially flat, generally exhibit a topographical relief that results both from the cross-sectional configuration of conductors as well as the surface microstructure thereof Typically, very intense illumination impinging on a surface of an article being inspected over a solid angle of incidence is employed to mitigate negative affects of the topographical relief
The following patents are believed to represent the state of the art in high intensity illumination for the inspection of substantially flat patterned article surfaces such as electrical circuits on printed circuit boards (PCBs), ball grid array substrates (BGAs), lead frames, reticles and semiconductors:
U.S. Pat. No. 4,421,410 to Karasaki describes an illuminator comprising a half reflecting mirror disposed above a printed wiring board. Concentrated light is reflected off the mirror and directed onto the wiring board at an angle substantially normal to the surface of the board and diffuse light emanating from fiber optics is simultaneously directed onto the surface at a large angle of incidence. An image of a line on the surface is transmitted through the mirror to a sensor.
U.S. Pat. No. 4,877,326 to Chadwick describes a high intensity illuminator providing focused quasi lambertian illumination to a region of the surface of an article to be inspected. The illuminator includes a half reflecting mirror, first and second and third elliptical cylindrical reflectors and first, second and third lamps, all having mutually parallel elongate axes. Two of the reflectors and two of the light sources are spaced from each other and illuminate the surface with focused light at a large angle of incidence. The half reflecting mirror, the third reflector, and the third lamp are arranged to reflect focused light along an axis normal to the surface to fill the gap between the first and second reflectors. Each lamp is located at one focus of a reflector, and the illuminated region is located at the second focus of the reflectors. Forth and fifth planar reflectors are provided at the longitudinal ends of the first, second and third reflectors, and a sensor is provided to image the illuminated region by sensing light reflected therefrom which passes through the half reflecting mirror.
Israel patent 81450 in the name of Orbotech Ltd. describes a high intensity illuminator similar in structure to that described in U.S. Pat. No. 4,877,326, but employing light supplied via fiber optics, and effectively having a numerical aperture substantially smaller than the numerical aperture of the apparatus described in U.S. Pat. No. 4,877,326.
U.S. Pat. No. 5,058,982 to Katzir describes a high intensity illuminator comprising a beam splitter cube and first, second and third elliptical cylindrical reflectors, two of which are spaced from each other. Light received via fiber optics is provided at one focus of each reflector. The reflectors are oriented so that the second focus of each reflector illuminates a region of a surface to be inspected. A third illuminator and a condensing lens are provided and oriented to direct light through the beam splitter and onto the surface to be inspected along an axis normal thereto. A sensor is oriented to receive light reflected from the surface via the beam splitter cube.
U.S. Pat. No. 5,153,668 to Katzir describes an illuminator for illuminating an area to be inspected on the surface of an article, in which the illumination is configured to be substantially circularly symmetric over a solid angle around an optical axis normal to the surface. A sensor is provided to image the surface through a gap between the illuminators.
U.S. Pat. No. 4,801,810 to Koso describes an elliptical reflector, comprising approximately one half of an elliptical cylinder, which is used to illuminate the surface of a printed circuit board. The axis of the elliptical cylinder is oblique to the surface of the printed circuit board. A lamp is disposed under the reflector at one focus of the ellipse, while the region illuminated is located at the other focus. An imaging system images the illuminated region through an aperture formed in the reflector.
The illuminator employed in Inspire™ automated optical systems manufactured and sold by Orbotech Ltd., and described in copending PCT application PCT/IL98/00285 (unpublished), is a high intensity illuminator comprising a first light source that emits light over a continuous wide angle of illumination toward a surface of an article to be inspected and has a blocking element that blocks a portion of the continuous angle of illumination to form two separate portions of illumination. A second light source is employed to supply illumination to the region blocked by the blocking element. Concentrating optics are provided to concentrate the illumination onto the article. The illumination is provided at a first angle to the normal, and an imaging sensor is provided to image the illuminated region of the article at a second angle to the normal.
Systems which image a surface to be inspected along an imaging axis that is normal to the surface being inspected typically employ at least three separate sources of illumination. In systems that employ less than three sources of illumination to provide an intense solid angle of illumination, the surface is imaged along an axis which is oriented at a non-normal angle thereto.
Additionally, conventional systems that illuminate and image a surface to be inspected along an axis that is normal to the surface being illuminated acquire images via beam splitting apparatus that introduces undesired aberrations into the image.
SUMMARY OF THE INVENTION
The present invention generally seeks to provide high intensity illumination for the automated optical inspection of patterned articles in which two light sources together provide a solid angle of illumination, the spatial uniformity of which is adjustable.
One aspect of a preferred embodiment of the invention provides illumination of a region on the surface of an article over a solid angle using two independently adjustable sources of illumination, wherein the axis of at least one source of illumination is substantially normal to the surface. Preferably, the region illuminated is imaged by a sensor whose axis of imaging is also substantially normal to the surface.
According to another aspect of a preferred embodiment of the invention, a region of an article to be inspected is illuminated with a first illuminator, including a reflective surface which is apertured at a location which overlies the region to be inspected. Supplemental illumination of the region is provided
Adler Avraham
Ben Shlomo Moshe
Banner & Witcoff , Ltd.
Cariaso Alan
Orbotech Ltd.
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