Television – Special applications – Manufacturing
Reexamination Certificate
1998-05-29
2001-01-23
Britton, Howard (Department: 2713)
Television
Special applications
Manufacturing
C348S095000
Reexamination Certificate
active
06177954
ABSTRACT:
The present invention relates to a mounted camera used in conjunction with an illumination source having a diffuser associated therewith, a reflective surface, and a field lens, to provide a compact inspection system which is extremely small in size and facilitates use within the small confines of semiconductor processing equipment.
BACKGROUND OF THE INVENTION
There are a variety of known inspection systems which illuminate a flat surface to be inspected such as a laser-etched art work semiconductor lead framework. However, most of the known inspection systems are of a relatively large size which do not easily fit within the small confines of currently available semiconductor processing equipment.
In particular, known arrangements typically affix a ring of LEDs to the underside of rather large and bulky inspection equipment. The ring of LEDs is centered about the optical axis which extends normal to the inspection surface. This illumination geometry is useful for imaging “mirror melting” by a laser of desired art work on a diffusely reflecting metal surface. In the area affected by the laser, the diffused surface finish is melted to convert that surface area into a highly specular surface finish. This specular surface finish reflects the low-angle dark field illumination off at an equivalent low-angle causing it to appear dark in the field of view. The diffuse background finish reflects some of the incident low-angle illumination along the optical axis into the camera lens and hence that area appears bright. This combination causes the “mirror melting” laser mark to appear in high contrast, e.g. black on a white surface, rendering it fairly easy to decipher by conventional machine vision systems.
If the lead frame surface finish is highly specular, however, the dark field illumination geometry described above will cause the surface to appear black, hence rendering invisible any “mirror melting” art work, e.g. a dark field on a dark field. On such a highly specular surface for laser etching to be visible under a dark field illumination the surface must be optically “roughed up” by the laser. For example, the surface must be etched so as to form small craters or pits. Under dark field illumination, only the rim of the laser pits will reflect light to the camera while the valleys of the pits will reflect the light to the surrounding environment. If the pits are small enough and spaced closely enough together they can be made to appear as a “solid” feature. If the pits are isolated and enlarged, however, they appear as bright rings on a dark background, potentially causing problems with the inspection algorithms currently used in prior art systems.
SUMMARY OF THE INVENTION
Wherefore, it is an object of the present invention to overcome the aforementioned problems and drawbacks associated with the prior art designs.
The present invention relates to an miniature inspection system for observing an object, where the inspection system has a camera, an illumination source associated with a diffuser, a field lens and a penta-prism. The inspection systems provides bright field illumination to a desired surface.
Additionally, the illumination source provides for diffused illumination of the object to be observed. In applications where the marks on the object being observed are relatively small, the illumination source does not have to be significantly larger in size than the camera aperture itself.
The term “diffuse”, as used in this specification and the appended claims, means a light source which is dispersed over a broad range of incident angle of azimuth and elevation with respect to the object being observed, and the light source approaches complete coverage over the area where the light is directed, i.e. greater than 25% of the possible angular range of incident light. The term “concealed”, as used in this specification and appended claims, when referring to the diffuser and the object to be inspected, means that the surface emitting the diffused light from the diffuser is positioned such that the emitting surface of the diffuser can not directly illuminate the object, i.e. only indirect illumination of the object by reflection of light off the beam splitter or the side wall(s) of the housing or supplying light through the beam splitter can occur.
Further objects and advantages of the present invention are apparent from the following description and disclosure, references being made to the drawings setting forth features of the present invention in greater detail.
REFERENCES:
patent: 4618938 (1986-10-01), Sandland et al.
patent: 5386293 (1995-01-01), Barnard et al.
patent: 5420689 (1995-05-01), Siu
patent: 5623303 (1997-04-01), Inoue et al.
patent: 5867741 (1999-02-01), Maruyama et al.
patent: 5877494 (1999-03-01), Larsen et al.
Britton Howard
Davis and Bujold
Diep Nhon T
Northeast Robotics LLC
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