Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
1998-07-08
2001-09-18
Mancuso, Joseph (Department: 2621)
Image analysis
Applications
Manufacturing or product inspection
Reexamination Certificate
active
06292580
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an illumination system for use in conjunction with wire bonding equipment used in the fabrication of semiconductor devices.
2. Brief Description of the Prior Art
In the fabrication of semiconductor devices, one of the operations generally required involves the bonding of wires between two bonding locations, generally between bond pads on the semiconductor device and lead fingers of a lead frame. This bonding operation requires the use of a wire bonder. A wire bonder uses fine gold wire to couple the bond pads on the semiconductor chip to the individual leads or pins to which connection is to be made, such as, but not limited to, the lead fingers of the lead frame. With the continued diminution in the geometry of semiconductor devices as well as the components within and on the semiconductor devices, it has become increasingly difficult to accurately locate the bond pads and leads or pins to which connection must be made. Bond pads are now approaching dimensions of 5 mils or 25 microns. It is necessary that the bonder know precisely where the connections are to be made on a chip by chip basis since the bond locations can differ from chip to chip, even on essentially identical chips.
To mitigate this problem, a machine-vision system was developed to locate the exact positions where these connections or bonds are to be made. The vision system automatically magnifies, displays, measures and locates different parts of the device at which bonds are to be made. This vision system includes mainly electronics, software, camera, optics and illumination units. Since ambient light is generally insufficient to properly illuminate the chip and lead frame components to which the bond is to be made, illumination units are required to provide the required light to make visible the device to which a bond is to be made while the camera takes pictures through the optics. This picture is digitally stored in the electronics hardware and is digitally processed by the software.
To view different parts of the object, different kinds of lighting are required. In general, an axial light is used to view the die surface because the die surface is generally very smooth and reflects incident light without scattering. Accordingly, incident light directed parallel to an optical axis normal to the surface of the die is reflected back almost entirely parallel to the optical axis. An off axis light is used to view the lead frame which has a generally rough surface and scatters light impinging thereon. The light on the lead frame must be applied evenly to avoid dark spots in the picture, the dark spots (e.g. shadows) introducing features which are not actually a part of the structure being viewed and therefore being undesirable. Accordingly, for viewing of the lead frame, incident light comes from around the object and is diffused so that it scatters in all directions and at all angles. The amount of scattering depends upon the surface roughness of the light conductor which is preferably a highly light transmissive plastic, preferably an acrylic such as Plexiglass or a polycarbonate such as Lexan. The degree of diffusion can vary, depending upon the type of product being bonded. Axial light is also referred to herein as “top light” while off axis light is also referred to herein as “ring light”.
In general, in prior art illumination systems for use in conjunction with the bonding operation in semiconductor fabrication, two large moving air-cooled light boxes located at an isolated region on the bonding machine are used to generate the required light. This light is collected using light collecting reflectors and is transferred to the working area using flexible fiber optic cables. At the working area, these fiber optic cables are formed into a standard shape to provide the required type of lighting. This method of generating a large amount of light at an isolated area and transferring it to the required location is highly inefficient and expensive.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided a patentably novel illumination system to increase the efficiency and decrease the cost of illumination for wire bonders while providing additional features such as software programmability of the illumination system. Multiple units of miniature light sources, preferably incandescent bulbs, light emitting diodes (LEDs) or a combination thereof are used to produce the required light. These miniature light sources are mounted in a specially designed light transmitting mount which is a light conductor which is preferably a highly light transmissive plastic, preferably an acrylic such as Plexiglass or a polycarbonate such as Lexan. The mount collects the light and directs it in a controlled fashion with minimal energy loss.
Briefly, there are provided a top light, a ring light and, optionally, an oblique light. The ring light has a central bore extending therethrough along the ring light axis and is shaped to transmit light emanating within the ring light in a conical, circular or rectangular pattern which surrounds the area to be illuminated. For viewing of the lead frame, the incident light comes from around the object and is diffused so that it scatters in all directions and at all angles. The amount of scattering depends upon the surface roughness at the edge of the light conductor from which the light exits the light conductor. Maximum light is passed through the light conductor by shaping the exterior surface of the ring light to reflect light emanating from the light sources along or toward the ring light axis and at the device being fabricated whereby a sufficient amount of the scattered light is reflected back along the axis of the ring light. This is generally accomplished by having the exterior surface parabola-shaped, though other combinations of geometries and light source positioning can also provide the desired result. The central bore along the optical axis permits the reflected light to travel through the bore to the optics and back to the camera as in the prior art. The ring light is fabricated from a highly light transmissive, preferably moldable medium, such as, for example, acrylics and polycarbonates of the types previously described herein.
A top light is provided to pass a light beam through the bore along the axis of the ring light whereby the light passes through the beam splitter and impinges on the device being fabricated and is then reflected back to the beam splitter and reflected therefrom to the camera in conjunction with optics in the optical path as in the prior art. The top light can have any combination of shape and positioning of the one or more light sources therein to provide a light beam along the ring light axis and through the bore therein. This light is reflected back through the bore in the ring light.
An optional oblique light has a shape and construction similar to the top light and is positioned to provide a light beam to the device being fabricated at some acute or obtuse angle, as required for a special purpose. All of the lights are controllable individually by software associated with the machine vision system.
Incorporation of the design in accordance with the present invention not only eliminates the problems faced with the current system, but also provides added advantages, among these being cost savings, better control over the illumination level, elimination of unreliable moving parts, no cooling requirement, high efficiency in use of generated light, small and light weight, fast response time and longer means time between failures.
REFERENCES:
patent: 5153668 (1992-10-01), Katzir et al.
patent: 5394246 (1995-02-01), Sugawara
patent: 5535006 (1996-07-01), Telschow et al.
patent: 5686994 (1997-11-01), Tokura
patent: 5859924 (1999-01-01), Liu et al.
Harris Charles K.
Koduri Sreenivasan K.
Woodall Joe D.
Wright Lance C.
Bayat Ali
Brady III Wade James
Mancuso Joseph
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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