Etching a substrate: processes – Nongaseous phase etching of substrate – With measuring – testing – or inspecting
Reexamination Certificate
1998-06-26
2001-02-27
Gulakowski, Randy (Department: 1746)
Etching a substrate: processes
Nongaseous phase etching of substrate
With measuring, testing, or inspecting
C216S013000, C438S007000, C438S016000
Reexamination Certificate
active
06193899
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of flexible or rigid circuit board fabrication and to the field of chemical milling, and, more specifically, to a system and method for optically aligning films and optically aligning substrates to films that are used to fabricate flexible or rigid circuit boards or used as part of a chemical milling process.
BACKGROUND OF THE INVENTION
A circuit on a printed circuit board is created by placing a sheet of film having the circuit design over a copper-clad panel that is coated with photosensitive material. When the film is exposed to light, the photosensitive coating on the panel is chemically altered. After further processing, select portions of the copper on the circuit panel are etched away in accordance with the circuit pattern on the film. This creates a circuit pattern on the panel.
Printed circuit boards often include many layers of circuitry, and each separate circuit requires a different film. It is important that the all the circuits on the printed circuit board be properly aligned. Thus, when the printed circuit board is being created, the films having the circuit designs must be properly aligned. The films are usually aligned two at a time, one film being above the other (though not necessarily touching).
In addition, a film and a substrate may also have to be aligned. Examples of a substrate include a panel used to make a printed circuit board, a metal sheet for chemical milling, or flexible circuit bearing material, such as polyimide. One reason why a substrate and a film may have to be aligned is because the substrate may include holes or layers of circuitry, and the film must be aligned with these features on the substrate.
A film may also need to be aligned with a fixed reference plate, such as a punch press base. A film is aligned to a punch press base for the purpose of punching registration holes.
Registration schemes that align the films to each other or a film to a substrate are known, and one such scheme uses a camera. In the camera scheme, one film or substrate has a black spot on it, and the other film or substrate has a clear spot on it. The clear spot is larger in size than the black spot. The camera, which is placed above or below the film/film layer or film/substrate layer in vertical alignment with the clear spot, views the film or substrate having the black spot while the that film or substrate is moved. The camera produces a video signal, which is sent to a video capture board. The capture board conditions the video signal for readability by a computer, which is attached to the capture board. The computer determines when the clear spot is centered above the black spot, and, when this happens the two films or the film and substrate are properly aligned.
The camera scheme has several disadvantages. First, it is expensive because it requires a camera, lens, illumination, a precise camera mount, a video capture board, a powerful computer, and expensive software. Additionally, the camera scheme also requires a skilled operator because the camera must be properly focused and the light intensity must be properly set. The camera scheme is also slow, as it can take up to several seconds to align the films. Therefore, it is desirable to have a faster, lower cost system that requires minimal operator intervention to align films or substrates.
SUMMARY OF THE INVENTION
The present invention provides a system and method for optically aligning films to films, films to substrates or reference points, and substrates to substrates. The optical alignment system of the present invention includes a light source, an upper film or substrate, a lower film or substrate, and a photodetector. In one embodiment of the present invention, the upper film or substrate has an aperture, and the lower film has a set of four apertures, each of the set of four apertures being smaller than the aperture of the upper film or substrate. The light source is positioned above the upper film or substrate, and the photodetector is positioned below the lower film or substrate. The light source shines light on the upper film or substrate at a point directly above the set of four apertures in the lower film or substrate. In one embodiment, the photodetector is divided into four quadrants, and each quadrant detects the amount of light traveling through a different one of the four apertures. The position of the upper film is adjusted until each quadrant detects a substantially equal amount of light. When each quadrant detects a substantially equal amount of light, the aperture in the upper film or substrate is centered over the set of four apertures in the lower film or substrate, and the upper film or substrate is aligned with the lower film or substrate.
In an alternate embodiment of the present invention the light source is placed below the lower film or substrate, and the photodetector is placed above the upper film or substrate. The number of apertures and the pattern of the apertures in the films and substrates can vary.
The invention described herein may be used to align films and substrates used to make printed circuit boards. There are also other applications for the present invention. These applications include aligning components, such as lead frames, used in the manufacturing of integrated circuits, aligning shadow masks for cathode ray tubes, and aligning close tolerance mechanical parts, such as rotary encoders. The invention described herein could also be used in the graphical arts field to align exposures on printing plates and to register screen print images, such as those used to print CD ROM's or textiles. The present invention may also be used to monitor the relative positions of films and substrates.
REFERENCES:
patent: 3207904 (1965-09-01), Heinz
patent: 5604354 (1997-02-01), Lauverjat
patent: 0298642. (1989-01-01), None
patent: 0298642 (1989-01-01), None
patent: 0626623 (1994-11-01), None
patent: 2435080 (1980-03-01), None
patent: 58-100853 (1983-06-01), None
patent: 58100853 (1983-06-01), None
Ahmed Shamim
Fenwick & West LLP
Gulakowski Randy
LandOfFree
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