Data processing: generic control systems or specific application – Generic control system – apparatus or process – Digital positioning
Reexamination Certificate
2001-02-23
2004-03-02
Patel, Ramesh (Department: 2121)
Data processing: generic control systems or specific application
Generic control system, apparatus or process
Digital positioning
C700S056000, C700S058000, C700S057000, C700S186000, C700S195000, C700S121000, C358S296000, C358S300000, C358S301000, C358S302000
Reexamination Certificate
active
06701197
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to the field of printed circuit board fabrication and especially to the field of fabrication of double sided printed circuit boards.
BACKGROUND OF THE INVENTION
PCT patent publication WO 00/02424, the disclosure of which is incorporated herein by reference, describes a scanning laser direct imaging (LDI) system for writing an electric circuit pattern on a printed circuit board substrate.
FIG. 1
is a reproduction of
FIG. 1
of the above referenced publication. Some details of its operation are given below. Further details of the operation and an explanation of the figure can be found in the publication. In such systems, a laser beam or beams, modulated with pattern data, is scanned across a sensitized printed circuit board substrate
78
to write a latent image of a desired electrical circuit pattern.
The substrate is optionally inverted and a second pattern in side to side alignment with the first pattern is written on the other side of the substrate. In accordance with some printed circuit board fabrication techniques, substrate layers may be sequentially laminated to previously produced substrate layers and an electrical circuit pattern is written on the outermost side of each sequentially added layer in a build up fashion. The latent patterns are developed to form etching masks on the substrate. The masked substrate is etched to form the desired electrical circuit pattern.
Among the problems which arise in printed circuit board fabrication is the side to side alignment of printed circuit patterns on various substrate layers, and mutual alignment among patterns printed on various substrate layers. One method utilized to obtain suitable alignment is disclosed in the embodiment of
FIGS. 1
,
2
,
14
,
15
and
16
, of the publication (
FIG. 2
is a reproduction of
FIG. 14
of the above referenced publication.). PC board substrate
78
is formed with a plurality of holes
150
at least some of which are preferably aligned, at least roughly, in the scan direction. A base on which the substrate is mounted is formed with openings larger than the holes in the substrate and the holes in the substrate are positioned generally in correspondence to the openings in the base. One or more detectors
152
are positioned below the scan line of the scanner.
As the printed circuit board is transported past the scan line, the scanner scans across the holes in a substrate layer. Based on signals detected by detector
150
via the holes and the openings, the locations of the holes in the substrate layer with respect to the scanner are detected. The base is optionally rotated and scanning of the printed circuit board substrate then commences with the position of the scanning lines pattern being referenced to the location of the holes.
It should be noted that the position of the scanning beam that passes through holes
150
is scanned together with another beam that impinges a scale
80
that is used to determine the true instantaneous (scan dimension) position of the beam in the scan direction. Furthermore, the relative cross-scan position of the holes (and thus the board) is determined utilizing a second scale, typically operatively associated with the base.
When scanning the second side of the substrate, the procedure is repeated to determine the position of the holes and thus the position of the already scanned pattern on the first side of the substrate (or the position of already scanned patterns on lower layers in a build up board) with respect to the coordinate space of the LDI system. This allows for the data in the scanning of each subsequent side to be aligned with respect to previously scanned sides.
Optionally, an additional series of holes in the board and pins on the base, or a guide rail along the base, may be used for rough alignment of the substrate. Such pins are shown in
FIG. 16
of the reference. In some conventional systems, only such mechanical means are used for aligning the patterns on the two sides of the substrate. The system may include means for rotating the board to improve alignment.
Measuring systems employing imagers, and especially CCD cameras, are known in the art for use in determining the positioning of a PC board in an LDI scanner. Generally, such cameras may be used to detect various markings on a printed circuit board laminate layer, or to detect an edge of a printed circuit board laminate layer and to relate the detected position of the marking or the edge with a scanner position.
SUMMARY OF THE INVENTION
An aspect of some embodiments of the invention is concerned with alignment of the images written on two sides of a PC board.
In exemplary embodiments of the invention, no holes need be made in the printed circuit board in order to provide alignment of the images on both sides.
In some embodiments of the invention, an alignment pattern is written on a first side of the board while an image is written on another side with a scanner in predetermined orientation in relation to the alignment pattern. The scanner used to write the image is provided with at least one detector which can detect the position of the alignment pattern, when the PC board is flipped over. The position of the detector or detectors with respect to the scanner beam is precalibrated relative to the scanner, so that knowledge of the location of the alignment pattern defines the position of the already written image (on the first side now facing away from the scanner) with respect to the scanning system. The at least one detector can be, for example, at least one camera which views the alignment pattern when the PC board is flipped over. This allows for the alignment of the image to be written on the second side with that already written on the first side.
Optionally, the cameras are mounted on a calibrated rail system that allows for at least limited motion of the cameras in the cross scan direction. This allows the at least one camera to move so that it can image the alignment pattern. The provision of this motion is desirable (but not always required) to accommodate the inexact positioning of the PC board when it is flipped over.
Alternatively or additionally, the scanner is equipped with at least one additional camera or other imager, that can view the alignment pattern before flipping the PC board. Such a system is described in Applicant's copending U.S. patent application Ser. No. 09/708,160 filed Nov. 8, 2000, the disclosure of which is incorporated herein by reference. This document describes a system by which an alignment pattern, such as that described above, is imaged and the location of the scanned image is determined with respect to the camera system. Use of such a system helps to calibrate the locations of images determined by the cameras that view the flip side of the PC board with the scanner.
Alternatively or additionally, the positional relationship between the cameras that view the two sides of the PC board is determined by providing a substrate with holes that can be imaged from both sides of the board. This allows for the determination of a transformation between the coordinate systems of the cameras that view both sides. One non-limiting method for accurate determination of the positions of the holes in the coordinate systems is described, for example in PCT publication WO 00/02424, the disclosure of which is incorporated herein by reference.
In other embodiments of the invention, an alignment pattern is written on the second side of the board at the same time as the scanner image is being written on the first side of the board. This pattern can be provided by a fixed or movable source, for example a light source that writes a reticule on the second side. This alignment pattern is thus in alignment with the image written on the first side. When the PC board is turned over, the alignment pattern is imaged by at least one detector (such as at least one camera) that views the same side of the board that is available for scanning (writing) by the scanner. The scanner is pre-calibrated with the cameras (for ex
Alon Dan
Ben-Ezra Barry
Gino Hanan
Gross Abraham
Kling Boris
Fenster & Company
Orbotech Ltd.
Patel Ramesh
LandOfFree
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