Optics: measuring and testing – By alignment in lateral direction – With registration indicia
Reexamination Certificate
1999-03-11
2001-07-31
Kim, Robert (Department: 2877)
Optics: measuring and testing
By alignment in lateral direction
With registration indicia
C356S399000
Reexamination Certificate
active
06268920
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to registration techniques for aligning master art work films or sheets with substrates for forming printed circuit wiring on rigid or flexible printed circuit panels, and more particularly to apparatus and method for aligning art work and substrate with enhanced precision.
BACKGROUND OF THE INVENTION
Consumer demands for smaller products, at lower cost with faster operation and more features, are placing demands on the size and density of printed circuits. One of the most challenging tasks for the manufacturer of circuit boards is to form electrical connections to contact a series of drilled or individually punched holes.
Mechanically formed holes contribute large-tolerance errors to the precision of the overall circuit board, which reduces the potential for increased wiring density. In addition, the production costs of circuit boards are also affected by the use of finer drills which provide more room for circuitry but have shorter lives, and tend to wander. A costly by-product of alignment tolerance is the requirement for drilling smaller stacks of boards on the drilling machine as a result of drill wander. Drilling is already a slow and costly operation, and restriction to drilling fewer circuit boards simultaneously contributes additional costs and production delays.
A common practice for registration on existing machines is to use two CCD cameras to align the circuit board panel with master image films by observing two drilled holes across the width of the circuit board panel. As illustrated in
FIG. 1
, a typical circuit board panel includes two holes spaced apart along a horizontal, or X axis, for use in alignment. The registration of the circuit board panel to a master film is typically done with a dot on the film to be centered within the perimeter of a hole in the circuit board panel, as illustrated in FIG.
2
.
In these conventional schemes, it can be assumed that drilling tolerance is of the order of +/−20 microns, although, depending upon number of factors, mechanical drilling may only be accomplished within a tolerance of +/−75 microns, with predominantly random factors contributing to positional errors.
FIG. 3
displays a 100-hole Gaussian simulation of errors encountered in the hole location in one axis, as simulated using a random number generator. The distribution probability of the error of the ultimate hole location along a given axis is displayed in the form of a bell curve, as illustrated in FIG.
4
. In the X-axis direction, the hole locations are averaged over the two spaced holes, with resultant registration as illustrated in FIG.
5
.
When these hole locations are used to position a circuit board panel relative to an image on a master film, the drill error is reflected in misalignment of panel and film. In addition, there is a high probability that the two positioning holes in the circuit board panel will typically and frequently occupy positions with errors that are displaced in opposite directions from one another. This induces a rotational error in the panel that can increase the positional error over the drilling error, for example, by 12% on a 610×710 mm panel, as illustrated in FIG.
6
.
Alternative conventional schemes use four targets to position the panel relative to the master film, as illustrated in
FIG. 7
, by using moving cameras or multiple cameras. This provides the stability of a two-point sample in both X and Y axes and reduces the rotational error, but increases cost and reduces production rate.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention, optical targets improve registration accuracy when aligning master film images to holes in circuit board panels that are generated in accordance with the invention. One application registers the master film images to drilled holes near the outer perimeter of a printed circuit board. Accuracy of registration is based upon the impact of sample size when characterizing position data that has a random component. The position of an individual point is subject to the full error tolerance. In accordance with one embodiment of the present invention, additional samples are collected to increase the accuracy of the calculated location of the centroid or middle point of the position samples.
REFERENCES:
patent: 5170058 (1992-12-01), Berasi et al.
patent: 5643699 (1997-07-01), Waldner
Fenwick & West LLP
Kim Robert
Lee Andrew H.
Olec Corporation
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