Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-11-16
2001-06-05
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S202100
Reexamination Certificate
active
06243188
ABSTRACT:
FIELD OF INVENTION
The invention relates generally to light beam scanning systems, and more particularly to mirrors for use in such systems.
BACKGROUND OF THE INVENTION
Laser scanning systems, such as those used for marking, laser imaging, laser drilling, semiconductor processing, and other material processing, and other similar application of XY scanning, include two mirrors that position a laser beam relative to a target. The laser beam is first directed over a predetermined horizontal range by an X-mirror. The Y-mirror then intercepts the beam and re-directs it over a predetermined vertical range. The Y-mirror must be long enough to intercept the beam over the entire horizontal range associated with the X-mirror. Accordingly, the Y-mirror is generally larger, and thus, heavier and has greater inertia, than the X-mirror.
The two mirrors must move with equal speed for precise re-direction of the laser beam. Accordingly, the maximum speed with which the mirrors can be driven is determined by the maximum rate at which the larger, heavier mirror smoothly accelerates. The rate of acceleration of a given mirror is essentially limited by the resonant frequency of the mirror, since driving the mirror any harder results in imprecise movement. Generally, the larger Y-mirror has a lower resonant frequency, and thus, a slower rate of acceleration.
To maximize the rate of acceleration, the inertia of the mirror should be as low as possible and the mirror should also be as stiff as possible, so that the mirror responds rapidly and precisely to a drive signal. Accordingly, there is a trade-off between minimizing the weight, and thus, the inertia, of the mirror, and maximizing the stiffness of the mirror.
In prior systems, the weight and inertia of the Y-mirror is minimized by undercutting the comers of the mirror. The cuts are typically symmetric about an axis of symmetry, which is perpendicular to the axis of rotation. The length of the mirror along its axis of rotation is fixed by the rotational range of the X-mirror and the beam aperture, and thus, the undercuts must leave intact an elongated center span of the mirror. The stiffness of the mirror is also essentially provided by the center span. Accordingly, the sizes of the corner cuts are determined as a trade-off between minimizing the weight of the mirror and leaving enough material around the center span to provide sufficient stiffness.
The speed with which the mirrors can be driven determines how quickly the system can, for example, produce a desired mark or image, or the number of holes that can be drilled per second, and so forth. There is thus a need for a laser scanning mirror that can be driven rapidly, without adversely affecting the precision with which it is positioned.
SUMMARY OF THE INVENTION
The invention is a laser scanning system mirror that is non-symmetrical about its axis of symmetry, such that the mirror is stiffest at the bottom end, that is, at the end by which the mirror is driven. The greater stiffness at the bottom of the non-symmetrical mirror, and preferably up to its center of inertia, results in an increase in the resonant frequency of the mirror. Accordingly, the non-symmetrical mirror can accelerate more rapidly than a conventional mirror of the same length, even though the non-symmetrical mirror weighs more than the conventional mirror. Preferably, the non-symmetrical mirror is used as the Y-mirror in a laser scanning system.
The non-symmetrical mirror may have undercut top corners, with the bottom corners left essentially intact. Alternatively, the mirror may have a sloped back face, such that the thickness of the mirror decreases from the bottom of the mirror to the top. As appropriate, stiffeners may be attached to the bottom end of the mirror.
Examples of application in which the present invention is particularly advantageous include electronic manufacturing and repair operation in which a light beam is used to perform profiling, marking, cutting, drilling and trimming of silicon and other semiconducting material, the trimming and cutting of thick and thin films on semiconductors, the drilling of via holes in printed circuit boards, and the inspection of solder paste and component placement on printed circuit boards, among other.
REFERENCES:
patent: 3998530 (1976-12-01), Kaschak
patent: 4364000 (1982-12-01), Burke, Jr.
patent: 4655543 (1987-04-01), Montagu
patent: 4874215 (1989-10-01), Montagu
patent: 5150249 (1992-09-01), Montagu
patent: 54-119259 (1979-09-01), None
Pelsue Kurt
Stukalin Felix
Cesari & McKenna LLP
General Scanning Inc.
Phan James
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