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Systems and methods for measuring sample surface flatness of continuously moving samples

Systems and methods for measuring sample surface flatness of continuously moving samples description/claims

This application is a continuation of U.S. Non-Provisional Patent Application No. 11/241,318, entitled “Systems and Methods for Measuring Sample Surface Flatness of Continuously Moving Samples,” filed Sep. 30, 2005, which claims priority under 35 U.S.C. 119 to U.S. Provisional Patent Application No. 60/617,843, entitled “Machine for Measuring Sample Surface Flatness of Continuously Moving Parts or Sheet Material,” filed Oct. 13, 2004. The complete disclosure of each of the foregoing priority applications is hereby fully incorporated herein by reference.

The invention relates generally to measuring sample surface flatness of objects, and more particularly to quantifying the surface flatness of continuously moving samples using a shadow moiré image processing technique and phase-sensitive analysis.

Surface flatness is a common measurement specification over a wide range of manufacturing industries. Flatness critically affects, for example, the reliability and assembly yield of electronic products, the cosmetic appearance and handling characteristics of paper products, and the mechanical fit and functionality of fabricated metal components. Non-flatness, or warpage, is a frequent problem in manufacturing, due to inadequacies in design, materials, and/or processing of components. The ability to distinguish and reject components whose non-flatness exceeds user specifications is valuable on the production line because it allows the manufacturer or user to avoid problems in later manufacturing steps, maintain product quality, and recognize processing problems early.

Shadow moiré measurement techniques have previously been applied to measure surface flatness in printed circuit boards and other electronic packaging components. Shadow moiré is an optical method for measuring relative vertical displacement of (semi-) continuous opaque surfaces. It is a full-field technique, i.e., it simultaneously acquires optical data across an entire sample. Shadow moiré is based on the geometric interference of a shadow grating projected on the sample surface and a real grating on a flat reference surface. For example, when a printed circuit board is viewed through a grating and a shadow of the grating is cast upon the surface of the printed circuit board, the shadow and the grating can interact to create a shadow moiré fringe pattern that is indicative of the warpage of the surface of the printed circuit board.

FIG. 1 illustrates an exemplary system 100 for measuring surface flatness of a sample 105 utilizing traditional shadow moiré measurement techniques. The system 100 comprises a light source 110, a grating 120 suspended above a sample 105, and a camera 115, e.g., a charge coupled device (CCD) camera, associated with a computer 125. The grating 120 is of the Ronchi type, comprising a generally planar plate of transparent material that includes multiple parallel and evenly spaced opaque lines extending across the surface of the plate. Typically, the grating 120 has a periodicity of 50 to 500 lines per inch. The center-to-center distance between the lines, the pitch (“P”) of the grating, is constant. The grating 120 is generally parallel to the sample 105. The light source 110 is a continuous or pulsed white light source of the line source type, wherein the line is parallel to the lines of the grating 120 surface.

FIG. 2 illustrates an exemplary instance 200 of the shadow moiré technique. Referring to FIGS. 1 and 2, the light source 110 illuminates the grating 120 and the sample 105 at an oblique angle of incidence. The light 111 projects a shadow 215 of the grating 120 (i.e., a shadow of the opaque lines of the grating 120, referred to herein as a “shadow grating” 215) onto the sample 105. The camera 115 captures one or more images 112 of the grating 120, the sample 105, and the shadow grating 215. The camera typically observes the image(s) 112 at an angle of 0° (normal). A stationary support structure (not shown) holds the sample 105 in place during the period in which the camera 115 captures the image(s) 112.

The overlap of the shadow grating 215 and the real grating 120 in the image(s) 112 is a periodic function of the distance between them. When the surface of the sample 105 is curved or warped, a series of dark and light fringes (moiré fringes) are produced as a result of the geometric interference pattern created between the reference grating 120 and shadow grating 215. The moiré fringes are indicative of the warpage of the sample 105. In other words, the moiré fringes correspond to contour lines of the topography of the upper surface of the sample 105. The computer 125 associated with the camera 115 comprises software that can quantify the warpage from the shadow moiré fringe pattern.

FIG. 3 is a schematic view of an exemplary shadow moiré fringe pattern 300 that could be received by the camera 115 (FIG. 1) in the above-described circumstances. The shadow moiré fringe pattern 300 comprises a series of dark and light fringes 305. In general, the greater the warpage of the sample 105, the larger the number of fringes 305. Each successive fringe represents a height change of the sample surface of W, the height per fringe. W can be calculated with the following equation:

W = P

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Method for detecting surface defects on a substrate and device using said method
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Method for determining the position of a measurement objective in the z-coordinate direction of an optical measuring machine having maximum reproducibility of measured structure widths
Industry Class:
Optics: measuring and testing

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