Optics: measuring and testing – Shape or surface configuration – Triangulation
Reexamination Certificate
2000-02-17
2002-12-17
Pham, Hoa Q. (Department: 2877)
Optics: measuring and testing
Shape or surface configuration
Triangulation
C356S237500
Reexamination Certificate
active
06496270
ABSTRACT:
TECHNICAL FIELD
This invention relates to methods and systems for automatically generating reference height data for use in a three-dimensional inspection system. The invention is particularly well adapted for use in 3D inspection systems for solder paste and component inspection where 3D data is to be obtained from at least one reference region of the circuit. A baseline (zero) reference height data is used to calculate the height of paste, leads, or components. Other applicable calculations and measurements include area, volume, x & y position and orientation.
BACKGROUND ART
Over the past several years, the use of 3D inspection for solder paste, components, microelectronic assemblies etc. has proven to be beneficial for both process control and random defect detection. In particular, 3D systems have shown capability of correlating defects at the end of line (i.e., electrical test) with solder paste volume. Hence, 3D process control can be used to maximize yield. Unfortunately, because board warpage is on the order of the inspection tolerance, and additional stackups include tilt and positioning of the board, some method of finding a baseline local reference plane or surface is needed.
The data to provide such a reference may be obtained from bare or covered conductor traces, pads, 3D fiducials, board fiducials, ground planes, or fiberglass backgrounds. Specially fabricated opaque 3D fiducials which have built-in contrast and predetermined locations, would perhaps be ideal but are not practical in many cases due to retooling cost. Therefore, data from the circuit boards, the configurations of which vary greatly, is needed.
SMT boards are being produced with increasing density and, when vision systems are utilized for inspection, time-consuming setup procedures are often required to “teach” the inspection locations and criteria for 3D inspection. In contract manufacturing environments, where changeover is frequent, time-consuming setup reduces the value of the vision system in the overall process. In contract manufacturing environments changeover is so frequent that use of CAD data and supplementary data like Gerber files becomes unwieldy due in part to limited availability of such information.
Although the use of CAD download to specify interconnect locations (i.e., chip pad sites) has mitigated the problem to some degree, the CAD data often lack specific, or at least the best, information needed for 3D inspection. 3D inspection and measurement systems require a height reference for accurately determining the height, area, and volume of solder paste and/or lead or component height, presence/absence, and position (x,y, and orientation). For example, it is desirable to place inspection windows on bare conductor pad regions in close proximity to a paste deposit, but this is rarely possible because available pad areas will be covered by paste. In order to define an accurate height reference plane at the feature to be inspected, numerous reference sites surrounding the feature need to be defined. Special board designs to place fiducials at predetermined locations are possible, but rarely practical because of board re-tooling and design costs. As a result, traces on the board, which may be covered by solder mask, are often manually specified by the user to provide reference height information. Manually identifying reference points to do 100% inspection of a large (18″×18″) board can take several hours. Contract manufacturers require the programming of such a board to be less than 30 minutes, and preferably much less.
A system which provides the benefit of three-dimensional inspection, which is preferably 100% of every board, yet provides a method for fast, automatic learning, is advantageous. Built-in error detection is particularly advantageous in contract PCB manufacturing environments where frequent changeover is required and many board designs are produced in relatively low volume.
Mengel, P., “Automated Inspection of Solder Joints on PC Boards By Supplementary Processing of 3D and Gray-Level Images”, IECON 1990, November 1990 discloses the use of 3D and gray-level information for PCB inspection, including the use of CAD/CAM data for specifying the geometric positions and tolerances of components. In the absence of CAD data, a “teach-in” on a sample PCB is performed. “An interactive interface” is disclosed which permits correction or optimization of testing instructions for special format devices.
U.S. Pat. No. 5,088,828, Doemens et al., discloses the use of evaluation windows on a PCB for recognizing defects of interconnects and defines zero datum. A triangulation-based 3D sensor is used for measurement. Also disclosed is the use of a detector for fluorescent light arising upon incidence of the laser beam on the insulating material. The invention includes a step of comparing the dimensions of the interconnect with stored spacing criteria by identifying the width or areas having a height of zero. Scan fields offset with respect to one another are used to determine warping.
U.S. Pat. No. 5,450,204, Shigeyama et al., discloses a 3D inspection machine for measuring the position, area, and thickness of amount of creamed solder and comparing with stored reference data. The sensor is effectively a phased shifted 3D Moire system. An inspection file is produced by downloading CAD data for a screen mask.
U.S. Pat. No. 5,822,449, Kobayashi et al., discloses a method for teaching without exclusively using the inspection machine. Data about pictures and decision criteria are stored and composed, and by being externally obtained, avoids manual entry operation. An adjustment step is provided for parameters including the positions of components, data of lands, bridge detection, and mounting qualities. Also, step ST17 is teaching modification to modify data which results if the “improper portion is found as the results of the automatic inspection”.
U.S. Pat. No. 5,465,152, Bilodeau et al., discloses the use of opaque fiducials as index pads (reference points) “designed in” at predetermined locations of a substrate for coplanarity and warpage determination. This approach generally must be included at the board design stage which would incur substantial tooling costs and delays.
U.S. Pat. No. 5,862,973, Wasserman, combines video camera inspection with structured light for solder paste detect detection and statistical process control.
U.S. Pat. No. 5,902,353, Raymond, discloses relative height measurement of components where “key points”, which may be points on the board under test or on components, are used and the height measurement compared with a reference to determine faulty placement. The preferred height detection system disclosed is a triangulation-based PSD point detection system. Component-bycomponent programming, automatic or manual, can include parts list, component and board geometries, machine instructions, and solder paste stencil information. The use of a miniature video camera is suggested for manual fiducial alignment and for manually specifying key points for each component. The set of key points for component measurement preferably includes at least one reference.
None of the prior art references teach or disclose a method and system for automatic learning of reference points in a 3D inspection machine, wherein a machine vision subsystem automatically locates and analyzes image data for establishing a baseline height reference.
DISCLOSURE OF INVENTION
The primary object of the present invention is to provide a method and system for automatically generating reference height data for use in a three-dimensional inspection system.
In carrying out the above object and other objects of the present invention, a method is provided for automatically generating reference height data for use in a 3D inspection system. The method includes automatically determining positional location of at least one local reference area on an object separate from but relative to a predetermined site on the object.
Preferably, the step of automatically determining includes the steps of i
Kelley Robert W.
Rohrer Donald K.
Svetkoff Donald J.
Weisgerber John J.
Brooks & Kushman P.C.
GSI Lumonics Inc.
Pham Hoa Q.
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