X-ray or gamma ray systems or devices – Specific application – Tomography
Reexamination Certificate
2001-03-21
2001-11-27
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Tomography
C378S058000, C378S098800
Reexamination Certificate
active
06324249
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to laminography, and more specifically to systems which use an electronic linear scan method for high speed, high resolution generation of laminographic images.
BACKGROUND OF THE INVENTION
Rapid and precise quality control inspections of the soldering and assembly of electronic devices have become priority items in the electronics manufacturing industry. The reduced size of components and solder connections, the resulting increased density of components on circuit boards and the advent of surface mount technology (SMT), which places solder connections underneath device packages where they are hidden from view, have made rapid and precise inspections of electronic devices and the electrical connections between devices very difficult to perform in a manufacturing environment.
Many existing inspection systems for electronic devices and connections make use of penetrating radiation to form images which exhibit features representative of the internal structure of the devices and connections. These systems often utilize conventional radiographic techniques wherein the penetrating radiation comprises X-rays. Medical X-ray pictures of various parts of the human body, e.g., the chest, arms, legs, spine, etc., are perhaps the most familiar examples of conventional radiographic images. The images or pictures formed represent the X-ray shadow cast by an object being inspected when it is illuminated by a beam of X-rays. The X-ray shadow is detected and recorded by an X-ray sensitive material such as film or other suitable means.
The appearance of the X-ray shadow or radiograph is determined not only by the internal structural characteristics of the object, but also by the direction from which the incident X-rays strike the object. Therefore, a complete interpretation and analysis of X-ray shadow images, whether performed visually by a person or numerically by a computer, often requires that certain assumptions be made regarding the characteristics of the object and its orientation with respect to the X-ray beam. For example, it is often necessary to make specific assumptions regarding the shape, internal structure, etc. of the object and the direction of the incident X-rays upon the object. Based on these assumptions, features of the X-ray image may be analyzed to determine the location, size, shape, etc., of the corresponding structural characteristic of the object, e.g., a defect in a solder connection, which produced the image feature. These assumptions often create ambiguities which degrade the reliability of the interpretation of the images and the decisions based upon the analysis of the X-ray shadow images. One of the primary ambiguities resulting from the use of such assumptions in the analysis of conventional radiographs is that small variations of a structural characteristic within an object, such as the shape, density and size of a defect within a solder connection, are often masked by the overshadowing mass of the solder connection itself as well as by neighboring solder connections, electronic devices, circuit boards and other objects. Since the overshadowing mass and neighboring objects are usually different for each solder joint, it is extremely cumbersome and often nearly impossible to make enough assumptions to precisely determine shapes, sizes and locations of solder defects within individual solder joints.
In an attempt to compensate for these shortcomings, some systems incorporate the capability of viewing the object from a plurality of angles. One such system is described in U.S. Pat. No. 4,809,308 entitled “M
ETHOD
& A
PPARATUS FOR
P
ERFORMING
A
UTOMATED
C
IRCUIT
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OARD
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OLDER
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UALITY
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”, issued to Adams et al. The additional views enable these systems to partially resolve the ambiguities present in the X-ray shadow projection images. However, utilization of multiple viewing angles necessitates a complicated mechanical handling system, often requiring as many as five independent, non-orthogonal axes of motion. This degree of mechanical complication leads to increased expense, increased size and weight, longer inspection times, reduced throughput, impaired positioning precision due to the mechanical complications, and calibration and computer control complications due to the non-orthogonality of the axes of motion.
Another approach for acquiring shadowgraph X-ray images uses a slit scan geometry with an electronic detector to reduce scattering and interference from adjacent regions of the object being inspected. For example, U.S. Pat. No. 4,383,327 entitled “R
ADIOGRAPHIC
S
YSTEMS E
MPLOYING
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ULTI
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INEAR
A
RRAYS
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ADIATION
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ETECTORS
”, issued to Kruger describes a scanning radiographic system which uses a multi-linear array operating in a time delay and integration (TDI) mode to generate a slit-scan shadowgraph image of a moving object. Kruger discloses the use of a beam of electronic radiation (e.g., X-rays) generated by a suitable source of electronic radiation. The beam of electronic radiation is directed towards, and aligned with, an array of electronic radiation detectors. Each of the detectors on the array is adapted to generate a signal having a magnitude proportional to the amount of radiation it senses. The array also includes, as an integral part thereof, signal processing capabilities whereby the signals generated by each of the detectors may be stored in respective storage elements. These stored signals, at controlled time intervals, are all shifted to the storage elements of other, adjacent, detectors. Once the signals have been shifted, the signals are augmented by new signals, if any, generated by the respective detectors of the storage elements in which the signals are stored. After having been shifted through several storage elements, these augmented signals may exit from the array to be further processed and conditioned so as to enable an image to be created through a suitable visual system. In connection with the above shifting and processing of radiation signals, the opaque specimen is passed between the source of electronic radiation and the array at a controlled speed and in a known pattern. This controlled speed is synchronized with the controlled time intervals at which the signals are shifted from storage element to storage element. Furthermore, the shifting pattern—that is the sequence that the signals follow as they are shifted from storage element to storage element within the array—is designed to be the same as the movement pattern of the opaque specimen through the beam of electronic radiation. When the shifting pattern of the detector signals is the same as the movement pattern of the opaque specimen, a non-blurred image may be generated. That is, each pixel, or small area, of the image is generated from radiation that passes through a corresponding small area of the specimen. At any instant of time, this radiation falls upon a given detector and generates a signal for that pixel. As the specimen moves, causing the radiation passing through the same small area thereof to likewise move and fall upon an adjacent detector, the pixel signal generated prior to the movement is shifted to the storage element associated with the detector receiving the radiation after the movement. At each storage element, the resolution of the pixel signal is augmented by having it updated to reflect the amount of radiation passing through the corresponding area of the specimen at that particular time. In this fashion, each pixel in the accumulated image results from an integration process. This process is commonly referred to as a time delay and integration (TDI) mode. As shown in Kruger, the angular relationship between the X-ray source, the specific row of image points of the body being examined and the image-recording elements is substantially the same during the production of the X-ray image, i.e., the procedure results in a traditional slit scan transmission X-ray showgraph or radiograph of the object. This TDI (Time Delay and Integration) method of scanni
Agilent Technologie,s Inc.
Porta David P.
Yun Jurie
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