Electronics circuitry manufactured using variations on standard printing techniques has been demonstrated. During the printing process, various conducting, insulating, and semiconducting layers are deposited on a substrate. The materials in these layers take the place of inks in conventional printing. Once all of the layers have been deposited and cured, the result is a working electronic device that can be produced at high volume and at low cost.
Feature size and layer thickness in prototype production runs are in the range of a few microns to a few hundred microns. These features will likely shrink in size as new materials are developed for higher performance applications.
The area, thickness, and registration of various layers are important to the correct functioning of the printed circuit components. Some of the materials, particularly precious-metal based conductive inks, can be costly to waste. The speed with which reel-to-reel or web printing processes can run means that processes must remain under tight control to avoid the manufacture of large volumes of non-functioning product.
An inspection system for inspecting web printed electronic circuitry includes a strobed illuminator, a detector, a motion encoder, and a processor. The strobed illuminator is adapted to project light through a reticle to project a pattern of light onto an area of the web. The projected light occurs in a pulse sufficiently short to essentially freeze the web motion. The system projects the pattern of light onto the area of the web in at least two different positions of the web each position corresponding to a different phase of the projected light. A detector is adapted to acquire at least two images of the area, each image corresponding to one of the at least two different phases. The motion encoder provides a position output relative to a position of the web. The processor is coupled to the encoder, the illuminator and the detector. The processor is adapted to synchronize the illuminator with the web motion to expose the area of the web. The processor co-sites the at least two images and can construct a height map image with the co-sited images.
Three-dimensional inspection systems for printed electronic circuitry should be capable of micron-level accuracy while being able to perform inspections during high-speed web processing. Various embodiments of the present invention generally employ a technique for mapping, or otherwise measuring, height of features on a web. Three-dimensional phase profilometry is a known technique. See, for example, U.S. Pat. Nos. 6,049,384 and 6,750,899, which patents issued to the assignee of the current application. Essentially, a light pattern is projected onto a substrate and is analogous to the pattern of dark and light areas cast onto a floor by sunlight passing through a Venetian blind. Just as the sunlight passing through a Venetian blind will present a pattern of parallel, straight stripes on a flat floor, the pattern of light on a flat surface, will be one of parallel, straight stripes, but varying in intensity according to the sinusoidal pattern of opacity of the reticle. Continuing the analogy to sunlight passing through a Venetian blind, it will be understood that when viewed from above, the pattern of stripes of sunlight will be shifted laterally if they strike an object (like a sleeping cat) having a height different from the height of the flat floor. Similarly, because the light is projected onto a flat surface at an angle to the plane of the flat surface, the pattern of stripes presented on the flat surface is shifted laterally from the presence of an object having a height different from the height of the flat surface.
Sensor 26 is disposed to acquire an image of a portion, or field of view, 28 on web 24. Sensor 26 may include a stroboscopic illuminator, or may be coupled to one or more stroboscopic illuminators. The stroboscopic illuminator(s) is/are configured to fire a pulse of illumination that essentially freezes the motion of the web during image acquisition. In this regard, even though web 24 undergoes continuous motion, a number of clear, stop-action, images can be acquired. Each of the stroboscopic illuminator(s) is coupled to a reticle such that sequentially-fired bursts of illumination produce differing phases or fringe patterns at each discrete location in the image. Web motion encoder 30 provides a signal to a controller within sensor 26, or coupled to sensor 26, that is indicative of the relative displacement of web 24 between sequential firings of different-phase image acquisitions. In this manner, the motion signal can be used to co-site the temporally-spaced images so that the only difference in the image is that of the phase or fringe patterns. Accordingly, processing of the fringe patterns can then be effected in accordance with known techniques to derive height characteristics of features on the web.
While embodiments of the present invention can be practiced using two distinct phase patterns or fringe patterns, it is preferable to employ three distinct phase patterns. The utilization of at least three patterns produces height maps that are unaffected by reflectivity and illumination changes and simplifies computations. Additionally, it is expressly contemplated that four or more phase patterns can also be used in accordance with embodiments of the present invention.
In order to increase vibrational immunity of the inspection system, it is preferred that the successive acquisition of at least two images be accomplished within a relatively short period of time, such as two milliseconds. In this way, even a system that is undergoing vibration will have moved relatively little in the time between image acquisitions. This is important because while the web encoder will provide a signal relative to the motion of the web between successive image acquisitions, vibration of the system may result in a displacement in any direction, and that displacement may not be fully transduced by the web motion encoder. Accordingly, vibration does have the ability to introduce error, and it is important to ameliorate its effects.
Embodiments of the present invention generally provide the ability to obtain three-dimensional information of the components, circuits, or features on web 24. Since the images themselves contain two-dimensional information relative to those circuits, features, or patterns, the provision of a height map allows the volume of each such circuit, component, feature, or circuit to be calculated. This quantity can be used to inspect web 24 in real-time.
In accordance with another embodiment of the present invention, the system includes a low-resolution, high-speed mode wherein data from a plurality of pixels in image detector 108 are combined to form a larger effective pixel. This larger effective pixel allows for higher-speed applications.
Finally, embodiments of the present invention also include the detection or measurement of the height of web 24 itself. This is important because if web 24 is deformed, to some extent, during processing, calculations that assume web 24 is flat, may unduly affect height computations of components. Accordingly, it is contemplated that areas of web 24 that are known to have no components, features, or circuits, may be observed by sensor 26 to determine the height of web 24. Further, a plurality of three or more observations can be acquired to generate a three-dimensional plane that approximates web 24. Further, one or more sensors can be used to simply determine the height of web 24 proximate field of view 28. Such sensors include known laser-triangulation sensors, distance sensors, or any other suitable sensors.
Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
The present application is based on and claims the benefit of U.S. provisional patent application Ser. No. 60/879,720, filed Jan. 10, 2007, the content of which is hereby incorporated by reference in its entirety.
Number | Date | Country | |
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60879720 | Jan 2007 | US |