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  In-circuit test fixture with integral vision inspection systemUSPTO Application #: 20070013772Title: In-circuit test fixture with integral vision inspection system Abstract: An in-circuit test fixture performs both electrical tests on a Printed Circuit Assembly (“PCA”) and reads distinguishing features of a feature of interest of the PCA. The in-circuit test fixture physically supports an image sensor array. A light focusing means has a position relative to the distinguishing features and the image sensor such that a focused real image of the distinguishing features is imaged onto the image sensor. The image sensor outputs image information of the distinguishing features. A processor performs image analysis based on the image information of the distinguishing features to determine if defects exist. (end of abstract) Agent: Agilent Technologies Inc. - Loveland, CO, US Inventors: Yew Fei Tham, Wee Sheng Yong, Chris Richard Jacobsen USPTO Applicaton #: 20070013772 - Class: 348087000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070013772. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The invention relates to the field of the automated testing of printed circuit assembly assemblies. BACKGROUND OF THE INVENTION [0002] A printed circuit assembly ("PCA") is subject to many different types of defects during the assembly process. Accordingly, various test and inspection techniques are employed to locate these defects. Today, there are three general test methods used to find PCA defects: electrical test, optical (or visual) inspection, and x-ray inspection. Of these, electrical test, and in particular a technique known as "in-circuit test", is the most mature and most commonly used technique. However, as physical access to nodes on the PCA via bed-of-nails probing decreases, in-circuit test is becoming more difficult. [0003] Some prevalent defects on PCA assemblies are missing, incorrect type or mis-oriented components. Missing components can occur when the components are either never loaded onto the board or they fall off during the assembly process. An incorrect type of component can occur when a component with the wrong electrical value is inadvertently loaded onto the board. Improperly oriented components can occur when a component is loaded onto the board with a reversed polarity. Prior methods for detecting defects at the electrical test stage of the process include in-circuit test, which can include functional tests, and additionally include capacitive measurement test, scan test, automated optical test, and automated x-ray test. [0004] In-circuit test, including unpowered in-circuit analog test (for discrete analog components) and digital in-circuit test for digital components, utilizes an in-circuit tester. The in-circuit tester includes a bed-of-nails test-head having a number of tester interface pins. A fixture having a number of probes is mounted over the bed-of-nails of the tester such that the fixture probes align with and contact the tester interface pins. A PCA under test is mounted in the fixture such that the fixture probes electrically contact various nodes of interest on the PCA under test. Analog in-circuit tests detect manufacturing defects on the PCA for analog parts such as missing components, incorrect components, mis-oriented components, solder opens, and shorts on the PCA under test by probing the appropriate nodes to which the component under test should be attached, and measuring the value, in appropriate units (e.g., resistance, capacitance, etc.), of the component under test. Digital in-circuit tests detect manufacturing defects on the PCA for digital parts such as missing parts, incorrect parts, mis-oriented parts, solder opens, and shorts on the PCA under test by probing the appropriate digital nodes and applying digital values to the input nodes and collecting digital states on the output nodes. [0005] Similarly, in functional test, input and output connections on the edge of the board are made and analog and digital signals are applied that test the large functional blocks of the board. [0006] Capacitive measurement test, such as AGILENT TECHNOLOGIES' TestJet.RTM. probe and technique (described in detail in U.S. Pat. No. 5,254,953 to Crook et al.), detects when a device pin is not properly connected to its trace on the PCA. The technique uses an external plate, suspended over the device under test and separated from the lead frame by the plastic or ceramic material of the device housing. The lead frame and external plate form a small capacitor that can be measured by stimulation with an AC source. When the device pin is not electrically connected to the trace, an additional capacitance results in series with the TestJet.RTM. capacitor. This additional capacitance exists due to the tiny air gap between the pin and trace. This is a very small capacitance, much smaller than the TestJet.RTM. capacitor, so the series combination of the TestJet.RTM. and this additional pin capacitor is smaller than either capacitor. [0007] The above techniques each require at least some physical probing of the PCA nodes and are therefore ineffective for PCA assemblies with limited nodal access. To overcome loss of test coverage in non-probed areas of the PCA, alternate test methodologies have emerged. These include automated optical inspection (AOI) and automated x-ray inspection (AXI). Although these methodologies can detect missing devices very effectively, they each suffer from their own limitation and disadvantages. The major disadvantage of these techniques is that they require expensive manufacturing line equipment entirely separate from the in-circuit tester, and therefore also require an entirely new test step to be added to the manufacturing process. The cost of adding such machines to the manufacturing process may be appropriate in some cases, but in other cases the need to do so represents a large disadvantage to these methods. [0008] Additionally, some devices are electrically untestable even with probing. The primary example of this is parallel bypass capacitors. While it is theoretically possible (e.g., on the bench with a single device under test (DUT)) to detect a single missing capacitor, in practice such detection is often not possible. The tolerances and guardbands that must be added to the test limits completely hide small measurement differences due to a single (or even multiple) missing capacitors. As MSI and LSI are replaced by VLSI components, FPGAs and large ASICs, the ratio of bypass capacitors to digital components is increasing, which decreases the number of possible faults that are detectable by even a perfect electrical test. [0009] Coverage for all electrical and imaging test techniques can be quantified. Coverage gaps for each test stage can be identified with a coverage tool. Such coverage tools are described in U.S. Pat. No. 6,792,385 to Parker et al. and owned by AGILENT TECHNOLOGIES, INC., the assignee of the present invention. In this patent, potentially defective properties are enumerated for a board, without regard for how the potentially defective properties might be tested. For each potentially defective property enumerated, a property score is generated. Each property score is indicative of whether a test suite tests for a potentially defective property. Property scores are then combined in accordance with a weighting structure to characterize board test coverage for the test suite. Use of these tools can determine which defects should be tested with electrical methods and which can be tested with imaging methods for optimal defect coverage. [0010] Since most manufacturing lines already use electrical testers (primarily in-circuit testers), it would be beneficial to have the ability to provide extra test coverage during the in-circuit stage of the manufacturing process. Accordingly, it is an object of the invention to detect additional defects on a PCA while the PCA is being electrically tested on an in-circuit tester. SUMMARY OF THE INVENTION [0011] The present invention provides broad test coverage of defects on a Printed Circuit Assembly ("PCA") while the PCA is being electrically tested on an in-circuit tester by adding digital imaging capability to the in-circuit tester. [0012] More particularly, the present invention comprises an in-circuit test fixture which performs both electrical tests on a PCA and images distinguishing features of a feature of the PCA. The in-circuit test fixture physically supports an image sensor array. A light focusing means has a position relative to the distinguishing features and the image sensor such that a focused real image of the distinguishing features is imaged onto the image sensor array. The image sensor array outputs image information of the distinguishing features. A processor performs image analysis, which might include pattern recognition, based on the image information of the distinguishing features to determine if defects exist. [0013] The present invention also includes a method for performing both in-circuit electrical tests on a PCA and for imaging distinguishing features of a feature of the PCA using a single test fixture of an in-circuit tester comprising the steps of: loading the PCA into the test fixture; focusing a digital camera on distinguishing features of a feature of interest of the PCA; capturing an image of the distinguishing features of the feature of interest with the camera; analyzing the image; and outputting results of whether or not the feature of interest of the PCA has a defect. BRIEF DESCRIPTION OF THE DRAWINGS [0014] FIG. 1 is a diagrammatic view of one embodiment of the in-circuit test fixture with an integral vision inspection system of the present invention. [0015] FIG. 2 shows a electrolytic capacitor loaded onto the PC board 105 with the correct orientation. [0016] FIG. 3 shows the electrolytic capacitor loaded onto the PC board with a reversed orientation. [0017] FIG. 4 shows a more detailed diagrammatic view of an embodiment of the in-circuit test fixture with an integral vision inspection system of the present invention. [0018] FIG. 5 is semi-diagrammatic view of a light image sensor for the acquisition of the digital image signals, or image information, using the image sensor array. [0019] FIG. 6 shows a hardware interface between the sensing elements and the ICT tester or external personal computer. [0020] FIG. 7a is a representation of a stored template. Continue reading... Full patent description for In-circuit test fixture with integral vision inspection system Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this In-circuit test fixture with integral vision inspection system patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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