Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Nonquantitative
Utility Patent
1997-07-16
2001-01-02
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Nonquantitative
C324S548000
Utility Patent
active
06169395
ABSTRACT:
FIELD OF INVENTION
This invention relates generally to testing of electronic assemblies and more specifically to testing to determine if polarized parts are installed with the correct polarity.
BACKGROUND OF THE INVENTION
There is an ongoing need in electronic manufacturing testing and failure testing to automatically determine whether polarized parts are attached with the proper electrical orientation. Electrolytic capacitors, diodes, integrated circuits and other devices are often mechanically symmetrical but electrically asymmetrical. That is, they can physically be attached or mounted with any of several orientations but only work properly when attached or mounted with one particular orientation. Electrolytic capacitors are a particular problem because they may function for some time when attached with the terminals reversed. As a result, they may pass typical conventional circuit tests at the time of manufacturing, but they may degrade in capacitance value over time, increase leakage current over time, or they may later fail catastrophically (explode). The need for detecting those devices that will degrade is important economically because repair before final assembly of a product is much less expensive than repair of a shipped product. For those devices that may explode, it is especially important from both a safety and cost perspective to determine installation polarity before full operating voltage is first applied. There is a need for automatic testing for capacitor polarity and in particular, there is need for automatic testing using equipment that is already in place for testing other parts of an electronic assembly.
Many commercially available testers for loaded printed circuit boards have two kinds of probes for providing electronic stimulus signals and for measuring electronic responses. Contacting probes make physical contact with conductive surfaces within the electronic assembly. Typically, a sharp pointed “nail” is used to penetrate a protective coating and to make contact with a trace or pad on a printed circuit board. Non-contacting probes induce or measure electromagnetic fields near the electronic devices being tested. For example, non-contacting capacitive probes are used to detect open solder joints on loaded printed circuit boards. An example of a commercially available printed circuit board tester using “bed-of-nails” fixtures and non-contacting probes is the Hewlett-Packard 3070 Series II Test System with HP TestJet non-contacting probes. An example of use of non-contact testing for integrated circuits may be found in U.S. Pat. No. 5,254,953 (Identification Of Pin-Open Faults By Capacitive Coupling Through The Integrated Circuit Package) issued Nov. 19, 1993 to David T. Crook and Kevin W. Keirn (Crook et al). There is a need for automatic testing of polarity of assembled electronic components using existing test probe hardware such as “bed-of-nails” probes and non-contacting probes.
SUMMARY OF THE INVENTION
Polarity of an electrolytic capacitor is determined by measuring electromagnetic coupling between the capacitor and a non-contacting probe. In one configuration, the device under test is actively stimulated and a response is detected by a noncontacting capacitive probe placed near the body of the device under test. Alternatively, instead of applying a stimulus to the leads of the device under test and making a measurement at the probe, the probe may be stimulated with measurements made at the leads of the device under test.
In a first embodiment, a single voltage measurement is made. In a second embodiment, a single current measurement is made. In a third embodiment, multiple voltage and current measurements are made under two different test configurations. In the third embodiment, two electromagnetic coupling coefficients are unknown fixed coefficients in two linear equations. The variable parameters in the two linear equations are the voltages at each of the terminals of the device under test and the current flowing through the capacitive probe. In the first configuration for the third embodiment, a first terminal of the device under test is stimulated and the second terminal is held at a reference voltage (or connected to a common signal return). In the second configuration of the third embodiment, the first terminal is held at the reference voltage (or connected to a common signal return) and the second terminal is stimulated. After measuring the four terminal voltages and the two probe currents, the two equations are solved for the two unknown electromagnetic coupling coefficients. The relative size of the electromagnetic coupling coefficients determines the measured polarity of the device under test.
REFERENCES:
patent: 4745359 (1988-05-01), Leitz
patent: 4779040 (1988-10-01), Aldinger
patent: 5159526 (1992-10-01), Marek
patent: 5450014 (1995-09-01), Lee
patent: 5502375 (1996-03-01), Marek
patent: 5504422 (1996-04-01), Bundschuh et al.
patent: 0185255 A1 (1986-06-01), None
Agilent Technologies
Brown Glenn W.
Winfield Augustus W.
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