Genrad, Inc.

Moses Khazam

Steven M Blumenau

Anthony J Suto

Charles P Smith

Karl Karash

Aldo Mastrocola

Richard Pye

Fadi H Daou

A hybrid scanner for switching internal analog buses to system pin channels. Semiconductor switches switch most scanner buses to system pin channels, but mechanical relays perform switching for at least one bus used for high-current test signals. To perform low-impedance guarding and/or high-current backdriving, the low impedance, high current bus is typically connectable to one or more overdriver circuits and a guard voltage potential through mechanical relays. The scanner is capable of supporting in-circuit tests covering the most significant regions of the fault spectrum can be made more reliable and much smaller and less costly than the scanners conventionally used in traditional broad spectrum testers. It turns out that this test-supporting capability can be achieved by adding only a few mechanical relays to an otherwise semiconductor-switch-based scanner. Only those necessary to support low-impedance and high-current test operations.

Hybrid scanner for use in an improved MDA tester

A method for testing for short circuits between UUT pins that are nominally connected to nodes on a circuit board which the UUT is mounted and open circuits between pins and nodes nominally connected thereto. The method is used in a system that responds to the capacitances between a plate positioned above the UUT and respective nodes to which the pins are connected. A group of pins are selected such that no two pins of the group are nominally connected together. The pins are connected together in the tester and if the capacitance between the plate and the pin group is less than a first threshold an open circuit is indicated. The presence of a short circuit is indicated by a capacitance greater than a second threshold that is greater than the first threshold.

Capacitive open-circuit and short-circuit tests of component connections

To test for proper connections of integrated-circuit connection pins (22) on a circuit board (12) to the conductive paths to which they should be connected, a tester (10) applies signals of different frequencies to paths to be connected to different IC pins provided by the same integrated-circuit package (24). The resultant composite electric-field signal in the vicinity of the integrated-circuit package (24) is coupled to a capacitive probe (42), and the probe signal is subjected to frequency analysis (58-1, 58-2 , . . . 58-J) to determine whether the applied frequency components are present in the signal with sufficient magnitudes. If the magnitude in the sensed signal of an applied frequency component is not great enough, the tester generates an indication that the corresponding IC pin has not been properly connected.

Simultaneous capacitive open-circuit testing

In a method for testing whether a pin (12) of an electronic component (14) on a circuit board under test (18) has been properly connected to a circuit-board track (16), a source (20) drives the track (16), and a capacitive probe (34) located above the component (14) generates a resultant output. The pin (12) is determined to be connected correctly if that output exceeds a threshold determined for that pin (12) during a training process in which similar measurements have been made on a known good board for that pin and other pins on the same electronic device. The threshold is determined by dividing the capacitance measurement made during the training process for that pin into connection-dependent and connection-independent parts, the latter being the part that would result even in the absence of a proper pin connection. Determination of the pin-independent part is made, without disconnecting the pin in question, by operations that take advantage of symmetries in the pattern of lead-frame conductors predominately responsible for the connection-dependent component of the measured capacitance. The threshold is the sum of the connection-independent part and a percentage of the connection-dependent part.

Capacitive open-circuit test employing threshold determination

An output circuit (62) for generating a signal in the form of a voltage between an output signal node and an output reference node (60) receives power from a pair of voltage regulators (Q1 and 68, Q2 and 70). The regulators are connected in power-circuit series so as to be powered by the difference between the output potentials of two opposite-polarity supplies without a direct low-impedance connection between the power-supply ground (73) and the output reference node (60). To avoid large current flow in any external path between an output reference node (60) of an electronic circuit and the ground node (73) of its power supply, a current sensor (R1, R2, 86) senses the net current that the power supplies provide to the circuitry that includes the regulators, and it controls variable loads (Q3, Q4) that selectively drive current into and draw current from the reference node (60) so as to drive the net current to zero.

Ground-loop interruption circuit

A time-interval meter (10) employs a counter (16) to count the number of cycles of the output of an oscillator (18) that occur between a pulse on a start input line (12) and a subsequent pulse on a stop input line (14). The result is a coarse measurement. A filter (28) filters the output of the oscillator (18) to produce a sinusoidal signal, and the meter (10) refines the coarse measurement by employing analog-to-digital converters (20 and 22) to measure the values assumed by the sinusoidal signal at the occurrences of the start and stop pulses. A calculation circuit (24) employs an inverse trigonometric function of the converter outputs to determine the difference between the phases of the sinusoidal signal at the occurrences of the start and stop pulses, and it adds the time difference associated with this phase difference to the coarse measurement indicated by the cycle count to yield a total interval duration.

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Lexington, MA, United States of America

Moses Khazam