Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Reexamination Certificate
1999-03-10
2001-09-11
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
C324S761010
Reexamination Certificate
active
06288555
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a fixture for use in measuring an electrical characteristic of a pogo pin.
In a semiconductor tester, stimulus and response signals are applied to and received from the device under test (DUT) by a test head. The DUT is mounted on a load board having contact pads connected to the pins of the DUT. The test head is equipped with spring-loaded contact elements known as pogo pins. A pogo pin is composed of a socket which is firmly secured in an insulating member, such as a plastic header or a circuit board, a barrel which is press fit into the socket, a plunger which is a sliding fit inside the barrel, and a spring inside the barrel and urging the plunger toward a projecting position. The load board is positioned so that the tips of the plungers are in contact with the conductive pads on the load board and the load board is then displaced toward the test head, establishing electrically conductive pressure contact between the tip of each plunger and the respective contact pad.
It is necessary for reliable and accurate operation of the tester that the electrical characteristics of the pogo pins, specifically the impedance of the pogo pins, lie within a fairly narrow range and be known with fairly high degree of accuracy.
Impedance has a frequency-independent resistive component and a frequency-dependent reactive component. Manufacturers of pogo pins conventionally specify only the resistance of a pogo pin.
In a high speed test of an integrated circuit device, frequency components of 500 MHz or higher may be involved, and in this case it may be desirable that the signal path between the test head and the DUT have a bandwidth greater than 1 GHz. The resistance value specified for a pogo pin is of no substantial relevance to the behavior of the pin at such high frequencies. For example, ideally there is a good sliding electrical contact between the plunger and the barrel but if there is instead a poor sliding electrical contact between the plunger and the barrel, and a significant part of the signal energy passes through the spring, the inductance of the spring may contribute a large reactive component of impedance that far outweighs the resistance of the pogo pin.
A time domain reflectometer (TDR) or a network analyzer can be used to measure high frequency electrical behavior of a conductive element. However, it is very difficult to couple the barrel or plunger of a pogo pin to a time domain reflectometer or network analyzer.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention there is provided a measurement fixture for use in measuring an electrical parameter of a rod-form conductive element, comprising an insulating support member, a transmission line connector having ground and signal conductors for connection to a measurement instrument, said transmission line connector being mounted on the insulating support member, a first conductive element mounted on the support member and connected to the signal conductor of the transmission line connector, a holder for removably receiving the rod-form element, said holder including a conductive member in electrically conductive contact with the rod-form element when positioned in the holder, and a mounting structure mounting the holder relative to the support member so that when the rod-form element is positioned in the holder, an end of the rod-form element can be brought into electrically conductive contact with the first conductive element, said mounting structure including a resistor structure electrically connected between the conductive member of the holder and the ground conductor of the transmission line connector and having an electrical resistance substantially equal to the characteristic impedance of the transmission line connector.
In accordance with a second aspect of the invention there is provided a method of testing a rod-form conductive element, comprising providing a measurement fixture including an insulating support member, a transmission line connector having ground and signal conductors for connection to a measurement instrument, said transmission line connector being mounted on the insulating support member, a first conductive element mounted on the support member and connected to the signal conductor of the transmission line connector, a holder for removably receiving the rod-form element, said holder including a conductive member in electrically conductive contact with the rod-form element when positioned in the holder, and a mounting structure mounting the holder relative to the support member so that when the rod-form element is positioned in the holder, an end of the rod-form element can be brought into electrically conductive contact with the first conductive element, said mounting structure including a resistor structure electrically connected between the conductive member of the holder and the ground conductor of the transmission line connector and having an electrical resistance substantially equal to the characteristic impedance of the transmission line connector, fitting the rod-form element in the holder and sliding the rod-form element to a position in which an end of the rod-form element engages the first conductive element, and employing the measurement instrument to launch a stimulus signal into the rod-form element by way of the transmission line connector and measure a response signal received therefrom.
In accordance with a third aspect of the invention there is provided a method of testing rod-form conductive elements, comprising (a) providing a measurement fixture including an insulating support member, a transmission line connector having ground and signal conductors for connection to a measurement instrument, said transmission line connector being mounted on the insulating support member, a first conductive element mounted on the support member and connected to the signal conductor of the transmission line connector, a holder for receiving the rod-form element, said holder including a conductive member in electrically conductive contact with the rod-form element when positioned in the holder, and a mounting structure mounting the holder relative to the support member so that when the rod-form element is positioned in the holder, an end of the rod-form element can be brought into electrically conductive contact with the first conductive element, said mounting structure including a resistor structure electrically connected between the conductive member of the holder and the ground conductor of the transmission line connector and having an electrical resistance substantially equal to the characteristic impedance of the transmission line connector, (b) fitting a first rod-form element in the holder, (c) sliding the rodform element to a position in which an end of the rod-form element engages the first conductive element, (d) employing the measurement instrument to launch a stimulus signal into the rod-form element by way of the transmission line connector and measure a response signal received therefrom, (e) removing the rod-form element from the holder, (f) fitting a second rod-form element in the holder, and (g) repeating steps (c)-(e).
REFERENCES:
patent: 4588241 (1986-05-01), Ardezzone
patent: 5645433 (1997-07-01), Johnson
patent: 5688127 (1997-11-01), Staab et al.
Credence Systems Corporation
Kerveros J
Metjahic Safet
Smith-Hill John
Smith-Hill and Bedell
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