Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-06-24
2001-11-27
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S754090, C324S757020
Reexamination Certificate
active
06323667
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electroconductive contact probe unit for testing printed circuit boards, semiconductor devices and semiconductor wafers by using an electroconductive needle member resiliently urged by a compression coil spring.
BACKGROUND ART
According to a conventionally known electroconductive contact probe unit for use in a contact probe for electrically testing electroconductive patterns of printed circuit boards and semiconductor products, each electroconductive needle member is received in a tubular holder so as to be axially slidable in and out of the holder and is resiliently urged by a compression coil spring in the direction to project out of the holder to the extent permitted by an arrangement for preventing the electroconductive needle member from completely projecting out of the holder. In such an electroconductive contact probe unit, a forward end of the electroconductive needle member is resiliently engaged with an object to be tested so that an electric signal may be transmitted between the object to be tested and an external circuit such as a testing circuit.
However, during the testing process, when electric current from the object to be tested is conducted through the compression coil spring via the electroconductive needle member, the electric signal encounters an inductance which is proportion to the square of the number of turns of the compression coil spring. Therefore, when the electric signal that is conducted through the contact probe unit consists of a high frequency signal (for instance in the range of several tens of MHz to several GHz), the high frequency signal is conducted along the spiral path of the compression coil spring, and the resulting increases in the inductance and electric resistance may corrupt the electric properties of the detected signal.
DISCLOSURE OF INVENTION
In view of such problems of the prior art, a primary object of the present invention is to provide an electroconductive contact probe unit which is reliable in use, and can handle high frequency signals.
A second object of the present invention is to provide an electroconductive contact probe unit which is low in inductance and electric resistance.
A third object of the present invention is to provide an electroconductive contact probe unit which is simple in structure and economical to manufacture.
A fourth object of the present invention is to provide an electroconductive contact probe unit which can establish a favorable electric contact even when the surface of the object to be tested is covered by oxide film or other foreign matters.
According to the present invention, these and other objects of the present invention can be accomplished by providing an electroconductive contact unit, comprising: a support hole passed through a support member; an electroconductive needle member slidably received in the support hole, the needle member including a head portion projecting out of an end of the support hole, and a stem portion extending from the head portion coaxially and away from an end of the head portion projecting out of the support hole; and a compression coil spring coaxially received in the support hole so as to urge the head portion out of the support hole; the compression coil spring including a closely wound portion in which adjacent turns of the compression coil spring contact each other at least when the compression coil spring is compressed to a certain extent; the closely wound portion has an outer diameter substantially smaller than an inner diameter of a corresponding part of the support hole so that the closely wound portion curves as the compression coil is compressed; the stem portion overlapping the closely wound portion of the compression coil spring so that the stem portion comes into contact with the closely wound portion when the compression coil spring is compressed and the closely wound portion has thereby curved at least to a certain extent.
Thus, the electric signal conducted by the compression coil spring is allowed to pass axially through the closely wound portion, instead of conducting the electric signal through a spiral path along a coarsely wound portion of the compression coil spring, and thereby suffering from the increases in the inductance and the electric resistance. At the same time, the coarsely wound portion of the compression coil spring provides the necessary spring force for the needle member. Preferably, the closely wound portion is located in such a manner that the closely wound portion axially overlaps a rear end of the electroconductive needle member under a rest condition where the electroconductive needle member is not in contact with any object.
To ensure that the closely wound portion of the compression coil spring allows the electric current to be conducted axially through the length of the compression coil spring, electroconductive film may be deposited around the closely wound portion to form the closely wound portion into a substantially integral tube.
According to a typical arrangement for a contact probe unit, the electroconductive needle member further comprises a large diameter portion between the head portion and the stem portion, and an outer end of the support hole is provided with a small diameter portion so that an extent by which the head portion projects from the support hole is determined by abutting of the large diameter portion with a shoulder surface defined between the small diameter portion of the support hole and a remaining part of the support hole. Also, the closely wound portion preferably extends to an end of the compression coil spring remote from the head portion of the electroconductive needle member, and abuts an electroconductive pad which is connected to an external circuit which may consist of a testing circuit or a relay plate.
To keep the compression coil spring attached to the needle member during the assembly process, and thereby facilitate the assembly process, the electroconductive needle member may further comprise a collar portion formed between the head portion and the stem portion or between the large diameter portion and the stem portion for resiliently engaging an associated coil end of the compression coil spring. Additionally or alternatively, the associated coil end may be soldered or otherwise secured to the collar portion or the stem portion adjacent to the head as the case may be.
To obtain a contact probe unit having two moveable ends in an economical fashion, a free end of the closely wound portion may project out of a second small diameter portion provided in the support hole at the other open end thereof while an inner diameter of the second small diameter portion is larger than the free end of the closely wound portion but smaller that a remaining part of the closely wound portion.
To fully implement a contact probe unit having two moveable ends both of which are capable to cleaning the parts to be accessed or capable of penetrating a layer of oxide film or other foreign matters that may deposit on the parts to be accessed, the compression coil spring may include an intermediate closely wound portion, and a pair of coarsely wound portion on either axial end thereof so that one end of the compression coil spring engages the first mentioned electroconductive needle member while the other end of the compression coil spring engages a second electroconductive needle member which similarly includes a head portion projecting out of the other end of the support hole, both the first and second electroconductive needle members being provided with respective stem portions which are adapted to contact the closely wound portion at least when the compression coil spring is compressed to a certain extent.
REFERENCES:
patent: 4931726 (1990-06-01), Kasukabe et al.
patent: 5003255 (1991-03-01), Kazama
patent: 5990697 (1999-11-01), Kazama
patent: 3340431A (1985-05-01), None
patent: 64-71141 (1989-03-01), None
patent: 3-202780 (1991-09-01), None
patent: 06148236 (1994-05-01), None
patent: 06201725 (1994-07-01), None
patent: 07115253 (1995-05-01),
Brown Glenn W.
Deb Anjan K
NHK Spring Co. Ltd.
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