Electronic device test set and contact used therein

A contact for use in a test set which can be mounted to a load board of a tester apparatus. The contact, which serves to electrically connect at least one lead of a device being tested with a corresponding metallic trace on the load board, has a first end defining multiple contact points. As the contact is rotated about an axis generally perpendicular to a plane defined by the contact, successive contact points are sequentially engaged by a lead of the device being tested.

TECHNICAL FIELD

The present invention relates broadly to the field of testing of electronic devices such as integrated circuits. More narrowly, however, the invention deals with test sets for interfacing pads or leads of a device to be tested with corresponding pads of a circuit board of a test apparatus. A specific embodiment of the invention focuses upon the construction and mounting of a contact of the test set.

BACKGROUND OF THE INVENTION

The testing of integrated circuit devices is performed to ensure that such devices, when sold to a customer, are of as high a degree of quality as possible. Various types of test apparatus have been utilized over the years to accomplish testing. Typically, a tester includes a printed circuit board which has defined thereon a plurality of conductive traces. These traces on the circuit board, or load board, are associated with corresponding functions of the test apparatus.

In order to accomplish testing, it is necessary to interconnect a lead, in the case of a leaded device under test, or a pad, of a nonleaded device under test, to a corresponding trace on the load board. A test set or test socket having a plurality of contacts is interposed between the device under test and the load board in order to effectuate interconnection. A contact is engaged, at an upper end thereof, by the lead or pad of the DUT, depending upon the type of DUT being tested, with its corresponding trace on the load board. A lower end of the contact is in engagement with a trace on the load board.

As technology has progressed, the size, shape and electronic properties of contacts have evolved in response to the construction of test sets and load boards and the architecture of devices to be tested. At one time, it was considered necessary to have a wiping action at the various locations of engagement of the contact ends by the lead or pad of the DUT and the pad on the load board. Such wiping action was deemed to facilitate a good transmission path through the contact because of a good connection at either end thereof. It has become more apparent, however, that the measure of wiping action formerly considered necessary to maintain a good transmission path need not be of a degree as was formerly believed. Further, it has been recognized that excessive wiping action can damage component parts at the various points of engagement of the contact, and thereby significantly decrease the life of the test socket and tester load board. Consequently, various attempts have been made to minimize abrading of one surface relative to another. Various elastomeric mounting means have been devised in an effort to minimize abrasion and consequent deterioration of components.

Another problem which has been discovered is the diminishment of effectiveness of testing as a result of the employment of matte tin on leads and pads of various types of DUTs. Such a material is applied to DUT components which facilitate soldering to an ultimate host circuit board. Because of its softness, however, it easily can progressively become adhered to the contact which the DUT engages as rubbing across engaged surfaces occurs during the testing function. Eventually, matte tin can build up to the point where signal integrity through the contact can become diminished.

It is to these dictates and shortcomings of the prior art that the present invention is directed. The present invention is a contact having a structure which minimizes tin buildup on the contact.

SUMMARY OF THE INVENTION

The present invention is a contact for use in a test set mountable to a load board of a tester apparatus. The contact serves to electrically connect at least one lead of a device to be tested (DUT) with a corresponding metallic trace on the load board. The contact has a first end which defines multiple contact points engageable by the lead of the DUT. It further has a second end having an arcuate edge in engagement with the metallic trace. The arcuate edge enables rolling across the metallic trace when the first end of the contact is engaged by the lead of the DUT and made to rotate about an axis generally perpendicular to a plane defined by the contact. The contact is elastomerically mounted as part of the test set intermediate the load board and the DUT. Rotation of the contact about the axis when the first end of the contact is engaged by the lead of the DUT is thereby facilitated.

A test set employing the contact can utilize multiple contact points which take the form of a plurality of ridges. In one embodiment of the invention, the ridges are generally parallel to one another. Similarly, the ridges can be substantially parallel to the axis which is generally perpendicular to the plane defined by the contact.

By so structuring the contact, the contact will have ridges which are sequentially engageable by the lead of the DUT as the contact rotates about the axis from a first orientation, wherein the first end of the contact is initially engaged by the lead of the DUT, to a second orientation, wherein the contact is in a configuration for operational testing.

An inward-most ridge with respect to the test set is the only ridge which is engaged by the lead of the DUT when the contact is in its first orientation. Successively outward ridges are sequentially engaged as the contact is made to rotate about the axis from the first orientation to the second orientation.

The present invention is thus an improved test set structure and contact for use in such a test set. More specific features and advantages obtained in view of those features will become apparent with reference to the DETAILED DESCRIPTION OF THE INVENTION, appended claims and accompanying drawing figures.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawing figures, wherein like reference numerals denote like elements throughout the several views,FIG. 1illustrates a test socket10in accordance with the present invention. The test socket10is intended for use with a tester typically employed for ascertaining quality of integrated circuit devices used in electronic appliances. The tester interfaces with a tester load board12which has electrically conductive traces14formed on a surface16thereof to enable electronic communication between the tester and an integrated circuit device18to be tested. That is, electrical signals are transmitted between the device under test18and the test apparatus through the test socket10.

It will be understood that various types of integrated circuit devices18are able to be tested utilizing a test socket or test set in accordance with the present invention.FIG. 1illustrates a leaded device having externally-extending leads58diverging from the body59of the device18. It will be understood, however, that leadless devices, as illustrated inFIG. 2, can be accommodated. Such devices have pads61rather than leads58.

While it is to be understood thatFIG. 1illustrates a device under test (DUT) package in an elevational view showing a single lead, a plurality of leads58are typically part of the device18. In such cases, a contact24, as will be discussed hereinafter, will be provided for engagement by each lead58. It will be understood that substantially identical leads extend, in the case of the type of device18illustrated, along both of opposite sides of the device package18.

In operation, downward pressure is brought to bear upon the body59of the device18by a plunger mechanism (not shown). As the plunger depresses the device18downward, contacts24, which are mounted in an elastomeric fashion as will be discussed hereinafter, are caused to be rotated with respect to an axis which extends generally perpendicular to a plane defined by the contact24. An axis with respect to which contact24might rotate is identified by reference numeral68inFIG. 3.

FIG. 1illustrates a location of the device18and an orientation of contact24when lead58has first engaged the front, or inner, end26of contact24.FIG. 2illustrates an orientation of contact24(a second orientation) when the device is in a test position. It will be understood that, in view of the construction of contact24as will be discussed hereinafter, an arcuate surface28at the rear end30of contact24will roll across trace14on the load board12with virtually no translational or rotational sliding of that surface along the trace14.FIGS. 1 and 2illustrate a wall70against which rear end30of contact24abuts. Such a wall70is defined in the housing of the test socket10. It will be noted that the wall70is at a rather large acute angle with respect to the surface16of load board12. Typically the angle is somewhere within a range of between 72°-78°. The wall70serves to be engaged by rear end30of contact24in order to preclude sliding of edge28along trace14.

The contact24illustrated in the drawing figures includes a protrusion40. Protrusion40functions to engage, when mounted by elastomers46-48, a shoulder49defined by the housing32. Engagement of the shoulder49by protrusion40serves to limit the degree of upward movement of the contact24and the distance the front end26of the contact24will extend beyond an upper surface of the housing32when the contact24is not engaged by a device to be tested.

As previously discussed, elastomers46,48affect mounting of contact24. The test socket housing32is, therefore, provided with a pair of channels50,52which extend along axes generally transverse to a plane defined by contact24when it is mounted in the housing32. Elastomers46,48are received within channels50,52respectively. Rear elastomer48is pre-loaded and, as a result of the arcuate surface28at the rear end30of contact24being in engagement with the load board12, will engage an upper edge of the rear end30of contact24at a location to urge the front end26of contact24upwardly. Similarly, front elastomer46is under compression and also serves to urge contact24upward. Contact24will, in its neutral orientation, be positioned and oriented as seen inFIG. 1. This is a first orientation of contact24and the one it occupies prior to a device18being brought into engagement with the upper end26of contact24by device18.

FIG. 1illustrates multiple contact points defined by upper end26of contact24. The contact points are, as best seen inFIG. 3, generally parallel extending ridges60,62,64. WhileFIG. 3illustrates three parallel ridges extending generally parallel to the axis68, a smaller contact, as shown inFIGS. 1 and 2, might well be provided with only two ridges60,62.

FIG. 1illustrates the locations of ridges60,62relative to each other at the time of first engagement by lead58of device18. It will be noted that ridge60is engaged by lead58, and ridge62is not. The spacing between lead58and ridge62, when the contact24is in this orientation, is illustrated by reference numeral66.

As pressure continues to be applied to device18, contact24will be caused to rotate generally counterclockwise about axis68. At some point, lead58will engage ridge62, and ridge60will be rotated downwardly away from lead58. In the case of a three-ridge embodiment, second ridge62will also be withdrawn from lead58as third ridge64engages the lead.

It has been found that such a multiple contact point contact24is particularly effective in dealing with matte tin typically provided on lead58to facilitate soldering to an ultimate host board. The multiple ridge construction serves to help control a buildup of tin on front end26of contact24. The first ridge60has a tendency to collect the most tin. A non-desirable buildup is deterred by providing multiple ridges. The first ridge serves a sacrificial function in absorbing the greatest transfer of tin.

FIG. 3illustrates a contact24having a narrowed front end26. Such an embodiment defines a smaller land71with spaced shoulders72on either side thereof. Such a feature, it is envisioned, would be used when the device being tested were leadless and had a pad generally flush with the bottom of the body of the device18. Such a land embodiment could even serve to function in an environment wherein the pad or pads of the DUT are recessed within the body of the integrated circuit.

It will be understood that this disclosure, in many respects, is only illustrative. Changes may be made in details, particularly in matters of shape, size, material, and arrangement of parts without exceeding the scope of the invention. Accordingly, the scope of the invention is as defined in the language of the appended claims.