Securement of test points in a test head

Details Securement of test points in a test head Securement of test points in a test head

1998-10-15

2002-07-09

Nguyen, Vinh P. (Department: 2858)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C324S754090

Reexamination Certificate

active

06417684

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a test head having a device for making contact with test points of an electric component under test, wherein the test points are preferably arranged closely next to one another.
Test heads of the type mentioned here are used to make simultaneous contact with a plurality of test points, arranged one next to the other, of an electric component under test, for example a semiconductor component. The test head comprises a plurality of pin shaped contact elements which are composed of an elastic material and wherein the test points are brought to bear against one assigned test point. The contact force is applied here by folding out and/or bending under spring extension the contact elements in a direction perpendicular to their longitudinal extent when the contact elements are placed on the test points or the test points are placed on the contact elements, respectively. The contact elements are arranged in feed through openings of two guide panels which are spaced apart from one another. The contact elements must be axially movably mounted in the feed-through openings of the guide panels owing to their function. It is desired to prevent a situation in which contact elements which are in the ready-to-operate position of the test head, may drop out of the test head or the feed-through openings, in the direction forced by gravity, for example between two test procedures. DE 23 64 786 suggests providing a support head in the end region of a contact element having external dimensions which are greater than the clear width of the feed through openings. The enlargement of the diameter of the contact elements which is brought about by the support head gives the respective contact element an increased space requirement. The resulting relatively large distance between the contact elements makes it no longer possible to make contact with small test points which are arranged in a very tight space, as is frequently the case with semiconductor components under test, for example.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a test head in which the contact elements can be arranged closely next to the other and can easily be replaced.
The test head uses a plurality of contact elements, each in the form of an elongate strip of elastic and resilient electrically conductive material and having contact tips at the opposite ends. A test head is used for making contact with test points of an electric component under test and with contact points on a board, for example. A plurality of spring elastic, elongated electric contact elements have opposite ends which respectively contact a test point at one end and a contact point at the other end. A plurality of at least two and preferably three guide panels are located in the space between the test points and the contact points. A respective, first, second and third opening is provided in the first, second and third panels for each of the contact elements, with two respective openings in adjacent panels for each of the contact elements being laterally offset and misaligned so that the contact element passing through them is held in a friction locked fashion.
The test head of the invention guides the contact elements in respective assigned feed through opening of the guide panels for movement in an axially displaceable fashion. Feed through openings of different guide panels assigned to each contact element are arranged laterally offset from and misaligned with respect to one another in such a way that the contact element is held in the panel openings, or at least in one of the openings, in a frictionally locked fashion. The holding forces which act on the contact element result from the frictional engagement between the feed through opening or openings and the contact element arranged therein are so high that in a ready to operate position of the test head, that is, when the contact elements are not bearing against the test points of a component under test, the contact elements are held in the feed-through opening or openings and are reliably prevented from dropping out of the test head under their own weight. The holding forces acting on the contact elements due to frictional engagement are also so small that the contact elements can be displaced in the axial direction during a test procedure. The contact elements fold out and/or bend out under spring extension in the intermediate space between the guide panels in the direction perpendicular, or essentially perpendicular, to their longitudinal extent, and as a result, contact force is applied. The contact elements of the component under test may be arranged close to each other, spaced at a preferably very small distance, so that even the functioning of components for testing, which have small test points which are arranged in a very tight space, can be tested. It is therefore possible to avoid enlarging the diameters of the contact elements in order to hold them on the test head, that is, in the feed through openings of the guide panels. A further advantage of the frictional locking holding of the contact elements is that they can be mounted in a service friendly fashion, making it easy to both introduce them into the test head and to replace them when necessary. For this purpose, each contact element merely has to be pulled out of the respective feed through openings of the guide panels or pressed through them.
In a particularly preferred embodiment of the test head, a third guide panel is arranged in the intermediate space between a first guide panel and a second guide panel of the device for making contact. At least one of the feed through openings assigned to a contact element in one of the panels is laterally offset with respect to the other feed through openings for that contact element in the other guide panels. Preferably, the feed through opening of the third or intermediate guide panel is arranged laterally offset with respect to the respective feed through openings of the first and second guide panels, curving or deforming the contact elements in a defined fashion when the test head is assembled. The folding force is completely eliminated while the frictional engagement is formed between the contact elements and in each case at least one assigned feed through opening of the guide panels. The third guide panel also ensures that the contact elements do not touch one another, particularly during a test procedure, so that, if appropriate, electrical insulation between the contact elements can be dispensed with, and this reduces the cost of the test head.
An embodiment of the test head is preferred in which the free end of each contact elements has a contact tip facing towards and/or facing away from the respective test point. This enables contact to be made with very small test points which are arranged close to each other. The small contact face of the contact tip on a test point makes the surface pressure which is produced relatively large forming a good electrical contact. In a first embodiment variant, the pin-shaped contact elements, which are preferably composed of a spring elastic and resilient material, run to a point or are pointed at one or both free ends to form the contact tip or tips. The respective contact element and its contact tips are therefore of integral construction. In another embodiment, the contact tip is a separate component which is attached to the free end of the contact elements. As a result, contact elements with different shapes and/or different sizes of contact tips can be used individually for each test head, which improves the adaptability of the test head. Irrespective of the design of the contact tip, its greatest diameter or greatest width can be smaller or greater than the diameter of the contact element or else they can correspond. The transition from the contact element to the contact tip is either fluid and continuous or else the transition has at least one shoulder.
Other features and advantages of the present invention will become apparent from the following description

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