Roller contact with conductive brushes

Details Roller contact with conductive brushes Roller contact with conductive brushes

2002-10-28

2004-03-30

Pert, Evan (Department: 2829)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C324S762010

Reexamination Certificate

active

06714028

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to the field of cantilever type electrical contactors, and more particularly to those that wipe (as “wipe” is defined below) across the termination surface or area of a device under test while making contact therewith.
2. Description of the Prior Art
In the field of miniature electronic devices there are numerous devices, such as miniature capacitors having conductive end terminations, that require testing to insure the quality of their electronic capabilities. These devices are presently tested using one of two types of contactors where the contactors are used to temporarily connect to the conductive ends for the purpose of electrical measurement. The first type is a “wiping” or cantilever contactor and the second is an “actuated” contactor.
A cantilever-type contactor typically has a flat spring metal arm which is canted or angled with respect to the device to be contacted. At the free end of the arm is a contactor. The contacting area of the device under test (hereinafter called a “DUT”) is moved, actually or relatively, such that the contactor rubs or passes, i.e., “wipes”, across the area and the cantilever arm is deflected slightly. The spring in the arm applies pressure on the contact area of the DUT, sufficient pressure for good electrical contact. This wiping technique can use one cantilever arm and one, opposite, stationary contact point, or two cantilever arms, one at each end of the DUT.
The wiping method, although simple and reliable, has certain drawbacks. The contacting pressure, supplied by the cantilever arm, needs to be controlled carefully. Too little pressure will result in poor electrical contact, too much pressure can damage the termination, i.e., the contacting areas of the device being contacted, particularly when the terminations are coated with a tin or tin/lead solder plating. Termination damage to the device is defined as any removal of, or serious injury to, the solder plating, which is typically only 100-200 micro-inches thick. The cantilever contact tip, being relatively stationary, wipes across the entire exposed length of the device termination, creating a relatively large mark on the termination, greatly increasing the chances of termination damage.
Also, due to the increasing miniaturization of electronic devices, minimal clearance exist between the surface of the holding fixtures needed to hold the DUT and the device terminations. The result is that the cantilever tips periodically come into contact with the holding fixture. Since the cantilever tip is relatively stationary, it is abraded by the test fixture material, which is typically FR-4 glass epoxy, or a similar non-conductive material, which tends to have a moderate or high abrasive quality. The cantilever tips become rough from this contact and tend to further damage the DUT terminations. Also, the contactor tips become dirty, either by oxidation or adherence of contaminants to the contact tips, or a combination of both. Access to the contact tips for cleaning is difficult due to the close proximity of the contact tips to the DUT and the device holding fixture(s).
The actuated contactor technique uses moving contact tips, usually in a reciprocating motion, which are brought into contact with the DUT. The contact tips are actuated for each test cycle, moved until they make contact with the DUT, then remain stationary during the measurement process. After measurement, the contacts are moved away from the DUT and the holding plate or fixture is indexed, bringing the next DUT into position for the next measurement. Actuated contacts can be made with very small tip sizes in order to reduce any marking of the termination ends of the tested device, unlike the wiping contact technique. Due to the high throughput of production testing equipment, this actuation cycle must be done at a very high speed and at rapid rates. For example, a component tester such as the Palomar Model 3300 would require 37,500 contactor actuation cycles per hour, running 150,000 parts per hour. If the components used for the actuation mechanism lasted 30,000,000 cycles, they would have to be replaced every 40 days, assuming 20 hours of machine run time per day. If the actuation time was only 10 micro-seconds in each actuation direction, the system throughput would be decreased by 10,000 parts per hour. Actuated contacts can also push or pull the DUT out of its holding plate/fixture, and the contact tips tend to be more expensive, requiring moving or flexible electrically conductive components, such as gold plated springs, or very flexible wire segments.
Prior art cantilever type contactors also include a roller supported by an axle that is, in turn, housed between a pair of spaced-apart flanges and held therein by an overhead axle clamp to form a rolling contactor. The flanges are supported by the cantilever arm and, when testing is under way, the arm and flanges are lowered to a point where the roller is brought into contact with the top of the device termination. The DUT is moved under the roller, making contact therewith, and test signals, passed through the device from the other end (or vice versa), are received in the roller and passed upward through the axle, then to the flanges, and into the arm for transmittal to a test device located at the remote end of the cantilever arm. Thus designed, contact between the roller and the DUT termination is a product of three distinct downward forces, to wit: the downward force of the cantilever spring arm, the downward force of the axle clamp, and the downward force of the axle against the inside rim of the roller. When measurement takes place, these three downward forces are balanced by the upward force of the DUT through contact between the DUT termination surface and the outer surface of the roller.
While the use of these rollers has ushered in a general improvement over the prior art of high speed device testing, the three combined forces often prove too severe for the DUT termination and cause damage to the surface of the termination. Once the surface is damaged, the device is no longer able to perform its electrical functions in high quality electronic environments and is relegated to other, low quality uses. Accordingly, there continues to be a need for a testing contactor that will provide rapid, positive contact with the DUT termination yet not be as positive in downward force as to cause damage to the termination surface.
In addition, the prior art contactors are in some cases, ganged together and set side-by-side in groups of four (4) or more so that four different DUTS could be brought into simultaneous contact with one set of four contactors to increase the throughput of the machine. The prior art does not provide adequate control to the level of the rollers causing one or more rollers to lie above or below another. To insure positive contact with the highest roller, the other rollers are pushed down harder to bring all the rollers, including the highest roller, into positive contact with the termination surfaces of their respective DUTs resulting in different pressures being brought to bear on the various devices. This difference in pressure often causes false readings on test equipment as well as damage to the DUT termination surfaces.
This invention is a contactor that will allow rapid and repeated electrical connection to the terminations of many types of DUTS with little or no damage or markings to their respective surfaces. The electrical contactor according to this invention is a significant advance over the prior art. It eliminates the damage done to the solder plating on the terminations of devices due to the “wiping” action of the cantilever type contactors and is simpler and has a longer life than the actuated type contactor. It is particularly useful in component handlers and testers for the processing and testing of electrical circuit components, for example ceramic capacitors. (As used herein the term “component” refers to ceramic capacitors and any other elect

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