Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With rotor
Reexamination Certificate
1998-05-29
2001-02-20
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With rotor
C324S758010
Reexamination Certificate
active
06191572
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to testing of printed circuit boards for use in electronic products and, specifically, to a press for engaging a printed circuit board to a probe card assembly.
BACKGROUND OF THE INVENTION
After printed circuit boards have been manufactured, and before they can be used or placed into assembled products, they must be tested to verify that all required electrical connections have been properly completed and that all necessary electrical components have been attached or mounted to the board in proper position and with proper orientation.
Other reasons for testing are to determine and verify whether the proper components have been used and whether they are of the proper value. It is also necessary to determine whether each component performs properly (i.e., in accordance with the specification). Some electrical components also may require adjustment after installation.
Most testers utilize a “bed-of-nails” design, which includes a probe surface having plural (thousands) of sockets that are interconnected to test equipment, such as a computer with the appropriate software. Test probes are insertable in these sockets and protrude upwardly from the probe surface. These probes are configured to match the input/output connection points of the electronic components, such as integrated circuits, resident on the printed circuit board (PCB) being tested. Further, the probes are biased upwardly such that, to ensure proper alignment, a card must be placed over the probes and sufficient downward force must be provided to the PCB such that proper electrical connection is made between the inputs/outputs of the electronic components and the test equipment, via the biased test probes.
Fixturing systems have been developed for purposes of handling printed circuit boards for testing. The most common of such fixturing systems is a vacuum fixture. There are many disadvantages associated with vacuum fixturing. In vacuum fixturing, atmospheric pressure acts directly on a PCB with a vacuum beneath it, forcing the board against spring loaded testing probes. Problems arise from the need to maintain a seal around and across the board. Maintaining a vacuum seal in an automated environment is even more troublesome. Warped printed circuit boards are commonly encountered and require a separate effort or effect to push and seat them in the fixture gasketing material. PCBs with holes or apertures generally complicate vacuum fixturing techniques because of the difficulty associated with maintaining a proper seal. Also, probe density is limited by atmospheric pressure. The seals and gasketing required also involve much periodic maintenance, and contaminants and other foreign matter may be aspirated by the fixture due to the vacuum. Furthermore, vacuum fixtures generally do not provide sufficiently forceful contact between the probes and PCBs to displace contaminants present on the board surfaces, thereby necessitating additional costs and chemical disposal issues associated with pre-cleaning the boards before testing.
In response to the aforementioned problems associated with vacuum fixturing systems, other fixturing systems have been developed, including pneumatically powered systems. The typical pneumatic fixturing system incorporates a flat plate attached to a cylinder. Pneumatic pressure is applied to the cylinder which in turn forces the plate against the printed circuit board disposed on the probes. Testing problems arise from the fact that the center of the plate receives the majority of the force applied by the cylinder. Accordingly, the periphery of the board may not sufficiently contact and be tested by the probes. This is especially true with large and/or thin PCBs. Further, such pneumatic systems are not height adjustable relative the probes and thus are unable to accommodate boards of varying thicknesses and/or component heights.
Accordingly, what is needed in the art is a printed circuit board testing system that enables rapid and evenly distributed pressing of the boards to the test probes, allows adjustability of the press height so as to accommodate differently sized boards, and is modifiable to multiple configurations so as to enable multiple modes of operation.
SUMMARY OF THE INVENTION
According to the principles of the present invention, a mechanical press enabling quick and accurate testing of printed circuit board top and bottom sides in conjunction with a conventional probe card testing assembly is disclosed. The press provides a fixed-stroke actuator coupled with a moveable frame, thereby permitting adjustment of the press relative to the workpiece. In one embodiment, the press comprises plural actuators operating in unison to provide even distribution of force over the PCB.
In the preferred embodiment of the invention, a mechanical press is provided incorporating a stationary frame attached to the probe card testing assembly top plate. Four elongated rotatable lead screws protrude through the upper surface of the stationary frame in order to moveably support a press assembly, thereby permitting height adjustment. Each of the lead screws has a timing belt pulley or similar means for synchronous power transmission disposed above the stationary frame upper surface for driving the lead screw. A timing belt or similar continuous belt or chain engages each belt pulley, thereby synchronizing the rotation of the lead screws. The timing belt is further engaged with the teeth of a bi-directionally rotatable drive shaft proximal the stationary frame. The drive shaft and, accordingly, the lead screws are bi-directionally rotated in unison by an electrically-powered programmable motor thereby permitting the press assembly to be moved upwards or downwards. The press assembly which is suspended by the lead screws comprises a movable frame, a plate attached to the movable frame, and an actuator attached to the plate. The press assembly has four synchronized force-applying members that, when actuated, cause the plate to move rapidly downward a distance of approximately four inches. A shuttle system comprising a drawer and a pair of rails may optionally be provided to allow automatic and convenient circuit board insertion into and removal from the testing assembly. The drawer has a partially open bottom surface and is sized to accommodate a printed circuit board placed therein. The rails are attached to the stationary frame and are configured to engage the drawer and permit horizontal movement of the drawer along at least a portion of their length.
REFERENCES:
patent: 4357575 (1982-11-01), Uren et al.
patent: 4471298 (1984-09-01), Frohlich
patent: 4818933 (1989-04-01), Kerschner et al.
patent: 4845843 (1989-07-01), Babcock
patent: 5094584 (1992-03-01), Bullock
patent: 5614819 (1997-03-01), Nucci
Fowler Dwight
Jacobsen Chris R.
Agilent Technologie,s Inc.
Metjahic Safet
Tang Minh
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