Electronic card assembly fixture

Details Electronic card assembly fixture Electronic card assembly fixture

1998-10-09

2001-12-25

Metjahic, Safet (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

06333637

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to electronic card assemblies that are probe tested using a pneumatic actuated Side Access Unit (SAU) and, more particularly, to an electronic card assembly test fixture that prevents misalignment of the test probe of the SAU with respect to the test pads of the electronic card.
BACKGROUND OF THE INVENTION
Electronic card assemblies are tested prior to shipment with a vacuum test fixture. The cards are tested by inserting a probe into the card edge connector by means of a pneumatic actuated Side Access Unit (SAU). The force created by the SAU displaces the card in the same direction of the force being applied. This movement can cause the test probes in the test fixture to become perturbed or misaligned with the test pad of the card being tested, preventing adequate probe contact with the test pad.
Test pads on the electronic card require precise alignment, and are located on 25 mil and 50 mil centers. The test pad diameters are small, as little as 20 mils in diameter. Therefore, the test probe of the SAU, when misaligned by as little as 0.003″ to 0.005″ due to test pad movement, can result in testing inaccuracies.
It has been suggested that stationary, or permanently located mechanical stops could be used to oppose the SAU-generated displacement. However, the dimensional tolerances of the finished edge of the electronic card are too great for this scheme to work.
The present invention reflects the discovery that a card edge opposer cam assembly can provide a mechanical stop having a zero tolerance. The opposer cam of the assembly is pneumatically actuated from a common pneumatic system that serves the SAU. The opposer cam is placed against the edge of the electronic card opposite the edge associated with the SAU. This occurs before the SAU is pneumatically engaged. In this manner, the force generated by the SAU is prevented from moving the card test pads out of alignment with the probes.
DISCUSSION OF RELATED ART
In U.S. Pat. No. 4,063,172, issued to Faure et al on Dec. 13, 1977, for MULTIPLE SITE, DIFFERENTIAL DISPLACEMENT, SURFACE CONTACTING ASSEMBLY, a multiple site probe is illustrated. The probes are used to test points on an assembly. The test is performed with the test probes disposed 90 degrees to the horizontal position of the assembly being tested. The test device does not ensure that the assembly being tested is precisely held in alignment. By contrast, the card edge opposer cam of this invention precisely holds the card being tested in alignment in the “X” axis and in the “Y” axis.
In U.S. Pat. No. 4,857,009, issued on Aug. 15, 1989 to Christensen, for FIXTURE LATCHING MECHANISM, a test fixture is shown. The test fixture is aligned to a tester interface on the Hewlett Packard Test Platform. This is the same type of test platform shown in the electronic card assembly of the present invention, but the device does not align the card being tested in the test fixture.
In U.S. Pat. No. 4,950,980, issued to Pfaff on Aug. 21, 1990, for TEST SOCKET FOR ELECTRONIC DEVICE PACKAGES, a socket having an array of terminals is illustrated. The socket is adapted to interconnect with a high pin density integrated circuit. The device tests dual-in-line packages (DIPS). The DIPS are components that are installed on electronic card assemblies to make up the completed assembly. This device is not related to the testing of electronic card assemblies prior to their shipment to the customer.
In U.S. Pat. No. 5,068,601, issued on Nov. 26, 1991 to Parmenter, for DUAL FUNCTION CAM-RING SYSTEM FOR DUT BOARD PARALLEL ELECTRICAL INTER-CONNECTION AND PROBER/HANDLER DOCKING, a device under test (DUT) board connection is illustrated. The device has a circular design that does not conform to the rectangular perimeter of electronic card assemblies. The device tests semiconductors, the components that make up electronic card assemblies.
In U.S. Pat. No. 5,180,975, issued to Andoh et al on Jan. 19, 1993, for POSITIONING DEVICE AND IC CONVEYOR UTILIZING THE SAME, a device is shown for testing integrated circuit components that make up a completed electronic card assembly.
In U.S. Pat. No. 5,471,148, issued on Nov. 28, 1995 to Sinsheimer et al, for PROBE CARD CHANGER SYSTEM AND METHOD, a probe system is shown. The system is not related to testing completed electronic card assemblies, the probe being used to test semiconductor wafers.
In U.S. Pat. No. 5,644,246, issued to Lee et al on Jul. 1, 1997, for PROBE CARD LOCKING DEVICE OF A SEMICONDUCTOR WAFER PROBE STATION, a locking device is shown. The locking device tests semiconductor wafers and, again, is not related to testing completed electronic card assemblies.
In the IBM TECHNICAL DISCLOSURE BULLETIN, Vol. 27, No. 2, dated July 1984, a fixture is shown for feeding and registering circuit boards of different lengths.
In Soviet Union Patent No. 10,119,679, a device is illustrated for testing electronic card ASMs. The test probes of this device are engaged vertically in the “Z” axis. Alignment does not appear to depend upon any force applied along the “X” or “Y” axes. By contrast, the card edge opposer cam of the present invention provides a mechanical stop to maintain precise alignment.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a test fixture for an electronic card assembly. The electronic card assemblies are probe tested by pneumatically actuating a Side Access Unit (SAU), which makes contact with the test pads of the card assembly. The test pad diameters are as small as 20 mils, and are located on 25 mil and 50 mil centers. These very exacting tolerances require precise alignment with the test probe. However, when a test probe is advanced into position to test these pads, its forward movement imparts a forward movement to the test pads, thus misaligning the probe with respect to the test pads.
The test fixture provides a pair of cams oppositely situated from the SAU. These cams are pneumatically actuated slightly prior to, or instantaneously with, the SAU. The actuation of the cams provides a mechanical stop with zero tolerance, so that the misalignment caused by the forward movement of the test probes is eliminated. The pneumatically actuated cams provide an opposing force that counteracts the force imparted by the probes of the SAU, and is accurate up to 0.025″ variation in the dimensions of the card edge. The test fixture provides alignment in both the “X” and “Y” axes.
The pneumatically actuated cams of the fixture each comprises a rounded card contact surface on a first, distal end about which each cam pivots. Each cam is rotatively connected to a mounting bracket at this first distal end. The connection is accomplished by a first pin that is disposed in a first hole in the cam, and which aligns with a hole in the mounting bracket. The mounting bracket is in turn attached to a pneumatic cylinder at an opposite end. The piston of the pneumatic cylinder is attached to a second distal end of the cam, and provides the force that causes the cam to pivot about its first distal end. The piston is attached to the second distal end of the cam through a second pin. The second pin is rotatively disposed in a second hole of the cam, and is guided in a slot formed in a pivot block attached adjacent the cam and its second cam hole. As the piston pushes the second pin, the cam is caused to pivot about its first pin, causing its rounded surface on the first distal end to come into camming contact with the card edge.
It is an object of this invention to provide an improved test fixture for an electronic card assembly.
It is another object of the invention to provide a test fixture for an electronic card assembly that prevents misalignment caused by probes of the Side Access Units.


REFERENCES:
patent: 3970934 (1976-07-01), Aksu
patent: 4063172 (1977-12-01), Faure et al.
patent: 4714879 (1987-12-01), Krause
patent: 4749943 (1988-06-01), Black
patent: 4857009 (1989-08-01), Christensen
patent: 4950980 (1990-08-01), Pfaff
patent: 5068601 (1991-11-01), Pa

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