Printed circuit board tester having a flex and wiping action free vacuum actuated edge connector

An automated tester for a wired PC board is adapted to receive a wired PC board and secure it in a predetermined position by vacuum pressure. After the board is fully secured in position, the vacuum pressure applied to a fixture having an array of electrical contacts forces the contacts into position on the contact fingers of the PC board to provide electrical connection through the tester to connectors whereby the board can be tested. The contact array is controlled in position to make contact with the board fingers only after all board motion induced by the vacuum pressure pulldown has ceased, thereby minimizing scraping action between array contacts and PC board fingers. The fixture further includes a linkage arm arrangement which increases the contacting force of the array at the point of making connection to the PC board fingers to augment the reliability of contact.

FIELD AND BACKGROUND OF THE INVENTION 
The present invention relates to test sets for testing wired PC boards. 
Large PC boards completely wired with components and interconnections are 
typically tested by securing them onto a surface. An array of electrical 
contacts are formed into contact with the electrical connection fingers on 
the connector edge of the PC board. Prior art designs have suffered from 
unreliability due at least in part to a lack of sufficient physical force 
to make reliable contact between a large number of arrayed contacts and 
the many PC board fingers. This is particularly true on automated designs 
in which the fingers and contact arrays are brought together 
automatically. Prior art devices are also known in which the array of 
contacts are pivoted downward onto the PC board fingers with the combined 
motion resulting in an undesirable wiping motion between the array 
contacts and PC board fingers. 
BRIEF SUMMARY OF THE INVENTION 
In accordance with the teaching of the present invention, a wired PC board 
tester is provided in which high reliability of electrical contact between 
PC board electrical contact fingers and a connector array of the tester is 
achieved without wiping action. 
In implementing the preferred embodiment of the present invention, a PC 
board support surface is provided as a top surface of a frame having below 
it an interior chamber capable of receiving a vacuum. The vacuum is 
communicated to the support surface and in particular to apertures 
therethrough in order to receive and securely hold a PC board for testing. 
The vacuum also draws the support surface downward. An array of electrical 
contacts adapted to be lowered into electrical contact with the connector 
fingers along a peripheral edge of the PC board is actuated by a fixture 
responsive to the chamber vacuum to lower the array contacts into 
electrical connection with the fingers only after the vacuum has secured 
the PC board onto the surface and the full downward motion thereof under 
the influence of the vacuum has ceased. In this manner, any wiping action 
between fingers and array contacts is substantially reduced. The fixture 
is provided with a linkage converting the vacuum pressure to downward 
motion of the array of contacts onto the PC board fingers in such a manner 
as to greatly amplify the downward force over the last fractional portion 
of the range of motion of the array. This greatly increases the available 
pressure, forcing the array contacts into electrical connection with the 
PC board fingers so as to increase the reliability of connection 
therebetween. 
The frame includes a plurality of electrical connectors which are wired to 
spring-loaded contacts in a contact board of the frame located below the 
PC board support surface. The PC board support surface contains through 
contacts positioned in locations to make connection to the spring-loaded 
contacts in the frame contact board when the PC board surface is deflected 
downwardly under the influence of the vacuum applied to the frame 
interior. The contact array includes mating connections which are also 
spring-loaded and adapted to contact the through connections of the PC 
board support surface and, by predetermined interconnection, provide 
electrical connection to predetermined ones of the array contacts adapted 
to make electrical connection to the PC board fingers. In this manner the 
array selectively defines the connection between frame connectors and PC 
board fingers.

DETAILED DESCRIPTION 
The present invention contemplates an automated tester for a wired PC board 
in which high reliability of contact between PC board fingers and a 
fixtured array of contacts is achieved by a mechanical linkage that 
enhances the pressure at the point of contact, and in which the wiping 
action resulting from selective engagement of the array of contacts with 
the PC board fingers is minimized. 
An exploded view of such a test system is illustrated with respect to FIG. 
1. As shown there, a frame is defined by first, second, and third side 
panels 12, 14, and 16 and a front side panel 18 adapted to receive a 
plurality of electrical connectors 20. An interior is defined by the frame 
sides 12, 14, 16, and 18 and bottom plate 24 along with a top, connector 
board 26. The interior thus formed contains a vacuum conduit 28 adapted to 
provide connection of a vacuum source through the connector frame side 18 
through the connector board 26 via aperture 30 to a sealed chamber 22 
above the board 26 as described below. 
Above the connector board 26 is a diaphragm board 32 and on top of that a 
diaphragm 34. The entire assembly of contact board 26, diaphragm board 32, 
and diaphragm 34 are sealed together to form chamber 22 by a set of clamps 
36 and sealing bars 38. The diaphragm board 32 contains registration pins 
40 adapted to mate within corresponding holes 42 in the connector board 
26. Springs 44 are provided between the connector board 26 and diaphragm 
board 32 to resiliently support the diaphragm board 32 above the connector 
board 26 under the influence of a vacuum applied through the aperture 30. 
The sealing bar 38 is positioned on connector board 26 outside and 
surrounding the diaphragm board 32, permitting it to recede toward the 
connector board 26 against the resilient force of the spring 44 and under 
the pressure effects of the vacuum applied through the aperture 30. The 
diaphragm 34, however, is forced against the sealing bar lip 38 by the 
clamp 36. 
The diaphragm 34 has a region covered by sealing tape 48 onto which a wired 
printed circuit (PC) board 50 is placed. The diaphragm board 32 and 
diaphragm 34 will typically have apertures in the region covered by the 
printed circuit board 50 in order to communicate the vacuum applied 
through port 30 through the diaphragm board 32 and diaphragm 34 to the 
printed circuit board 50, resulting in securely forcing it downwardly onto 
the diaphragm board 32 and tape 48. Board 32 is resiliently supported by 
the diaphragm 34 within the clamps 36 and resiliently supported by the 
springs 44 above the connector board 26. 
FIG. 2 illustrates apertures 52 through the diaphragm board 32 and 
diaphragm 34 with the printed circuit board removed and within the bounds 
of tape 48 whereby vacuum is applied to the underside of board 50. Board 
50 may have to be sealed by tape. 
Returning to FIG. 1, electrical connection to the contact fingers of the 
printed circuit board 50 is provided through an array 54 of electrical 
contacts fixed within a contact bar 56 which is in turn supported by arms 
58 of a fixture 60, adapted to selectively lower the array 54 and bar 56 
over the printed circuit board 50 in response to the vacuum applied 
through the aperture 30 as described more fully below. The arms 56 are 
pivoted about pivots 62 in response to up and down motion of a gallows 
frame assembly comprising a cross bar 64 activated by a push rod 66 and 
connecting to side arms 68. The side arms 68 connect through pivots 70 on 
either side to a rear arm 72, rearwardly hinged about a pivot 74. A 
connector link 76 is secured between the pivots 62 and 70 such that up and 
down motion of the gallows assembly transmitted through arms 68 results in 
forcing arm 58 to rotate about a pivot 78, raising the contact array bar 
56 with downward motion of the arms 68 and lowering the bar 56 to force 
the array of contacts 54 into electrical connection with the connector 
fingers of the PC board 50, with upward motion of the arms 68 induced by 
application of vacuum to the fixture 60 through the aperture 30. 
The structural and operational features of the fixture 60 are more fully 
illustrated with respect to the views of FIGS. 4 and 5. In FIG. 4, the 
fixture 60 is illustrated with the contact bar 58 lowered in solid lines 
and raised in response to depression of the arms 68 in dashed lines. The 
fixture 60 includes a housing 80 which is typically attached by bolt or 
other means to the diaphragm board 32, through an aperture 82 of the 
diaphragm 34. 
Directly below the diaphragm board 32 and separated by a space 84 is the 
contact board 26, having therein a plurality of spring-loaded feed 
throughs 86. These have contact tips 88 which are spring-loaded and face 
through connectors 90 in the diaphragm board 34. The spring-loaded 
feadthroughs 86 in the contact board 26 are typically electrically 
connected to connectors 20 inserted into the side frame 18 via wires 92 as 
illustrated in FIG. 3. 
Returning to FIG. 4, the contact bar 58 includes additional spring-loaded 
contacts 96 which face the feadthroughs 90 and provide electrical 
connection thereto through spring-loaded contacts 98 when the connector 
bar 58 is lowered over the diaphragm board 32. Contacts 96 are wired to 
contacts at array 54 in a desired pattern which can be changed by bolting 
a new bar 56 to arms 58. 
As can be seen in FIG. 4, the connector link 76 couples up and down motion 
of the arm 68 through pivot 70 between link 76 and back arm 72 into 
rotational motion of the front arm 58, resulting in the application or 
removal of the bar 58 and contact array 54 to fingers 100 on the printed 
circuit board 50. The nature of the linkage effectively amplifies the 
force applied by arms 68 at the lower end of travel of bar 58. This 
results in a substantial increase of the downward force applied to the 
connector bar 58, greatly amplifying the force between the array 54 of 
contacts and the fingers 100, thereby increasing the reliability of 
connection therebetween. Link 76 also allows bar 56 to be raised high 
enough to facilitate changing board 50. 
FIG. 5 provides an interior sectional view of the fixture 60, and in 
particular the housing 80. As shown there, the push rod of the gallows 
assembly is applied centrally through a dome portion 102 of the housing 80 
to a bottom plate 104 which is urged resiliently downward by a set of, 
typically four, springs 106 installed between recesses in the dome 102 and 
plate 104. The housing 80 includes a bottom plate 108 and a bellow 
diaphragm 110 is peripherally secured between the facing edges of the 
bottom plate 108 and upper portion of the housing 80, looping upward and 
then down underneath the plate 104. 
In the position illustrated in FIG. 5, a chamber 112 is formed in the 
region between the plate 104 and the dome 102 of housing 80. An aperture 
114 in the bottom of the plate 108 communicates through a corresponding 
aperture in the diaphragm board 32 to the region between the diaphragm 
board 32 and the connector plate 26, which is in turn in communication 
with the vacuum applied through the aperture 30. This vacuum is applied 
through the aperture 114 to the chamber 112 through passages into the dome 
102. This vacuum pressure forces the plate 104 upwardly taking with it the 
push rod 66 and in turn forcing the contact bar 58 to swing downwardly 
bringing the array 54 contacts into electrical connection with the fingers 
100 on the printed circuit board 50 as illustrated in FIG. 4. The springs 
106 are set with sufficient tension, however, to prevent upward motion of 
the push rod 66 until the effect of the vacuum has forced or drawn the 
printed circuit board 50 downwardly against the resilient effect of the 
diaphragm 34 and springs 44 the full extent of its travel. This minimizes 
the wiping action between the resilient or spring-loaded contacts in the 
array 54 and the fingers 100 of the printed circuit board 50. 
The passage between the aperture 114 and the chamber 112 is preferably 
fitted with an adjustable restriction in order to adjust the impedance in 
the flow of gas between the chamber 112 and the vacuum source. This 
permits an adjustment over the rate of lowering of the contact bar 58 and 
contacts in the array 54. 
It should be noted that where the above description calls for the use of 
spring-loaded electrical feedthrough connections, plunger connections 
according to U.S. Pat. No. 3,435,168 are of preferred design. Typically 
many such connections are made from board 26 to contacts on the underside 
of board 50. 
This completes the description of the solely exemplary preferred embodiment 
of the present invention. The actual scope of the invention is to be 
defined solely in accordance with the following claims.