Adjustable fast press with PCA shuttle and modular expansion capabilities

A mechanical press for testing printed circuit boards in conjunction with a conventional probe card testing assembly is presented. A press assembly attached to a press mount mounted over the probe card testing assembly includes a movable frame including a plate that is height-adjustable relative the movable frame and a plurality of synchronized force-applying members that are actuatable to extend the plate downward a predetermined distance with equal downward pressure across the plate. The plate is height-adjustable within the movable frame via four elongated rotatable screws that protrude through the upper surface of the press mount in order to moveably support the press assembly. Each screw has a timing belt pulley for synchronous power transmission disposed above the stationary frame upper surface. A timing belt or similar continuous belt or chain engages each belt pulley, thereby synchronizing the rotation of the screws. A shuttle system including 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.

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.

DETAILED DESCRIPTION
 The drawing figures are intended to illustrate the general manner of
 construction and are not to scale. In the description and in the claims
 the terms left, right, front and back and the like are used for
 descriptive purposes. However, it is understood that the embodiment of the
 invention described herein is capable of operation in other orientations
 than is shown and the terms so used are only for the purpose of describing
 relative positions and are interchangeable under appropriate
 circumstances.
 As shown in FIG. 1, a PCB press 10 includes a stationary frame 20 having
 flanges 50, which are attached to a conventional probe card testing
 assembly 30. Probe card testing assembly 30 includes a conventional probe
 card 40 used for testing a printed circuit board 160. PCB press 10
 comprises press assembly 100, which is a fast-acting press that moves
 press plate 150 rapidly through a fixed stroke. Press assembly 100 is
 height adjustable within frame 20 by means of lead screw assemblies 70A,
 70B, 70C, and 70D disposed substantially proximal the peripheral corners
 of press assembly 100. For purposes of clarity, only the details of lead
 screw assembly 70A are described in detail, however, lead screw assemblies
 70B-70D comprise substantially identical elements. Lead screw assembly 70A
 comprises an upper bearing portion 86A that rotates within but is
 constrained in the axial direction by bearing journal 88A disposed in
 press mount 60 of frame 20. Lower portion 90A of lead screw assembly 70A
 is threaded into a threaded boss 92A in press assembly upper plate 110
 such that, when lead screw 70A is rotated, upper plate 110 (and with it
 press assembly 100) are drawn toward or forced away from press mount 60 of
 frame 20. Disposed atop lead screw assembly 70 is a driving member 80A,
 which preferably comprises a gear, chain sprocket, timing belt pulley or
 similar apparatus for receiving synchronized power transmission.
 With reference to FIGS. 1 and 2, in the illustrative embodiment, four lead
 screw assemblies 70A-70D are disposed proximal the peripheral corners
 72,73,7475 of press assembly upper plate 110 (shown in dashed lines in
 FIG. 2). A conventional link-and-roller chain 170 engages driving members
 80A-80D in conventional fashion to cause the rotation of all of lead screw
 assemblies 70A-70D to be synchronized. By synchronizing the rotation of
 lead screw assemblies 70A-70D, each of which have the identical helical
 pitch, upper plate 110 can be moved toward or away from press mount 60 of
 frame 20 while maintaining upper plate 110 in a precisely horizontal
 attitude. For added stability, stabilizer rail 211 is rigidly mounted in
 press mount 60 so as to slidingly engage a stabilizer bushing 212 in press
 assembly upper plate 110. Additional stabilizer rails may be added as
 required for the particular application. Lead screw assemblies 70A-70D may
 be manually adjusted or, as shown in FIG. 2, a drive motor 190 may be
 coupled via sprocket 210 to chain 170 thereby providing a power-adjustment
 feature. Although a conventional link-and-roller chain is disclosed in the
 illustrative embodiment, a timing belt, gear train, flexible shafting, or
 any other conventional means of synchronously driving a plurality of
 parallel shafts is contemplated within the present invention.
 FIG. 3 is a partial cross-section of FIG. 1 along line 3--3 with the press
 plate 150 near the fully extended position (press plate 150 is shown fully
 retracted in FIG. 1). With reference to FIGS. 1 and 3, press assembly 100
 comprises side plates 101A and 101B, which are rigidly attached to
 opposite sides of press assembly upper plate 110. Each of side plates 101A
 and 101B support substantially equivalent actuator mechanisms 120A (FIG.
 3) and 120B (not shown). Accordingly, for the sake of brevity, only the
 actuator mechanism supported by side plate 101A is discussed in detail
 herein. Side plate 101A has a channel 102A formed therein. Disposed within
 channel 102A is a linear gear, also known as a rack, 104A. Rack 104A
 engages driven pinions 106A and 108A and also engages a drive pinion 112A.
 Driven pinions 106A and 108A are coupled to bell crank arms 116A and 118A,
 respectively. Crank pins 122A and 124A, respectively, are disposed
 transversely in bell crank arms 116A and 118A, respectively, such that the
 distance from the center of pinion 106A to crank pin 122A is equal to the
 distance from the center of pinion 108A to crank pin 124A. Crank pin 122A
 engages a corresponding slot 132A in press plate 150 and crank pin 124A
 engages a corresponding slot 134A in press plate 150.
 In operation, rotary actuator 114 rotates drive pinion 112A, which in turn
 causes rack 104A to translate along channel 102A. Translation of rack 104A
 causes pinions 106A and 108A to rotate in unison, which causes bell crank
 arms 116A and 118A also to rotate in unison, thereby extending press plate
 150 downward. Guide rail 300 is rigidly mounted to press assembly upper
 plate 110 such that it engages a guide bushing 310 in press plate 150.
 Guide rail 300 thereby constrains press plate 150 to move vertically along
 guide 300 as bell crank arms 116A and 118A rotate. Because bell crank arms
 116A and 118A move in unison, press plate 150 is extended downward with
 equal downward pressure at both ends.
 It should be observed that, unlike linear actuators or ball-screw type
 presses, the vertical force exerted by bell crank arms 116A and 118A is a
 function of 1/sin of the angle between bell crank arms 116A and 118A and
 the horizontal. Since 1/sin approaches infinity as the angle approaches 90
 degrees, the vertical force multiplication exerted by bell crank arms 116A
 and 118A is highest at the beginning and end of the stroke. Thus, the
 actuator mechanism 120A moves rapidly through most of the stroke yet is
 able to exert a substantial downward force on the PCB being tested with a
 modest torque exerted at pinions 106A and 108A. In the illustrative
 embodiment, the distance between the center of pinions 106A and 108A is
 two inches. Thus, the total stroke of press plate 150 with bell crank arms
 116A and 118A moving through 180 degrees is four inches.
 FIG. 4 is an isometric perspective view of press assembly 100. As noted
 above, side plate 101B supports an actuator mechanism 120B, which is a
 functionally identical, mirror image of actuator mechanism 120A discussed
 herein. Preferably, rotary actuator 114 comprises a conventional
 double-ended actuator having a common shaft 115 that drives both driven
 pinion 112A of actuator mechanism 120A and a corresponding driven pinion
 112B of actuator mechanism 120B. In this way, rack 104A and rack 104B are
 translated synchronously within corresponding channels 102A and 102B. This
 in turn ensures that actuator mechanism 120A and 120B are synchronized
 and, therefore, that equal pressure is applied to all four corners of
 press plate 150. Rotary actuator may 114 may be electrically or vacuum
 operated, but is preferably a conventional pneumatic rotary actuator.
 Brackets 125A and 125B depend from side plates 110A and 110B and provide
 an installation platform for optional conventional equipment that may be
 used to test electronic elements disposed on the upper surface of a PCB.
 As seen in FIG. 5, PCB press 11 is shown with press assembly 100 disposed
 within stationary frame 210 which comprises a dual-bay version of frame
 20. Also shown is an optional shuttle system 220 enabling mechanical
 placement of circuit board 160 upon testing assembly 30. Shuttle system
 220 consists of at least one drawer 230 and a drawer support that may take
 the form of a set of rails 240, 241 and 242. Rails 240, 241 and 242 allow
 drawer 230 to move in and out of frame 20 and to be placed in a position
 below press assembly 100 for circuit board 160 testing. Movement of drawer
 230 in an out of frame 20 may be manually or automatically produced.
 Drawer 230 has a substantially open bottom surface 250 that simultaneously
 supports a circuit board 160 placed thereon and enables interfacing forced
 by press plate 150 between circuit board 160 and probe card 40. Shuttle
 system 220 protects the fragile probe card assembly by providing a bed
 into which the operator places the PCB remote from the probe card assembly
 and thus enables precise regulation of the extent to which the PCB
 contacts the probe card assembly.
 Although the invention has been described in terms of the illustrative
 embodiment, it will be appreciated by those skilled in the art that
 various changes and modifications may be made to the illustrative
 embodiment without departing from the spirit or scope of the invention. It
 is intended that the scope of the invention not be limited in any way to
 the illustrative embodiment shown and described but that the invention be
 limited only by the claims appended hereto.