METHOD AND APPARATUS FOR HOLDING A PRINTED CIRCUIT BOARD IN A PRECISE POSITION DURING PROCESSING

Abstract: A printed circuit board holding mechanism includes a vertically movable pin support table having at least one tooling pin mounted thereon. A pair of elongated conveyor rails are separated and oriented parallel with respect to each other. The conveyor rails each support a number of pulleys, which pulleys have a drive belt mounted thereon. A segment of each conveyor rail includes a clamping rail that is spring biased downwardly. Clamping rails mounted on opposing rails are oriented to face each other so that foils associated with each clamping rail can engage opposite top edges of a printed circuit board when the movable pin support table is actuated upwardly. The movable pin support table is actuated upwardly so that the tooling pin mounted thereon contacts a bottom surface of the printed circuit board to move the printed circuit board up and off of the drive belts and into engagement with the foils associated with the clamping rails. On or more slotted support strips mounted on the rails are contacted by the pin support table and move with the table to contact the bottom surface of the printed circuit board to provide edge support for the board. In this orientation, the printed circuit board is no longer supported by the resilient drive belts, rather, the printed circuit board is securely held between the clamping rails and the tooling pin.

Description: METHOD AND APPARATUS FOR HOLDING A PRINTED CIRCUIT BOARD IN A PRECISE POSITION DURING PROCESSING FIELD OF THE INVENTION This invention relates to a method and apparatus for holding a printed circuit board and; more particularly, to a method and apparatus for holding a printed circuit board while the board is subjected to a solder paste printing process. BACKGROUND OF THE INVENTION The present invention relates to printed circuit board manufacture and; more particularly, to solder paste printers. Solder paste printers are typically employed to form solder paste patterns on printed circuit boards for subsequently mounted electrical components. Generally, solder paste printers include a conventional conveyor system for transporting a printed circuit board through a number of processing stations, including a print station. The conveyor system typically includes a pair of elongated longitudinal rails oriented parallel with respect to each other. The rails each have a number of pulleys mounted thereon, and at least one of the pulleys is motorized. Each of the rails further includes a drive belt mounted on the pulleys, whereby movement of the pulleys causes a printed circuit board positioned on the conveyor to move along the conveyor. One processing station includes the operation of positioning a stencil, which stencil has a planar surface with a number of apertures defined thereon, onto the printed circuit board. Solder paste is thereafter uniformly distributed, in a manner well known in the art, over the planar surface with a squeegee, so that solder is deposited at designated sites on the board. Specifically, a controlled downwardly directed force is exerted on the solder paste by the squeegee so that the solder paste is forced through the number of apertures defined on the stencil and onto the printed circuit board for forming the solder paste patterns thereon. Another processing station can include a mechanical arm assembly that picks and places electrical components onto the printed circuit board. It is important to hold the circuit board substantially flat as well as in a predetermined orientation during printed circuit board processing operations which are conducted at each processing station. Positioning and holding the printed circuit board substantially flat as well as in the predetermined orientation can be difficult because the circuit board substrate is comprised of a relatively thin and flexible material. The downwardly directed forces exerted on the printed circuit board by the squeegee can cause the board to bend or flex while the solder paste patterns are deposited thereon. The resulting solder paste patterns formed on the printed circuit may not register with the designated sites on the circuit board. The problem is further compounded when electrical components subsequently positioned do not electrically connect with the designated sites, resulting in printed circuit board failure. It is important that the printed circuit board not move from the predetermined orientation while depositing the solder paste patterns on the board with the squeegee. This can occur as a result of the printed circuit board being supported on drive belts constructed of an elastic material such as rubber. If the printed circuit board moves from the predetermined orientation during the solder paste printing process, the solder paste patterns formed on the printed circuit board may be misaligned. A prior mechanism for holding a printed circuit board in position is shown and described in U.S. Patent No. 5, 157, 438 to Beale (hereinafter "Beale"). In Beale, the mechanism for holding the printed circuit board in position for solder paste printing includes supporting the circuit board with a plurality of elongated members ( or support rods) that cooperate with a platform and a number of pneumatic cylinders to actuate the support rods. Beale further includes a mechanism that clamps the edges of the circuit board to the elastic drive belts of the conveyor for minimizing vertical movement of said board. One drawback in Beale is that the clamping mechanism clamps the edges of the printed circuit board to the elastic drive belts, which belts themselves can move as previously mentioned. In addition, another drawback is that the edge clamping mechanism in Beale incorporates clamping foils positioned on each side of the printed circuit board that require actuating devices and controls for such actuating devices. The actuating devices and controls add to the expense and complexity of the clamping functions. With the increased number of electrical components that are affixed to printed circuit boards, there are increased requirements for precision tolerances in solder paste patterns. Accordingly, a need exists for a printed circuit board holding mechanism that holds the printed circuit board in a precise position during solder paste printing operations and which overcomes limitations and deficiencies of the prior art. SUMMARY OF THE INVENTION One object of the present invention is to provide an improved printed circuit board holding mechanism for securely holding a printed circuit board in a predetermined position during solder paste printing. In accordance with principles of the present invention, a solder paste printing apparatus is set forth having the improved printed circuit board holding mechanism which securely holds a printed circuit board in a predetermined position while the printed circuit board is subjected to a solder paste printing process. In one embodiment, the printed circuit board holding mechanism includes a vertically movable pin support table having at least one tooling pin or other support member mounted thereon. The circuit board holding mechanism further includes a pair of elongated conveyor rails that are separated and oriented parallel with respect to each other. The conveyor rails each support a number of pulleys, which pulleys have a drive belt mounted thereon. At least one segment of each conveyor rail further includes a clamping rail that is spring biased downwardly. The clamping rail is dimensioned to engage opposite top edges of the printed circuit board when the movable pin support table is actuated upwardly. The movable pin support table is actuated upwardly so that the tooling pin or other support member mounted thereon contacts the bottom surface of the printed circuit board to move the printed circuit board up and off of the drive belts and into engagement with the clamping rails. In this orientation, the printed circuit board is no longer supported by the resilient drive belts, rather, the printed circuit board is securely held between the clamping rails and the tooling pin or other support member. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects of this invention, the various features thereof, as well as the invention itself, can be more fully understood from the following description when read together with the accompanying drawings in which: Fig. 1 is a partial top plan view of a solder paste printer conveyor system having principles of the present invention; Fig. 2 is a partial side view of the slotted board support strip mounted on the conveyor system shown in Fig. 1 ; Fig. 3 is a partial cross-sectional view of the printed circuit board holding mechanism; and Fig. 4 is partial cross-sectional view of the printed circuit board holding mechanism of Fig. 1 shown in an engaged relationship with a printed circuit board. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides an improved printed circuit board holding mechanism for use in conjunction with a solder paste printing apparatus. In one embodiment of the present invention shown in Figs. 1 and 2, solder paste printing apparatus 5 generally includes conveyor system 10 for transporting printed circuit board 15 through a number of processing stations. Conveyor system 10 typically includes a pair of elongated longitudinal conveyor rails 20 oriented parallel with respect to each other. Conveyor rails 20 each have a number of pulleys 25 mounted thereon, whereby at least one of the pulleys 25 is motorized by, for example, one or more electric motors 26. Drive belt 30 is mounted on the pulleys 25 associated with each rail 20 so that when rotational motion is transposed to the pulleys 25 by the motor, drive belts 30 move linearly. Solder paste printing apparatus 5 further includes a movable printed circuit board pin support table 35 having one or more tooling pins 40 and 41 mounted thereon. Pin support table 35 can be actuated, for example, by a hydraulic or pneumatic cylinder (not shown) to vertically move towards and/or away from printed circuit board 15. Pin support table 35 can be constructed from a rigid and sturdy material such as steel or a metal alloy. Tooling pins 40 and 41, which are mounted on pin support table 35, may be in the form of a cylinder having one end 40a and 41a respectively mounted on the pin support table 35 and another end 40b and 41b respectively adapted to intermittently contact bottom surface 15a of printed circuit board 15. A number of slotted board support strips 55 are slidably attached to each of the conveyor rails 20. Each slotted board support strip 55 can slide vertically upward and/or downward with respect to a mounting screw 56 associated with slotted board support strip 55. Each board support strip 55 includes a first end 55a adapted to intermittently contact pin support table 35 and a second end 55b adapted to intermittently contact bottom surface 15a of printed circuit board 15. While in Fig. 1 the slotted board support strip 55 is shown as being narrow in its dimension perpendicular to the slot, and four such strips are shown, it is to be understood that narrow dimension may be lengthened to, for example, up to the dimension of table 35 to provide support along the entire bottom of board 15. Also, while slotted board support strip 55 and screw 56 mount are illustrated herein, it is understood that other mechanisms may be utilized to move upward and/or downward with table 35 and provide support to bottom surface 15a of printed circuit board 15. For example, slotted board support strips 55 may not be mounted on conveyor rails 20 at all, but rather mounted directly on pin support table 35. Referring to Figs. 1 and 3, at least one segment 50 of each conveyor rail 20 includes a clamp rail support 23 having hollow interior cavity 60 dimensioned to accept a piston 65 having a first end 65a and a second end 65b. First end 65a of piston 65 is dimensioned to conformingly contact first end 70a of helical compression spring 70 which is also positioned in cavity 60. Second end 70b of compression spring 70 conformingly contacts an annular collet 73 formed on an interior portion of cavity 60. When first end 65a of piston 65 is moved upwardly, spring 70 is compressed which forces a second end 65b of piston 65 to extend outwardly from aperture 75 formed on a wall of cavity 60. Clamp rail 80 is coupled to second end 65b of piston 65. Clamp rail 80 includes clamping foil 85 which may be integrally formed on clamp rail 80. Each clamping foil 85 is oriented to extend inwardly so each clamp foils 85 mounted on opposing rails 20 face each other and are dimensioned to overlap opposite top edges 15b of printed circuit board 15. It is to be understood that clamping foil 85 may be separate from clamp rail 80 and joined to clamp rail 80 by adhesives, screws or other conventional attachment devices. Also, it is to be understood that clamp rail 80 with its clamping foil 85 may extend along the entire length of clamp rail 80 or only in segment 50 or even less than the length of segment 50, as desired to hold down printed circuit board 15. During operation and as shown in Fig. 4, pin support table 35 moves upwardly until one end 41b of tooling pin 41 contacts bottom surface 15a of printed circuit board 15. After tooling pin 41 contacts bottom surface 15a of printed circuit board 15, pin support table 35 continues moving upwardly and lifts printed circuit board 15 off conveyor system 10. Printed circuit board 15 continues to move upwardly until top edge 15b of printed circuit board 15 contacts each of foils 85 defined on clamping rails 80. Upon contacting foils 85 of clamping rails 80 with printed circuit board 15, clamping rails 80 and foils 85 move upwardly, however, clamping rails 80 and foils 85 are spring biased downwardly. Upward movement of clamping rails 80 and foils 85 is limited by the distance that compression spring 70 can travel. Compression of compression spring 70 generates a downwardly directed pre-load force on clamping foil 85 which is transposed to top edge 15b of printed circuit board 15 to securely hold printed circuit board 15 in a sandwiched position between foils 85, second ends 55b of board support strips 55 and one end 41b of tooling pin 41. Also, during the same movement in which the pin support table 35 moves upwardly, the pin support table contacts first ends 55a of slotted board support strips 55. After initial contact, and as pin support table 35 continues its upward movement, slotted board support strips 55 slide upwardly along mounting screw 56 until second ends 55b of slotted board support strips 55 contact bottom surface 15a of printed circuit board 15 and lifts the printed circuit board 15 off drive belt 30. At the upper limit of movement of pin support table 35, printed circuit board 35 is securely held in a suspended position off conveyor, system 10 (Fig.4). Printed circuit board 15 is supported on bottom surface 15a by slotted, board support strips 55 and tooling pin 41 and top edges 15b of printed circuit board 15 ar&held by clamping rails 80 and associated foils 85. In this orientation, printed circuit board 15 is securely held so that motion of printed circuit board 15 during processing is significantly reduced or eliminated. As shown in Fig. 4, the height of slotted board support strip 55 and tooling pin 41 are preferably equal so that substantially the same support is provided to bottom surface 15a of printed circuit board 15. Also, while tooling pin 41 is '.shown as having a substantially conical portion 41b, it is to be understood that tooling 41 may be of any desired shape or dimension and used in a suitable number across upper surface 35a of pin support table 35 to provide support for an interior region of bottom surface 15a of printed circuit board 15.

Claims: What is claimed is: CLAIMS 1. An apparatus for supporting a circuit board, comprising: a horizontally disposed conveyor for transporting the circuit board to a processing station; a pair of clamp rails including first and second rails mounted on opposite sides of the conveyor at the processing station, the clamp rails being biased vertically downward to releasably engage the circuit board in the processing station; and at least one moveable tooling pin positioned on a pin support table located below the conveyor at the processing station, the support table being movable in an upward vertical direction, where upon upward vertical movement of the support table, the at least one tooling pin contacts a bottom surface of the circuit board at the processing station for lifting the circuit board off of the conveyor and ensures contact of a top edge portion of the circuit board against the clamp rails. 2. The apparatus for supporting a circuit board of claim 1, wherein the tooling pin is a cylinder having one end adapted for mounting on the pin support table and another end adapted to contact the bottom surface of the circuit board. 3. The apparatus for supporting a circuit board of claim 1, further including a plurality of vertically disposed elongated board support strips mounted on the conveyor for vertical upward and downward movement with respect to the conveyor. 4. The apparatus for supporting a circuit board of claim 3, wherein each support strip includes a first end adapted to contact the pin support table and a second end adapted to contact the bottom surface of the circuit board when the pin support table moves in an upward direction, the strips supporting bottom edges of the circuit board against the pair of clamp rails . 5. The apparatus for supporting a circuit board of claim 4, wherein each elongated strip includes an elongated slot, a pin positioned in the slot and fixed to the conveyor travels within the slot such that movement of the elongated strip is limited by the length of the elongated slot. 6. The apparatus for supporting a circuit board of claim 1, wherein each clamp rail includes a clamping foil which engages the top edge portion of the circuit board. 7. The apparatus for supporting a circuit board of claim 1 , wherein the conveyor includes: a pair of elongated longitudinal conveyor rails oriented parallel to but spaced from each other; a plurality of pulleys mounted on each conveyor rail; a motor coupled to at least one pulley of the plurality of pulleys; a drive belt mounted on the pulleys on each conveyor rail, such that upon rotational motion of the pulleys by the motor, the drive belts move in a linear direction. 8. The apparatus for supporting a circuit board of claim 1, further comprising a clamp rail support at the processing station, the clamp rail support having a hollow interior cavity dimensioned to accept a piston, the piston having a first end and a second end, the first end being dimensioned to contact a first end of a helical spring positioned in the cavity and the second end of the piston being coupled to the clamp rail, a second end of the spring being seated in an annular collet formed on an interior portion of the cavity, wherein if the first end of piston is moved upwardly, the spring is compressed to enable the second end of the piston to extend outwardly from an aperture formed on a wall of the cavity to move the clamp rail upwardly. 9. A method of processing a circuit board, comprising the steps of: (i) positioning the circuit board on a substantially horizontal conveyor and moving the circuit board to a processing station; (ii) moving a horizontally disposed pin support table located below the conveyor at the processing station upwardly such that a tooling pin mounted on the pin support table contacts a bottom surface of the circuit board to lift the circuit board upwardly off of the conveyor; (iii) moving the circuit board upwardly until opposite top edge portions of the circuit board contact foils defined on a pair of downwardly biased clamping rails, the foils and the tooling pin supporting the circuit board; and (iv) processing the circuit board. 10. An apparatus for supporting a circuit board, comprising: a conveyor for transporting the circuit board through a number of processing stations; means for releasably engaging the circuit board; and means for lifting the circuit board off of the conveyor system and into engagement with the means for releasably engaging the circuit board to support the circuit board in a suspended position. 11. The apparatus for supporting a circuit board of claim 10, wherein the means for releasably engaging the circuit board includes at least one pair of clamp rails. 12. The apparatus for supporting a circuit board of claim 11, wherein each clamp rail includes a clamping foil that is adapted to engage a top edge region of the circuit board. 13. The apparatus for supporting a circuit board of claim 12, wherein each clamp rail is coupled with a rail support having a hollow interior cavity dimensioned to accept a piston. 14. The apparatus for supporting a circuit board of claim 13, wherein the piston includes a first end and a second end, the first end being dimensioned to contact a first end of a helical spring positioned in the cavity and the second end of the piston being coupled to the clamp rail, a second end of the spring being seated in an annular collet formed on an interior portion of the cavity, wherein if the first end of piston is moved upwardly, the spring is compressed to enable the second end of the piston to extend outwardly from an aperture formed on a wall of the cavity to move the clamp rail upwardly. 15. The apparatus for supporting a circuit board of claim 10, wherein the means for lifting the circuit board off of the conveyor system includes a movable pin support table having a mounting surface adapted to accept a tooling pin. 16. The apparatus for supporting a circuit board of claim 15, wherein the tooling pin includes a cylinder having one end mounted on the pin support table and another end adapted to contact a bottom surface portion of the circuit board. 17. The apparatus for supporting a circuit board of claim 16, wherein the means for lifting the circuit board off of the conveyor system further includes a number of elongated board support strips slidably mounted on the conveyor system. 18. The apparatus for supporting a circuit board of claim 17, wherein each board support strip includes a first end adapted to contact the pin support table and a second end adapted to contact the bottom surface of the circuit board. 19. The apparatus for supporting a circuit board of claim 16, wherein the means for lifting the circuit board off of the conveyor system further includes a number of elongated board support strips, each strip having a first end mounted on the pin support table and a second end adapted to contact the bottom surface of the circuit board.

Inventors: ASHTON AUGUSTUS T, WILLSHERE RICHARD, ASHTON, AUGUSTUS, T., WILLSHERE, RICHARD
Applicants: SPEEDLINE TECHNOLOGIES INC, SPEEDLINE TECHNOLOGIES, INC.
Application year: 2000
Main classification: H05K13
IPC codes: H05K3, H05K13