Abstract:
The circuit board pallet comprises one or more flat metallic spring arms positioned over magnetized pins. The magnetized pins comprise a magnetic material, such as steel. The magnetized pains contact a permanent magnet embedded inside or attached under the pallet. The metallic spring arms comprise a flexible magnetic material, such as spring steel. The metallic spring arms hold a circuit board to the pallet by a magnetic force created by the permanent magnets which attracts the spring arms towards the pins. The magnetized pins can also be used to secure component placement jigs to the circuit boards pallet.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is directed, in general, to a pallet with a spring arm and magnetized pin for accurately positioning and holding a printed circuit board during manufacturing processes.  
       BACKGROUND OF THE INVENTION  
       [0002]     Circuit board manufacturing is well known in the art. Electrical components such as processors, memory, capacitors, diodes, resistors, and the like attach to a blank circuit board to create a board for installation in an electrical device such as a computer. The blank circuit board must be held in place during the manufacturing process, usually through the use of a circuit board pallet. The circuit board must perfectly align with the pallet for accurate application of solder and components.  
         [0003]     The circuit board undergoes a step called solder stenciling during the manufacturing process. During the solder stenciling step, the printed circuit board enters a solder stenciling machine. A portion of the solder stenciling machine lowers onto the printed circuit board from above and deposits solder onto the printed circuit board. Clamps for holding circuit boards to the pallet must not protrude above the surface of the top of the pallet because the protrusions interfere with the solder stenciling machine, preventing the machine from contacting the board and depositing the solder paste. The solder stenciling machine exerts a slight suction or adhesion which can lift the circuit board upwards after solder deposition. Pallets must be machined to hold the printed circuit board in position during solder stenciling and other steps of the circuit board manufacturing process.  
         [0004]     Recessed spaces, or cavities, in pallets allow the circuit board to remain flat when components extend through to the back side. Cavities in the pallet can also be used when components have previously been mounted to the back side of the circuit board. Pallets may also have a means for attaching a jig to the top of a circuit board. Jigs have cut-outs used to align and support components mounted to the front of circuit board.  
         [0005]     Pallets vary in size and thickness depending on the size of the printed circuit board. Since the pallets are reused numerous times, an apparatus for positioning and holding the printed circuit board must be simple, reliable, easy to manufacture and inexpensive. The printed circuit board must be held in position so that it does not move from side to side or upward, away from the pallet. If the circuit board bends or moves, components, solder and leads will not align properly. Therefore, a way to apply pressure to the printed circuit board to hold it in place without deformation is needed.  
         [0006]     There exists in the art several methods to secure printed circuit boards to the pallet. Some pallets are made by machining a suitable material to create a recessed space in the pallet for receiving the entire printed circuit board. When positioned within the recessed space, the printed circuit board lies flat and level with or parallel to the top surface of the pallet. Various shaped pins or clamps position and hold the circuit board in place.  
         [0007]     One method of holding circuit boards to pallets uses adhesive tape. Either adhesive tape holds the back side of a circuit board to the pallet, or adhesive tape stretches across a portion of the top the circuit board, clamping the circuit board to the pallet. A drawback to adhesive tape is loss of adhesion. Over time, the sticky qualities of adhesive tape degrade, and circuit boards will not be held securely. Heat from processes such as solder reflow accelerates the degradation of the tape. As a result, tape must be replaced frequently.  
         [0008]     U.S. Pat. No. 6,012,713 discloses a pallet for holding a printed circuit board during the solder stenciling step wherein one or more lever arms cut from the pallet material hold the printed circuit board. The lever arm or arms exert pressure against the printed circuit board by compression or through tension by the addition of a pin to the lever arm.  
         [0009]     Tension and compression clamps are suitable for thick and sturdy circuit boards capable of handling the horizontal stress or pressure. Newer circuit boards, however, are made from very thin and/or flexible materials. Compression clamps can warp thin circuit boards, especially when subject to light vertical forces, like the upward force created by the solder stenciling machine. Tension clamps with pins can bend or even tear very thin circuit boards.  
         [0010]     A need exists for a repeatable method of positioning and holding very thin circuit boards to reflow pallets without damaging or deforming the circuit board.  
       SUMMARY OF THE INVENTION  
       [0011]     An apparatus that meets the need identified above is a circuit board pallet comprising one or more flat metallic spring arms positioned over magnetized pins. The magnetized pins comprise a magnetic material, such as steel. The magnetized pins contact a permanent magnet embedded inside or attached under the pallet. Alternatively, the magnetized pins are made from a permanent magnet. The metallic spring arms comprise a flexible magnetic material, such as spring steel. The metallic spring arms hold a circuit board to the pallet by a magnetic force created by the permanent magnets which attracts the spring arms towards the pins. The spring arms mount to the pallet so that they swivel about a vertical axis, rotating away from the magnetized pins to allow for placement and removal of circuit boards. The spring arms mount in a recess such that the mounts do not extend above the top plane of the pallet.  
         [0012]     In one embodiment of the invention, the magnetized pins extend upwardly from the pallet surface into positioning holes located on the circuit board. In another embodiment, the magnetized pins are flush with the pallet&#39;s top surface.  
         [0013]     Another embodiment of the invention comprise a jig placed on top of a circuit board, holding the circuit board to the pallet. The jig is comprised of the same material as the pallet, having openings for the placement of electronic components. Magnetic material or permanent magnets embedded in the jig hold the jig in place above the pallet&#39;s magnetized pins by a magnetic force.  
         [0014]     Another embodiment of the invention comprises a long metallic spring arm mounted to at least one location on the pallet. The long metallic spring arm substantially extends over an entire edge of a circuit board. The long metallic spring arm holds a circuit board to the pallet by a magnetic force created by at least one permanent magnet which attracts the spring arm towards at least one magnetized pin. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0015]     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will be understood best by references to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0016]      FIG. 1A  shows a prior art circuit board pallet with a flexible tension arm.  
         [0017]      FIG. 1B  shows a prior art circuit board pallet with flexible compression arms.  
         [0018]      FIG. 2  shows an exploded view of the invention and an exemplary circuit board.  
         [0019]      FIG. 3A  shows a cross section of the pallet and a circuit board.  
         [0020]      FIG. 3B  shows a cross section of a circuit board secured to the pallet.  
         [0021]      FIG. 3C  shows an alternate embodiment of the magnetized pin.  
         [0022]      FIG. 3D  shows an alternate embodiment of the magnetized pin.  
         [0023]      FIG. 4A  shows an exploded view of the pallet used with a jig.  
         [0024]      FIG. 4B  shows a cross section of alternate embedded couplings on a jig.  
         [0025]      FIG. 5  shows an alternate embodiment of the metallic spring arm. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]      FIG. 1A  shows a prior art circuit board pallet  100  with a flexible tension arm  140  and a pin  122 . Additional fixed pins  120  aid in locating and securing circuit boards. Pins  120  and  122  engage with circuit board locator holes. Force from tension arm  140  pulls the circuit board away from fixed pins  120 , holding a circuit board in place. Flexible tension arm  140  is machined from the pallet material. A cavity around arm  140  allows room for flexing. Tension arms made from other suitable materials using a spring and shaft apparatus placed inside a cavity on the pallet are known in the art.  
         [0027]      FIG. 1B  shows a prior art circuit board pallet  102  with flexible compression arms  150 . Additional fixed pins  120  aid in locating and securing circuit boards. Compression arms  150  are machined from the pallet material. A cavity around the compression arms  150  allows room for flexing. A shelf area  135  around the cavity perimeter contacts the back edge of a circuit board. Compression arms  150  press against circuit boards placed into cavity  130 , securing circuit boards against the opposite wall of cavity  130  and fixed pins  120 . Compression arms made from other suitable materials using a spring and shaft apparatus placed inside a cavity on the pallet are known in the art.  
         [0028]      FIG. 2  shows an exploded view of the pallet  200  and an exemplary blank circuit board  260 . At least one pin  230  inserts into pallet  200 , pin  230  backed by a permanent magnet  240 . Pin  230  is made of a magnetic material, such as steel. Epoxy  250  or some other material bonds permanent magnet  240  to the back side of pallet  200 . Alternatively, magnet  240  is pressed into the back side of pallet  200  without requiring an adhesive. A swivel joint pin  210  secures a thin, flexible metallic arm  220  to pallet  200  so that arm  220  pivots about a vertical axis. Metallic arm  220  comprises a flexible magnetic material, such as spring steel. Metallic arm  210  secures in a shallow cavity  205  so that the top of swivel joint pin  210  is at or below the plane of the top surface of pallet  200 . Placement of magnetized pins  230  on the pallet corresponds with alignment holes  265  on circuit board  260 . Metallic arm  220  attaches outside the perimeter defined by circuit board  260  when placed on pallet  200 . Metallic arm  220  extends to contact magnetized pin  230 . After circuit board  260  engages with pallet  200 , metallic arm  220  pivots over circuit board  260  and magnetized pin  230 . The magnetic force of magnetized pin  230  attracts the metallic arm  220 , securing circuit board  260 . Metallic arm  220  is thin enough to not interfere with the solder reflow process.  
         [0029]     Other non-magnetized locator pins not shown here may also assist in alignment of circuit board  260  on pallet  200 . Various pin shapes for interfacing with circuit boards and means for securing pins to the pallet are known in the art. An alternative embodiment uses pins made from a permanent magnet. One skilled in the art will understand how to adapt this invention to known pin variations and configurations. Although the drawings show circuit board  260  resting on the top surface of pallet  200 , the invention can be adapted for pallets where the circuit board is located in a recessed cavity on the top side of the pallet. Additional cavities in pallets are commonly used to allow circuit boards to remain flat while components extend through to the back of the circuit board.  
         [0030]      FIG. 3A  shows a cross section view of pallet  200  and circuit board  260 . At least one pin  230  inserts into pallet  200 . Pin  230  comprises a magnetic material, such as steel. Epoxy  250  or some other material secures permanent magnet  240  to the back side of pallet  200 , in contact with magnetized pin  230 . Swivel joint pin  210  secures thin, flexible metallic arm  220  so that it can pivot about a vertical axis. Metallic arm  220  secures in shallow cavity  205  so that the top of swivel joint pin  210  is at or below the plane of the top surface of pallet  200 . Metallic arm  220  comprises a flexible, magnetic material, such as spring steel. Placement of magnetized pin  230  on pallet  200  corresponds with alignment holes  265  on circuit board  260 . Metallic arm  220  attaches outside the perimeter defined by circuit board  260  when placed on pallet  200 . Metallic arm  220  extends above magnetized pin  230 .  
         [0031]      FIG. 3B  shows a cross section of circuit board  260  secured to pallet  200 . Alignment hole  265  in circuit board  260  is placed over the magnetized pin. After circuit board  260  engages with pallet  200 , metallic arm  220  pivots over circuit board  260  and magnetized pin  230 . The magnetic force of magnetized pin  230  attracts the metallic arm  220 , securing circuit board  260 . In this embodiment, magnetized pin  230  protrudes from pallet  200  into alignment hole  265  on circuit board  260 , but magnetized pin  230  does not protrude far enough through circuit board  265  to contact metallic arm  220 .  
         [0032]      FIG. 3C  shows an alternate embodiment of magnetized pin  230 . In this embodiment, magnetized pin  230  protrudes from pallet  200  into alignment hole  265  on circuit board  260 , extending far enough through circuit board  265  to physically contact metallic arm  220 .  
         [0033]      FIG. 3D  shows another embodiment of magnetized pin  230 . In this embodiment, magnetized pin  230  does not protrude past the plane of the top surface of pallet  200 . Magnetized pin  230  will not aid alignment of circuit board  260 . Magnetized pin  230  does not physically contact metallic arm  220  with circuit board  260  placed on pallet  200 .  
         [0034]      FIG. 4A  shows an exploded view of pallet  400 , an exemplary blank circuit board  460  and a circuit board component jig  480 . Pin  420  helps position circuit board  460  through alignment hole  465  on pallet  400 . Magnet  440  contacts the back of pin  420 , magnetizing pin  420 . Cavities  495  in pallet  400  allow for circuit board  460  to remain flat when components extend past the back side of circuit board  460 . An integrated coupling  485  on jig  480  aligns over magnetized pin  430  and circuit board alignment hole  465 . The magnetic attraction of magnetized pin  430  holds jig  480  down, over circuit board  460 . Cut-outs  490  in jig  480  assist in positioning and holding components to circuit board  460  during various steps in the manufacturing process. The use of jigs for positioning and holding components to circuit boards is known in the art.  
         [0035]      FIG. 4B  shows cross sections of coupling  485 . One alternative of coupling  485  comprises cap  486  made of magnetic material embedded inside jig  480 . Another alternative of coupling  485  comprises magnet  488  secured to the jig above alignment hole  487 . Magnet  488  must be oriented with the same polarity as the corresponding magnet  440  on the pallet or else the magnets will repel each other rather than attract to each other.  
         [0036]      FIG. 5  shows an alternate embodiment of the pallet  500 . A long metallic spring arm  520  mounts  510  to at least one location on pallet  500 . Long metallic spring arm  520  substantially extends over an entire edge of a circuit board  560 . Long metallic spring arm  520  holds circuit board  560  to pallet  500  by a magnetic force created by at least one permanent magnet  540  which attracts spring arm  520  towards at least one magnetized pin  530 .  
         [0037]     A preferred form of the invention has been shown in the drawings and described above, but variations in the preferred form will be apparent to those skilled in the art. The preceding description is for illustrative purposes only, and the invention should not be construed as limited to the specific form shown and described. The scope of the invention should be limited only by the language of the following claims.