Patent Document

FIELD OF THE INVENTION 
   The present invention relates to an apparatus for supporting a printed circuit board or other substrate typically having components mounted on one side during installation of other components on the opposite side. 
   BACKGROUND OF THE INVENTION 
   Printed circuit boards (PCB) have long been used as the base for sophisticated electronic systems. An electrically insulating sheet, originally phenolic impregnated fabrics and now generally fiberglass reinforced resins, is coated with copper cladding and has appropriate patterns etched into the cladding. In years past, most electronic components had wire leads that extended through holes drilled into the cladding pattern and filled with solder to make the required connections. More recently, surface bonding of relatively short leads to the cladding has become common, allowing for high-speed robotic placement of components. 
   Today, electronic devices are increasingly miniaturized and it has become desirable to mount component on both sides of a PCB. However, there are a number of problems associated with installing parts on the second side after components have been mounted on the first side. The board cannot be held flat with downwardly projecting components of various sizes and thicknesses mounted on the lower side. This problem is most acute when solder paste is to be printed on the second side. Holding the PCB flat and level under a paste application stencil during solder paste application and then during component placement is very difficult. 
   In high production run circumstances, aluminum plates or similar materials have been machined out in a pattern corresponding to the topography of the first side of the PCB with components installed. This approach is not practical for manufactures or subcontractors producing a limited quantity of a very great number of PCB configurations, each requiring its own “hogged-out” support plate. 
   Supports have also been made by casting a plaster-like material into a mold corresponding to a particular PCB to form a support having pockets for receiving the components on the downwardly extending board side. 
   While effective where a large number of identical boards are to be manufactured, these methods are not cost effective where only a few boards are to be made or where custom boards are being manufactured. 
   A number of different devices having a plurality of adjustable length upstanding fingers have been developed to support an irregularly shaped article. Typical of these devices is the device for supporting parts during machining as described by Barozzi in U.S. Pat. No. 4,936,560, the casting support device describe by Godding in U.S. Pat. No. 4,200,272, and the core support system described by Bourassa et al. in the U.S. Pat. No. 3,530,994. 
   While these supports are generally effective for their intended purposes, they are overly complex, and do not always provide positive support across the supported object. 
   A circuit board support system using a plurality of spaced-apart, parallel, upwardly extending pistons is described by Fadiga et al. in U.S. Pat. No. 3,942,778. This support is used to press the back of the boards against test sensors. Since the pistons are not lockable to match a particular PCB, each succeeding board must be pressed down against the pistons, risking damage. Further, the system is not readily useful in installing components on the back of the board, since the pistons continue to press upwardly so that the board may not lie truly flat and may move during back-side component installation. 
   Thus, there is a continuing need for improved supports for holding a substrate, such as a printed circuit board, having components mounted on one side while additional components are installed on the opposite side, that will support the board in a precisely level position, that will provide strong, consistent support for the board during second surface stencil printing and soldering operations, that can easily be locked in the support position appropriate to a series of similarly configured boards, that precisely indexes board edges and that is easily unlocked and reconfigured for other boards. 
   U.S. Pat. No. 5,897,108 describes a series of plates with aligned holes through which spring loaded pins protrude. A top and bottom plate hold the pins in position laterally, while a middle plate is moved out of alignment to clamp the pins, holding the pins in vertical alignment to the underside topology of the substrate. 
   U.S. Pat. No. 5,897,108 further describes a means for moving the middle plate out of alignment, and then describes two ways to do so. 
   The first way is to move the middle plate by applying force against the edge of the middle plate with screws. Typically, one of the middle plate&#39;s edges protrudes out further than the edges of the top and bottom plates while the pin holes are in alignment. Screws can then be placed through the frame that surrounds the three plates. The screws push against the middle plate&#39;s edge and move it out of alignment. While this method is simple, it will eventually permanently deform the middle plate at the point where force is applied. 
   The preferred way described in U.S. Pat. No. 5,897,108 is to use a cam, which uses holes in the top and bottom plates to anchor the cam at its ends. The cam&#39;s lobe is then pushed against the middle plate, thereby moving it out of alignment when the cam is rotated. This method is not as robust as it could be, in that the anchor points of the cam wear easily because the plates are very thin (typically 0.048″ thick) and made from aluminum. 
     FIGS. 1-3B  illustrate a version of U.S. Pat. No. 5,897,108 that is currently used. It should be noted that while the patent shows a system with a wide array of pins, the units can be made in strips  2 , typically three pins wide, having front-end rail  4 , rear-end rail  6 , and side rails  8 . The strips  2  are then stacked next to each other to make up wider arrays as manufacturing operations, machine conditions and substrate size dictate (compare the first figure of the patent with  FIG. 1  of the current method). 
   While this version still uses a cam  28 , it no longer uses the top and bottom plates  22  and  18  as anchor points. Instead, a cam slot retainer (the cam receptacle)  32  is anchored to the middle (clamping) plate  20  with four screws  38 . One end of the cam is then fixed with a cam block housing (the cam hub)  24 , which in turn is anchored to the very bottom (base) plate  10  of the system. The cam block housing&#39;s position can be adjusted back and forth with an adjustment screw  26 , and four screws  40  then hold the block in position to the bottom, as seen in  FIGS. 2 and 3 . Elastically compressible elements, such as pin springs  14 , are positioned in recesses formed in base plate  10  and preferably separated by plastic insert plates  12 . These compressible elements exert an upwardly directed biasing force on pins  16 , which protrude through the apertures  36  in the bottom, middle and top plates. With the cam&#39;s hub  24  anchored at the base  10 , the cam lobe rotates inside the cam slot retainer  32 , which in turn moves the middle plate  20  out of alignment, thereby distorting and locking pins  16  in position. A T-handle Allen wrench  34  is used to engage the cam  28  and rotate it to its locked and unlocked positions. 
   There are also two plate return springs  30  that push against the front-end rail  4  and the cam slot retainer  32 . When the pins  16  are unlocked by rotating the cam  28  to the unlocked position, the middle plate  20  is moved to its aligned position relative to the top and bottom plates  22  and  18  with the help of the springs  30 . The cam slot retainer  32  was designed, not as a true cam receptacle (although it could have been, thus alleviating the need for the springs), but to have some “slop” built in to allow for manufacturing tolerances in the system. The springs  30  are therefore necessary to help the middle plate  20  to return to an aligned position. In addition, the pins  16 , being made of an elastic material, help move the middle plate  20  to its aligned position when the plate is unlocked, but the springs  30  are used to finish the movement. 
   Not shown in the figures is a ball plunger that goes through the front-end rail  4  and screws into the cam slot retainer  32 , pressing against the cam  28 . The cam  28  has a dimple in its side so that when the cam  28  is in the locked position, the plunger engages the detent and keeps the cam  28  in the locked position. 
   The cam  28 , the cam slot retainer  32  and the cam block housing  24  are expensive to manufacture (approximately $44.00 per unit). Furthermore, additional tooling is required (the Allen wrench—a $3.00 item). The present invention provides simpler methods, equally robust, which improve on the patented and current methods of manufacture. 
   SUMMARY 
   The present invention provides an improved method for clamping spring loaded pins that support substrates, such as printed circuit boards, which have even profiles, and uneven profiles due to components being installed on one side, during manufacturing operations to the opposite side of the substrate. Typically, the substrate needs support to prevent flexing during manufacturing operations such as solder paste printing, pick-and-place operations, and any other operation where it is desirable to keep the substrate from flexing. 
   In accordance with one aspect of the present invention, an apparatus for supporting a substrate is disclosed comprising a first plate having a plurality of recess positions formed in a predetermined pattern. An elastically compressible element is positioned in at least some of the first plate recess positions. A second plate is disposed above the first plate and has a plurality of uniform apertures in a pattern corresponding to the predetermined recess pattern. A third plate overlies the second plate and has a plurality of uniform apertures in a pattern corresponding to the second plate aperture pattern. A fourth plate overlies the third plate and has a plurality of uniform apertures in a pattern corresponding to the second plate aperture pattern. A plurality of deformable pins is provided for insertion into at least some of the apertures in the second, third and fourth plates when the apertures are aligned. The pins have cross sections corresponding to the second, third and fourth plate apertures. An anchor block is secured to the third plate. Means are provided for moving the third plate between an aligned position in which the apertures in the second, third and fourth plates are aligned and a clamping position in which the third plate is not aligned with the second and fourth plate apertures. The means for moving the third plate is configured to move the third plate to the clamping position by translating the anchor block in a horizontal direction. The means for moving the third plate may comprise such mechanisms as a cam lever, a knob or a draw latch. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a current version of a substrate support system; 
       FIG. 2  is a cross-sectional view of the substrate support system of  FIG. 1 ; 
       FIG. 3A  is another cross-sectional view of the substrate support system of  FIG. 1 ; 
       FIG. 3B  is a close-up cross-sectional view of the substrate support system of  FIG. 3A ; 
       FIG. 4  is a perspective view of one embodiment of a substrate support system in accordance with the present invention; 
       FIG. 5  is a cross-sectional view of the substrate support system of  FIG. 4 ; 
       FIG. 6  is a perspective view of another embodiment of a substrate support system in accordance with the present invention; 
       FIG. 7  is a cross-sectional view of the substrate support system of  FIG. 6 ; 
       FIG. 8  is a perspective view of yet another embodiment of a substrate support system in accordance with the present invention; 
       FIG. 9  is a cross-sectional view of the substrate support system of  FIG. 8 ; 
       FIG. 10  is a perspective view of yet another embodiment of a substrate support system in accordance with the present invention; and 
       FIG. 11  is a cross-sectional view of the substrate support system of  FIG. 10 . 
   

   DETAILED DESCRIPTION 
   Persons of ordinary skill in the art will realize that the following disclosure is illustrative only and not in any way limiting. Other embodiments of the invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. 
     FIGS. 4-5  illustrate a substrate support system  42  for supporting PCB&#39;s having components installed on one surface while installing other components on the opposite surface. If desired, a PCB with no installed components may also be supported. 
   Substrate support system  42  comprises elastically compressible members  14  positioned on base plate  10 . Base plate  10  is configured to receive and maintain the lateral position of members  14  in a plurality of recess positions. These recess positions can be achieved in a variety of ways, such as disposing insert plates  12  between members  14 , as seen in  FIG. 5 , and/or by forming simple recesses in base plate  10 . In a preferred embodiment, insert plates  12  are formed from plastic. However, it is contemplated that other materials may be suitable to form insert plates  12  as well. If desired, recesses may be integrally formed in base plate  10  by molding, machining or the like. Elastically compressible members  14  may be any suitable material that exerts an upwardly directed biasing force when compressed. Resilient foamed plastics and metal or plastic springs are preferred. For best results, members  14  are conical or frusto-conical compression springs having a base that substantially fills the bottom surface of the enclosed space created by insert plates  12  or recesses in base plate  10  and a relatively narrow peak. 
   Substrate support system  42  also comprises a plurality of plates sandwiched together. These plates include a bottom plate  18 , a middle clamping plate  20  and a top plate  22 . In a preferred embodiment, front-end rail  4 , rear-end rail  6  and side rails  8  are secured to base plate  10  to form a frame around the periphery bottom plate  18 , middle plate  20 , top plate  22 , and the components disposed between bottom plate  18  and base plate  10 . Front-end rail  4 , rear-end rail  6  and side rails  8  may be secured to base plate  10  by any suitable manner known in the art, such as by adhesive bonding, soldering, threaded fasteners, etc. 
   Bottom plate  18  is disposed above elastically compressible members  14  and may be supported by insert plate  12 . Bottom plate  18  includes a pattern of apertures having axes corresponding to the axes of compressible members  14 , respectively. These apertures are preferably somewhat narrower than compressible members  14 . Middle plate  20  overlies bottom plate  18  and has a surface pattern of apertures substantially identical to the pattern of apertures in bottom plate  18 . Top plate  22  overlies middle plate  20  and has a surface pattern of apertures substantially identical to the pattern of apertures in bottom plate  18  and middle plate  20 . In a preferred embodiment, the apertures in the bottom, middle, and top plates are substantially equal in diameter and smaller in diameter than the elastically compressible members  14 . Bottom plate  18  and top plate  22  may be secured to the frame created by rails  4 ,  6  and  8 . 
   Deformable pins  16 , such as rubber-like pins, are inserted in the aligned apertures through plates  18 ,  20  and  22 . Pins  16  may be formed from any suitable material having the desired friction characteristics. Excellent results are obtained with hard rubber pins, nylon pins or other harder plastics, where the harder materials have circumferential or longitudinal shallow surface grooves or serrations. In a preferred embodiment, pins  16  are formed from a slightly deformable material having a hardness in the 75 to 90 range on the Shore A scale. 
   The lower ends of pins  16  rest against springs  14 . A PCB having components installed on one side is pressed against the array of pins  16 , with components pushing pins  16  downwardly against springs  14  distances corresponding to the thickness of the components. If desired, a PCB with no components installed can also be placed over the array of pins  16  for installation of components on the upper side. The PCB could, of course, comprise any suitable substrate upon which components are to be mounted in any manner. 
   System  42  employs cam lever  44  to move middle plate  20  into and out of alignment with the corresponding apertures in adjacent second bottom plate  18  and top plate  22 , in order to lock and unlock the position of pins  16 . Cam levers  44  can be obtained off the shelf for less than $5.00 each. The levers  44  preferably have a threaded pin  52  that can be anchored to a cam pin anchor block  54 , which is disposed within the rail frame, after passing through front-end rail  4 . The cam pin anchor block  54  is anchored to the middle plate  20 . The cam pin block  54  may be secured to the middle plate  20  by any means known in the art, such as threaded fasteners  38 . The portion of cam pin block  54  through which cam lever pin  52  passes can be threaded. However, the cam lever  44  would then have to be fixed in position such that the cam pin  52  could not be further tightened or loosened beyond a certain point. Such a design maintains the middle plate&#39;s unaligned “throw” at a constant distance (typically only 0.035″ to 0.050″). This configuration can be accomplished by fixing the cam lobe retainer  50  in place, or by placing a flat washer on the threaded cam pin  52  and putting a set screw through the cam pin block  54  down to the flat washer on the cam pin  52 . In this fashion, the cam lever  44  may be prevented from rotating beyond a certain point. 
   Although cam lobe retainer  50  is shown in the figures as conforming to the cam lever&#39;s lobe  47 , it could be as simple as a flat washer made from a material such as Teflon, nylon or plastic. This design keeps the cam lobe  47  and the outside surface of the front-end rail  4  from wearing. 
   The cam pin block  54  may also have a non-threaded hole through which the cam pin  52  passes. The pin  52  would then have retainer nuts  56  applied at its end after pin  52  passes through cam pin block  54 . Two nuts  56  could be used to secure the pin  52  at a specific distance, thereby allowing the cam lever  44  to swivel freely while keeping the middle plate throw distance constant. 
   The cam lever&#39;s lobe  47  may be configured such that cam lever  44  is locked when the lever arm  45  is perpendicular to the unit or parallel to the unit. Parallel is the preferred locking position since the parallel lever  44  would not interfere with other units when the strips are stacked next to each other. 
   The cam lever  44  can also have a simple spring-loaded lock button  46  that when depressed allows the lever  44  to move freely. In the lock position, the lock button  46  engages the cam pin  52  and prevents the lever  44  from being moved unless the button  46  is depressed. As would be appreciated by one ordinarily skilled in the art, these types of cam levers can be purchased off the shelf. 
   The cam lobe  47  can also have a bump or protrusion  48  in it that engages a detent in the cam lobe retainer  50 , thereby acting as a simple type of lock. As a result, machine vibration or accidental bumping would not move the lever arm  45 . It would have to be deliberately moved out of the locked (or even the unlocked) position. 
   Similar to the substrate support system in  FIGS. 1-3A , plate return springs  30  may press against the front-end rail  4  and the cam pin block  54  in order to allow the middle plate  20  to return to its aligned position when the cam lever  44  is thrown to its unlocked position. A single spring (not shown) could also be placed onto the cam pin  52  in between the front-end rail  4  and the cam pin block  54  in lieu of the plate return springs  30 . In order to accommodate this configuration, the cam pin block  54  would be modified to provide clearance for the spring. 
   In operation, cam lever  44  is rotated to move middle plate  20  to the clamping position. The rotation of cam lever  44  and cam pin  52  causes the translation of cam pin anchor block  54  in a horizontal direction based on the direction of the rotation. For the purposes of this disclosure, translation means the movement of a body from one point of space to another such that every point of the body moves in the same direction and over the same distance without any rotation. Since cam pin block  54  is anchored to the middle plate  20 , the movement of cam pin block  54  results in the direct movement of middle plate  20 . As a result, when the cam lever  44  is being rotated in a locking direction, the pin apertures in middle plate  20  become misaligned with the pin apertures in the bottom and top plates  18  and  22 , thereby causing the portion of each pin  16  adjacent to middle plate  20  to become distorted and locking the pin  16  in position. Since the bottom, middle and top plates are contiguous, no pin material can bulge between them. Therefore, the pin itself is not distorted and remains vertical so that the relationship between pin ends and PCB components is not changed. 
   Operations such as stenciling solder paste, placing components and soldering leads may then be performed with a stable, level PCB without any distortion or damage to the components on the underside of the board. The cam pin block  54  is simple to manufacture and its cost is estimated at $10.00. Therefore, the new locking system of substrate support system  42  would only cost about $15.00 ($5.00 lever plus $10.00 cam pin block) versus $47.00 (cam, cam slot retainer, cam block housing, and Allen wrench) for the version in  FIGS. 1-3A . Additional tooling, such as the Allen wrench, is not required to lock and unlock the system of the present invention. 
   An alternative embodiment of the present invention is illustrated in  FIGS. 6-7 , which show another simplified method for moving the middle plate  20  out of alignment. The substrate support system  62  of  FIGS. 6-7  is similar to the substrate support system  42  of  FIGS. 4-5 . System  62  employs a threaded anchor block  66  that is anchored to the middle plate  20  by any means known in the art, such as threaded fasteners  38 . However, instead of using a cam lever, a knob  64  having an attached threaded stud is employed. The threaded stud of knob  64  passes through the front-end rail  4  and screws into the threaded block  66 . By tightening (i.e. rotating) the knob  64 , a user can move the middle plate  20  out of alignment, thereby locking pins  16  in position. 
   Although  FIGS. 6-7  show a four-armed knob, knob  64  may be designed in a variety of different configurations, including a one-armed knob or a knob with a knurled edge and no arms. However, since quite a bit of pressure has to be applied, having the arms is helpful. As with system  42 , no additional tooling is required for substrate support system  62 . Although, it is contemplated that a hex socket in the end of the knob with a knurled edge could allow for an Allen wrench to be used to further tighten the knob. 
   In a preferred embodiment, plate return springs  30  are employed, as with system  42 . Preferably, either the two plate return spring design or the single spring on the threaded stud design is applied as discussed above. 
   The knob and stud can be obtained for as little as $5.00 each, so that system  62  achieves similar savings as system  42 . 
   Another alternative embodiment of the present invention is illustrated in  FIGS. 8-9 , which show a substrate support system  72  similar to substrate support systems  42  and  62 . Substrate support system  72  comprises a knob  74  having a threaded stud. However, the anchor block  76  through which threaded stud passes is not threaded, and again, two threaded stud retainer nuts  78  are used to lock the threaded stud in position. Anchor block  76  may be secured to the middle plate  20  by any means known in the art, such as threaded fasteners  38 . The knob  74  preferably has a companion piece having detents that is anchored to the front-end rail  4 . In this configuration, protrusions  80  on the knob  74  can mate with the detents and ramp into a locked position with only slight rotation of the knob  74 , as the middle plate  20  clamps the pins  16 . 
   Plate return springs  30  are preferably employed as discussed above with systems  42  and  62 , with similar savings resulting. In a preferred embodiment, the ramp on the protrusions  80  is slight, as a large displacement over a short distance would be difficult to achieve since a significant force is required to lock the pins  16 . 
   Yet another alternative embodiment of the present invention is illustrated in  FIGS. 10-11 , which show a substrate support system  82  similar to substrate support systems  42 ,  62  and  72 . However, instead of using a cam lever or knob, substrate support system  82  comprises a simple draw latch  84  that is anchored to an anchor block  88 , which is anchored to the middle plate  20 . These anchoring attachments may be achieved by any means known in the art, such as by threaded fasteners. The clip  86  to which draw latch  84  latches is preferably anchored to the front-end rail  4  using such anchoring means as threaded fasteners  38 . Plate return springs  30  are once again preferably utilized, and no additional tooling, such as an Allen wrench, is required. 
   Substrate support systems  42 ,  62 ,  72 , and  82  are similar in that they all have a simple yet robust design that utilizes an anchor block, with similar cost savings resulting. 
   While the substrate support system of U.S. Pat. No. 5,897,108 allows for means to move the middle plate out of alignment and lock the pins into position, the evolution of this invention has called for a more robust system that can repeatedly take higher forces than originally anticipated. Moreover, the present designed-as-built configuration can be further simplified without losing overall performance, repeatability and reliability, resulting in fewer components, no additional tooling and significant cost savings. 
   While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention.

Technology Category: 5