Abstract:
A printed circuit board support including a first member having a planar upper surface for supporting a printed circuit board. At least one second member is movably coupled to a first side of the first member and movable toward and away from the side of the movable member, and a bias source biases the second member in a direction away from the first member.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a self-adjusting printed circuit board support for use at a printed circuit board screen printing station. More particularly, the present invention relates to a self-adjusting printed circuit board support for use at a screen printer station in a printed circuit board assembly line.  
           [0003]    2. Description of Related Art  
           [0004]    A common step used during the assembly of active and passive devices onto a printed circuit board is a screen printer station. Typically at this station the circuit is already on the printed circuit board and solder is squeegeed through a screen or template onto the circuit in preparation for subsequent stations where active and passive components are placed on the board. In addition, a screen printer may be used as well to place the circuit pattern on the printed circuit board. Prior art tooling or supports used for holding the printed circuit board in the screen printer station are generally designed for the narrowest printed circuit board, thus leaving large areas of larger printed circuit boards unsupported. Other known support devices require the use of multiple fixed supports which are each designed for a specific width of the various sized printed circuit boards to be assembled.  
         SUMMARY OF THE INVENTION  
         [0005]    A universal printed circuit board support which can fully support various sizes of printed circuit board in a screen printer and in the fabrication and/or assembly environments is desirable, and is provided by the present invention.  
           [0006]    In one aspect on the invention a printed circuit board support comprises a first member having a planar upper surface for supporting a printed circuit board. At least one second member is movably coupled to a first side of the first member and movable toward and away from the side of the movable member; and a bias source biases the second member in a direction away from the first member.  
           [0007]    In another aspect, the present invention provides a printed circuit board support for use at a printed circuit board assembly station which is width-wise adjustable to support printed circuit boards of various width-wise dimensions.  
           [0008]    The support comprises a pair of parallel outer rails, each of which has outer surfaces for abutting engagement with one of a pair of spaced surfaces on a positioning device at the assembly station. A pair of parallel inner rails are provided between and spaced from the pair of outer rails, and a mid-block is provided between and spaced from the pair of inner rails. The mid-block and inner and outer rails have upper surfaces for supporting the printed circuit board at the assembly station. A first plurality of rods, each of which is fixed at one end thereof to the first one of the outer rails, extend through a first respective plurality of transverse holes in a first one of the inner rails. A second plurality of rods, each fixed at one end thereof to a second one of the outer rails, extend through a second respective plurality of transverse holes in a second one of the inner rails. A plurality of components for biasing each one of the outer rails and the inner rails outwardly from the mid-block are associated with the rods. The outer rails are moveable toward each other against the bias of the plurality of biasing components by compressive forces applied against the outer rails to fit the outer rails in abutting engagement with the spaced surfaces on the positioning device.  
           [0009]    The self adjusting printed circuit board support of the present invention provides maximum support for a wide variety of sizes of printed circuit boards used, for example, in the production of memory modules. When used in a typical screen printer the self-adjusting printed circuit board support of the present invention supports in its length-wise direction the entire length of a printed circuit board. When compressed width-wise, it self adjusts to support the entire width of the printed circuit board.  
           [0010]    The support of the present invention is readily compressed by hand to allow placement into or onto a positioning device between a space defined by surfaces of the positioning device and the support expands upon its release to fill the space. When the support is left in the assembly station during a change over to a different width circuit board, the support will automatically adjust to the width fixed by any width-wise adjustment in the space between the surfaces of the positioning device.  
           [0011]    The above and other features and advantages of the invention will be more readily understood from the following detailed description which is provided in conjunction with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a perspective view of a self-adjusting printed circuit board support for use at a printed circuit board assembly station in accordance with the present invention;  
         [0013]    [0013]FIG. 2 is an exploded view of the support of FIG. 1;  
         [0014]    [0014]FIG. 3 is a top plan view of the support of FIG. 1;  
         [0015]    [0015]FIG. 4 is a side elevational view of the support of FIG. 3;  
         [0016]    [0016]FIG. 5 is a cross-sectional view taken along line V-V of FIG. 3;  
         [0017]    [0017]FIG. 6 is a perspective view of the support of FIG. 1 in a fully compressed state and with a printed circuit board thereon;  
         [0018]    [0018]FIG. 7 is a perspective view of a screen printer with its cover removed;  
         [0019]    [0019]FIG. 8 is a cross-sectional view taken along line VIII-VIII of FIG. 7; and  
         [0020]    [0020]FIG. 9 is a top plan view of the screen printer showing a self-adjusting printed circuit board support installed therein and supporting a printed circuit board.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    With reference to FIGS.  1 - 4 , there is shown an embodiment of a self-adjusting printed circuit board support  10  in accordance with the present invention. The support  10  has a pair of parallel outer rails  12 , 14  each of which has an outwardly extending lip  13 , 15  for abutting engagement with a plurality of spaced surfaces  90 - 95  (FIG. 8) on a positioning device  97  (FIGS. 7 &amp; 8) at an assembly station. A pair of parallel inner rails  24 , 26  are located between and spaced from the pair of outer rails  12 , 14 . The support  10  also includes a mid-block  16  which is located between and spaced from the pair of inner rails  24 , 26 . The mid-block  16  has an upper surface  17  for supporting a printed circuit board at the assembly station. Likewise, the inner  24 ,  26  and outer  12 ,  14  rails have an upper surface, co-planar with the upper surface of mid-block  16 , for supporting the printed circuit board.  
         [0022]    A pair of rods  18 , each fixed at one end thereof  19  to a first one  12  of the outer rails  12 , 14 , extend through a first plurality of transverse holes  22 , 23  in a first one  24  of the inner rails  24 , 26 . A second pair of rods  25 , each fixed at one end  27  thereof to a second one  14  of the outer rails  12 , 14 , extend through a second pair of transverse holes  29 , 32  in a second one  26  of the inner rails  24 , 26 . The first and second pair of rods  18 , 25  extend through respective holes  30 , 31  in the mid-block  16 . Each hole  30 , 31  in the mid-block  16  has therein a linear ball bearing assembly  28  (FIG. 5) for supporting a respective one of the rods  18 , 25 .  
         [0023]    Each one of the transverse holes  22 , 23 ; 29 , 32  in the two inner rails  24 , 26  has a counter-sunk portion  33 , 37  on each side for seating a coil compression spring  34 , 34 ′; 35 , 35 ′ therein. Each one of the rods  18 , 25  has a circumferential recess  53  at each end thereof. The recess  53  receives an E-clip  54  (FIG. 5) therein after the rods  18 , 25  are passed through respective springs  34 , 34 ′; 35 , 35 ′, respective inner rails  24 , 26 , respective springs  34 , 34 ′; 35 , 35 ′ and the inner-block  16 . Each E-clip  54  abuts an underside of a respective linear ball bearing assembly  28  (FIG. 5) to prevent the its respective rod from passing through the linear ball bearing assembly  28  under the bias of the springs  34 , 34 ′; 35 , 35 ′. However as shown in FIG. 3, the E-clips  54  have an outer dimension which is smaller than holes  60 , 61 ; 62 , 63  in the inner rails  24 , 26  and holes  64 , 65 ; 66 , 67  in the outer rails to permit the rods  18 , 25  to pass through the inner rails  24 , 26  and into the outer rails  12 , 14  when the support  10  is in a compressed state as shown in FIG. 6.  
         [0024]    The coiled compression springs  34 , 35  function to bias each one of the outer rails  12 , 14  and inner rails  24 , 26  outwardly from the mid-block  16 . The outer rails  12 , 14  are moveable toward each other against the bias of the coiled compression springs  34 , 34 ′; 35 , 35 ′ to position the support  10  between spaced surfaces on the positioning device  97  of a screen printer, and upon release the support expands to provide contact between the outer surfaces  13 , 15  on the outer rails  12 , 14  with the spaced surfaces on the positioning device  97 .  
         [0025]    The printed circuit board support of the present invention is particularly suitable for use at a screen printer assembly station.  
         [0026]    The printed circuit board support functions such that the outer rails  12 , 14  are moveable between a fully open position as shown in FIGS. 1 and 3 when no compressive forces are applied thereto, and a fully compressed position when force is applied to compress the support as shown in FIG. 6 wherein the outer rails  12 , 14  are in contact with the inner rails  24 , 26  and the inner rails are in contact with the mid-block  16 .  
         [0027]    When no compressive forces are applied to the outer rails  12 , 14 , the rods  18  extending from the outer rail  12  and the rods  25  extending from the other outer rail  14  extend through respective inner rails  24 , 26  and into linear ball-bearing assemblies  28  in the transverse holes  30 , 31  through the mid-block  16  as shown in FIG. 3. When the printed circuit board support is fully compressed as shown in FIG. 6, the rods  18  extending from the first outer rail  12  pass through the transverse holes  30 , 31  of the mid-block  16 , the holes  60 , 61  in the inner rail  26  and into holes  64 , 65  of the second outer rail  14 . In like manner, the rods  25  connected to the second outer rail pass through a second set of transverse holes  30 , 31  in the mid-block  16 , through holes  62 , 63  in the first inner rail  24  and into a pair of holes  66 , 67  in the first outer rail  12 .  
         [0028]    The mid-block  16  is elongated and has a plurality of perforations  21  which extend through the mid-block  16  from the upper support surface  17 . When in position in the screen printer  70  as shown in FIG. 7, the support  10  is positioned over a conduit  76  which is in communication with a vacuum source  74 . The pull of the vacuum generated by the source  74  through the port  76  and the perforations  21  act to draw the printed circuit board against the upper support surface  17 , and thus hold the printed circuit board in position during the screen printer operation.  
         [0029]    The outer rails  12 , 14  each have a pair of support handles  36 , 38 ;  40 , 42  secured respectively thereto by rivets or screws  44 . The support handles  36 , 38 ;  40 , 42  are manually engageable for applying compressive forces to the printed circuit board support  10  during installation in the positioning device  97  of the screen printer station.  
         [0030]    A portion of a screen printer station  70  is shown in FIGS. 7 and 8 with a cover (not shown) removed. The positioning device  97  includes opposing step-like spaced surfaces  90 , 92 , 94 ; 91 , 93 , 95  formed from sheet metal. Each one of the shaped surfaces has a leg  92 , 93  connected to and extending upwardly from a steel plate  96 , and an upwardly extending portion  90 , 91  spaced outwardly by horizontal portion  94 , 95 . Internal conveyor belts  72 , 73  are spaced above horizontal portions  94 , 95 , respectively.  
         [0031]    As shown in FIG. 8, the lips  13 , 15  of the outer rails  12 , 14  are in abutting engagement with the step-like spaced surfaces  92 ; 93  when the support  10  is released.  
         [0032]    With reference to FIGS. 7 and 8, the support  10  is positioned on the steel plate  96  and is held thereon by magnets  50  which are positioned in recesses  52  located in the underside of the mid-block  16 .  
         [0033]    Printed circuit boards  80 , 81 , 82  are sequentially supplied to the screenprinter  70  by a pair of feeder conveyor belts  85 , 86 . Each printed circuit board is transferred from the conveyor belts  85 , 86  to the internal conveyor belts  72 , 73  of the screenprinter  70 . The conveying system is indexed such that each printed circuit board stops in the position shown in FIG. 7. The positioning device  97  including the steel plate  96  and the sheet metal opposing step-like spaced surfaces  90 , 92 , 94 ; 91 , 93 , 95  are raised to lift the support  10  upwardly between the internal conveyor belts  72 , 73  to contact the underside of the printed circuit board  81 . The printed circuit board  81  is drawn to the support  10  by the vacuum applied through port  76 , to the underside of the support  10 , and through the perforations  21  in the mid-block  16 . The vacuum acts to retain the printed circuit board  81  against the upper support surface  17  of the mid-block  16 , and the upper surfaces of the inner  24 ,  26  and outer  12 ,  14  rails, with the printed circuit board overhanging the sides of the support  10  by a very slight distance. The printed circuit board  81  is lifted off the internal conveyor belts  72 , 73  at which position the screenprinting step is carried out. After screenprinting, the support  10  is lowered by the screenprinter positioning device  97  to return the printed circuit board  81  to the internal conveyor belts  72 , 73 . The internal conveyor belts  72 , 73  in turn passes the printed circuit board  81  to exit conveyor belts  87 , 88  that are external to the screenprinter  70  while another printed circuit board is fed by the feeder conveyor belts  85 , 86  to the screenprinter  70 .  
         [0034]    In an alternative embodiment, a pair of snugger bars  78 , 79  (FIG. 9) engage the side surfaces of the printed circuit board  81  while in the screenprinter  70  and after the board  81  and support  10  are lifted by the positioning device  97 . In this embodiment, both the vacuum  74  and the snugger bars  78 , 79  hold the printed circuit board in a fixed position during the screenprinting operation. After the printing operation, the snugger bars  78 , 79  are retracted, and the support is lowered by the positioning device  97  to place the printer circuit board  81  back on the internal conveyor belts  72 , 73  for passage to the external conveyor belts  87 , 88 .  
         [0035]    Thus, the present invention provides a universal printed circuit board support which can fully support various sizes of printed circuit board in a screenprinter and/or in other fabrication and assembly environments.  
         [0036]    Although the present invention has been described with preferred embodiments, it is to be understood that modifications and variations may be utilized without departing from the spirit and scope of this invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be part of the invention, provided they come within the scope of the appended claims and their equivalents.