Abstract:
An improved vacuum box assembly for use in printed circuit board manufacturing where the printed circuit board is supported during manufacturing operations on the second side of the board. The vacuum box uses a unique and improved side plate that securely retains commercially available substrate support devices within the vacuum box. The side plate has a retention cavity configured to receive one or more substrate support devices therein. The side plate retains the substrate support device in a desired position. Open or unoccupied regions of the retention cavity may be sealed by use of specifically configured vacuum blocking plates.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application claims the benefit of co-pending U.S. Provisional Application Ser. No. 60/826,855, filed Sep. 25, 2006, which is incorporated by reference herein in its entirety. 

   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. More specifically, the present invention enables the use of one or more substrate support members with known vacuum box assemblies to facilitate printed circuit board manufacturing processes. 
   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 ohmic connections. More recently, surface bonding of relatively short leads to the cladding has become common, allowing for high-speed robotic placement of components thus increasing manufacturing productivity. PCBs typically have components on one side with various height profiles and require even support while manufacturing processes are done to the opposite side such as screen printing and pick-and-place operations. 
   Industry manufacturing processes for printed circuit boards generally provide that the PCB or substrate be held in place by constructing a vacuum box whose edges correspond to the perimeter edges of the substrate, whereupon the substrate becomes the top lid of the box and is held down or in place by a vacuum. Substrates are typically made of phenolic impregnated fabrics and more recently, fiberglass reinforced resins. Under various manufacturing operations the substrates can flex and frequently require underside support within the constructed vacuum box so that precise placement of components or cladding can be performed. 
   A vacuum box is commonly used in PCB manufacturing for screen-printing of circuitry or other operations such as component placement (i.e., pick-and-place). The vacuum box is generally an adjustable device that is used to support the PCB during manufacturing. One exemplary vacuum box is manufactured by MPM Corporation and has been used very successfully by the electronics assembly industry, specifically the surface mount technology industry. There are likely over 5000 such vacuum box systems world wide that are used as a means of holding the PCB substrate in place during the screen printing of solder paste onto the PCB substrate and/or component placement. The general configuration and use of a standard vacuum box is described in greater detail below with reference to  FIGS. 1   a  through  7 . 
   The vacuum box  100  is designed to accommodate PCB substrates from about 1.5″ to 15.0″ wide and up to lengths of 14.5″. Referring to  FIGS. 1   a  and  1   b , the vacuum box  100  has a table  1  that forms the bottom of the vacuum box  100  with vacuum holes  2  in the table that apply a vacuum capable of retaining the PCB using a large volume of air flow. Under the table  1  is a plenum (not shown) that surrounds the holes in the table  1  and accommodates the ductwork that couples the table  1  with the vacuum source. The table  1  supports a fixed front rail  3  (See also  FIGS. 2   a  and  2   b ) and a moveable rear rail  4  (See also  FIGS. 3   a  and  3   b ) that make up two opposing sides (i.e., front and rear) of the box. On each outer side of the front and rear rails  3  and  4  is the conveyor system  5  with conveyor belt  5   a , typically placed as close to the front and rear rails as possible, for transporting the PCBs to and from the vacuum box  100 . 
   The front rail  3  (see  FIGS. 2   a  and  2   b ) is fixed to table  1  by mechanical fasteners  9  and is typically 17″ long. At the top of the front rail  3  is a thin blade  6  upon which one edge of the PCB substrate sits, typically along the length of the PCB substrate, and is parallel to the direction of travel for the conveyor system  5 . 
   The rear rail  4  (see  FIGS. 3   a  and  3   b ) is moveable along slot  7  (see  FIG. 1   a ) in the table  1  and is also 17″ long. The slots  7  are usually configured as T-Slots that are configured to receive a mating T-Bolt or threaded fastener for slideably coupling two or more members (i.e., movable rear rail  4  with table  1 ). The T-Slots  7  of  FIG. 1   a  formed table  1  engage T-Slot nuts and bolts  9 , which engage mounting, brackets in the rear rail  4  (see  FIG. 3   a ). In use, the T-Slot nuts  9  are loosened, whereupon the rear rail  4  can be moved and adjusted to the width of the PCB substrate and then tightened to fix the position of the rear rail  4  with respect to the front rail  3 . 
   Similar to the front rail  3 , at the top of rear rail  4 , is another thin blade  8  upon which the opposite edge of the PCB substrate engages. The thin blade  8  is parallel to the direction of the conveyor system  5  upon which the PCB substrate traverses. The PCB substrate then straddles the two rails (front rail  3  and rear rail  4 ) with the thin blades  6 ,  8  supporting the PCB substrate along the length of the PCB edges. It is common for the edges of the PCB to actually protrude past the front and rear edges established by the thin blades  6  and  8  by about 0.100″ on each side so that the PCB can engage and ride along the conveyor (See  FIG. 6 ). 
   The front and rear rails  3  and  4  have clamping rails  10  which engage side plates  11  (See  FIGS. 1   a ,  1   b  and  4 ) by way of a clamping block  12 . The clamping rail  10  on the front rail  3  is located higher than the clamping rail  10  on the rear rail  4  (see  FIGS. 2   a  and  3   a ), which in turn requires that four unique side plate configurations be used. The side plates are generally designated front and rear as well as left and right side plates. The industry commonly utilizes side plate nomenclature to designate the operative position of the side plates and this nomenclature is marked on the side plates via stamping or other known marking methods (e.g., screen printing, engraving, etching etc.). Correspondingly, the side plates are marked according to the intended installation position (e.g., LF-left front  11   a , LR-left rear  11   b , RF-right front  11   c , and RR-right rear  11   d ). The four side plates  11   a - d  make up the other two opposing sides of the vacuum box  100 , with the PCB substrate forming the top or lid. The side plates typically have notches  30  cut into them so that each side plate  11   a - d  can be drawn as close to the opposite rail (front or rear rails  3  and  4 ) and thus the notch  30  receives the clamping rail  10  of the opposing front or rear rails  3  and  4 . As a result, the side plates  11   a - d  may be positioned at a minimum separation distance from each other and thus accept a narrow PCB. 
   The side plates  11   a - d  (see  FIGS. 1   a - c  and  4 - 6 ) have one surface that is generally smooth/flat (i.e., devoid of protrusions on at least one side surface). The front and rear side plates for the vacuum box  100  (e.g., left or right side) are positioned in sliding relationship with respect to each other, see  FIGS. 1   a - c . The pair of front and rear side plates may then be adjusted to the width of the PCB substrate and thus dimensionally define the distance between the front and rear rails  3  and  4 . Additionally, the pair of coupled side plates can be positioned at various distances along the front and rear rails which in turn establishes the length of the PCB substrate. In summary, the two pair of side plates are in sliding relationship with each other as well as adjustable along the length of the front and rear rails which in turn forms a box that is adjustable in both width and length to accommodate various sizes of printed circuit boards. 
   Referring to  FIG. 4 , on the opposite side of the side plate  11   a  is a clamping block  12  that interlocks with the clamping rails  10  of either front or rear rails  3  and  4 . The clamping block  12  is securely attached to the side plate  11  usually by screws, pins or combinations of both. A screw  13  at the top of clamping block  12  is tightened which drives a pin  14  into a clamp lip  15 , which in turn displaces a clamp lip  15  such that the clamp lip  15  engages a rear notch surface  16  of the corresponding clamp rail  10 . The interaction and physical engagement between the clamp lip  15  of the clamping block  12  and rear notch surface  16  of the clamping rail  10 , secures the clamping block  12  and side plate  11  in position with respect to the front and rear rails  3  and  4 . Reference should be made to  FIGS. 5 and 6 , which illustrate how the side plates/clamping blocks engage the clamping rail. 
   Generally, the side plates  11   a - d  come in several sizes; extra-small, small, medium, large and extra-large that accommodate the various widths of any given PCB substrate up to 15.00″ wide. Each size has a corresponding front-left, rear-left, front-right and rear-right side plate and is designated as discussed above. The side plate sizes typically overlap slightly with the next larger size thus allowing for a continuum of PCB widths from the minimum size up to a maximum that may be accommodated within the vacuum box  100 . All of the mounting hardware for each size side plate is generally similar. For example, the clamping block  12 , screw  13 , pin  14  and clamping lip  15  are interchangeable with the various side plates  11 . Additionally, it is understood that front-left and front-right side plates are mirror images of each other and the same is true for the rear-left and rear-right side plates. 
   The side plates  11   a - d  have a clamping block  12  usually made of stainless steel that engages the clamping rails  10  on the front and rear rails  3  and  4 . Correspondingly, the side plates  11   a - d  may slide along the clamping rail  10  thus allowing the side plates  11   a - d  to be adjusted to the length of any PCB substrate. The side plates  11  are configured to support the PCB substrate along its width at the front and rear edges of the PCB substrate (with respect to the direction of travel along the conveyor system for the PCB). Additionally, there is little-to-no overhang of the PCB in relation to the side plates  11   a - d.    
   After the front and rear rails  3  and  4  are set and the four side plates  11   a - d  are clamped down using clamping blocks  12 , they form four sides of the vacuum box  100  and support the PCB  33  substrate around its perimeter. The table  1  forms the bottom of the box and the PCB substrate itself forms the lid or top of the vacuum box. Vacuum is then pulled through the holes  2  in the table  1  and suction holds the PCB  33  substrate down against the thin blades  6  and  8  of the front and rear rails  3  and  4  and the side plates  11   a - d . The vacuum box  100  essentially forms a cube with, theoretically, no holes or substantial air leaks. However, any given PCB substrate can have numerous holes and slots in them and the vacuum box itself is not airtight. In this regard, to operatively retain the PCB, a large volume of air is drawn in as vacuum to compensate for any leakage in the vacuum box/PCB assembly. Consequently, it is desirable to keep vacuum leakage to a minimum for efficiency concerns. 
   In operation (see  FIG. 6 ), the table  1 , front and rear rails  3  and  4  including side plates  11   a - d  move up and down to engage the PCB  33 . At a predetermined stop point the conveyor  5  with the PCB  33  translating there along, will stop and the vacuum box  100  (the front and rear rails and side plates  11   a - d , including the table  1 ) is raised to engage the PCB  33 , lifting the PCB  33  off of the conveyor rails and belts  5 ,  5   a . An upper fixture (not shown) holding a stencil frame  101  and stencil  102  is then lowered onto the PCB  33 . Cameras  104 , in conjunction with an assembly line computer system, aligns the apertures in the stencil  102  with a corresponding target or “land” pattern on the PCB  33 . After alignment, solderpaste is then squeegeed onto the PCB  33  and the stencil  102  is lifted away, leaving a corresponding amount of solderpaste on the PCB. The table  1  and vacuum box  100  assembly then lowers, placing the edges of the PCB  33  (lengthwise) back onto the conveyor belts  5   a . The PCB is then shuttled to the next station (typically for pick-and-placement of components), and a new PCB  33  moves into the printer station whereupon the procedure is repeated. 
   Today, electronic devices are increasingly miniaturized and it has become desirable to mount components 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. For example, 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. During manufacturing, the PCB is required to be held flat and level so that paste application and component placement can be accurately performed upon the second side. This solder paste application and component placement is very difficult if the PCB is not properly secured and held in place. 
   In the past, several attempts have been made to provide PCB support within the vacuum box so that screen-printing and component placement may be performed. Firstly, in high production run circumstances, aluminum plates or similar materials have been machined in a pattern corresponding to the topography of the first side of the PCB so that components protruding from the first side may pass-through the plate. As a result, the aluminum plate then provides structural support to the PCB during the manufacturing process. This approach is not practical for manufactures or subcontractors producing a limited quantity of printed circuit boards or for boards of vastly different configurations because each PCB design/configuration would require a custom support plate which is expensive and time consuming to machine. 
   Secondly, internal vacuum box supports have 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, this method is not cost effective where only a few boards are to be made or where custom boards are being manufactured. 
   Thirdly, during set up of the vacuum box a series of fixed PCB substrate supports have been used that fit between the table surface and the PCB. These supports are usually held to the table by magnets. These supports are typically either pins or blades. The pins are usually about 0.125″ to 0.250″ in diameter and correspond to the height of the front, rear and side plates and are secured using a magnetic base. The blades are typically 0.050″ to 0.0625″ thick and up to 2.00″ wide and are the same height as the rails and side plates and have a magnetic base. These fixed height supports must be positioned to engage the PCB substrate where no components have been installed otherwise damage to the components may occur during screen-printing or component placement. Also, support can be uneven, and where PCB substrates are populated with a high density of components, it may be very difficult to locate an area that is unpopulated with components. 
   Fourthly, a series of gel packs  19  were implemented to provide PCB support within the vacuum box, see  FIG. 7 . The gel packs are essentially packets of gel or other deformable medium that are positioned inside the vacuum box, which conforms to the underside topology of the PCB during printing or component placement. This solution, although somewhat effective, has been less than successful, in that the vacuum box requires the gel packets  19  to be individually constrained using independent mounts  20  to allow vacuum to pass between the individual packets. 
   Moreover, the gel packs  19  can accommodate component topologies of only limited height. Furthermore, because the gel packets  19  have limited compressibility, they may push the PCB substrate up off the edge(s) of one or more sides of the vacuum box, breaking the vacuum seal and possibly causing misalignment of the PCB registration to the stencil apertures. This is particularly true if a gel packet is under a high profile part, which requires substantial displacement of the gel. In this situation the gel packet  19  would then have to be removed from this position, leaving the PCB substrate unsupported in this area. Conversely, when pressure is applied to the stencil/PCB as the squeegee passes over the substrate, the gel packs  19  may compress and only provide limited support and thus permit the PCB to deflect. 
   Additionally, the spacing  21  between the gel packets should be optimized such that the majority of the vacuum holes in the table are able to apply vacuum to the PCB. The deficiencies with the gel pack solution can become significant, especially if the PCB substrate is very thin. 
   Finally, another attempt to provide internal PCB support within the vacuum box uses various substrate support devices placed within the vacuum box, where the support devices provide a plurality of deformable or adjustable pins that conform to the component topology of the PCB. However, this attempt to provide support using such substrate support devices requires that custom devices be manufactured or modified that correspond to the length and/or width of the PCB. Thus, customizing each substrate support device to fit within the perimeter of the front and rear rails  3  and  4  and side plates  11   a - d  is not cost effective, time efficient or practical unless a manufacturer is only making one size PCB, which is unlikely in the present electronics manufacturing environment. This solution lacks the flexibility that PCB manufacturers need to produce and assemble many different sizes of PCB substrates. 
   Efforts to provide internal vacuum box support for a printed circuit board, having components mounted on one side while additional components are installed or operations performed on the opposite side, have not met with much success to date. 
   SUMMARY OF THE INVENTION 
   The present invention enables the use of commercially available substrate support devices within typical vacuum boxes used during the manufacturing of printed circuit boards by the electronics assembly industry, specifically the surface mount technology industry. Typically, the printed circuit board requires 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, a side plate for use in a vacuum box is disclosed. The side plate comprising a top edge, a bottom edge, an inside-facing edge, an outside-facing edge, a front surface, a rear surface. A retention cavity extending downwardly from the top edge towards the bottom edge to form a bottom cavity edge, the retention cavity extending from the inside-facing edge towards the outside-facing edge to form a cavity side edge. A retention member movably coupled to the side plate. The retention member comprises a first end, a second end, a top edge, a bottom edge. The first end of the retention member is coupled to the side plate adjacent to the top edge of the side plate and the cavity side edge. The top edge of the retention member is substantially even with the top edge of the side plate. 
   From a combination aspect of the present invention, there is combined a side plate assembly and a substrate support device. The side plate assembly is configured for use in a vacuum box. The side plate assembly comprises a top edge, a bottom edge, an inside-facing edge, an outside-facing edge, a front surface, a rear surface, a retention cavity extending downwardly from the top edge towards the bottom edge to form a bottom cavity edge. 
   The retention cavity extends from the inside-facing edge towards the outside-facing edge to form a cavity side edge. The side plate also has a retention member movably coupled to the side plate. The retention member comprises a first end, a second end, a top edge, a bottom edge. The first end of the retention member is coupled to the side plate adjacent to the top edge of the side plate and the cavity side edge. The top edge of the retention member is substantially even with the top edge of the side plate. 
   The combination also includes a substrate support device positioned in the retention cavity. The substrate support device includes a plurality of displaceable pins, the pins being movable with respect to the substrate support device and retainable in a preset position. 
   In one embodiment, the side plate is coupled with a clamping block which may also be releasably coupled using at least one magnet. The side plate may further include a support shelf extending perpendicularly away from the side plate, where the support shelf positioned substantially even with the bottom cavity edge. The support shelf may have one or more magnets attached thereon. 
   In another exemplary embodiment, the side plate may include a retention member that is removable from the side plate. Additionally, the retention cavity may extend from the inside-facing edge towards the outside-facing edge a distance equal to a multiple of a width of a substrate support device. Also the outside-facing edge may substantially follow an inside contour of the vacuum box. The combination may also use pneumatic devices to retain the pins of the substrate support device. 
   In another exemplary embodiment, the present invention is a method of configuring a vacuum box for use in manufacturing printed circuit boards. The method has a first step of providing a vacuum box comprising a front rail, a rear rail, a table, a first set of side plates, a second set of side plates, the first and second set of side plates each having a retention member and a retention cavity. Secondly, the method has a step of adjusting the vacuum box to substantially match a perimeter of a printed circuit board by establishing distances between the front rail, the rear rail, the first set of side plates and the second set of side plates. The method continues by positioning at least one retention member to expose the retention cavity and placing at least one substrate support device across the first and second sets of side plates. The next step is positioning at least one retention member to retain the at least one substrate support device within the retention cavity. Finally, the method concludes with the step of securing the at least one substrate support device with respect to the vacuum box. 
   An alternate embodiment includes the step of installing at least one vacuum blocking plate to minimize a vacuum leak within the vacuum box. The method may further include a step of installing at least one dovetail clamping bracket and/or bridge member to retain the at least one substrate support device within the vacuum box. 
   For a fuller understanding of the nature and advantages of the present invention, reference should be made to the ensuing detailed description and claims, taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views. 
       FIG. 1   a  is a top view of a typical vacuum box substrate support system; 
       FIG. 1   b  is an isometric view of the typical vacuum box substrate support system shown in  FIG. 1   a;    
       FIG. 1   c  is an isometric view of two sets of side plates as utilized in the typical vacuum box substrate support system shown in  FIG. 1   a;    
       FIG. 2   a  is a front view of a front rail assembly of the vacuum box of  FIG. 1   a;    
       FIG. 2   b  is a side view of a front rail assembly of the vacuum box of  FIG. 1   a;    
       FIG. 3   a  is a front view of a rear rail assembly of the vacuum box of  FIG. 1   a;    
       FIG. 3   b  is a side view of a rear rail assembly of the vacuum box of  FIG. 1   a;    
       FIG. 4  is a side view of a left front side plate of the vacuum box of  FIG. 1   b    
       FIG. 5  is an exploded side view of the vacuum box assembly of  FIG. 1   b;    
       FIG. 6  is a side view of the vacuum box assembly of  FIG. 1   b;    
       FIG. 7  is an isometric view of the vacuum box assembly of  FIG. 1   b  using a plurality of gel packs for substrate support; 
       FIG. 8  is an isometric view of one embodiment of a vacuum box assembly in accordance with the present invention; 
       FIG. 9   a  is a side view of one embodiment of a side plate in accordance with the present invention; 
       FIG. 9   b  is an isometric view of two sets of side plates in accordance with one embodiment of the present invention; 
       FIG. 10  is a perspective side view of one embodiment of a vacuum box assembly illustrating the dovetail clamping brackets in accordance with the present invention; 
       FIG. 11  is a side view of a dovetail clamping bracket in accordance with the present invention; 
       FIG. 12  is a top view of a plurality of bridge members in accordance with the present invention; 
       FIG. 13   a  is a side view of an alternate embodiment of a side plate in accordance with the present invention; 
       FIG. 13   b  is an isometric view of two sets of side plates in accordance with one embodiment of the present invention; 
       FIG. 13   c  is an isometric view of one embodiment of a vacuum box assembly in accordance with the present invention; 
       FIG. 14   a  is front view of a vacuum blocking plate in accordance with the present invention; and 
       FIG. 14   b  is a side view of the vacuum blocking plate of  FIG. 14   a.    
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention enables the use of commercially available substrate support devices with standard vacuum boxes commonly used in the electronics assembly industry. In the following description, numerous specific details are set forth in order to provide a more thorough description of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without these specific details. Other embodiments of the invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. In some instances, well-known features have not been described in detail so as not to obscure the invention. 
   Turning now to  FIG. 8  which illustrates a vacuum box  100  having a front rail  3 , a rear rail  4 , a left-front side plate  800 , a left-rear side plate  810 , a right-front side plate  820 , a right-rear side plate  830 , a substrate support device  840  and a clamping block  12  affixed to each side plates  800 ,  810 ,  820 ,  830 . The front and rear rails  3  and  4 , clamping blocks  12  and general vacuum box operation has been discussed and described in detail above and is not repeated to avoid undue prolixity. It is contemplated that the vacuum box  100  may be used with or without the application of vacuum to support the printed circuit board during manufacturing processes. 
   The substrate support device  840  is generally a strip comprising a plurality of movable/deformable pins that conform to the topology of a printed circuit board (PCB) and spans the distance between the left ( 800 ,  810 ) and right ( 820 ,  830 ) sets of side plates. One exemplary substrate support device  840  (known in the industry as “Red-E-Set”) is manufactured by Production Solutions, Incorporated of Poway, Calif. The “Red-E-Set is generally about 1.25″ in width, 18.50″ in length and 1.50″ in height. This version of the substrate support device  840  was originally disclosed in U.S. Pat. No. 5,897,108, entitled Substrate Support System, issued to Gordon et al., on Jan. 26, 1998, the disclosure of which is incorporated by reference herein in its entirety. 
   The substrate support device  840  fabricated according to U.S. Pat. No. 5,897,108 is an apparatus that has a plurality of pins arranged in an array or matrix. The pins are spring loaded and able to move up and down within a housing and thereby conform to the topology of a PCB/substrate surface. The pins are locked into position by a series of plates that move in relation to each other. Such an arrangement is disclosed in U.S. Pat. No. 5,897,108, which describes a series of plates with aligned holes through which the spring-loaded pins protrude. A top plate and a bottom plate hold the pins in position laterally, while a middle plate is moved out of alignment to clamp the pins, thus holding the pins in vertical alignment to the underside topology of the substrate. There are several means that may be used to move or displace the middle plate. For example, the middle plate may be displaced by mechanical means such as a treaded member, a gear driven member, or a cam driven member. Other mechanisms such as pneumatic devices, hydraulic chambers, electro-mechanical devices, electronic solenoids or combinations thereof may be implemented as the mechanical displacement means. Furthermore the mechanical displacement means may be actuated either manually or automatically. However, it is contemplated that other mechanical displacements means are possible and would be readily appreciated and understood by one of ordinary skill in the art. 
   A side plate  800  is shown in  FIG. 9   a , which is configured to retain one or more substrate support devices  840  adjacent to an upper region of the side plate. It should be understood that the left and right side plate pairs are mirror images of each other. Furthermore, the structure, configuration and operation of the side plates will be discussed and described in detail with reference to one plate (left-front  800 ), however the following disclosure is applicable to the other side plates  810 ,  820  and  830 . 
   The left-front side plate  800  has a top edge  800   a , a bottom edge  800   b , an inside-facing edge  800   c , an outside-facing edge  800   d , a front surface  800   e  and a rear surface  800   f . The inside-facing edge  800   c  is generally orientated towards the center most region of the vacuum box  100 . Conversely, the outside-facing edge  800   d  is configured to contour the inside surface of the front rail  3 . The left-front side plate  800  generally defines a rectangular plate having an over height “H,” width “W” and thickness “T.” The height of the side plate  800  is substantially similar to the height of the front rail  3 . 
   The width of the side plate  800  may vary according to the size of the PCB/substrates that are being produced. It is contemplated that the side plate  800  may come in small, medium, large and extra-large widths that would retain from one to several substrate support devices  840 . For example, a small side plate would retain one to two substrate support devices; a medium side plate would accommodate one to three devices; a large side plate would retain one to seven devices and an extra-large side plate could accommodate one to ten substrate support devices  840 . In one embodiment, the size (width) of the side plate is generally a multiple of the width of a substrate support device  840 . However, it is contemplated that other variations are possible and would be readily appreciated and understood by one of ordinary skill in the art subsequent to reviewing this disclosure. 
     FIG. 9   b  illustrates two sets of extra-large side plates arranged in sliding relationship with one another. As illustrated, there is a left-front side plate  900 , a left-rear side plate  910 , a right-front side plate  920  and a right-rear side plate  930 . The extra-large side plates  900 - 930  have been configured to retain and support one to ten substrate support devices and correspondingly have a width that is greater than the small side plate  800  of  FIG. 9   a.    
   The thickness of the side plate  800  is generally defined from the material from which the side plate is fabricated. In one embodiment, the side plate  800  is fabricated from martensitic (magnetic) stainless steel and may range from 0.010″-0.060″ in thickness. However, one of ordinary skill in the art of machine design would appreciate that other suitable materials may be used to fabricate the side plate. For example, galvanized steel of various thicknesses may be used as well as polymers or composite/laminate sheets. 
   As illustrated in  FIG. 9   a , the outside-facing edge  800   d  of the left-front side plate  800  has a first receiving notch  29  formed thereon. The first receiving notch  29  is positionally located to receive the clamping rail  10  of the front rail  3 . For the rear side plates ( 810 ,  830 ) the first receiving notch  29  may be located lower than the first receiving notch for the front side plates ( 800 ,  820 ). It is contemplated that the first receiving notch  29  for the relevant side plate be located to adequately receive the respective clamping rail to which the side plate will be attached. The first receiving notch  29  is further configured to align with the operative mechanism of the clamping block  12  that is coupled to the left-front side plate  800 . 
   The clamping block  12  is aligned with the first receiving notch  29  and mounted to the front surface  800   e  of left-front side plate  800  using mechanical fasteners such as threaded members  48 , pins  49 , rivets, magnets, adhesives or other mechanical fastening means now known or later developed. In one embodiment, it is contemplated that the clamping block  12  is releasably coupled with the left-front side plate  800  so that different width left-front side plates may be independently attached to the same clamping block  12 . As a result, a user is enabled to use one clamping block  12  with several different side plates. This reduces the number of clamping blocks a user has to have in inventory and provides increased flexibility in the manufacturing process. 
   Also illustrated in  FIG. 9   a  is a second receiving notch  30  formed on the inside-facing edge  800   c  of the left-front side plate  800 . The second receiving notch  30  is positionally located to receive the clamping rail  10  of the opposing rear rail  4 . For the rear side plates ( 810 ,  830 ) the second receiving notch  30  may be located higher than the notch for the front side plates ( 800 ,  820 ). It is contemplated that the second receiving notch  30  for the relevant side plate be located to adequately receive the opposite clamping rail therein. The second receiving notch  30  allows the side plates to substantially overlap each other and thus obtain a minimum width for accommodating small PCBs/substrates. 
   Further illustrated in  FIG. 9   a , is a substrate support device receiving cavity  22  formed within the left-front side plate  800 . The receiving cavity  22  is a notch or cutout that extends from the inside-facing edge  800   c  towards the outside-facing edge  800   d  of the left-front side plate  800  to form a bottom cavity edge  22   a . The receiving cavity  22  also extends from the top edge  800   a  towards the bottom edge  800   b  of the left-front side plate  800  to form a cavity side edge  22   b.    
   The receiving cavity  22  is generally configured to accept one or more substrate supporting devices  840 . The distance the receiving cavity  22  extends from the inside-facing edge  800   c  is a function of the overall width “W” of the particular side plate configuration (i.e., small, medium, large or extra-large side plate). The distance the receiving cavity  22  extends from the top edge  800   a  is dependent upon the height and configuration of the particular substrate support device  840  utilized. However, it is preferred that the substrate support device  840  be positioned so that the pins of the device partially extend above the top edge  800   a  of the side plate to thereby guarantee that, in use, the PCB substrate fully engages the pins of the substrate support device  840 . 
   Adjacent to the top edge  800   a  and cavity side edge  22   b  is pivotally attached a retention member  27 . In one embodiment, the retention member  27  is pivotally attached to the side plate using a rivet, however other means for pivotal connection are possible such as threaded members, bushing, bearings, pins or combinations thereof. The retention member  27  is a drawbridge or gate that provides access and retention means for one or more substrate support devices  840 . The retention member  27  has a first end  27   a , a second end  27   b , a top edge  27   c  and a bottom edge  27   d . The retention member  27  substantially extends from the cavity side edge  22   b  towards the inside-facing edge  800   c  of the side plate  800 . In one embodiment, the retention member  27  does not extend all the way to the inside-facing edge  800   c  and thus provides a region of clearance for an opposing side plate. The first end  27   a  of the retention member  27  may be rounded so that when the retention member  27  is rotated the corners of the first end  27   a  do not extend above the top edge  800   a  of the side plate  800 . The rounded first end  27   a  allows the retention member  27  to rotate below the plane established by the top edges of the side plate/vacuum box without interfering with the placement of the PCB substrate. 
   In another exemplary embodiment, the retention member  27  may be removably attached to the side plate. For example, the retention member  27  is removed so that the substrate support device  840  can be positioned and then the retention member  27  is reinstalled. In this embodiment, the retention member  27  may be removably secured to the side plate by various means such as a tongue and grove configuration; a dovetail joint; a mortise and tenon arrangement or other designs that provide removable placement of the retention member  27 . 
   In accordance with the present invention, the retention member  27  is movable between a first position  850  and second position  860 . In the first position  850 , the retention member  27  is rotated or moved such that convenient access to the retention cavity  22  is permitted. For example, the retention member  27  may be rotated into a vertical orientation so that one or more substrate support devices  840  may be positioned on the bottom cavity edge  22   a  and span across the side plates. 
   In the second position  860  (horizontal orientation), the retention member  27  is rotated or moved such that bottom edge  27   d  of the retention member  27  may engage or rest on the substrate support device  840  and the top edge  27   c  of the retention member  27  is substantially event with the top edge  800   a  of the side plate  800 . Consequently, the top edges  27   c  and  800   a  of the retention member and side plate form a combined edge that supports the width of the PCB substrate. Additionally, the pins of the substrate support device  840  will provide support along retention member  27 . The retention member  27  also provides substantial vacuum blocking in the second position  860 . 
   In one embodiment, the retention member  27  is fabricated from martensitic (magnetic) stainless steel. In one non-limiting example, the retention member may range from 0.010″-0.060″ in thickness. However, one of ordinary skill in the art would appreciate that other suitable materials and thicknesses may be used to fabricate the retention member  27 . For example, galvanized steel of various thicknesses may be used as well as polymers or composite/laminate sheets. 
   There are several types of adjustable substrate support devices  840  commercially available to the electronics assembly industry, specifically the surface mount technology industry. The adjustable substrate support devices  840  generally fall into two classifications manual or automated. The manual substrate support devices typically require actuation of a mechanism to lock the support pins in place. The actuation usually requires turning and/or torquing a screw, cam or lever associated with the substrate support device. Consequently, this manual actuation may cause the substrate support device to shift or move with respect to placement within the side plate/vacuum box assembly. In response to this situation, the present invention provides mechanical means for securing the substrate support device within the vacuum box assembly. 
   Reference is now made to  FIGS. 10 through 12 , which illustrate a vacuum box  100  having a front rail  3 , a rear rail  4 , a left-front side plate  800 , a left-rear side plate  810 , a plurality of substrate support devices  840 , and a pair of dovetail clamp brackets  900 . As shown in  FIG. 11 , the dovetail clamp bracket  900  has a dovetail boss  39  that is configured for operative engagement within a dovetail recess  38  formed within the front and/or rear rail  3  and  4  (see  FIGS. 2   a,    2   b,    3   a  and  3   b ); a set screw  42  for positionally securing the dovetail clamp bracket within the dovetail recess  38 . The dovetail clamp bracket  900  also has a plate  910  attached to the dovetail boss  39 . The plate  910  has a slot  41  for receiving a mechanical fastener there through. 
   In operation, the dovetail clamp brackets  900  are inserted into the dovetail recesses  38  of the front and rear rails  3  and  4 , as shown in  FIG. 10 . The dovetail clamp brackets  900  are positioned with the plates  910  adjacent to the end of one or more substrate support devices  840  such that the slot  41  is aligned with one or more threaded cavities  840   a  formed on the substrate support devices  840 . The dovetail clamp brackets  900  are locked in place by engaging the setscrew  42 , which binds the dovetail boss  39  within the dovetail recess  38 . Next, a mechanical fastener  905  such as a bolt or screw is passed through the slot  41  and operatively engaged with the threaded cavity  840   a  of the substrate support device  840 . It is contemplated that other mechanical fasteners  905  may be used such as thumbscrews, spring-loaded pins, Allen head screws or other fasteners that releasably retain components. Thru use of the dovetail clamping bracket  900 , the substrate support device  840  is mechanically secured to the vacuum box assembly. 
   In the event, that the number of substrate support devices  840  extend beyond slot  41  formed within the dovetail clamp bracket  900 , a bridge member  920  may be added to the assembly. The bridge member  920  is provided in various lengths that correspond with the widths of the PCBs, see  FIG. 12 . The bridge members  920  are configured to retain from two to several substrate support devices  840 . The bridge members  920  have slots  41  as described above as well as structural webbing  43  to provide strength and prevent distortion of the bridge member during use. The bridge members  920  are positioned adjacent to the slot  41  in the dovetail clamp bracket  900  and mechanical fastening members are passed through the slots  41  in the bridge member  920  to threadably engage the substrate support devices  840 . 
   In another exemplary embodiment, the side plates may be configured to secure the automated substrate support devices using a magnetic bond between the side plate and the substrate support device. The automated substrate support devices generally utilize an electro-mechanical, hydraulic or pneumatic configuration to retain the support pins in place. As a result, there is minimal external force applied to the substrate support device, which could shift or move the device with respect to placement within the side plate/vacuum box assembly. 
   Reference is now made to  FIGS. 13   a  and  13   b , which illustrate another embodiment for the left-front side plate  960 . In accordance with this alternate embodiment, the majority of the left-front side plate  960  is similar to the previously described left-front side plate  800  and like structure is not repeated here to avoid undue prolixity. However, this embodiment of side plate  960  adds a small support shelf  36 , which extends perpendicularly away from the side plate  960 , see  FIG. 13   b . The support shelf  36  is either integrally formed with the side plate  960  or comprises a separate component structurally attached to the side plate  960  by way of fasteners, screws, press-fit connectors, and/or adhesives. The support shelf  36  has an upper surface  36   a  that is flush with the bottom cavity edge  22   a  such that a flat planar surface is formed upon which one or more substrate support devices may rest. The support shelf  36  is further configured with one or more magnets  37  that are attached to the shelf by mechanical means such as press fit, adhesives or a combination of both. However, it is contemplated that other attachments are possible and would be readily appreciated and understood by one of ordinary skill in the art subsequent to reviewing this disclosure. 
     FIG. 13   b  illustrates two sets of extra-large side plates arranged in sliding relationship with one another. As illustrated, there is a left-front side plate  970 , a left-rear side plate  975 , a right-front side plate  980  and a right-rear side plate  985 . The extra-large side plates  970 ,  975 ,  980 , and  985  have been configured to retain and support one to ten substrate support devices and correspondingly have a width that is greater than the small side plate  960  of  FIG. 9   a.    
   Reference is now made to  FIG. 13   c , which is an isometric view illustrating a vacuum box  100  having a front rail  3 , a rear rail  4 , a left-front side plate  970 , a left-rear side plate  975 , a right-front side plate  980 , a right-rear side plate  985 , a substrate support device  840  and a clamping block  12  affixed to each side plates  970 ,  975 ,  980 ,  985 . The side plates  970 ,  975 ,  980 , and  985  incorporate the support shelf  36  and magnet  37  of the alternate embodiment. As illustrated, the substrate support devices  840  are retained by magnetic force which is produced by the magnets  37  and physically couples the substrate support devices  840  with the support shelf  36  and side plates. 
   In the event that the substrate support device retention cavity  22  is not completely occupied with substrate support devices  840 , a substantial vacuum leak may be present. For example, when a medium side plate is installed into the vacuum box and only one substrate support device is positioned within the vacuum box. This would leave an unblocked portion of the retention cavity  22  that would cause a vacuum leak. 
   In response to this situation, one or more vacuum blocking plates  44  may be installed to seal the unoccupied portion of the retention cavity  22 . Reference is made to  FIG. 10 , which illustrates an installation of vacuum blocking plates  44 . Additionally, an exemplary vacuum blocking plate is illustrated in  FIGS. 14   a  and  14   b . The vacuum blocking plate  44  is configured in various widths to accommodate various unoccupied regions in the retention cavity  22 . The vacuum blocking plate  44  may have a magnet  45  applied to all or half of the plate. The magnet  45  may be configured to provide clearance for the retention member  27  of the side plate. Furthermore, the vacuum blocking plate may have a notch  47  formed there on to accommodate the support shelf  36  of the alternate embodiment. In use, the vacuum blocking plate  44  is positioned on the side plate to substantially cover the unoccupied portion of the retention cavity. The vacuum blocking plate  44  is held in place by the magnet  45 , which adheres to the side plate by way of magnetic force bonding the vacuum blocking plate  44  with the side plate. 
   The invention provides several advantages not found in known printed circuit board/substrate support assemblies. For example, the present invention enables the use of standard commercially available substrate support devices within commonly used vacuum box assemblies. Consequently, common off-the-shelf substrate support devices may be implemented more frequently, thus increasing manufacturing efficiencies. The present invention also reduces manufacturing costs by avoiding the need to use custom designed or modified substrate support devices within a typical vacuum box assembly. 
   Although the above provides a full and complete disclosure of the preferred embodiments of the invention, various modifications, alternate constructions and equivalents will occur to those skilled in the art. For example, although the invention has been described with reference to a rivet, other types of connections between the side plate and retention member can be utilized as desired. Moreover, different types of removable fasteners can be used between the support shelf and the substrate support device to practice the invention. Additionally, the side plate may be either removable or may be permanently attached to the clamping block. Therefore, the above should not be construed as limiting the invention, which is defined by the claims.