Abstract:
A platform and method for leveling the upper surface of a printed circuit board placed upon a work table. The platform comprises a substantially flat plate, the plate having a fastener for planerly securing the printed circuit board thereto, and at least one support having a length between a first end and a second end, the second end of the at least one support attached to the plate, and wherein the length of the at least one support is selected such that an angle between the plate and the work table compensates for any angular displacement of the printed circuit board relative to the plate. The method comprises fastening the printed circuit board to a platform, securing the platform to the work table, and angularly adjusting the upper surface of the printed circuit board by altering an angle between the platform and the work table.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to devices and methods for handling printed circuit boards during manufacturing processes. More particularly, this invention relates to an apparatus and methods for leveling the upper surface of a printed circuit board on the tooling table of a pick-and-place machine. 
     2. Background Information 
     Pick-and-place machines are commonly used to mount components, such as integrated circuit chips, capacitors, and resistors, onto printed circuit boards (PCBs). The use of pick-and-place machines to increase the speed with which components are surface-mounted to PCBs is well known in the art. Pick-and-place machines remove components from a stored position or a feeder, align the components with the PCB, and place the components in the proper position on the PCB. Pick-and-place machines are used to populate both single-sided and double-sided PCBs. 
     The pick-and-place machine contains a device, such as a robotic arm, to move components from stored positions to the PCB surface. The robotic arm typically contains a gripping mechanism, such as a suction nozzle head, to grip components in the stored position and transport them to the PCB. Some pick-and-place machines have robotic arms that move in the X and Y-axes only, while other pick-and-place machines have robotic arms that move in the Z-axis or in a combination of all three axes. 
     To ensure the proper placement of components on the PCB, the alignment of the PCB with the pick-and-place machine, in particular the robotic arm, must be calibrated. The PCB is secured to the tooling table of the pick-and-place machine to ensure a fixed alignment of the PCB on the table. The tooling table may then be adjusted in the X, Y, and Z axes and examined by eye for proper positioning. Proper positioning of the PCB on the tooling table allows the robotic arm head to pick up a component from the stored position, scan the PCB, and then place the component in the proper position on the PCB. 
     The use of part decryption generators (PDGs) to populate PCBs with components is well-known in the art. A PDG is a program that instructs the pick-and-place machine where to place specific components on the PCB surface. The PDG also directs a camera or similar scanning device, which may be mounted on the robotic arm head, to scan the PCB surface. The PDG uses the results of this scan as a location guide for placement of components on the PCB surface. 
     When the PDG uses the robotic arm head to scan the PCB, it reads a Z-level where it contacts the PCB and assumes this level to be constant over the entire upper surface of the PCB. If the upper surface of the PCB is not at a fixed Z-level, i.e., is uneven due to warping, thickness variations or other abnormalities, the PDG will improperly place components on the PCB. If the PDG assumes a constant Z-level and some areas of the PCB are above or below that level, components in those areas will not be placed at the correct Z depth. With current pick-and-place equipment, an average of about ten percent of components are misplaced if the upper surface of the PCB is not level, and up to seventy-five percent of components may be misplaced in a severe case. The improper placement of components on PCBs not only causes problems with the success of PCB production, but the nozzle heads of the pick-and-place machine&#39;s robotic arm may be damaged by overdriving parts into PCBs. 
     The pick-and-place machine industry has provided mounting pins and clamps to hold PCBs to the tooling tables. The mounting pins are commonly solid pin dowels that thread into fixed locations in the tooling table. The height of the mounting pins may be adjusted by threading the pins into or out of the tooling table. The PCB may then be placed upon the mounting pins. Some pick-and-place machines provide clamps to pinch the PCB from the top above each of the mounting pins to support the PCB. Other pick-and-place machines come with a suction securing system. In these systems the mounting pins have holes drilled in them. The bottom side of each mounting pin is connected to a vacuum supply to create suction forces on the upper side of the mounting pin where it contacts the PCB. The suction forces hold the PCB down to the mounting pins, which in some cases may permit correction of warping. 
     There are a number of problems that result from securing PCBs to tooling tables with mounting pins. Double-sided PCBs contain components on the bottom side after population of one side with components. Because the mounting pins may only be placed at fixed positions in the tooling table of the pick-and-place machine, the mounting pins may contact the PCB where fragile components, such as capacitors, have been mounted. This contact may damage the components. 
     Another problem with the use of mounting pins is the difficulty in flattening out the upper surface of PCBs that are warped. Mounting pins secure the PCB by grasping the PCB from the top and from the bottom. The use of a plurality of mounting pins to support a PCB may not flatten out the PCB and remove the warping from its upper surface. Even a plurality of properly placed mounting pins may not be able to remove the warping from a large PCB because it is difficult to stretch or flatten out the PCB with mounting pins that provide only vertical support at limited points of contact. The use of mounting pins may cause some areas of the PCB to sag so that the upper surface of the PCB is not flat. 
     Yet another problem with the use of mounting pins to support PCBs upon tooling tables is the difficulty in achieving a repeatable flat surface for the PCB. If the pick-and-place machine is used to populate a different size or type of PCB, the location and height of the mounting pins will need to be modified to accommodate the new PCB. The mounting pins will have to be positioned and adjusted from scratch the next time the first line of PCBs is to be populated. A related problem results if one pick-and-place machine is set up for population of a given PCB line and it is desired to use a different pick-and-place machine for population of that PCB line. The mounting pin placement on the new pick-and-place machine will have to be adjusted from scratch to achieve the proper Z-level. 
     A need exists for a method and apparatus to provide a level upper surface for PCBs during population of components using pick-and-place machines that is repeatable, may be used for different pick-and-place machines with minimal effort, and that does not damage components on double-sided PCBs. 
     SUMMARY OF THE INVENTION 
     This invention comprises a platform and a method for leveling the upper surface of a printed circuit board placed upon a work table. In one embodiment, the platform comprises a substantially flat plate, the plate having a fastener for planerly securing the printed circuit board thereto, and at least one support having a length between a first end and a second end. The second end of the at least one support is attached to the plate, and the length of the at least one support is selected such that an angle between the plate and the work table compensates for any angular displacement of the printed circuit board relative to the plate. Another embodiment of the invention comprises a suction system as the fastener to secure the printed circuit board to the plate. Another embodiment of the invention comprises a plurality of legs that are adjustable. 
     Yet another embodiment of the invention is a platform comprising a flat plate, a suction system to planerly secure the printed circuit board to the plate, 
     a base adapted to be mounted to the work table, and a plurality of supports having lengths between first ends and second ends. The first ends of the supports are connected to the base, the second ends connected to the plate, and the lengths of the plurality of supports are selected such that an angle between the plate and the work table compensates for any angular displacement of the printed circuit board relative to the plate. 
     Another embodiment of the invention is a method comprising the acts of fastening the printed circuit board to a platform, securing the platform to the work table, and angularly adjusting the upper surface of the printed circuit board by altering an angle between the platform and the work table. In another embodiment of the invention the act of fastening comprises suctioning the printed circuit board to the platform to planerly secure the printed circuit board to the platform. 
     Yet another embodiment of the invention comprises a method for reproducibly leveling the upper surface of a printed circuit board placed upon a work table. This embodiment of the invention comprises the acts of fastening a template to a plate, securing the plate to the work table, angularly adjusting the upper surface of the template by altering an angle between the plate and the work table, and replacing the template with the printed circuit board. Another embodiment of this invention comprises the act of drilling at least one hole in the template and rotating a bolt through the at least one hole in the template to adjust the length of the at least one support. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of one embodiment of the platform of the invention; 
     FIG. 2 is a front view of the embodiment shown in FIG. 1 that illustrates a PCB on the platform where the upper surface of the PCB requires leveling; 
     FIG. 3 is a front view of the embodiment shown in FIG. 1 that illustrates a PCB on the platform where the upper surface of the PCB has been leveled to a constant Z-depth; 
     FIG. 4 is a side view of an alternative leg embodiment of the platform shown in FIG. 1; 
     FIG. 5 is a side view of the plate of the embodiment shown in FIG. 1 that illustrates the warping of a PCB; 
     FIG. 6 is a side view of the plate of the embodiment shown in FIG. 1 that illustrates the vacuum nozzle of the platform reducing the warping of the PCB to produce a flat upper surface; 
     Fig. 7 is a top view of an alternative embodiment of the plate; 
     FIG. 8 is a top view of a second alternative embodiment of the plate; 
     FIG. 9 is a perspective view of a nozzle placement guide mounted in the plate for use with the second alternative embodiment of FIG. 8; 
     FIG. 10 is a cross-sectional view taken along lines  10 — 10  of FIG.  9 . 
    
    
     DETAILED DESCRIPTION 
     Referring to the embodiment of the invention shown in FIG. 1, there is shown a platform, referred to in its entirety as  10 , resting upon a work table  12 . The work table  12  may be the tooling table of a of a pick-and-place machine, although it could be any surface used for manufacturing processes. Throughout this specification, “table” will be used to refer to any work surface for which a platform may be needed to produce a level and flat upper surface for a workpiece. A typical table  12  is a tooling table of a pick-and-place machine upon which a printed circuit board (PCB) may be secured for surface mounting of components. 
     The platform  10  in general comprises a plate  14 , at least one leg  16 , a fastener  18 , and a base  20 . The plate  14  is attached to the base  20  by at least one of the legs  16 . A PCB  50  may be placed upon the upper surface  22  of the plate  14 , as shown in FIGS. 2-6, and secured to the plate  14  with a fastener  18 . The upper surface  46  of the PCB  50  may then be leveled to a flat surface that does not vary in the Z plane. 
     As will be seen, the present arrangement addresses Z-axis alignment of a PCB  50  as two distinct but related issues that need to be resolved. First, there is the issue of Z-axis positioning of the upper surface  46  of the PCB  50 , assuming that the upper surface  46  of the PCB  50  is adequately flat. This must be addressed by height and ankle positioning of the PCB  50  as a whole. Second, there is the issue of flatness or evenness over the entire upper surface  46  of the PCB, because a given PCB  50  may not be adequately flat. This must be addressed by “smoothing” the deviations in the PCB&#39;s  50  upper surface  46 . 
     A. The Plate of the Platform 
     In the embodiment of the invention shown in FIG. 1, the plate  14  is generally rectangular in shape. The plate  14 , however, could be of any geometry, including a circular shape or a square shape. The plate  14  may be made of any hard, relatively rigid material, such as plastic or aluminum, and the thickness of the plate may vary. The plate&#39;s upper surface  22  is substantially flat so that it can provide a reference and a guide for achieving evenness or flatness. As shown in FIGS. 2 and 3, a thin foam layer  23  may be placed upon the upper surface  22  of the plate  14  to help cushion components  48  on the lower surface  45  of a PCB  50  when the PCB  50  is secured to the plate  14 . This foam layer  23  may be of varying thickness and may be made from a variety of resilient materials known to those skilled in the art. The plate  14  may also have a variety of holes or grooves formed in it as described in connection with the other elements of the platform  10  in the description that follows. 
     B. The Legs of the Platform 
     The platform  10  shown in FIG. 1 has four legs  16 , although any number of legs  16  or other supports could be used within the scope of the invention. In the embodiment shown in FIG. 1, the legs  16  connect the plate  14  to the base  20 . The base  20 , therefore, may be adapted so that it may be secured to the table  12 . FIG. 1 shows the base  20  connected to the table  12  using pins  21 , although the base  20  may be secured to the table  12  by a variety of devices. The legs  16  also could be used to connect the plate  14  directly to the table  12 . The base  20 , therefore, is not necessary for the platform  10  to function. If the platform  10  does not contain a base  20 , the first end  24  of each leg, which is the bottom portion of the leg  16 , may be configured so that it may be secured to the table  12 . Each leg  16 , therefore, could have a bolt, or any other securing device known to those skilled in the art, to secure the leg  16  to the table  12 . The legs  16  shown in FIG. 1 are solid. The first end  24  of each leg  16  is rigidly connected to the base  20 . The second end of each leg  16  is rigidly connected to the plate  14 . In this embodiment, therefore, the distance between the plate  14  and the base  20  (or table  12 ) is fixed. 
     FIG. 4 shows an alternative embodiment of a leg  16  that is adjustable in length. The leg  16  of FIG. 4 is shown connecting the plate  14  to the base  20  of the platform  10 . The embodiment of the leg  16  shown in FIG. 4 could be substituted for each leg  16  of FIG. 1, such that the distance and angle between the plate  14  and the base  20  (or table  12 ) would be adjustable. FIG. 4 illustrates one embodiment of an adjustable leg  16 , although those skilled in the art could develop other devices for producing a leg  16  that is adjustable in length without departing from the scope of the invention. 
     The leg  16  of FIG. 4 in general comprises a mounting bracket  30 , a bolt  32 , and a spring  34 . The mounting bracket  30  may be secured to the base  20  by a variety of devices known to those skilled in the art; FIG. 4 shows mounting bolts  38  used to bolt the mounting bracket  30  to the base  20 . In an embodiment that does not include a base  20 , the first end  24  of each leg  16 , which may be the mounting bracket  30 , may be adapted to secure the leg  16  to the table  12  with the mounting bolts  38  or with other devices known to those skilled in the art. In the leg  16  of FIG. 4, a second bolt  32  may extend through the plate  14  and into the mounting bracket  30  to secure the plate  14  to the base  20 . If the bottom portion of the bolt  32  is threaded, the bolt  32  may screw into threads  35  formed within a bore  36  in the mounting bracket  30 . Advancing or removing the threads  35  from the bore  36  provides adjustability of the height and angle of the upper surface  22  of the plate  14 . 
     The spring  34  may fit over the bolt  32  such that one end of the spring  34  is in contact with the plate  14  and the other end is in contact with the mounting bracket  30 . A washer  40  or other similar device may be connected to either the spring  34  or the bottom side of the plate  14  so that the spring  34  provides an even upward force on the plate  14 . As shown in FIG. 4, the spring  34  provides an upward force on the plate  14  so that the bolt  32  sits flushly in the top of the plate  14  and so the height of the plate  14  is easy to adjust. The plate  14  may have a receiving area  44  carved into its upper surface so that the top of the bolt  32  sits smoothly upon the upper surface  22  of the plate. 
     For the adjustability of the legs  16  to work smoothly, the plate  14  may have a bore  42  through its surface that is slightly wider in diameter than the bolt  32 . Because the platform  10  may have a plurality of legs  16  (as shown in FIG.  1 ), the plate  14  may form an angle with the table  12  such that the upper surface  22  of the plate  14  is not flat at a constant Z depth. The bore  42  in the plate  14 , therefore, allows the bolt  32  to fit through the plate smoothly even if the plate  14  is at a slight angle to the bolt  32 . If both the mounting bracket  30  and the plate  14  were to contain threads matching the bolt  32 , it may be difficult to adjust the height of the legs  16  when each of the legs  16  are at different heights and the legs  16  form an angle with the plate  14 . 
     This specification refers to, a first end  24  and a second end  26  for each leg  16 . The “first end”  24  of a leg will be used to refer to any part of the leg  16 , such as the bolt  32  or mounting bracket  30 , that connects the leg  16  to the base  20  (or to the table  12 ). Similarly, the “second end”  26  of a leg  16  will be used to refer any part of the leg  16 , such as the bolt  32  or washer  40 , that connects the leg  16  to the plate  14 . 
     As best shown in FIGS. 2 and 3, the legs  16  of the platform  10  allow the height of the plate  14  above the base  20  (or table  12 ) to be adjusted. The angle ø formed between the plate  14  and the base  20  (or table  12 ) may also be modified by adjusting the length of the legs  16 . FIGS.  2  and  3  illustrate two dimensions (an X-Z axes), although the angles may also be adjusted in the third dimension (Y-axis). 
     FIG. 2 shows a PCB  50  having components  48  already present on its lower surface  45 . When the PCB  50  of FIG. 2 is placed and secured upon the plate  14  (fastener  18  is not illustrated), the PCB  50  forms an angle Ω with the upper surface  22  of the plate  14 . The upper surface  22  of the plate  14  shown in FIG. 2 forms a plane parallel to the base  20  (and the table  12 ), such that the angle ø (not shown in FIG. 2) between the upper surface  22  of the plate  14  and the base  20  (or table  12 ) is zero. Because the upper surface  46  of the PCB  50  in FIG. 2 is not of uniform height in the Z dimension, the pick-and-place machine may make errors when placing components  48  on the upper surface  46  of the PCB  50 . 
     FIG. 3 shows the placement of the PCB  50  of FIG. 2 upon the platform  10  such that the upper surface  46  of the PCB  50  is of uniform height in the Z dimension. The legs  16  of the platform  10  have been adjusted in length to produce a level upper surface  46  for the PCB  50 . The angle Ω between the PCB and the plate  14  remains constant as the angle ø is increased by adjusting the length of the legs  16 . The necessity of the adjustment of the angle ø in FIGS. 2 and 3 resulted from a PCB  50  with components  48  mounted on its lower surface  45 . The adjustability of the legs  16  to alter the angle ø may also be necessitated by severe warping of different areas of the PCB  50 , by varying thicknesses of the PCB  50 , or by other factors. 
     The orientation of the plate  14  upon the legs  16  may be locked into fixed positions. FIGS. 2 and 3 show the use of lock nuts  39  near the mounting brackets  30 . These lock nuts  39  could be used to fix the positions of the bolts  32  within the bores  36 . This allows the platform  10  to be set up for a given line of PCB  50  production once at the beginning of a production run. The platform  10  may then be locked into position and used to produce a repeatable flat upper surface for the entire production run. The platform  10  may also be moved from one machine to another machine handling the same line of PCBs  50  without the need for burdensome alignment procedures to produce a flat surface. As described above, if the bolt  32  is rotated so that the position of the bolt  32  within the mounting bracket  30  is modified, the height of the plate  14  above the base  20  (or table  12 ) will change. When the rotation of the bolt  32  is completed, the leg  16  will lock into position (if the bolt  32  is not rotated) so that the height of the leg  16  is fixed. 
     In the embodiment of FIG. 1, where the legs  16  are fixed in position, the legs  16  would be pre-fit in height for a given line of PCBs so that the upper surface  46  of the PCBs  50  would have the desired uniform Z-axis dimension. 
     C. The Fastener of the Platform 
     The platform  10  shown in FIG. 1 contains a fastener  18  to secure a PCB  50  to the upper surface  22  of the plate  14 . FIGS. 2-6 illustrate a PCB  50  resting upon the upper surface  22  of the plate  14 . Throughout this specification, “fastener”  18  will be used to refer to any device or devices used to secure a PCB  50  in a substantially flat position on the upper surface  22  of the plate  14 . The fastener  18  could be a plurality of clamps that pinch the PCB  50  to secure it upon the plate  14 , or any other device known to those skilled in the art to secure the PCB  50  upon the plate  14 . 
     The fastener  18  shown in FIG. 1 comprises a suction system, referred to in its entirety as  52 . Throughout this specification, “suction system” will be used to refer to any device capable of securing the PCB  50  to and against the plate  14  through the use of suction forces. The suction system  52  of FIG. 1 comprises one or more vacuum nozzles  54  and a vacuum supply  56 , which may comprise a hose  58  connected to a vacuum source  60 . The vacuum source  60  may permit for the adjustment of the amount of vacuum applied. Some pick-and-place machines come equipped with vacuum supplies  56 , while other machines do not. If a pick-and-place machine is equipped with a vacuum supply  56 , that supply may be connected directly to the vacuum nozzles  54 . 
     As best shown in FIG. 7, the plate  14  may have one or more holes  64  in which the vacuum nozzles  54  fit. A hole  64  in the plate  14  may have threads  66  around its edges to secure the vacuum nozzle  54  within the hole  64 . In this embodiment, the vacuum nozzle  54  may have matching threads  68  (best shown in FIGS. 5 and 6) so that it may be secured within the holes  64  of the plate  14 . Any method known to those skilled in the art to secure the vacuum nozzles  54  within the holes  64  may be used. In one embodiment, the vacuum nozzle  54  might not have threads  68 . Instead, the vacuum nozzle  54  could fit in a threaded bolt with a hole through it, and the threaded bolt could then be secured in a hole  64  of the plate  14 . The vacuum nozzles  54  used in the invention may vary as known to those skilled in the art. 
     The operation of the suction system  52  to secure the PCB  50  to the plate  14  is best shown in FIGS. 5 and 6. FIG. 5 shows a warped PCB  50  resting upon the upper surface  22  of the plate  14 . The vacuum nozzle  54  of FIGS. 5 and 6 contains a bellow cup  70  that extends above the upper surface  22  of the plate  14 . When the power to the suction system  52  is turned on (FIG.  6 ), the bellow cup  70  grips the lower surface  45  of the PCB  50 . The suction force produced by the vacuum source  60  (shown in FIG. 1) suctions the lower surface  45  of the PCB  50  down until the lower surface  45  comes into contact (or very near contact) with the upper surface  22  of the plate  14 . As the bellow cup  70  grips the PCB  50 , the bellow cup  70  itself contracts such that the mouth of the bellow cup  70  is lowered to near the upper surface  22  of the plate  14 . 
     If the PCB  50  contains components  48  on its lower surface  45 , as in FIGS. 2 and 3, these components will come into contact with the upper surface  22  of the plate  14  when the power to the vacuum source  60  is turned on. In this case one or more bellow cups  70  may continue to extend above the upper surface  22  of the plate  14 . This makes achieving evenness somewhat more difficult because the upper surface  22  of the plate  14  can no longer serve as a single reference for flatness against which the PCB  50  can be forced. However, it can still serve as a visual reference that may be of assistance to an operator, particularly if it is possible to regulate the degree of vacuum so that no vacuum nozzle  54  induces a new degree of unevenness in the flatness of the PCB  50 . 
     Referring again to FIGS. 5 and 6 (which show a PCB  50  without components on its lower surface  45 ), the upper surface  46  of the PCB  50  will become substantially flat if a plurality of the vacuum nozzles  54  grip the PCB&#39;s lower surface  45  to bring the PCB  50  into flat contact with the upper surface  22  of the plate  14  (a flat reference). In one embodiment of the suction system  52 , therefore, a plurality of vacuum nozzles  54  may be connected to the vacuum source  60  by hoses  58 . The use of a plurality of vacuum nozzles  54  to grip the PCB  50  planerly secures the PCB  50  to the plate  14 . Throughout this specification, the term “planerly secured” will be used to refer to securing a PCB  50  to the plate  14  such that the upper surface  46  of the PCB  50  becomes flat. 
     FIGS. 1 and 7 show embodiments of the plate  14  that include a plurality of holes  64  into which the vacuum nozzles  54  fit. Each hole  64  in the plate  14  contains a mechanism, such as threads  66 , to connect a vacuum nozzle  54  to the hole  64 . In this embodiment, the location of the vacuum nozzles  54  will be fixed. In an alternative embodiment, shown in FIG. 8, the plate  14  may have one groove  80  or a series of grooves  80  in which the vacuum nozzles  54  may be mounted. Each groove  80  may contain one or more vacuum nozzles  54 . The vacuum nozzles  54  may be placed in any location within the grooves  80  so that the vacuum nozzles  54  are located in the best position below a given PCB  50  to grip the PCB  50 , to avoid contact with components  48 , and to planerly secure the PCB  50  to the plate  14 . 
     In the embodiment of FIG. 8, a nozzle placement guide  82  may be used to secure each vacuum nozzle  54  in the proper location within a groove  80 . FIG. 9 shows one embodiment of a nozzle placement guide  82  mounted within a groove  80  in a plate  14  with upper surface  22 . The nozzle placement guide  82  comprises a block of metal or rigid plastic with a placement hole  90  for a vacuum nozzle  54 , and two bolts  86  to hold the nozzle placement guide  82  to the plate  14 . The placement hole  90  may be threaded to receive a vacuum nozzle  54  to secure the vacuum nozzle  54  within the nozzle placement guide  82 . In one embodiment of the nozzle placement guide  82 , the placement hole  90  may not extend entirely through the nozzle placement guide  82 . Instead, the placement hole  90  could extend only partly into the nozzle placement guide  82 , and a port hole in the side or bottom of the nozzle placement guide  82  could be used to connect the nozzle placement guide  82  to a hose  58 , which would in turn be connected to a vacuum source  60 . Other devices known to those skilled in the art may also be used to attach a vacuum nozzle  54  to a nozzle placement guide  82 . 
     Each groove  80  of the plate  14  shown in FIG. 8 is flanked by two placement channels  84 , one on either side of the groove  80 . Referring again to FIG. 9, the nozzle placement guide  82  is bolted with bolts  86  into the placement channels  84 . As shown in FIG. 10, the placement channels  84  may have a stepped ridge  88  that provides a surface upon which the bolts  86  may rest. The bolts  86  may be loosened so that the location of the nozzle placement guide  82  within the groove  80  may be modified. The embodiment of the plate  14  shown in FIG. 8, therefore, may be used in combination with the nozzle placement guide  82  shown in FIGS. 9 and 10 to allow for the adjustment of the location of the vacuum nozzles  54  underneath the PCB  50 . Once the proper positioning of the nozzle placement guides  82  in the plate  14  is found, the nozzle placement guides  82  may be locked in place so that the layout of the vacuum nozzles  54  will be fixed for a given line of PCB  50  production. 
     As can be seen, while the plate  14  is still flat and still serves as the reference for evenness of the PCB  50 , it does not provide support for the PCB  50  at all points. The grooves  80  and channels  84  represent areas where the plate  14  does not provide support; thus, these must be narrowly dimensioned and dispersed in such a manner that, given the flexing qualities of the PCB  50  with which the plate  14  will work, the vacuum nozzles  54  do not introduce new deviations from unevenness. With this placement the upper surface  22  of the plate  14  still functions as the flatness guide and reference. 
     D. Operation of the Platform 
     The present invention provides a method and an apparatus for securing a PCB  50  to a table  12  with a desired Z-axis dimension and for leveling the upper surface  46  of the PCB  50 . The invention accomplishes this by fastening the PCB  50  to a plate  14  of the platform  10 , securing the platform  10  to the table  12 , and adjusting the upper surface  46  of the PCB  50  to produce a flat, level surface. As described above, the PCB  50  may be adjusted to a flat, level surface through the adjustment of legs  16  on the platform  10  that alter the angle of the plate  14  in relation to the base  20 , and by planerly securing the PCB  50  to the plate  14  through the use of suction forces. 
     In order to adjust and lock the height of the legs  16  of the platform  10 , a template, which is a PCB  50  that is identical in shape and orientation to a line of PCBs  50  to be produced, may be secured to the plate  14  using the suction system  52 . Holes can be drilled in the template above each bolt  32  in the plate  14  so that the length of the legs  16  may be adjusted. The legs  16  may then be adjusted by rotating the bolt  32  through the hole in the template without having to remove the template from the plate  14 . This adjustment procedure allows a machine operator to adjust the legs  16  of the platform  10  with the template, which is identical to a PCB  50 , remaining attached to the plate  14 . The plate  14 , therefore, does not have to be larger than a line of PCBs  50  for the legs  16  of the platform  10  to be adjusted. After the legs  16  are adjusted, the template may be replaced by a PCB  50  prior to a production run. This adjustment procedure may save space on the table  12  by allowing the plate  14  to be smaller in width than the line of PCBs  50  to be populated with components  48 . 
     This invention allows the user to achieve a flat upper surface  46  of a PCB  50  for population of components using a pick-and-place machine. In one embodiment, the platform  10  is not dedicated for a given line of PCBs  50 ; it may be adjustable so that it may be used for a variety of PCB  50  production lines. The flat upper surface  46  may be locked into place so that the platform  10  may be moved from one machine to another without requiring burdensome adjustments to reproduce a flat upper surface  46  for the PCB  50 . The invention also reduces the likelihood of damage to components mounted to the lower surface  45  of PCBs  50  and helps induce a flat upper surface  46  for PCBs  50  that are warped or are of varying thickness. 
     While the present invention has been described with reference to several embodiments thereof, those skilled in the art will recognize various changes that may be made without departing from the spirit and scope of the claimed invention. Accordingly, this invention is not limited to what is shown in the drawings and described in the specification but only as indicated in the appended claims.