Abstract:
A system for depositing solder paste on a print window of a printed circuit board through a stencil includes a housing providing a printing chamber, a depositor configured to move relative to the housing and to deposit the solder paste, a support device disposed in the printing chamber and configured to receive the circuit board and to selectively hold the circuit board stationary relative to the housing, a loading mechanism configured to receive the circuit board and to transport the circuit board along a second direction to the support device, a controller coupled and configured to control dispensing of the solder paste by the depositor and the transporting of the circuit board by the loading mechanism, and a rotational apparatus coupled to the support device and configured to rotate the support device, where the controller is configured to cause the rotational apparatus to rotate the support device more than about 10° and to cause the depositor to deposit solder paste onto the circuit board after the rotational device has rotated the support device more than about 10°.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to printed-circuit-board manufacturing and more particularly to printing large circuit boards.  
         BACKGROUND OF THE INVENTION  
         [0002]    The manufacturing of circuit boards involves many processes, one of which is screen printing solder paste and adhesives onto printed circuit boards so that electronic components can be placed onto the boards. Screen printing of solder paste is typically performed in a printer. The circuit board is mounted on a conveyor for insertion into the printer. The board is moved into the printer for printing of the solder paste onto the circuit board.  
           [0003]    To apply solder paste and surface mount components to a surface of a circuit board, several actions are taken using a stencil. The stencil has one or more (typically more) apertures that define a pattern corresponding to a pattern of pads already disposed on the circuit board. The stencil is placed substantially parallel to the surface of the board to be printed and the apertures are aligned with the pattern on the substrate surface. The solder paste or other material to be deposited is placed on top of the stencil for deposition into the apertures and onto the board. Once the apertures are filled with material, excess material may be removed from the top of the stencil, using for example a squeegee, so that substantially all of the material that remains is in the apertures. The stencil is separated from the board and the surface tension between the board and the material causes most of the material to stay on the board.  
           [0004]    Circuit boards come in a variety of standard sizes and solder printers are typically configured to accommodate a range of various sizes up to and including boards of about 24″×20″. For example, printers exist that can accommodate boards up to about 24″×20″, up to about 0.5″ thick, and up to about 80 pounds. Equipment, e.g., for holding and positioning the boards, and for applying solder paste to the boards, influence the sizes of boards that a printer can accommodate. For example, squeegees for applying solder paste are typically about 24″ to accommodate a 24″ substrate while providing desirable characteristics for spreading the solder paste. Some specialized printers exist for printing on larger substrates such as 36″ substrates. Some concerns with accommodating larger boards is that quality may degrade, and/or solder paste waste may increase, compared to printing smaller boards, e.g., due to using larger non-standard squeegees. Another concern regarding the size of boards that a printer can accommodate is the width of the printer itself. As the printer gets wider, a production line using the printer gets longer. As production lines are often tightly fit to available space, widening a printer may have significant practical implications upon a production line using the printer.  
         SUMMARY OF THE INVENTION  
         [0005]    In general, in an aspect, the invention provides a system for depositing solder paste on a print window of a printed circuit board through a stencil. The system includes a housing providing a printing chamber, a depositor configured to move relative to the housing and to deposit the solder paste, a support device disposed in the printing chamber and configured to receive the circuit board and to selectively hold the circuit board stationary relative to the housing, a loading mechanism configured to receive the circuit board and to transport the circuit board along a second direction to the support device, a controller coupled and configured to control dispensing of the solder paste by the depositor and the transporting of the circuit board by the loading mechanism, and a rotational apparatus coupled to the support device and configured to rotate the support device, where the controller is configured to cause the rotational apparatus to rotate the support device more than about 10° and to cause the depositor to deposit solder paste onto the circuit board after the rotational device has rotated the support device more than about 10°.  
           [0006]    Implementations of the invention may include one or more of the following features. The rotational apparatus is configured to rotate the support device about 90°. The rotational apparatus is configured to rotate the support device about 90° at a first rate in a coarse adjustment mode and is configured to rotate the support device at a second rate, slower than the first rate, in a fine adjustment mode. The support device includes a plurality of elongated guides for supporting bottom surfaces of edges of the circuit board, the system further comprising a flattening apparatus comprising a plurality of elongated members configured to retractably engage top surfaces of the edges of the circuit board and, in combination with the guides, to squeeze the edges of the circuit board. The controller is configured to cause the elongated members to be retracted before the depositor deposits the solder paste onto the circuit board. The depositor has a printable length, and wherein the controller is configured to cause the rotational apparatus to rotate the support device more than about 10° in response to determining that a dimension of the print window substantially parallel to the direction of travel of the circuit board is greater than the printable length.  
           [0007]    In general, in another aspect, the invention provides a method of printing a circuit board with solder paste using a solder printer. The method includes transporting the circuit board, that includes a print region that is to receive the solder paste, to a printing chamber of the solder printer along a first direction of travel, rotating the circuit board greater than about 10°, moving the circuit board into close proximity with the stencil with the print region in a desired relationship with respect to the stencil, and printing the solder paste onto the circuit board by inserting the solder paste through the stencil onto the print region of the circuit board.  
           [0008]    Implementations of the invention may include one or more of the following features. The rotating rotates the circuit board about 90°. The method further includes pressing edges of the circuit board before the printing. The rotating is initially rotating, the method further comprising further rotating the circuit board after the printing such that the circuit board is oriented substantially similarly as the board was situated before the initial rotating. The further rotating rotates the board substantially 90° in a direction opposite to that of the initial rotating. The initial and further rotating are performed at a first speed that is faster than a second speed used to rotate the circuit board, if at all, to fine tune alignment of the circuit board with the stencil. The method further includes determining whether a dimension of the print region substantially parallel to the first direction of travel is greater than a printable length associated with the printer, wherein the rotating is performed in response to determining that the dimension of the print region substantially parallel to the first direction of travel is greater than the printable length.  
           [0009]    Implementations of the invention may also include one or more of the following features. The circuit board is a first circuit board and the print region is a first print region, the method further including receiving a second circuit board for printing, transporting the second circuit board, that includes a second print region that is to receive the solder paste, to the printing chamber of the solder printer along the first direction of travel, determining that a dimension of the second print region substantially parallel to the first direction of travel is no greater than the printable length associated with the printer, moving the second circuit board into close proximity with the stencil with the print region in a desired relationship with respect to the stencil without rotating the second circuit board more than about 10°, and printing the solder paste onto the second circuit board by inserting the solder paste through the stencil onto the second print region of the second circuit board.  
           [0010]    In general, in another aspect, the invention provides a printer for printing a circuit board with solder paste through a stencil onto a print region of the circuit board. The printer includes a housing providing a printing chamber, an input configured to receive and transport the circuit board along a first direction of travel into the printing chamber, a support device disposed in the printing chamber and configured to receive the circuit board and to selectively hold the circuit board stationary relative to the housing, a solder paste depositor disposed in the printing chamber and configured to move relative to the housing in a second direction of travel substantially perpendicular to the first direction of travel and to deposit the solder paste, a rotational apparatus configured to rotate the support device and the circuit board, and a controller coupled to and configured to control the depositor, the input, the depositor, and the rotational apparatus to: transport the circuit board to the printing chamber along the first direction of travel; rotate the circuit board about 90°; move the circuit board into close proximity to the stencil with the print region in a desired relationship with respect to the stencil; and print the solder paste onto the circuit board by moving the depositor in the second direction of travel while dispensing the solder paste through the stencil onto the print region of the circuit board.  
           [0011]    Implementations of the invention may include one or more of the following features. The printer further includes a plurality of retractable flattening bars, wherein the controller is configured to cause the flattening bars to press on a top surface of the circuit board and to retract from the top surface before the solder paste is printed onto the circuit board. The controller is further configured to cause the rotational apparatus to rotate the support device and the circuit board about −90° after the solder is printed on the circuit board. The depositor in conjunction with the stencil determine a printable length associated the printer, and wherein the controller is configured to rotate the circuit board about 90° only if a dimension of the print region substantially parallel to the first direction of travel is greater than the printable length.  
           [0012]    In general, in another aspect, the invention provides a printer for depositing solder paste through a stencil, the printer including a housing and means, coupled to the housing and having a printable length substantially perpendicular to a print direction, for printing solder paste on a circuit board, that has a print window length substantially parallel to a direction of receipt of the board that is greater than the printable length, the circuit board being for receipt of the solder paste from the printing means in the print window.  
           [0013]    Implementations of the invention may include one or more of the following features. The printing means is configured to rotate the circuit board approximately 90° inside the housing prior to deposition of the solder paste. The printing means is configured to position the circuit board such that a width of the print window that is no greater than the printable length is disposed substantially parallel to the printable length.  
           [0014]    Various aspects of the invention may provide one or more of the following advantages. Substrates larger than 24″ may be accommodated within existing printer footprints. Substrates larger than 24″ in one dimension can be printed using a squeegee that is about 24″. Larger-than-normal circuit boards can be printed with solder without using a custom squeegee, with better quality/control than if a large, custom squeegee is used, and/or with reduced solder paste waste at changeover/stencil cleanup than if a custom, larger-than-normal squeegee is used. Standard printers and printer accessories such as squeegee blades and stencil wiper components can be used to print larger-than-normal circuit boards. Larger circuit boards can be solder printed using semi-standard stencil frames having one dimension be about 29″. Larger-than-normal circuit boards can be solder printed while using shorter squeegee blades, less print pressure down force, lighter and smaller squeegee blades, and less paste than using current techniques. Relatively long circuit boards can be solder printed in a non-specialized machine that can accommodate smaller circuit boards such that the machine need not sit idle when no relatively long circuit boards need to be processed. Larger and heavier-than-normal circuit boards, e.g., up to 80 pounds and 36″ in length, can be printed by using a printer implementing the invention than if existing printers are used. A production line for large circuit boards that uses a printer implementing the invention can be shorter than a production line using an existing large-board printer.  
           [0015]    These and other advantages of the invention, along with the invention itself, will be more fully understood after a review of the following figures, detailed description, and claims. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0016]    [0016]FIG. 1 is a front perspective view of a solder printer for printed circuit boards.  
         [0017]    [0017]FIG. 2 is a perspective view of a circuit board positioner system and table of the printer shown in FIG. 1.  
         [0018]    [0018]FIG. 3 is a perspective view of a relatively large circuit board being loaded onto a portion of the positioner system shown in FIG. 2.  
         [0019]    [0019]FIG. 4 is a schematic side view of a circuit board having its edges flattened by flattening bars shown in FIG. 2.  
         [0020]    FIGS.  5 - 8  are perspective views of the circuit board shown in FIGS.  3 - 4  being rotated, aligned, lifted, and printed on.  
         [0021]    [0021]FIG. 9 is a block flow diagram of a process of printing solder on the circuit board as shown in FIGS.  3 - 8 . 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0022]    Embodiments of the invention include printers configured to print circuit boards of relatively long lengths that have widths shorter than their lengths. The boards are loaded into a printer, rotated 90°, printed with solder paste, rotated back 90°, and expelled from the printer. The boards can be printed using equipment designed for printing swaths that are smaller than the board&#39;s length. The boards can be printed using printers with lengths in the direction of board flow that are the same as printers for printing shorter-length boards that are not rotated before printing. Other embodiments are within the scope and spirit of the invention.  
         [0023]    Referring to FIG. 1, a printer  10  includes a housing  12 , a rail feed mechanism  14  for carrying and loading a circuit board  16 , a work table  18  (FIG. 2), a solder-paste-depositing mechanism  20 , shown here as a print head that includes multiple squeegees  22  (only one shown in FIG. 1), a control computer  24 , and a rail output mechanism (not shown), similar to the rail feed mechanism  14 , for carrying and expelling the board  16 . The circuit board  16  contains circuit portions in the form(s) of metal contacts, pads, lead lines, and/or transmission lines to be connected to circuit components and to help connect circuit components, that will eventually be attached to the board  16 , together. The controller  24  is configured to execute one or more stored computer-readable, computer-executable software programs to perform functions described below. The printer  10  is configured to load the board  16 , print solder paste on the board  16  through a stencil  17  (FIGS.  6 - 7 ) that determines what portions of the board  16  receive the paste, and output the board  16  for further processing. Such further processing may include placing of circuit components on the board  16  and heating of the board  16  to solder the circuit components to the board  16 . The feed mechanism  14  and the output rail mechanism are configured to load the board  16  into, and unload the board  16  from, the printer  10 .  
         [0024]    The depositor  20  is configured to deposit solder paste through apertures in a stencil  17  (FIG. 6) onto the circuit board  16 . Although the depositor  20  is shown as a print head with squeegees  22 , other configurations are acceptable, such as a Rheometric pump with blades (see U.S. Pat. No. 5,947,022), enclosed print heads, etc. The depositor  20  is connected to an appropriate means for moving the depositor  20  under control of the controller  24  in a print direction (FIG. 8; or the opposite direction than as shown in FIG. 8). The depositor  20  is preferably sized in accordance with the size of a printing chamber  28 , which is sized to accommodate predetermined sizes of stencils. The stencils typically have a foil portion in which the apertures are formed. Typically, stencil frames measure 29″ perpendicular to the print direction, with the foil portion measuring about 24″ perpendicular to the print direction. The depositor  20  is preferably configured to deposit solder across an entire maximum length of the foil in a direction perpendicular to the direction of travel of the depositor  20 . The depositor  20  may, however, be configured to deposit solder paste over a larger or smaller length.  
         [0025]    The printer  10  has a printable length that is the length perpendicular to the print direction that may be printed with solder paste from the depositor  20  through the stencil  17 . Preferably, the depositor  20  is configured to deposit solder over the full distance of the foil, e.g., 24″ perpendicular to the print direction. Thus, as shown, the squeegees  22  extend the full length  100  (FIGS. 3 and 6) of an applicator portion of the depositor  20 . Also, the maximum printable length of the depositor  20  is preferably parallel to the length  100  of the depositor  20 , and thus the maximum printable length is used if the print direction is perpendicular to the length  100 .  
         [0026]    Referring also to FIG. 3, the circuit board  16  is a relatively large circuit board having a length  104  longer than about 24″. This circuit board is larger than normal in that it is longer than standard boards sizes that can be accommodated by non-custom/specialized printers. For example, the length  104  of the board  16  may be longer than the length  100  of the depositor  20 . More particularly, a print window  106  of the board  16  that is to be printed on may have a length  108  (i.e., dimension in the direction parallel to board travel) that is longer than the printable length of the printer  10 . The window  106  is shown as a rectangle although this is not required. A width  110  of the board  16  may be smaller than the length  100  of the depositor  20 , and preferably a width  112  of the window  106  is equal to or less than the printable length of the printer  10 . The circuit board  16  can have any of a variety of lengths, widths, and thicknesses, but preferably the length  104  is less than about 36″ and more than about 6″, the width  110  is preferably less than about 24″ and more than about 6″, and a thickness of the board  16  is preferably between about 0.062″ and about 1″. The circuit board  16  preferably weighs less than about 80 pounds. With such dimensions and weight, the printer  10  can be an Ultraflex® 3000 printer made by Speedline Technologies of Franklin, Mass., modified to accommodate greater weights of boards and to flatten the boards, and programmed to rotate at least boards larger than 24″ in length by about 90° prior to printing. The printer could be so modified without increasing the housing dimension along the axis of travel of the board  16  into and out of the printer  10 , and thus can be substituted for an unmodified Ultraflex® 3000 printer without affecting the length of a production line that includes the unmodified Ultraflex® 3000 printer.  
         [0027]    Referring also to FIGS.  1 - 2 , the printer  10  further includes a positioning system  30 , to be coupled to the work table  18 , that includes a theta motor  32 , an x-drive (not shown), a y-drive (not shown), and a z-drive  38 . The positioning system  30  is configured to position the board  16  in the printing chamber  28  for receiving solder from the depositor head  20 . The positioning system  30  is configured to respond to commands from the controller  24  to orient the table  18 , that holds the circuit board  16 , within the printing chamber  28  at a desired location and angle for receiving the solder from the depositor  20 . The commands received will depend upon information received by the controller  24  from a camera  25  (FIG. 6) that provides information as to the relative positions of the circuit board  16  and the stencil  17  (FIGS.  6 - 7 ). The x-drive includes a motor for moving an x-platform  34  along x-rails  35  and the y-drive includes a motor for moving a y-platform  36  along y-rails  37  in the x and y directions respectively. The x platform  34  holds a z-tower  48  from moving relative to the x platform in the x and y directions. The z-drive  38  is configured to raise and lower the z-tower  48  along the z axis. The theta motor  32  is coupled to the z-tower  48  and the work table  18 , and thus adjustments in z affecting the theta motor  32  also affect the work table  18 , and in turn the circuit board  16 .  
         [0028]    The theta motor  32  is configured to rotate the work table  18  in theta parallel to the x-y plane as indicated. The motor  32  has an upper half  52  and a lower half  54 . The upper half  52  is connected (e.g., bolted) to the work table  18  and the lower half  54  is connected (e.g., bolted) to the z-tower  48 . The motor  32  is a servo motor configured to have the two halves  52 ,  54  rotate about the z-axis with respect to each other. As the z-tower  48  is inhibited from rotational movement about the z-axis by the x platform  34 , rotation, of the halves  52 ,  54  with respect to each other causes the upper half  52 , that is connected to the table  18 , to rotate in theta about the z-axis.  
         [0029]    The theta motor  32  is configured to rotate the work table  18  in response to commands from the controller  24  in both coarse and fine modes. In the coarse mode, the motor  32  can rapidly rotate the work table  18 , that holds the circuit board  16 , about 90° either clockwise or counterclockwise for positioning the board  16  for receiving solder paste or repositioning the board to be output from the printer  10 . In the fine mode, the motor  32  responds to commands from the controller  24  to adjust the table  18  in theta within very small tolerances to align the board  16  with the stencil  17  through which solder paste will be applied to the board  16 . The motor  32  can rotate the table  18 , and thus the board  16 , much faster in the coarse mode than in the fine mode.  
         [0030]    Referring to FIGS.  2 - 4 , the work table  18  includes two belts  56  (only one shown), retractable flattening bars  60 , and two clamping bars  64  (only one shown). The belts  56  are driven by belt motors  58  over pulleys  59  and to frictionally engage bottom edges of the board  16  to transport the circuit board  16  into the printer  10  (FIG. 1) with the clamping bars  64  guiding the board  16 . At least one, and preferably one, of the clamping bars  64  is configured, and coupled to an appropriate driver, to move toward the other clamping bar  64  to hold and support the board  16  between the clamping bars  64 . The retractable flattening bars  60  are connected to appropriate drivers/motors for moving the flattening bars  60  as desired in response to commands from the controller  24 . The flattening bars  60  are configured to extend upward and over the edges  68 ,  70  of the board  16  and to rest on tops of the edges  68 ,  70  of the board  16 . Board support blades  57  are configured to move upward to raise the board  16  off the belts  56  and into contact with the flattening bars  60  to squeeze the board edges  68 ,  70  between the flattening bars  60  and the supports  57 , as shown in FIG. 4, to help flatten the board  16 . The flattening bars  60  are further configured to be retracted into their retracted positions shown in FIG. 3 (and in FIG. 4 in dashed lines) while the board  16  is further processed, e.g., by having solder paste printed on it from the depositor  20 .  
         [0031]    In operation, referring to FIG. 9, with further reference to FIGS.  1 - 8 , a process  80  for solder printing the circuit board  16  using the printer  10  includes the stages shown. The process  80 , however, is exemplary only and not limiting. The process  80  can be altered, e.g., by having stages added, removed, or rearranged.  
         [0032]    At stage  82 , the circuit board  16  is loaded into the printer  10 , and more specifically into the chamber  28 . The rail feed mechanism  14  carries the board  16  along the board&#39;s edges into the printing chamber  28 . As shown in FIG. 3, the board  16  rides along the belts  56  into the chamber  28  and the board  16  is stopped.  
         [0033]    At stage  84 , the board  16  is flattened along its edges  68 ,  70 . As indicated in FIG. 4, the flattening bars  60  move up and over the edges  68 ,  70  of the board  16 . The flattening bars  60  extend about ¼″ over the edges  68 ,  70  of the board  16 . The support blades  57  lift the board  16  off the belts  56  and into contact with the flattening bars  60  and the board edges  68 ,  70  are squeezed by the flattening bars  60  and the supports  57  in the z-axis. The flattening bars  60  retract and the clamping bars  64  (although only one may move) squeeze the board  16  in the x-y plane. As indicated in FIG. 4, the clamping bar  64  moves inward to clamp the board  16  such that the board  16  is held by the clamping bars  64  and supported by the support blades  57 .  
         [0034]    At stage  86 , the work table  18 , that holds the board  16 , is rotated 90° and x, y, and theta (Θ) fine adjustments are made. As shown in FIGS.  5 - 6 , the board  16  is rotated in coarse adjustment mode by the servo motor  32  under direction of the controller  24 . The camera  25  is moved between the circuit board  16  and the stencil  17  to show fiducial marks on the board  16  and the stencil  17 . The controller  24 , depending on the relative positions of the fiducial marks, provides commands to the x-driver, the y-driver, and the theta motor  32  as appropriate to fine tune the relative positioning of the board  16  with respect to the stencil  17 . When positioned as desired, the depositor  20  will be able to print solder paste into the entire print window  106  (e.g., the width  112  of the window  106  will be substantially parallel to the printable length of the depositor  20 ).  
         [0035]    A determination can be made as to whether the 90° rotation is desirable/needed. For example, the length  104  of the board  16  can be determined and if the length  104  is longer than the printable length of the printer  10 , then the board  16  can be rotated. Alternatively, the length  108  of the print window  106  of the circuit board  16  may be determined (e.g., using the camera  25 ) and compared against the printable length of the printer  10 . If the length  108  of the window  106  is longer than the printer&#39;s printable length, then preferably the board  16  is rotated about 90° in response to a command from the controller  24  to the motor  32  (thus indicating that the print window length  108  exceeds the printer&#39;s printable length), and is not rotated 90° otherwise. Further, the printer  10  may be configured such that the board  16  is rotated about 90° without a command from the controller  24  to the motor  32 . For example, all received boards may be rotated about 90° if the printer is programmed to handle a series of large boards  16  and the motor  32  automatically rotates the board  16  in response to an indication that the board  16  has been received by the table  18 . In this case, the command is implicit and the indication that the board  16  has been received serves as an indication that a print window larger than the printable length of the printer  10  is present. Alternatively, the printer  10  may be configured such that the board  16  is rotated about 90° always, or at least without a command from the controller  24  to the motor  32  or other indication that the window length  108  exceeds the printer&#39;s printable length.  
         [0036]    At stage  88 , the board  16  is moved along the z axis (FIG. 7) into contact with the stencil  17  and the depositor  20  is moved over the stencil  17  (FIG. 8) to deposit solder paste on the circuit board  16 . The stencil  17  can have a standard 29″ width for a circuit board with a 24″ width. The depositor  20  travels along the length of the circuit board  16  perpendicular to the direction of travel of the circuit board  16  through the printer  10 . If the depositor  20  is a print head using squeegees, as shown in FIG. 1, then the solder paste is deposited on the stencil  17  between the leading and trailing squeegees  22  and the trailing squeegee  22  pushes the paste through the stencil apertures and cleans the stencil  17  behind the depositor  20 . For a Rheometric pump depositor, solder paste is dispensed under pressure through the stencil apertures and a blade that is angled into the direction of travel cleans the solder paste from the stencil  17 .  
         [0037]    At stage  90 , the work table  18  and the board  16  are rotated to again have the length  104  of the board  16  align with the direction of travel of the board  16 , preferably by being rotated about 90° in the opposite direction from the rotation at stage  86  (i.e., −90°).  
         [0038]    At stage  92 , the circuit board  16  is output from the printer  10  by the rail output mechanism and the process  80  returns to stage  82  where another circuit board  16  is loaded.  
         [0039]    Other embodiments are within the scope and spirit of the appended claims. For example, due to the nature of software, functions described above can be implemented using software, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Further, while the description above focused on rotating the board  16  about 90° for printing, rotations of other amounts are possible. For example, the circuit board  16  could be rotated less than 90°, such as about any of 10°, 20°, 30°, 40°, 45°, 50°, 60°, 70°, or 80°, or any angle from about 10° to about 90° (in either direction). In at least these cases, the print window  106  may be oriented relative to the board  16  to facilitate printing when rotated the desired amount. Preferably, however, the board  16  is rotated at least 10°. Further, it has been assumed that the depositor  20  travels substantially perpendicular to the length  100  of the depositor  20 . If the depositor  20  travels non-perpendicularly to the length  100  of the depositor  20 , then the printable length of the depositor  20  will be reduced from that of the maximum printable length of the depositor  20  by an amount that depends on the angle of travel relative to the length of the depositor  20 . In this case, the circuit board  16  is preferably rotated at least 90° if the length  108  of the print region  106  is larger than this actual, albeit less than maximum, printable length of the depositor  20 . Further, blades or squeegees longer than the length  100  of the depositor  20  may be used, although these longer blades/squeegees may not increase the printable length of the depositor  20 . These longer blades/squeegees may be angled with respect to the depositor length  100 .  
         [0040]    While typically a printable length of the printer  10  is the printable length of the depositor  20 , the printable length of the printer  10  may be smaller than the printable length of the depositor  20 . The printable length of the printer  10  is the shorter of the depositor&#39;s printable length and the length of the stencil foil (or other area in the stencil having apertures for receiving solder paste, e.g. a portion of the foil having the apertures) perpendicular to the print direction. Thus, the controller  24  can determine whether the print window length  108  is longer than the printer&#39;s printable length, and cause the table  18  to be rotated if the length  108  is longer than the printer&#39;s printable length.