Abstract:
A compliant member configured to support a substrate during automated placement of components and a tray configured to support the compliant member and removably attach to a support member.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to component placement.  
         BACKGROUND  
         [0002]    In populating printed circuit boards (PCB), components are placed in solder paste on a board using high-speed automated equipment. The equipment typically includes a table capable of precise movement in an x-y plane and devices for placing components on PCBs that are held on the table using fixtures. One such component placement machine is the Fuji CP642 Chip Placer sold by Fuji North America, Vernon Hills, Ill.  
           [0003]    Referring to FIG. 1, one way to hold a PCB  10  for placement of components  12  on a primary side  13  of the PCB is to support the board  10  on a secondary side  14  using an array of height-adjustable pins  15  attached to a phenolic plate  16  that is mounted on the x-y table  17  of the component placement machine (not shown).  
           [0004]    The primary side of a PCB is the side on which components are placed first. The secondary side of a board may receive additional components after components on the primary side have been mounted.  
           [0005]    Referring to FIG. 2, the height of each pin  15  may be adjusted independently during set-up before a manufacturing run. Typically, each pin is adjusted by hand and, as a result, the height of a given pin  15  may be adjusted incorrectly leaving gaps  18 . The resulting inconsistent support may cause bending of board  10  and lead to damage of both PCB  10  and placed components  12 , increasing manufacturing costs. When a pin is too high, the component placement machine may damage (e.g., crack) components  12  or PCB  10 . When a pin is too low, a component may be seated improperly in the solder paste or not be placed at all. Setting the pins is time consuming. 
       
    
    
     DESCRIPTION OF DRAWINGS  
       [0006]    [0006]FIG. 1 is a perspective view of a known way of supporting a PCB during component placement.  
         [0007]    [0007]FIG. 2 is a section view of the known way shown in FIG. 1.  
         [0008]    [0008]FIG. 3 is a perspective view of another way of supporting a PCB.  
         [0009]    [0009]FIG. 4A is a perspective view of a way of supporting a PCB with components placed on its primary side.  
         [0010]    [0010]FIG. 4B is an exploded, partial sectional view of FIG. 4.  
         [0011]    [0011]FIGS. 5A, 5B, and  5 C are bottom, left, and top views of a support plate.  
         [0012]    [0012]FIGS. 6A, 6B, and  6 C are top, right, and bottom views of a support plate.  
         [0013]    [0013]FIGS. 7A, 7B, and  7 C are top, front, and right views of a support tray.  
         [0014]    [0014]FIGS. 8A, 8B, and  8 C are top, front, and right views of another support tray. 
     
    
     DETAILED DESCRIPTION  
       [0015]    Another way to support a substrate  10  during placement of components  12  on primary side  13  is shown in FIG. 3. Substrate  10  lies flat on foam  20 , which provides consistent and uniform support for substrate  10 . Substrate  10  could be, but is not limited to, a fiberglass substrate, ceramic substrate, or mylar flex circuit substrate. In one example, foam  20  could be RP-80 electro-static dissipative polystyrene foam available from Packaging Resources, Inc. of Tualatin, Oreg. An electro-static dissipative foam dissipates potentially harmful electro-static charges that may build up during component placement. Foam  20  could be any shape or size necessary to support substrate  10  and position substrate  10  at a height for component placement. In one example, foam  20  could be a substantially rectangular block having dimensions of about 17.5 inches long, about 4 inches wide, and about 1.436 inches thick.  
         [0016]    In some examples, foam  20  could be mounted to x-y table  17  using support tray  50  and one or more lightweight support plates  30 ,  31 . In some examples, the pair of support plates are identical while, in other examples, the pair of support plates could have different designs to reduce the overall mass used to support substrate  10  and conform to x-y table  17 . Support plates  30  could be attached to x-y table  17  using screws (not shown), for example. In some examples, support tray  50  is removably attached to support plates  30 . In one example, support tray  50  is attached to plates  30  using flat head screws. In other examples, support tray  50  could be attached using touch fasteners (e.g., Velcro™) or magnets of opposing polarity mounted to tray  50  and plates  30 . Foam  20  could be removably press fit into tray  50  in some examples, while in other examples foam  20  may be permanently attached to tray  50 .  
         [0017]    In some examples, foam  20  may also support substrate  10  during placement of components  19  on secondary side  14  of substrate  10 , as shown in FIGS. 4A and 4B, by allowing components  12  located on primary side  13  (shown in FIG. 5) to compress foam  20  locally without bending substrate  10 . In one example, surface  21  of foam  20  has a grid of cuts  24  to reduce the lateral forces internal to foam  20  and allow it to compress locally. Cuts  24  are made by removing material from foam  20  using a rotary blade having a thickness of about 0.052 inches. In one example, cuts  24  are about 0.75 inches deep and are spaced about 0.5 inches. Portions of the grid on surface  21  of foam  20  may also be removed to accommodate taller components  12 .  
         [0018]    Experiments have shown that using foam to support substrates resulted in lower defect rates and shorter set-up times. Table 1 shows data for four manufacturing runs placing components on the primary sides of printed circuit boards: two runs of “Koa” printed circuit boards and two runs of “Lancewood” printed circuit boards. One run for each board was performed using pin supports (“without foam”). Another run for each board used foam (“with foam”). Table 1 lists the number of boards manufactured in each run (“No. of Boards”) and the rate of first-pass accepts (FPA) from the first post-soldering visual inspection (“PVSI #1 FPA”). Table 1 also lists defects per million calculations for a first pass of component placement on the top side of the boards (“SMT1 Placement DPM”). Defects per million are calculated by dividing the total number of defects by the total number of opportunities and multiplying them by 1,000,000. Total opportunities is the number of boards in the manufacturing run multiplied by the number of components to be placed on each board. The Koa board has 1,760 placed components while the Lancewood board has 1063 placed components.  
                                                         TABLE 1                                   Koa       Lancewood               without   Koa with   without   Lancewood           foam   foam   foam   with foam                                    No. of Boards   3445   1400   53194   1457       PSVI #1 FPA   87.5%   91.4%   95.8%   95.1%       SMT1 Placement   228   99   88   48       DPM       Set-up time   40 min.   5 min.   6 min.   1.5 min.                  
 
         [0019]    Table 2 shows data for two manufacturing runs placing components on the secondary sides of Koa PCBs.  
                                             TABLE 2                                   Koa without foam   Koa with foam                                        No. of Boards   6436   789           PSVI FPA   95.6%   99.1%           SMT2 Placement   288   408/245           DPM           Set-up time   6 min.   1.5 min.                      
 
         [0020]    The defects per million for placement of components on the secondary side was higher for the foam supported boards (408 DPM) than for the pin supported boards (288 DPM). An inspection of failed boards for this manufacturing run revealed that 33 missing components were due to insufficient glue, a defect unrelated to board support. Not including the glue related defects, the defects per million for the foam supported boards was 245.  
         [0021]    Referring to FIGS.  5 A- 6 C, one example of a pair of support plates  30 L and  30 R are shown. Support plates  30  could be manufactured from 6061 T6 aluminum alloy or any other lightweight rigid material capable of holding a surface flat within a range of about 0.010 inches.  
         [0022]    Support plate  30 L is about 12.75 inches long about 7.55 inches wide and about 0.375 inches thick. Plate  30 L has a flat top surface  32 L for supporting tray  50  and a flat bottom surface  34 L that contacts x-y table  17 . Plate  30 L has openings  36 L to accommodate bolts that hold the plate to the x-y table  17 . For example, holes  36 L in plate  30 L have diameters of about 0.24 inches and are counterbored about 0.22 inches deep from top surface  32  at a diameter of about 0.375 inches.  
         [0023]    Plate  30 L could also have features for securing tray  50  to plate  30 L. In one example, plate  30 L has a series of nineteen threaded holes  38 L through plate  30 L, each hole having a diameter of about 4 millimeters. Holes  38 L are labeled to correspond with openings on plate  30 R. Numbers  39 L are engraved on top surface  32 L for each hole  38 L. Holes  38 L and labels  39 L between “5” and “9” are omitted due to the thickness of plate  30 L at that location, which is reduced to accommodate belts in x-y table  17 . The labeling of holes  38 L plate  30 L corresponds with similarly positioned holes  38 R in plate  30 R.  
         [0024]    Plate  30 L includes an area  40 L of reduced thickness to accommodate x-y table  16  and to reduce the weight of plate  30 L, resulting in less wear on table  16  over time. Area  40 L has thicker areas, such as rib  42 L for example, where plate  30 L requires higher strength or stiffness. In one example, plate  30 L is about 0.1 inches thick in area  40 L.  
         [0025]    Support plate  30 R is about 12.75 inches long, about 8.13 inches wide, and about 0.375 inches thick. Support plate  30 R has many of the same features as plate  30 L described above and corresponding features are labeled with the same number followed by an “R”.  
         [0026]    Referring to FIGS.  7 A- 7 C, support tray  50  is an open box including four walls  51  and a flat base  52  and has a length of about 17.75 inches long, a width of about 4.25 inches, and a wall thickness of about 0.125 inches. Tray  50  is built from 5052 T6 aluminum alloy but could be constructed from any rigid, lightweight material capable of holding a flatness of about 0.10 inches. Walls  51  are about 1.375 inches high although they may be lower to accommodate taller components on the primary side of a substrate. Material is removed from portions  53  of walls  51  to reduce the mass of tray  50 , as shown in FIGS. 7B and C. In one example, walls  51  are about 0.375 inches high at portions  53 .  
         [0027]    Tray  50  has one or more countersunk openings  54  permitting tray  50  to be attached to plates  30 L and  30 R using at least two four-millimeter flat-head screws (not shown). In one example, tray  50  has seven openings  54 L, through which screws could attach tray  50  to support plate  30 L and seven openings  54 R, through which screws could attach tray  50  to support plate  30 R. Pairs of openings  54 L and  54 R are labeled so that an operator may attach tray  50  to support plates  30 L and  30 R in a consistent position. Tray  50  also include several openings  55  through base  51  to further reduce the mass of tray  50 . When tray  50  is attached to support plates  30 L and  30 R, labels  39 L and  39 R are visible through openings  55  adjacent to holes  54 L and  54 R.  
         [0028]    In some examples, only one tray  50  is mounted to support plates  30 , while in another example, more than one tray  50  could be mounted to support plates  30 L and  30 R for supporting larger boards  10 .  
         [0029]    Referring to FIGS.  8 A- 8 C, tray  60  could be a different size than tray  50  and include many of the same features of tray  50 . In one example, tray  60  is an open box made 5022 T6 aluminum alloy and has dimensions of about 17.75 inches long, about 2.25 inches wide, about 1.375 inches high, and a wall thickness of about 0.125 inches. Similar to tray  50 , tray  60  could be lower in height to accommodate taller components on primary side  13  of substrate  10 . Foam (not shown) for tray  60  is about 17.5 inches long, about 2 inches wide and about 1.436 inches thick.  
         [0030]    Other embodiments are within the scope of the following claims.