Abstract:
An apparatus and method for performing operations on an electronic substrate includes a frame, a transportation system that moves the substrate through the apparatus, a substrate support system coupled to the frame that supports the substrate during a manufacturing operation on the substrate, wherein the substrate support system includes a deformable material, and a device coupled to the frame that performs an operation on a surface of the substrate. Manufacturing operations are performed on the substrate while the substrate is substantially evenly supported by the deformable material.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to apparatus and methods for processing substrates such as circuit board assemblies, and more specifically to apparatus and methods for supporting a circuit board during the printing of solder paste on the circuit board, dispensing of material on the circuit board, placing of components on the circuit board, or some other operation.  
         BACKGROUND OF THE INVENTION  
         [0002]    The manufacturing of circuit boards involves many processes, one of which is surface mounting electrical components to the circuit boards. To surface mount components to a first surface of a circuit board, a dispenser deposits solder paste or adhesive onto the first surface of the circuit board, and then components are pressed against the solder paste or adhesive. After the first side of the circuit board has been populated with components, the board is inverted and the process is repeated to surface mount components to the second side of the board. The solder paste dispenser is typically a stenciling machine, and typically a turret-type device presses the components into the solder paste or adhesive.  
           [0003]    When a circuit board is subjected to these manufacturing processes, it is often desirable to uniformly support the board across the lower surface so that the upper surface remains in substantially the same plane while a force is applied to the topside of the circuit board. Known means of supporting a circuit board during manufacturing operations are described in Beale, U.S. Pat. No. 5,157,438; Rossmeisl, U.S. Pat. No. 5,794,329; Barozzi, U.S. Pat. No. 4,936,560; Dougherty, U.S. Pat. No. 5,152,707; and Hertz, U.S. Pat. No. 6,264,187.  
         SUMMARY OF THE INVENTION  
         [0004]    In general, in one aspect, the invention provides an apparatus for performing operations on a surface of an electronic substrate. The apparatus includes a frame, a transportation system that moves the substrate through the apparatus, a substrate support system that supports the substrate during an operation on the substrate and that includes a deformable material, and a device coupled to the frame that performs an operation on the surface of the substrate.  
           [0005]    Implementations of the invention may include one or more of the following features. The support system of the apparatus can be moveable from a lowered position to a raised position such that in the raised position, the deformable material contacts a side of the electronic substrate.  
           [0006]    Further implementations of the invention may include one or more of the following features. The deformable material can be a low durometer gel. Alternatively, the deformable material can be a rheomagnetic fluid. The support member may include an electromagnetic cavity and the rheomagnetic fluid may be at least partially disposed in the electromagnetic cavity. Thin-walled tubes can be used to contain the rheomagnetic fluid. The support member can include a plurality of electromagnetic cavities, and a tube of rheomagnetic fluid can be disposed in each of the plurality of electromagnetic cavities. The electromagnetic cavities can be energized to solidify the rheomagnetic fluid.  
           [0007]    In general, in another aspect, the invention provides a method of performing an operation on an electronic substrate. The method includes loading the substrate into a processing machine, supporting the substrate with a deformable material that conforms to a surface of the substrate, performing a manufacturing operation on the substrate, and removing the substrate from the processing machine. The electronic substrate can be a circuit board. The deformable material can be returned to a home position after the substrate is removed from the processing machine.  
           [0008]    Generally, in another aspect, the invention provides an apparatus for supporting an electronic substrate during a manufacturing operation. The apparatus includes a frame and means coupled to the frame for supporting electronic substrates, including a deformable material which conforms to a surface of the substrate to be supported during manufacturing.  
           [0009]    Implementations of the invention may include one or more of the following features. The supporting means may include a low durometer gel as the deformable material to support the substrate. Alternatively, the supporting means may include a rheomagnetic fluid as the deformable material. The supporting means can include further means for solidifying the rheomagnetic fluid.  
           [0010]    The invention will be more fully understood after a review of the following figures, detailed description and claims. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0011]    For a better understanding of the present invention, reference is made to the drawings which are incorporated herein by reference and in which:  
         [0012]    [0012]FIG. 1 is a top view of a printing apparatus in accordance with one embodiment of the invention;  
         [0013]    [0013]FIG. 2A is a schematic diagram of support gel in a preparation stage in one embodiment of the invention;  
         [0014]    [0014]FIG. 2B is a schematic diagram of support gel in a conformed stage in one embodiment of the invention;  
         [0015]    [0015]FIG. 2C is a schematic diagram of support gel in a post-loaded stage in one embodiment of the invention;  
         [0016]    [0016]FIG. 3A is a schematic diagram of rheomagnetic fluid in a pre-energized phase in one embodiment of the invention;  
         [0017]    [0017]FIG. 3B is a schematic diagram of rheomagnetic fluid in a loaded phase in one embodiment of the invention; and  
         [0018]    [0018]FIG. 3C is a schematic diagram of rheomagnetic fluid in an energized phase in one embodiment of the invention.  
         [0019]    [0019]FIG. 4 is a schematic diagram of a top view of the rheomagnetic fluid support system in one embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0020]    Embodiments of the present invention are described below with reference to screen printers or stencil printers that print solder paste onto circuit boards. As understood by those skilled in the art, embodiments of the present invention can be used with electronic substrates other than circuit boards, such as electronic components, and with machines other than screen printers such as pick and place machines or dispensing machines.  
         [0021]    Referring to FIG. 1, internal components of a printer  5  in accordance with one embodiment of the invention that applies solder paste to circuit boards are shown. The printer is an improvement over screen printers described in U.S. Pat. No. 5,794,329, which is hereby incorporated by reference.  
         [0022]    As shown in FIG. 1, the printer  5  includes a tractor feed mechanism  12 , edge tractor mechanisms  14 , a rigid support table  16 , a board support mechanism  20 , a moveable gantry  24 , a controller  23 , a squeegee/adhesive applicator  28 , and a camera  30  carried on a carriage  32 . The support mechanism  20  is located on and attached to the support table  16 . The camera  30  carried on the carriage  32  is moveable along the gantry  24  in a linear X-axis of motion. The gantry  24  is moveable along tracks  26  in a linear Y-axis of motion. The squeegee/adhesive applicator  28  is attached to the printer  5  in a position above the level of the circuit board  10 .  
         [0023]    Boards  10  fed into the printer  5  usually have a pattern of pads or other, usually conductive surface areas onto which solder paste will be deposited. When directed by the controller of the printer, the tractor feed mechanism  12  supplies boards  10  to a location where the camera  30  records an image of the circuit board  10 . The image is sent to the controller, which signals for the edge tractor mechanisms  14  to shuttle the board  10  to a second location over the rigid support table  16 , beneath a solder stencil. Once arriving at a position over the support table  16 , the circuit board  10  is in place for a manufacturing operation. To successfully perform operations on the board  10 , the board  10  is supported by the support mechanism  20 . The support mechanism  20  is raised from beneath the circuit board  10  at the direction of the controller. When the solder stencil and the circuit board  10  are aligned correctly, the stencil is lowered toward the board  10  for application of the solder paste or the board can be raised toward the stencil by the support mechanism. The squeegee/adhesive applicator  28 , positioned above the circuit board  10 , is shown in phantom in FIG. 1. The adhesive applicator  28  can vary the amount of solder paste or adhesive delivered on the stencil and applied by the squeegee. The squeegee  28  wipes across the stencil, thereby pushing solder paste through the stencil onto the board  10 . After solder paste has been deposited on the circuit board  10 , the support mechanism  20  moves downward away from the position of the board, under control of the controller. The controller then controls movement of the board  10  to the next location using the tractor mechanism  18 , where electrical components  11  will be placed on the board.  
         [0024]    As discussed, the circuit board  10  enters on the tractor feed mechanism  12  and stops when in a position over the table  16  where deposition of solder paste will occur. Throughout the process of printing the solder paste on the circuit board  10 , a force is applied to a top surface of the board  10  by the squeegee. In order for the solder paste to be applied evenly, the circuit board  10  is supported using the support mechanism  20  to oppose the force being applied to the topside of the board  10 . In embodiments of the invention, the support mechanism  20 , which is attached to the printer above the surface of the table  16 , includes a deformable material  42  in a support bed  40 . The entire support mechanism  20  is attached to the printer frame in such a way that it can be raised to the surface of the circuit board  10 , allowing the deformable material  42  to conform to the underside topography of the board  10  during printing. In this way, the deformable material  42  evenly supports the underside of the circuit board  10  due to its ability to conform to the topography of the circuit board  10 .  
         [0025]    Referring to FIGS.  2 A- 2 C, the support mechanism  20  is shown in greater detail. The support mechanism  20  includes a base  44 , a housing  40  and a deformable material  42 . The deformable material  42  is a low durometer gel contained in the housing  40 , which functions as a support bed for containing the deformable material. In one embodiment, the low durometer gel  42  is a polyurethane gel, manufactured and distributed by Northstar Polymer, LLC, located in Minneapolis, Minn. under part no. MPP-V37A. In FIG. 2A, the support mechanism is shown moving in the direction of arrow  41  toward a circuit board  10  to support the board  10  in the printer  5 . The underside of the circuit board is populated with electrical components  11 .  
         [0026]    [0026]FIG. 2B shows the support mechanism  20  in contact with the board  10  after a print operation has occurred. In FIG. 2B, a stencil  45  is still in contact with the board  10 . Under compression caused by the contact of the gel  42  with the board  10 , the gel  42  conforms to the underside topography of the circuit board  10 , as shown in FIG. 2B, to provide evenly distributed support to the circuit board  10 . The gel  42  is of a consistency such that it remains contained within the housing  40  even while under compression. Controlled by the controller, the gel  42  and support bed  40  are retracted from the surface of the board  10  in the direction of arrow  43  at the completion of processing the circuit board  10 , and the entire support mechanism  20  returns to a home position, shown in FIG. 2C, where it will remain until the next board  10  is aligned for processing. As shown in FIG. 2C, the low durometer gel  42  returns to a relaxed state when the support mechanism  20  is in the home position. The low durometer gel  42  is then ready to conform to a board topography during a next print cycle.  
         [0027]    Alternatively, in another embodiment of the invention, which will now be described with reference to FIGS.  3 A- 3 C and FIG. 4, a support mechanism  120  may be used to support a circuit board during printing in place of support mechanism  20 , previously described. The support mechanism  120  includes a base  44 , electromagnetic cavities  64 , magnetic windings  65  and a deformable material  142 . The deformable material  142  is a rheomagnetic fluid contained in thin-walled tubes  62 , which may be made of latex, that are partially disposed in the electromagnetic cavities  64 . In one embodiment, the rheomagnetic fluid is a mixture of small magnetic particles such as iron, and a viscous fluid such as oil or water, manufactured and available from Lord Corporation of Cary, N.C. under part nos. including MRF-132AD, MRF-132LD, MRF-241GS, MRF-240B5 and MRF-336AG. In one embodiment, the electromagnetic cavities are made of a magnetic material, such as iron. Common magnetic windings  65  line the base of the electromagnetic cavities  64 . The electromagnetic cavities  64  are attached via connecting wires  66  to a source that provides electric current under control of the controller. As shown in FIG. 4, the electromagnetic cavities  64  can be aligned across the length of the base  44  of the support mechanism  120 .  
         [0028]    The support mechanism  120  operates as follows. A circuit board  10 , having an underside populated with electrical components  11 , is positioned over table  16  for the deposition of solder paste. The support mechanism  120  is moved under the control of the controller in the direction of arrow  141  until the rheomagnetic material contacts the underside of circuit board  10 . While the support mechanism  120  approaches the underside of circuit board  10 , the rheomagnetic fluid  142  is in a free, or relaxed state. In the relaxed state, the rheomagnetic fluid  142  easily conforms to the topography of the board  10  upon contact with the board  10 . While the rheomagnetic fluid  142  is in contact with the board  10 , the electromagnetic cavities  64  are energized with an electric current via connecting wires  66 , which are also connected to a DC power source. The magnetic field is proportional to the direction and intensity of the electric current in the magnetic winding  65 . Enough current must be provided to generate a magnetic field strong enough to align the particles in the rheomagnetic fluid  142 . Energy from the electromagnetic cavities  64  transforms the tubes  62  of rheomagnetic fluid  142  from a fluid state to a rigid state. While in the rigid state, the rheomagnetic fluid  142  provides sufficient board support during manufacturing operations.  
         [0029]    The configuration of the rheomagnetic fluid  142  when energized is such that it rigidly supports the surface of the board  10 , whether the board  10  is populated with electrical components or not. The rheomagnetic fluid  142  will remain energized, or in a rigid state for as long as the electromagnetic cavities  64  remain energized with an electric current as shown in FIG. 3C. The rheomagnetic fluid remains energized in a shape conforming to a first circuit board  10  so that many circuit boards  10  having the same topography as the first circuit board  10  can be mass-produced without de-energizing and re-energizing the rheomagnetic fluid  142 . Upon completion of processing of a board  10 , the controller directs the support mechanism  120  to the lowered position in the direction of arrow  143 .  
         [0030]    If it is desired to process a second type of board, the electromagnetic cavities  64  are de-energized, thereby returning the rheomagnetic fluid  142  to a fluid state. The system resets for another print cycle when the support mechanism  120  is returned to a home position. The rheomagnetic fluid  142  is re-configured to support another set of circuit board assemblies with a different configuration of electrical components  11  by pressing the rheomagnetic fluid against the undersurface of a new circuit board  10  and energizing the electromagnetic cavities  64  with electric current once again.  
         [0031]    In the embodiments of the present invention described above, the low durometer gel when used as the deformable material fills the housing container completely. As understood by those skilled in the art, other configurations may include strips of low durometer gel contained in the support housing, or other appropriate and strategic configurations of the gel that amply support the underside of the circuit board.  
         [0032]    In embodiments of the present invention described above, the rheomagnetic fluid used as a deformable material is contained in an assembly of electromagnetic cavities, all of which comprise the support system. As understood by those skilled in the art, other configurations may include a single electromagnetic cavity containing rheomagnetic fluid such that the single container of rheomagnetic fluid is sufficiently energized to conform to the surface of the boards. The assembly of electromagnetic cavities may further be aligned across the width of the base of the support mechanism. In still further embodiments of the present invention, a connecting wire is attached to each of the electromagnetic cavities to provide electric current that energizes the electromagnetic cavities, which thereafter energizes the rheomagnetic fluid to make it rigid. As understood by those skilled in the art, other configurations may include a single set of connecting wires that provides electric current to all of the electromagnetic cavities in the assembly.  
         [0033]    In still further embodiments of the present invention, the support mechanism is attached to the printer frame so that it moves in an upward direction toward the underside of the circuit board during manufacturing, when directed by the controller. As understood by those skilled in the art, other configurations may include a support mechanism in a fixed position whereby the boards are lowered to the deformable material of the support mechanism during manufacturing.  
         [0034]    Having thus described at least one illustrative embodiment of the invention, various alterations, modifications and improvements will readily occur to those skilled in the art. Such alterations, modifications and improvements are intended to be within the scope and spirit of the invention. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The invention&#39;s limit is defined only in the following claims and the equivalents thereto.