Patent Publication Number: US-2012042795-A1

Title: Method and apparatus for printing on a substrate

Description:
RELATED APPLICATIONS 
     This non-provisional patent application claims priority benefit to earlier-filed U.S. provisional patent application titled “Method and Apparatus for Enhancing the Attributes of a Printed Composition” Ser. No. 61/376,090, filed Aug. 23, 2010, hereby incorporated in its entirety by reference into the present application. 
    
    
     BACKGROUND 
     1. Field 
     The present invention relates generally to screen printing or stencil foil plate printing application of pastes, inks, or other print compositions used for flexible circuitry, photovoltaics, biosensors, or graphical/visual applications. 
     2. Related Art 
     Screen printing is the process by which a suitable paste, ink, or printable material is transferred to a substrate through a mesh containing a stencil design in order to create a picture or pattern. 
     Screen printing or stencil printing generally provides a greater volume of paste coating thickness, which can be varied intentionally in its range of thickness better than other traditional plate-based paste or ink transference methods. Screen printed paste deposit thickness is determined largely by the selection of the fabric mesh and often the stencil thickness of the pattern. 
     One method of screen printing or stencil printing employs a nominal separation distance of the bottom side of a screen stencil to the top side of a substrate. In its static condition, this distance is known in the art as “off-contact” or “snap.” A mesh stencil in an off-contact condition is deformed intentionally by a squeegee that is thrust into the mesh, deflecting it toward the substrate. The squeegee tool applies simultaneous downward pressure and wiping action to the screen stencil, so that intimate contact is made between the squeegee, the screen stencil, and the substrate, which is typically supported by a table or platen. The wiping action of the squeegee delivers a paste to the stencil apertures or openings, and the screen or stencil plate separates back to its original offset from the paste and substrate during or after the print squeegee stroke. 
     Another method of printing uses a foil-based stencil plate with apertures formed therethrough in a desired pattern or design, allowing the passage of a paste to a substrate during the downward pressure and wiping action of a squeegee. In this method, the stencil plate is rigid and completely in contact with the area of the substrate to which the paste is applied. After the squeegee is wiped across the stencil design, the squeegee and stencil plate are separated from the substrate. 
     Both of the aforementioned stencil printing methods are performed with a planar platen as a support for the substrate and in the trade are generally known as flatbed printing. Another method supports the substrate on a rigid cylinder so that a squeegee, stencil, and the substrate contact the tangential point of the rigid cylinder. In this method, the squeegee typically remains stationary during printing, and the printing frame holding the screen stencil or stencil plate reciprocates to create the wiping action and coating action of the squeegee and floodcoater. The rigid cylinder holds the substrate with vacuum and, depending on its design, either reciprocates back-and-forth or stops intermittently in its forward motion, in conjunction with the movement of the substrate. This arrangement is generally known in the trade as cylinder press screen printing. 
     In another screen printing method, the screen mesh and stencil pattern or a stencil plate can be in the form of a cylinder with an internal squeegee. The internal squeegee contacts an internal surface of the cylindrical stencil and the cylindrical stencil rotates in conjunction with a substrate being fed between and at a tangential point of the cylindrical stencil and a rigid support cylinder. In this method, the squeegee typically remains stationary and has no transitional movement; the wiping action is caused by the cylindrical stencil&#39;s forward rotation. This arrangement is generally known in the trade as rotary screen printing. 
     In all of the above methods, a substrate, on which paste will be transferred or printed, may be introduced to the printing process either as a sheet, or as a continuous web of material. In some screen printing methods, the substrate is a discrete three-dimensional object versus a sheet that is placed against a platen. For example, a cylindrical substrate such as a bottle may serve a dual purpose as both substrate and its cylindrical support surface. 
     Print compositions, paste, or ink used in screen printing are made up from a number of ingredients, such as a functional load, pigment, dye, mordant, binder, catalyst or other modifiers. Each paste mixture exhibits different flow characteristics or viscosity depending on the nature of the initial mixture of assembled compounds or elements. Additionally, a print composition may be thixotropic in nature. That is, paste may change in its viscosity due to shearing or deforming that occurs in the process of printing. 
     Paste formulated for a screen printing or stencil plate printing process is intended to permit good flow characteristics for printability. However, the intention also is for the paste to exhibit static characteristics of maintaining a modulus of rigidity after the application of the paste has been completed. 
     In general, a paste designed for satisfying both the printability and the finished printed body rigidity requirements often has difficulty achieving both conditions well. A paste designed for fluidity to provide good printability tends to continue to flow out or sustain its confluence, contrary to body rigidity needs. This means that these pastes, once printed, have difficulty keeping a crisp line definition, and are subject to slumping, thereby reducing the height of the trace while widening its base. This condition adversely affects many production scenarios. 
     Conversely, a paste designed primarily for keeping a well-defined aspect ratio—the height of a printed line or trace in respect to its width—often does not fill stencil cavities well due to its resistance to shearing, and subsequently does not transfer consistently to a substrate. 
     Accordingly, there is a need for improved methods of screen or stencil printing that overcome the deficiencies of the prior art. 
     SUMMARY 
     Embodiments of the present invention provide a screen printing apparatus for applying paste to a substrate and agitating the paste during application thereof. The screen printing apparatus may comprise a stencil having apertures formed therethrough, a squeegee, and at least one pulse source. The squeegee may have an end portion configured to contact the stencil in order to transfer the paste through the apertures of the stencil via actuation of the stencil relative to the squeegee or actuation of the squeegee relative to the stencil while maintaining contact between the squeegee and the stencil. The pulse source or sources may be configured to pulsate or vibrate the paste on the stencil at a predetermined frequency and amplitude. 
     In accordance with another embodiment of the invention, a screen printing apparatus for applying paste to a substrate may include a frame, a stencil supported by the frame, a squeegee, a support surface positioned under the stencil to support the substrate between the stencil and the support surface, and at least one pulse source configured for agitating the paste applied onto the stencil. The stencil may have one or more apertures formed therethrough and the squeegee may be actuatable toward and away from the stencil and across at least a portion of the stencil. Specifically, the squeegee may be configured to press into the stencil and wipe across the stencil, transferring at least a portion of the paste through the apertures of the stencil. The pulse source or sources may be fixedly or actuatably attached to the frame, stencil, squeegee, and/or support surface and configured to agitate the paste applied onto the stencil. The pulse source may agitate the paste by pulsating or vibrating the component to which it is attached or by being directly inserted into the paste resting on the stencil. 
     In accordance with yet another embodiment of the invention, a method for screen printing may comprise the steps of inserting a substrate between a support surface and a first surface of a stencil, applying paste to a second surface of the stencil, and agitating the paste on the second surface of the stencil via vibration or pulsating of a pulse source. The method may also comprise the steps of placing a squeegee in contact with the paste and the second surface of the stencil and wiping the squeegee across at least a portion of the second surface of the stencil via actuation of the squeegee and/or the stencil relative to each other, thereby deflecting the stencil to the substrate to transfer the paste to the substrate. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Other aspects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Embodiments of the present invention are described in detail below with reference to the attached drawing figures, wherein: 
         FIG. 1  is a perspective view of a printing apparatus constructed in accordance with an embodiment of the present invention; 
         FIG. 2  is a perspective view of an alternative embodiment of the printing apparatus of  FIG. 1  having one or two squeegees; 
         FIG. 3  is a cross-sectional view of the printing apparatus of  FIG. 1  illustrating an off-set distance between a stencil and a support surface of the printing apparatus and further illustrating paste being spread by a flood coater across a stencil of the printing apparatus; 
         FIG. 4  is a cross-sectional view of the printing apparatus of  FIG. 3 , illustrating a squeegee of the printing apparatus actuated to deflect the stencil to a substrate; 
         FIG. 5  is a cross-sectional view of the printing apparatus of  FIG. 2  with no off-set distance between a stencil plate and the support surface, illustrating the squeegee of the printing apparatus wiping the paste into apertures of the stencil plate onto the substrate; 
         FIG. 6  is a cross-sectional view of the printing apparatus of  FIG. 5  after paste is applied to the substrate, illustrating the frame and stencil being separated from the substrate; 
         FIG. 7  is a cross-sectional view of an alternative embodiment of the printing apparatus constructed according to an embodiment of the present invention with a rotary support surface; and 
         FIG. 8  is a cross-sectional view of another alternative embodiment of the printing apparatus constructed according to an embodiment of the present invention with a rotary stencil, a rotary support surface, and a substantially stationary squeegee. 
     
    
    
     The drawing figures do not limit the present invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. 
     DETAILED DESCRIPTION 
     The following detailed description of the invention references the accompanying drawings that illustrate specific embodiments in which the invention can be practiced. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized and changes can be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled. 
     In this description, references to “one embodiment”, “an embodiment”, or “embodiments” mean that the feature or features being referred to are included in at least one embodiment of the technology. Separate references to “one embodiment”, “an embodiment”, or “embodiments” in this description do not necessarily refer to the same embodiment and are also not mutually exclusive unless so stated and/or except as will be readily apparent to those skilled in the art from the description. For example, a feature, structure, act, etc. described in one embodiment may also be included in other embodiments, but is not necessarily included. Thus, the present technology can include a variety of combinations and/or integrations of the embodiments described herein. 
     As illustrated, embodiments of the present invention include a screen printing apparatus  10  for applying paste  12  to a substrate  14 . The printing apparatus  10  is configured to control or optimize the flow of the paste  12  during printing. The paste  12  may include various pastes, inks, viscoelastic material, viscous fluids, elastic solids, or other print compositions used for flexible circuitry, photovoltaics, biosensors, graphical/visual applications, or any other printing applications. Other ingredients of the paste  12  may include functional load, pigment, dye, mordant, binder, catalyst or other modifiers. The substrate  14  may be plastic, metal, paper, cloth, or any printable two-dimensional or three-dimensional surface known in the art. 
     In general, the printing apparatus  10  may comprise a support structure, a frame  16  connected to or part of the support structure, a stencil  18  supported by the frame  16 , a squeegee  20  configured to deliver the paste  12 , a support surface  22  to support the substrate  14 , and one or more pulse sources  24  configured to agitate the paste  12  during printing. In some embodiments of the invention, as illustrated in  FIGS. 1 ,  3 ,  4 , and  7 , the printing apparatus  10  may also comprise a flood coater  26  configured to evenly apply the paste  12  across the stencil  18 . Furthermore, the printing apparatus  10  may comprise and/or be communicably coupled with a control system and/or various actuation devices configured to actuate one or more movable components of the printing apparatus  10 . 
     The support structure may fixedly or actuatably connect various components of the printing apparatus  10  with each other and may include the frame  12 , the support surface  22 , and/or a support carriage (not shown). Furthermore, various elements of the support structure may be fixedly or removably attached with each other, such as the frame  16  which may be slidably inserted into a frame holder  28 , as illustrated in  FIG. 1  and later described herein. Components of the support structure may also be actuatably attached with each other, such as the frame  16  being actuatable toward and away from the support surface  22  and/or actuatable back and forth in co-planar relationship with the support surface  22  in some embodiments of the invention. 
     The support carriage may be configured to suspend various components of the printing apparatus  10  above the stencil  18  and/or the support surface  22 , such as the squeegee  20 , flood coater  26 , and/or at least some of the pulse sources  24 . The support carriage may comprise various actuation devices, as described below, such as tracks, motors, and the like by which the squeegee  20  and the flood coater  26  may be actuated toward and away from the stencil  18  and/or back and forth across a width or length of the stencil  18 . Furthermore, in some embodiments of the invention, at least some of the pulse sources  24  may be actuatably coupled to the support carriage or some other part of the support structure. For example, the pulse sources  24  may be independently actuated or actuated in cooperation with the squeegee  20  and/or the flood coater  26 , as later described herein. 
     The frame  16 , as illustrated in  FIGS. 1-7  may be any support structure to which the stencil  18  is secured. For example, the frame  16  may extend around and attach to a periphery edge of the stencil  18 . The frame  16  may be supported an offset distance above the support surface  22 , as in  FIGS. 3 ,  4 , and  7 , or may be placed on or supported by the support surface  22 , as in  FIGS. 5 and 6 . In some alternative embodiments of the invention, as illustrated in  FIG. 8 , the frame  16  may be substantially cylindrical and rotatable, may be secured to or integrally formed with the stencil  18 , and may be manually or automatically rotatable, such as by way of the control system. In some embodiments of the invention, the frame  16  may be fastened from above and thereby suspended over the substrate  14 . 
     In some embodiments of the invention, as illustrated in  FIG. 1 , the frame  16  may further be supported by the frame holder  28  configured to receive the frame  16 . For example, different frames  16  supporting different stencils  18  may be exchanged within the frame holder  28  to produce different print patterns. The frame holder  28  illustrated in  FIG. 1  has a tray-like configuration such that the frame  16  may be slid therein. The frame holder  28 , frame  16 , and/or stencil  18  may be secured at or actuated to a particular offset or off-contact distance apart from the squeegee  20  and/or the flood coater  26  for printing. Alternatively, the printing apparatus  10  may be configured to actuate the squeegee  20  and/or the flood coater  26  to a particular offset distance apart from the frame holder  28 , frame  16 , and/or stencil  18 . In some embodiments of the invention, as illustrated in  FIG. 7 , the frame  16  and/or frame holder  28  may be actuatable back and forth from side to side or end to end in a substantially horizontal plane or in a plane substantially co-planar or tangential to the support surface  22 , either manually or automatically via the control system and/or actuation devices. 
     The stencil  18  or imaged stencil may be a sheet of material having apertures formed therethrough to allow passage of the paste  12  in select locations onto the substrate  14 . For example, the stencil  18  may be an impermeable or paste-blocking material with one or more apertures formed therein. The apertures may have any desired shape, size, design, or configuration to produce an intended design onto the substrate  14 . In some embodiments of the invention, the impermeable paste-blocking material may be supported on a meshed screen, configured to allow the paste  12  to pass therethrough. Alternatively, mesh threads or other intersticed matrix support materials may otherwise be attached to or integral with the impermeable sheet of material and transverse the apertures thereof. In some embodiments of the invention, the stencil  18  may comprise mesh threads or any intersticed matrix support material with portions thereof made impermeable in order to block the paste  12 , so that the paste  12  only passes through areas of the stencil  18  not made impermeable (i.e., the apertures), as illustrated in  FIG. 1 . For example, the stencil may comprise a mesh or intersticed matrix support in which a layer for blocking passage of the paste  12  is developed, grown, electroformed, or embedded to create a desired stencil pattern. In some embodiments of the invention, the stencil  18  may be made of metal, polymer foil, silk, steel, nylon, and/or polyester, as well as other woven materials and may be stretched over or otherwise held taut by the frame  16 . In some embodiments of the invention, the stencil  18  may be a foil or metal stencil plate, which is etched, laser cut, and/or electroformed to create the desired apertures therethrough, as illustrated in  FIGS. 2 ,  5 , and  6 . 
     The squeegee  20  may be any blade or rake configured to push or pull the paste  12  across the stencil  18 , pressing the stencil  18  against the substrate  14  and/or support surface  22 . For example, the squeegee  20  may be a rubber blade, a plastic blade, a metal blade, a ceramic blade, or any other blade configured for pushing or pulling paste or ink over a surface and/or deflecting the stencil  18  into intimate contact with the substrate  14 , as later described herein. Specifically, the squeegee  20  may be made of an elastomer material, a metal material, a ceramic material, polymeric resins, and/or plastics. In some embodiments of the invention, the squeegee  20  may be secured to a squeegee holder  30 , as illustrated in  FIGS. 1-8 . The squeegee  20  and/or squeegee holder  30  may be actuatable to move toward and away from the stencil  18  and/or to move across a width and/or a length of the stencil  18 . For example, the squeegee  20  may be configured to be actuated toward the stencil  18  until the stencil  18  is pressed against the substrate  14 , and then the squeegee  20  may be actuated across at least a portion of the stencil  18  while maintaining contact with the stencil  18 , as illustrated in  FIG. 4 . In some embodiments of the invention, such as embodiments where the stencil  18  is a stencil plate, as illustrated in  FIG. 2 , there may be two or more squeegees  20  which may move in opposite directions in either concurrent or alternating print cycles. Actuation of the squeegee  20  and/or the squeegee holder  30  may be manual and/or automatic. For example, the control system may be configured to control the actuation of the squeegee  20  toward and away from the stencil  18  and back and forth across the stencil  18 . The squeegee  20  and/or the squeegee holder  30  may be held in a skewed or oblique angle in relationship to its travel directions across the stencil  18 , and this angle may be adjustable manually or automatically. 
     In other alternative embodiments of the invention, as illustrated in  FIG. 7 , the squeegee  20  may be actuatable toward the stencil  18  until the stencil  18  is deflected to the substrate  14 . Substrate  14  may be fed between the stencil  18  and the support surface  22  while the squeegee  20  remains stationary. In yet another embodiment of the invention, as illustrated in  FIG. 8 , the squeegee  20  may be fixed throughout the printing process while the stencil  18  and/or the substrate  14  are actuated. 
     The support surface  22  may be a platen, table, or any other substantially planar support surface, as illustrated in  FIGS. 1-6 . Alternatively, the support surface  22  may be substantially cylindrical, as in  FIGS. 7 and 8 . The support surface  22  may have one or more holes (not shown) formed therethrough and configured to fix the substrate  14  in place on the support surface  22  via vacuum or suction. For example, vacuum may be applied on a first side of the support surface  22  while the substrate  14  is placed on a second side of the support surface  22 , thereby suctioning the substrate  14  to the support surface  22  via the holes formed through the support surface  22 . 
     The support surface  22  may be stationary or may be actuatable, thereby actuating the substrate  14  relative to the stencil  18  and/or the squeegee  20 . In some embodiments of the invention, as illustrated in  FIGS. 7 and 8 , the support surface  22  may be a cylinder support configured to be rotated manually and/or automatically and to help feed the substrate  14  through the printing apparatus  10 . For example, the control system may be configured to control a motor or another actuation device operable to rotate or otherwise actuate the support surface  22 . 
     The flood coater  26  may be any apparatus or component configured to spread the paste  12  across the stencil  18 . In some embodiments of the invention, the flood coater  26  may comprise and/or be supported by a flood coater holder  32 . The flood coater  26  and/or the flood coater holder  32  may be made of an elastomer material, a metal material, a ceramic material, polymeric resins, and/or plastics. The flood coater  26  and/or flood coater holder  32  may be actuatable toward and away from the stencil  18  and/or length-wise and/or width-wise across the stencil  18 . For example, the flood coater  26  may be configured to move toward and make contact with the paste  12  after it is applied onto the stencil  18 , and then may be actuated across at least a portion of the stencil  18  in such a manner as to spread the paste  12  in an even or substantially even layer across a majority of the stencil  18 . Actuation of the flood coater  26  and/or the flood coater holder  32  may be manual and/or automatic. For example, the control system may be configured to control the actuation of the flood coater  26  toward and away from the stencil  18  and back and forth across the stencil  18 . The flood coater  26  and/or the flood coater holder  32  may be held in a skewed or oblique angle in relationship to its travel directions across the stencil  18 , and this angle may be manually or automatically adjustable. 
     The pulse sources  24  may include one or more devices configured to agitate or excite the paste  12  to cause a controlled liquefaction and/or a mechanical response of dilatancy of the paste  12 , thereby enhancing desired flow characteristics and transfer of the paste  12  through the stencil  18  onto the substrate  14 . Specifically, the pulse sources  24  may vibrate or pulsate, thereby causing the vibration or pulsating movement of some of the printing apparatus components and/or the paste  12 . Whether vibration or pulsing causes shear thickening or shear thinning of the paste  12  may depend on the characteristics or formulation of the paste. The pulse sources  24  may be an ultrasonic transducer device, an electromagnetic device, a piezoelectric device, and/or an electromechanical device operable to pulsate or vibrate at one or more frequencies and at one or more amplitudes. The pulse sources  24  may include various mechanical components, electronic components, and/or circuitry configured to control the vibrational frequency and amplitude thereof. Furthermore, the pulse sources  24  may be integrally and/or communicably coupled with the control system, which may be configured to turn the pulse sources  24  on and off and/or vary the frequency and/or amplitude of the pulse sources  24 . The pulse sources  24  may be configured to vibrate at any frequency. However, in an example embodiment of the invention, at least some of the pulse sources  24  may vibrate at a frequency between approximately 15,000 Hz and 30,00 Hz, or more specifically between 20,000 Hz and 25,000 Hz. However, any frequency or amplitude may be used without departing from the scope of the invention. The amplitude and/or frequency of the pulse sources may be continuously variable or controlled substantially steplessly. 
     The pulse sources  24  may be attached to one or more of the support structure, frame  16 , frame holder  28 , squeegee  20 , squeegee holder  30 , flood coater  26 , and flood coater holder  32 , or any components attached to the printing apparatus  10 . Additionally or alternatively, one or more pulse sources  24  may be placed in direct contact with the stencil  18  and/or the paste  12 . For example, one of the pulse sources  24  may be inserted or immersed into the paste  12  during its deposit onto the stencil  18 , as illustrated in  FIGS. 3-6 . The pulse sources  24  may be cooperatively actuatable along with the squeegee  20  and/or the flood coater  26  such that their corresponding pulse sources  24  make contact with the paste  12  simultaneously while the squeegee  20  and/or the flood coater  26  makes contact with the paste  12 . Specifically, the pulse sources  24  may be fixed or actuatably attached to the support structure in a configuration that allows the pulse sources  24  to be actuated in cooperation with the squeegee  20  or flood coater  26 , but in such a manner that the pulse sources  24  do not directly contact the squeegee  20  or the flood coater  26 . For example, as illustrated in  FIGS. 4 ,  5 , and  7 , one of the pulse sources  24  may be fixed proximate to, but in a spaced apart relationship with, an end of the squeegee  20  configured to contact the paste  12 , such that the corresponding pulse source  24  contacts the paste  12  simultaneously when the end of the squeegee  20  contacts the paste  12  and/or the stencil  18 . Likewise, as illustrated in  FIG. 3 , one of the pulse sources  24  may be fixed proximate to, but in a spaced apart relationship with, an end of the flood coater  26  configured to contact the paste  12 , such that the corresponding pulse source  24  contacts the paste  12  simultaneously when the end of the flood coater  26  contacts the paste  12 . 
     In some embodiments of the invention, at least some of the pulse sources  24  may be positioned and configured to vibrate in multiple directions or along multiple axes relative to each other. For example, as illustrated in  FIGS. 1-2 , a first one of the pulse sources  24  may be mounted to a first side of the squeegee holder  30  and configured to vibrate back and forth along an x-axis, a second one of the pulse sources  24  may be mounted to an end of the squeegee holder  30  and configured to vibrate back and forth along a z-axis, and a third one of the pulse sources  24  may be mounted to a top of the squeegee holder  30  and configured to vibrate back and forth along a y-axis. In this example, embodiment, the x-axis, z-axis, and y-axis may each be substantially perpendicular relative to each other.  FIG. 1  illustrates a similar arrangement of pulse sources attached to the flood coater holder  32  and the frame holder  28 , such that these components may also be vibrated along three different axes simultaneously or at pre-determined intervals during the printing process. Each of the pulse sources  24  illustrated in  FIGS. 3-6 , configured to make direct contact with the paste  12 , may also be configured to simultaneously or sequentially vibrate along its corresponding axis direction during the printing process. This may be accomplished by a plurality of pulse sources  24  each configured to vibrate or pulsate along one particular axis. Alternatively, at least one pulse source  24  may be configured to sequentially vibrate along several different axes at different points during the printing process. 
     The control system may comprise any number or combination of controllers, circuits, integrated circuits, programmable logic devices such as programmable logic controllers (PLC) or motion programmable logic controllers (MPLC), computers, processors, microcontrollers, or other control devices and residential or external memory for storing data and other information accessed and/or generated by the printing apparatus  10 . The control system may be coupled with the actuation devices and/or the pulse sources  24 , to enable information to be exchanged between the various components of the printing apparatus  10  and to position and actuate components of the printing apparatus  10  for printing. The control system may be configured to implement any combination of the algorithms, subroutines, or code corresponding to method steps described herein. However, in alternative embodiments of the invention, at least some of the method steps described herein may be performed manually via physical actuation by a user of the printing apparatus  10 . 
     The control system and computer programs described herein are merely examples of computer equipment and programs that may be used to implement the present invention and may be replaced with or supplemented with other controllers and computer programs without departing from the scope of the present invention. The features of the control system may be implemented in a stand-alone device, which is then interfaced to the printing apparatus  10  or components thereof. The control features of the present invention may also be distributed among the components of the printing apparatus  10 . Thus, while certain features are described as residing in the control system, the invention is not so limited, and those features may be implemented elsewhere. 
     The control system may implement a computer program and/or code segments to perform some of the functions and method described herein. The computer program may comprise an ordered listing of executable instructions for implementing logical functions in the control system. The computer program can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, and execute the instructions. In the context of this application, a “computer-readable medium” can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer-readable medium can be, for example, but not limited to, an electronic, magnetic, optical, electro-magnetic, infrared, or semi-conductor system, apparatus, or device. More specific, although not inclusive, examples of the computer-readable medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a random access memory (RAM), a read-only memory (ROM), an erasable, programmable, read-only memory (EPROM or Flash memory), an optical fiber, and a portable compact disk read-only memory (CDROM). 
     The actuation devices may include pneumatic actuation devices, electronic actuation devices, and/or mechanical actuation devices, such as various motors, gears, pistons, tracks, ball bearings, and/or any combination of pneumatic or electro-mechanical components. The actuation devices may be configured for actuating physical movement of the frame  16 , frame holder  28 , stencil  18 , squeegee  20 , squeegee holder  30 , flood coater  26 , flood coater holder  32 , pulse sources  24 , support carriage, and/or the support surface  22 . For example, the squeegee  20  and/or squeegee holder  30  may be actuated and/or powered by a servo motor drive, an alternating current frequency-controlled motor drive, and/or a stepper motor drive. Furthermore, the support carriage may comprise one or more actuation devices configured for supporting and actuating the squeegee  20  and/or the flood coater  26 . 
     As illustrated herein, the components of the printing apparatus  10  described above may be configured in a variety of arrangements.  FIGS. 1-6  illustrate various embodiments of the printing apparatus  10  in a flatbed press configuration, with the stencil  18  being substantially planar and generally supported in a co-planar relationship with the support surface  22 .  FIG. 2  illustrates an embodiment of the invention using two squeegees  20 .  FIGS. 3 and 4  illustrate a flatbed press configuration with an offset distance provided between the substrate  14  and the stencil  18 . Specifically, as illustrated in  FIG. 3 , the frame  16  may support the stencil  18  at a given offset distance from the substrate  14  before application of the squeegee  20 . During printing, the stencil  18  illustrated in  FIG. 3  may be deflected downward by the squeegee  20 , traversing the offset distance to contact the substrate  14  on the support surface  22 .  FIG. 5  illustrates another flatbed press configuration with the frame  16  resting directly on the support surface  22  and/or holding the stencil  18  substantially directly against the substrate  14  in complete co-planar intimate contact during printing.  FIG. 6  illustrates the upward movement of the frame  16  of  FIG. 5  as it is being removed from the substrate  14  after printing. 
       FIG. 7  illustrates another embodiment of the printing apparatus  10  in a cylinder press configuration, with the support surface  22  being rotatable, the stencil  18  being substantially planar, the substrate  14  being fed between the support surface  22  and the stencil  18  during printing, and the frame  16  or frame holder  28  being movable along an axis substantially tangential to the support surface  22  during printing.  FIG. 8  illustrates yet another embodiment of the printing apparatus  10  in a rotary press configuration, with both the stencil  18  and the support surface  22  being rotatable and the substrate  14  being fed therebetween during printing, while the squeegee  20  remains stationary. 
     In use, the printing apparatus  10  provides the advantage of controlling and influencing the flow of the paste  12  during the wiping action of the squeegee  20 , during the coating action of the flood coater  26  on the stencil  18 , and/or during the separation of the stencil  18  from the paste  12  and the substrate  14 . Specifically, one or more of the pulse sources  24  may be actuated to pulse and/or vibrate during different steps of the printing processes and/or at different locations relative to the printing apparatus  10  and/or relative to the paste  12 . The vibration or pulsing may cause the paste  12  to flow more freely and fill openings of the stencil  18  more completely than prior art printing methods. Furthermore, the vibration or pulsing may allow the paste  12  to release more freely from the stencil  18  to achieve whole and proper transfer of the paste  12  to the substrate  14 . Once the paste  12  is on the substrate  14  and not in contact with any vibrating or pulsing elements, or once the pulse sources  24  are turned off, the paste  12  may return to its original state or desired default condition for further processing. 
     In some embodiments of the invention, as illustrated in FIGS.  1  and  3 - 4 , a printing method or a method of applying the paste  12  to the substrate  14  may comprise the steps of placing the substrate  14  between the support surface  22  and the stencil  18 , applying paste onto the stencil  18 , then actuating the flood coater  26  toward the stencil  18 . Once the flood coater  26  is a desired distance away from the stencil  18 , such that the flood coater  26  contacts the paste  12 , as illustrated in  FIG. 3 , the method may comprise the step of actuating the flood coater  26  across a width and/or length of the stencil  18 , evenly spreading the paste  12  across the stencil  18 . As the paste  12  is spread, it may fill or partially fill the apertures of the stencil  18 . Next, the printing method may comprise the steps of actuating the flood coater  26  away from the stencil  18  and actuating the squeegee toward the stencil  18  until it deflects the stencil  18  to the substrate  14  resting on the support surface  22 , as illustrated in  FIGS. 4 ,  5 , and  7 . 
     Then the printing method may comprise the step of actuating the squeegee  20  to be wiped across a width and/or length of the stencil  18 , placing the stencil  18  in intimate contact with the substrate and thereby delivering the paste  12  in the apertures of the stencil  18  to the substrate  14 . Alternatively, the method may include the step of actuating the frame  16  and/or stencil  18  to be actuated relative to the squeegee  20 , such that the paste  12  is passed through the apertures. Finally, the printing method may comprise the step of actuating the squeegee  20  and/or the stencil  18  to lift away from the substrate  14  and/or the support surface  22 , as illustrated in  FIG. 6 . 
     In the example embodiment of the invention illustrated in  FIG. 2 , the method may include the steps of actuating both the first and second squeegees  20  sequentially across the same or different portions of the stencil  18 . In the embodiments of the invention illustrated in  FIGS. 7 and 8 , the printing method may include the steps of feeding the substrate  14  via the rotating support surface  22  and/or any other feeding mechanisms known in the art, while the squeegee  20  remains substantially stationary, pressing into the stencil  18 . In some embodiments of the invention, as illustrated in  FIG. 8 , the frame  16  may support and/or be integrally formed with the stencil  18  and the printing method may comprise the steps of placing the paste  12  within the cylindrically-shaped stencil  18 , actuating the squeegee  20  to an inner surface of the stencil  18 , and rotating the stencil  18 /frame  16  and the support surface  22  by corresponding rotational speeds and directions to feed the substrate  14  therebetween or to allow the substrate to be fed therebetween. 
     The printing methods described above may also include a step of agitating the paste  12  with one or more of the pulse sources  24 . The pulse sources  24  may be activated at any point during the printing process. For example, in one step of the printing method, as illustrated in  FIG. 3 , a first one of the pulse sources  24  may directly contact the paste  12  while the flood coater  26  is actuated to spread the paste  12  across the stencil  18 . Additionally or alternatively, as illustrated in  FIGS. 4 ,  5 ,  7 , and  8 , a second one of the pulse sources  24  may directly contact the paste  12  while the squeegee  20  is actuated across the stencil  18  to apply the paste to the substrate  14 . Additionally or alternatively, as illustrated in  FIGS. 1 and 2 , one or more of the pulse sources  24  may contact and cause vibration of the frame  16 , the frame holder  28 , the squeegee  20 , the squeegee holder  30 , the flood coater  26 , and/or the flood coater holder  32  in order to agitate the paste  12  during any one of the printing method steps described above. 
     The method and printing apparatus  10  described herein is beneficial in providing wholeness and integrity to printed paste designs. This method and apparatus also allows for the printing of finer, higher resolution lines or features associated with a well-defined stencil, and may permit a better defined profile or aspect ratio of the deposited paste. Another benefit to the above-described screen printing process is to permit a manufacturer of paste greater latitude of formulation parameters. An intentional and temporary change of state of the paste  12  may be designed into the formulation in order to satisfy the several stages of the printing process. Embodiments of the invention in which the pulse sources  24  are inserted directly into the paste  12  may be beneficial in that only the paste  12  itself is vibrated or agitated, and not the stencil  18  or components (such as the squeegee  20 ) directly contacting the stencil  18 . Other benefits not described herein may also be realized through the use of the methods and the apparatus described herein. 
     Although the invention has been described with reference to the preferred embodiment illustrated in the attached drawing figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims.