Abstract:
Method and apparatus for lamination of substrates, e.g. rigid plastic layers, to manufacture laminated products. The methods include the sequential application of vacuum and mechanical force through a two-stroke process performed by a lamination apparatus having one or more force-producing stroke cylinders. Actuation of a cylinder to produce a first stroke creates a sealed chamber within the apparatus, enclosing a stack of substrates to be laminated. The sealed chamber may be evacuated of air by application of a vacuum. Subsequent actuation of a cylinder to produce a second stroke applies mechanical force to the sealed chamber, which compresses the substrates into a laminated product substantially free of air bubbles or voids.

Description:
FIELD 
       [0001]    Embodiments of the invention generally pertain to methods and apparatus for the lamination of rigid substrates, more particularly, to methods and apparatus for fabricating laminated microfluidic devices. 
       BACKGROUND 
       [0002]    The technology of manipulating minute volumes of biological and chemical fluids is widely referred to as microfluidics. The realized and potential applications of microfluidics include disease diagnosis, life science research, biological and/or chemical sensor development, and others appreciated by those skilled in the art. 
         [0003]    A microfluidic structure including a substrate having one or more microfluidic channels or pathways and a cover plate or a second or more substrates with fluid pathways that may or may not be interconnected, may commonly be referred to as a microfluidic chip or cartridge. Highly integrated microfluidic chips are sometimes called “labs on a chip”. 
         [0004]    Microfluidic structures or devices are commonly made from polymeric, “plastic” materials. Polymeric microfluidic structures have advantageous low material costs and the potential for mass production. However, the fabrication of polymeric microfluidic chips presents a variety of challenges. For example, microfluidic chips may contain sealed microstructures. These can be formed by enclosing a substrate having a pre-fabricated fluid pathway or other microfeatures with a thin cover plate, or with one or more additional substrates to form a three-dimensional fluid network. The pathways or other microstructures have typical dimensions in the range of micrometers to millimeters. This multilayer microfluidic structure is integrated, or joined together, by various conventional techniques. These techniques include thermal, ultrasonic and solvent bonding. Unfortunately, these techniques frequently alter the mated surfaces and yield distorted or completely blocked microfluidic pathways due, for example, to the low dimensional rigidity of polymeric materials under the aforementioned bonding conditions. 
         [0005]    The use of adhesive lamination may circumvent some of these potential difficulties by avoiding the use of excessive thermal energy or strong organic solvents. Conventional lamination systems employ opposing cylindrical rollers. The substrate materials for lamination are fed through a gap between the two moving rollers, which apply pressure to the leading edge of the stacked materials and bonds them together as they pass through the system. This process is an effective means to bond a flexible film to a substrate without entrapment of air bubbles, while providing minimum deformation to the laminated product. However, the curved surfaces of roller-based systems are not optimal for the lamination of rigid substrates. For example, such substrates may lack the flexibility required to feed through moving rollers in a manner that maintains the precise substrate registration critical for ensuring the integrity of the integrated microfluidic features. 
         [0006]    Alternative systems and methods for lamination of rigid substrates include planar press or “hinge” systems in which substrates are stacked, or “sandwiched”, between upper and lower platforms prior to application of a laminating force. One considerable drawback to this approach in the fabrication of microfluidic devices is the entrapment of air between the stacked substrates during lamination, resulting in deformations, such as bubbles or voids, in the final product. Such deformations may significantly compromise the function of the laminated microfluidic device, particularly when they arise in features such as fluidic channels or optical display windows. Accordingly, embodiments of the invention are directed to methods and apparatus for lamination of rigid structures that address these recognized shortcomings of the current state of technology, and which provide further benefits and advantages as those persons skilled in the art will appreciate. 
       BRIEF SUMMARY 
       [0007]    The present invention provides methods and apparatus for the lamination of substrates by the sequential application of vacuum and mechanical forces. Advantages of the methods and apparatus include the manufacture of rigid, laminated products that are substantially free of air pockets or voids. 
         [0008]    In one aspect, the method involves the steps of providing a stack of rigid substrate members on a base portion of a lamination apparatus, providing a first force to a cover portion of the lamination apparatus to sealedly contact the cover portion with a gasket on the base portion to create a sealed chamber between the base portion and the cover portion, applying a vacuum to the sealed chamber to evacuate air from the chamber, and providing a second force to the cover portion of the apparatus to compress the gasket and stack of substrates to produce a laminated product that is substantially free of air bubbles or voids. 
         [0009]    In one embodiment, the first force is provided by a long-stroke cylinder and the second force is provided by a short-stroke cylinder. In an alternative embodiment, the first force and the second force are provided by the same cylinder. In yet another embodiment, the method may further include the step of providing a resistance force to the first force, wherein the resistance force prevents compression of the gasket prior to the step of applying the vacuum to the sealed chamber. In certain embodiments, the resistance force is provided by a spring. 
         [0010]    In other embodiments, the rigid substrate members are substantially flat and may be polymeric materials. In yet another embodiment, the rigid substrate members are layers of a microfluidic device and may further include at least one flexible layer that may be an adhesive layer. 
         [0011]    In yet other embodiments, the method may also include the step of applying heat to the sealed chamber. 
         [0012]    Another embodiment of the invention is directed to an apparatus for laminating rigid substrate members that includes a base portion configured to support a stack of rigid substrates, wherein the base portion includes a compressible gasket and at least one alignment pin, a cover portion configured for sealedly contacting the compressible gasket to form a sealed chamber enclosing the stack of rigid substrate members, at least one stroke-producing cylinder configured to extend to the cover portion and apply a first force to bring the cover portion into contact with the alignment pin and gasket of the base portion to form the sealed chamber, and a vacuum port configured for attachment to a vacuum source. 
         [0013]    In certain embodiments, the apparatus further includes a second stroke-producing cylinder configured to extend to the sealed chamber and provide a second force to compress the gasket and stack of rigid substrates to produce a laminated product. In alternative embodiments, the apparatus includes at least one spring configured to provide a resistance force to the stroke-producing cylinder and the stroke-producing cylinder may further be configured to overcome the resistance force after formation of the sealed chamber and compress the gasket and stack of rigid substrates to produce a laminated product. 
         [0014]    In yet another embodiment, the apparatus may further include a heat source. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1A  is a cutaway view of one embodiment of the lamination apparatus of the present invention in a load position with cylinders refracted. 
           [0016]      FIG. 1B  is a close-up view of one embodiment of the lamination apparatus of the present invention with long-stroke cylinder extending towards alignment pin and gasket. 
           [0017]      FIG. 2A  is a cutaway view of one embodiment of the lamination apparatus of the present invention with long-stroke cylinder extended to gasket. 
           [0018]      FIG. 2B  is a close-up view one embodiment of the lamination apparatus of the present invention with the long-stroke cylinder extended to gasket, creating a sealed chamber. 
           [0019]      FIG. 2C  is a close-up view of one embodiment of the lamination apparatus of the present invention with short-stroke cylinder extending and compressing gasket. 
           [0020]      FIG. 3  is a close-up view of one embodiment of the lamination apparatus of the present invention with short-stroke cylinder extending and compressing stacked substrates into a laminated product. 
           [0021]      FIG. 4  is a close-up view of another embodiment of a lamination apparatus of the present invention in a load position with cylinders retracted and a spring in relaxed configuration. 
           [0022]      FIG. 5  is a close-up view of another embodiment of a lamination apparatus of the present invention with a cylinder extending to alignment pins and gasket with spring providing a resistance force. 
           [0023]      FIG. 6  is a close-up view of another embodiment of a lamination apparatus of the present invention with a spring resistance force overcome and compression of a stack of substrates into a laminated product. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIGS. 1A and 1B  show cutaway and close-up views, respectively, of one embodiment of a lamination apparatus  100  of the present invention in a load position. In this configuration, cylinder  110  and cylinder  120  are in a retracted position. In certain embodiments, cylinder  110  may be referred to as the “long-stroke cylinder” and cylinder  120  may be referred to as the “short-stroke cylinder”. In this embodiment, an upper surface of the apparatus is provided by cover portion  130 , which may be referred to as the “top vacuum chuck”, and a lower surface is provided by base portion  140 , which may be referred to as the “bottom vacuum chuck”. In this depiction, the apparatus is configured to receive a stack of substrates to be laminated. Top vacuum chuck may optionally be provided with a compliant silicone pressure pad  135 . Bottom vacuum chuck  140  may be provided with one or more alignment pins  145  to maintain precise register and alignment of surfaces and substrates during lamination. Gasket  150  provides for the formation of a sealed chamber between top vacuum chuck  130  and bottom vacuum chuck  140 . Gasket  150  may be fabricated from any material that maintains an airtight seal between top and bottom vacuum chucks while under compression. Illustrative gasket materials include any rubber or PVC material, e.g. silicone, butyl, neoprene, nitrile, vinyl, and the like. In operation, substrates for lamination  200  and  300  are placed on top and bottom vacuum chucks  130  and  140  while cylinders  110  and  120  are retracted. In other embodiments, the substrates may be stacked directly on each other and placed on either vacuum chuck. In other embodiments, lamination of two or more substrates is contemplated. In certain embodiments, lamination of at least three substrates is contemplated and may include a flexible substrate, such as a film, that may further comprise an adhesive material as described further herein. 
         [0025]      FIGS. 2A and 2B  show cutaway and close-up views, respectively, of one embodiment of a lamination apparatus  100  of the present invention with long-stroke cylinder  110  in an extended configuration. In operation, the first cylinder stroke, herein described as the “long-stroke” extends cylinder  110  to bring top vacuum chuck  130  into contact with gasket  150  of bottom vacuum chuck  140  to form a sealed chamber. Top substrate  200  and bottom substrate  300  are maintained in precise register by the one or more alignment pins  145  during formation of the sealed chamber. Short stroke cylinder  120  is not actuated during formation of the sealed chamber. The sealed chamber may be evacuated of air by application of a vacuum from a vacuum source. As used in connection with the present invention, the term “vacuum” describes negative pressure as compared to ambient pressure. The term does not require that an absolute or extremely negative pressure vacuum be drawn or maintained. Although in some instances, it may be possible and/or desirable to achieve large negative pressures in connection with the present invention. In operation, the vacuum will be sufficient to remove substantially all air from between substrates  200  and  300  in the sealed chamber. In this manner, all air is removed prior to lamination of substrates, preventing the problematic formation of air bubbles or voids in the final laminated product.  FIG. 2C  shows gasket  150  under compression, which may be accomplished by actuation of short-stroke cylinder  120  and/or by reducing air pressure in the sealed chamber. 
         [0026]      FIG. 3  depicts a close-up view of one embodiment of a lamination apparatus  100  of the present invention with short-stroke cylinder  120  in an extended configuration. In operation, the second stroke, herein referred to as the “short-stroke”, actuates short stroke cylinder  120 , which applies extended mechanical force to top vacuum chuck  130  and bottom vacuum chuck  140  to compress the substrates into laminated product  500 . The amount of mechanical force necessary to achieve substrate lamination will depend on the physical properties of the substrates, but will be readily apparent to one of ordinary skill in the art. Exemplary amounts of pressure or force applied to the apparatus to complete the laminating process are up to about 10 psi, more particularly between 0 to 2.5 psi. Illustrative compression times of the lamination process are from seconds to minutes. As described herein, the sequential actuation of the long-stroke and short-stroke cylinders enables initial formation of a sealed chamber that may be evacuated of air by vacuum followed by compression of the chamber by mechanical force to laminate substrates. The sequential application of vacuum and mechanical force as described herein prevents entrapment of air bubbles that create voids or defects in the laminated product. 
         [0027]      FIG. 4  depicts a close-up view of an alternative embodiment of a lamination apparatus  600  of the present invention in the load position. Cylinder  610  is retracted and resistance spring  615  is not under compression. Top vacuum chuck  630  and bottom vacuum chuck  640  are in an open configuration. Bottom vacuum chuck  640  is provided with one or more vacuum alignment pins  620  and gasket  645 . In this embodiment, all substrates to be laminated are provided as stack  650  on bottom vacuum chuck  640  when cylinder  610  is refracted. 
         [0028]      FIG. 5  depicts a close-up view of lamination apparatus  600  with cylinder  610  at extension. In this configuration, spring  615  is not compressed and provides a resistance force to cylinder  610 . In operation, the extension of cylinder  610  brings top vacuum chuck  630  into contact with gasket  645  on bottom vacuum chuck  640 , creating a sealed chamber. Top vacuum chuck and bottom vacuum chuck are aligned by the one or more alignment pins  645 , which maintains proper alignment and registration of the stacked substrates prior to lamination. Spring  615  provides a resistance force to cylinder  610  when contact is made between top and bottom vacuum chucks, which temporarily halts the downward movement of cylinder  610  to create the sealed chamber. The sealed chamber may then be evacuated of air by application of vacuum as described herein. 
         [0029]      FIG. 6  depicts a close-up view of lamination apparatus  600  with cylinder  610  at full extension. In operation, the resistance force provided by spring  615  has been overcome by cylinder  610 , which applies extended force to top vacuum chuck  630  and bottom vacuum chuck  640  to compress the sealed chamber and complete substrate lamination. The evacuation of air from the sealed chamber prior to full extension of cylinder  610  prevents entrapment of air bubbles in the laminated product  650 , a clear advancement in the art. 
         [0030]    The methods and apparatus described herein are suitable in the manufacture of any product comprised of at least one rigid substrate layer. One exemplary embodiment of the invention is directed to a method and apparatus for manufacturing a laminated, polymeric microfluidic structure. As used herein, the word “microfluidic structure” generally refers to structural features on a microfluidic substrate component with walls having at least one dimension in the range of about 0.1 micrometer to about 1000 micrometers. These features may be, but are not limited to, microchannels, microfluidic pathways, microreservoirs, microvalves or microfilters. 
         [0031]    Microfluidic structures, e.g. microfluidic cartridges or cards, are comprised of plastic bodies manufactured by a process of bonding together substrate layers. In an embodiment of the present invention, bonding together of layers is achieved by lamination. Each cartridge can be formed by a pair of substrate members or layers or of a plurality of layers bonded together. The term “layer” refers to any of one or more generally planar, solid substrate members comprising a cartridge. “Layers” or “substrates” are generally rigid structures but may also include glue layers or flexible sheets, films, pressure sensitive adhesives (PSA), or thermal adhesives. 
         [0032]    The term “polymeric” refers to a macromolecular structure or material having a molecular weight that is substantially higher than the constituent monomers and, which is produced by a polymerization reaction. All materials commonly and herein referred to as “plastic” materials are polymeric materials. Plastic is a preferred material for building microfluidic devices of the present invention. Plastics which may be used include olefins, cyclic polyolefins, cyclic olefin copolymers, polyesters, polyethylene terephthalate, polybutylene terephthalate, polystyrenes, polycarbonates, polypropylene, polyethylene, polyurethane, polyether sulfone, polyvinyl chloride, polyvinyl acetate, polyamides, polyimides, polyacrylate, polymethylmethacrylate (PMMA), polytetrafluoroethylenes, polydimethylsiloxane (PDMS), polysilane, cellulose triacetate, thermoplastics in general, and so forth. Composites and copolymers are also frequently used. The knowledge to select plastics or other solid substrates and conventional adhesives is widely known in related arts. 
         [0033]    The preceding specific embodiments are illustrative of the practice of the invention. Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope of this invention, and it should be understood that this invention is not to be unduly limited to illustrative embodiments set forth herein.