Abstract:
The invention relates to a method for attaching microelectronic devices, circuit boards and the like to a surface, and is particularly suitable for attaching a plurality of a semiconductor chips to an ink jet pen body. The method includes the steps of (a) providing a sheet of a thin film adhesive material having a first surface and a second surface opposite the first surface, the second surface being releasably attached to a carrier web; (b) simultaneously making a plurality of cuts in the sheet of thin film adhesive material, the cuts extending from the first surface to an interface between the second surface and the carrier web without significantly extending into the carrier web to provide one or more cut portions of adhesive film; (c) removing each cut portion of adhesive film from the carrier web; (d) engaging the second surface of each of the cut portions with predetermined locations on a receiving surface; and (e) providing one or more semiconductor chips in a desirably aligned configuration with respect to the predetermined locations and contacting each semiconductor chip with first surface of each of the cut portions. Use of the method and apparatus of the invention provides significant improvement in the application of adhesive films to surfaces in electronic component assembly.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to ink jet printers and in particular to methods for assembling ink jet pen components of multi-color pens using thin film adhesives.  
         BACKGROUND OF THE INVENTION  
         [0002]    Ink jet printers are continually undergoing design changes to improve the speed and print quality produced by such printers in order to provide printed images which have the appearance of laser printed media. One important advantage of ink jet printers over that of laser printers is that multi-color images may be produced relatively less expensively than with laser printers. Multicolor images are produced by depositing dots of different colors in precise patterns on the print media. One of the difficulties associated with multicolor printing is that the printheads of the individual ink jet pens used to produce the images must be aligned with each other so that the dot placement errors or minimized. Exact alignment of all critical printhead components during the assembly of an ink jet pen is extremely difficult to achieve. Even if the parts are initially aligned, it is difficult to maintain the alignment throughout the manufacturing process without the use of costly jigs. Even with elaborate alignment equipment, because of the size of the parts, extremely small alignment errors may have a major impact on the performance of the pens in a printer.  
           [0003]    The manufacture of a multi-color ink jet is typically a multi-step process. The most common multicolor printer uses individual ink jet pens for each color of ink. The components of the pens including the printheads are aligned and assembled with respect to their pen bodies. The individual pens are then attached to a carriage in side by side relationship. Once the pens are attached to the carriage, the pens may be individually adjusted to provide the desired alignment between the different pen colors. The components of each of the pens are aligned with respect to reference marks on the pen bodies and alignment between the individual color pens is conducted after all of the components of the pens are assembled and attached to the carriage. A disadvantage of this method for aligning the ink jet pens is that multiple alignment steps are required for the individual pens and there is a possibility that misalignment may occur due to wear or damage thereby requiring another costly alignment step.  
           [0004]    It is difficult to produce multicolor pens having two or more printheads attached to the same ink jet pen body because of the need to maintain alignment of the pen components. Thin film adhesives have attributes that make them desirable for use in the assembly of ink jet pens. For example, thin film adhesives are available that have substantially uniform thickness. However, such adhesives also have numerous attributes that render them difficult to handle or otherwise work with and thus the use of such adhesives are problematic in a production setting. There is a need therefore for manufacturing techniques and apparatus that facilitate the use of thin film adhesives in the manufacture of ink jet pens.  
         SUMMARY OF THE INVENTION  
         [0005]    With regard to the foregoing, the invention provides a method for attaching microelectronic devices, circuit boards and the like to a surface, and is particularly suitable for attaching a plurality of semiconductor chips to an ink jet pen body. The method includes the steps of (a) providing a sheet of a thin film adhesive material having a first surface and a second surface opposite the first surface, the second surface being releasably attached to a carrier web; (b) simultaneously making a plurality of cuts in the sheet of thin film adhesive material, the cuts extending from the first surface to an interface between the second surface and the carrier web without significantly extending into the carrier web to provide one or more cut portions of adhesive film; (c) removing each cut portion of adhesive film from the carrier web; (d) engaging the second surface of each of the cut portions with predetermined locations on a receiving surface; (e) providing one or more semiconductor chips in a desirably aligned configuration with respect to the predetermined locations and contacting each semiconductor chip with first surface of each of the cut portions; and (f) curing the thin film adhesive in order to substantially bond the chips to the receiving surface.  
           [0006]    In another aspect, the invention relates to apparatus for simultaneously cutting two or more strips of thin film adhesive and thereafter simultaneously applying the plurality of strips of thin film adhesive to a component of an ink jet pen in the manufacture of the ink jet pen.  
           [0007]    In a preferred embodiment, the apparatus includes a plurality of cutting/application assemblies desirably aligned with one another and spaced apart from one another a predetermined distance corresponding to desired application positions of the strips of thin film adhesive to an ink jet pen. A plurality of shafts capable of reciprocating movement relative to the cutting/application assemblies are provided, one each operatively associated with one of the cutting/application assemblies. A control assembly is provided for controlling movement of the shafts and for movably positioning the cutting/application assemblies relative to a workpiece such as a sheet of adhesive or an ink jet pen component. A plurality of rigid connecting members are provided for connecting each cutting/application member to the control assembly.  
           [0008]    Each of the cutting/application assemblies includes a stamping die having a perimeter defining a surface thereof of suitable configuration for cutting portions of thin film adhesive of a predetermined configuration from a sheet of thin film adhesive. An insert is movably positionable within a portion of the stamping die adjacent to the perimeter and has a surface suitable for receiving a cut portion of the thin film adhesive. Each of the shafts is operatively associated with one of the inserts and the control assembly.  
           [0009]    The invention advantageously facilitates the handling of thin film adhesives in the manufacture of microelectronic devices, such as ink jet pens. The invention provides conveniences in the cutting and application of thin film adhesives so that precisely cut portions of film material may be cut and accurately placed without undue handling thereof and without subjecting the film material to handling procedures that promote damage to the materials. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    Further advantages of the invention will become apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale, wherein like reference numbers indicate like elements through the several views, and wherein:  
         [0011]    [0011]FIG. 1 is a perspective view of a multicolor ink jet pen body showing semiconductor chip pockets therein;  
         [0012]    [0012]FIG. 2 is a perspective view of a single chip pocket and semiconductor chip for placement therein;  
         [0013]    [0013]FIG. 3 is a perspective view of adhesive placement relative to a semiconductor chip and chip pocket according to the invention and FIG. 3 a  shows a perspective view of an alternate adhesive placement;  
         [0014]    [0014]FIG. 4 is a cross-sectional side view of a sheet adhesive for use in accordance with the invention;  
         [0015]    [0015]FIG. 5 is a perspective view of apparatus for simultaneously placing adhesive in a plurality of chip pockets;  
         [0016]    [0016]FIG. 6 is a perspective view showing a portion of the apparatus of FIG. 5.  
         [0017]    [0017]FIG. 7 is a bottom perspective view of the apparatus portion of FIG. 6;  
         [0018]    [0018]FIG. 8 is a cross-sectional side view taken along lines  8 - 8  of FIG. 7;  
         [0019]    [0019]FIGS. 9 a - 9   c  are representational side views showing steps in accordance with invention for obtaining an adhesive strip for positioning in the chip cavity; and  
         [0020]    [0020]FIGS. 10 a - 10   b  are representational side views showing steps in accordance with the invention for positioning adhesive strips in a chip cavity. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    The invention relates to methods and apparatus for preparing, handling and installing thin film adhesives in the manufacture of microelectronic devices. The invention is particularly suitable for use in the attachment of semiconductor chips in the manufacture of ink jet pens. Accordingly, in accordance with a preferred embodiment, the invention will be described herein in the context of securing semiconductor chips in the manufacture of ink jet pens. However, it will be understood that the invention is suitable in other applications involving adhesive securement of components in the manufacture of microelectronic devices.  
         [0022]    With reference to FIGS. 1 and 2 there is shown in perspective view an ink jet pen body  10 , preferably a multicolor ink jet body, containing chip pockets  12 ,  14  and  16  on a first surface  18  thereof for the colors cyan, magenta and yellow. In the alternative, the pen body  10  may contain from two to four chip pockets. Preferably, the pen body  10  contains from three or four chip pockets, the fourth chip pocket being adapted for the color black.  
         [0023]    The chip pockets  12 ,  14  and  16  are recessed from the first surface  18  so that semiconductor chips  20  positioned in the pockets  12 - 16  do not extend above the top surface  18  of the pen body  10 . Each of the chip pockets  12 ,  14  and  16  contains an ink feed slot substantially in the center thereof, such as slots  22 ,  24  and  26 , for feed of ink to the chips  20  when they are mounted in the chip pockets  12 - 16 . The semiconductor chips  20  each contain an ink via  28  therein for ink flow communication between ink in the ink feed slots and a top surface  30  of the chips  20 . The chips  20  contain energy imparting devices such as resistor heaters or piezoelectric devices which upon activation cause ink to be ejected through orifice holes in a nozzle plate attached to the top surface  30  of the semiconductor chip  20 . The slots/chips are shown configured for feeding ink through the center of the chips. However, it will be understood that the invention is equally applicable for use with ink pens of the type wherein ink is fed around the edges or sides of the semiconductor chips  20  from ink feed slots offset from the center of the chip pockets  12 ,  14  and  16 . In an edge feed design, since ink flows around the edges of the chips  20 , the chips do not contain ink vias  28 .  
         [0024]    A nozzle plate, preferably a separate plastic or metal member, may be adhesively attached to the semiconductor chip  20  through a window or opening in a flexible circuit or TAB circuit. Alternatively, the nozzle plate may be integral with a flexible circuit or TAB circuit. The adhesive used to attach the nozzle plate to the semiconductor chip  20  may be a heat curable adhesive such a B-stageable thermal cure resin, including, but not limited to phenolic resins, resorcinol resins, epoxy resins, ethylene-urea resins, furane, resins, polyurethane resins and silicone resins. The adhesive between the nozzle plate and chip  20  is preferably cured before attaching the chip  20  to the chip pocket  12  of the pen body  10  and preferably has a thickness ranging from about 1 to about 25 microns.  
         [0025]    The flexible circuit or TAB circuit, which may be separate or integral with the nozzle plate, contains electrical traces and contacts for electrically connecting the energy imparting devices on the top surface  30  of the chip  20  with a printer control system. The design and manufacture of nozzle plates and flexible circuits or TAB circuits and attachment of the nozzle plates to a semiconductor chip are well known in the art and are described, for example in U.S. Pat. No. 5,305,015 to Schantz et al., the disclosure of which is incorporated by reference as if fully set forth herein.  
         [0026]    Because of the design of an ink jet pen having a pen body  10  containing two or more semiconductor chips  20  attached in chip pockets  12 ,  14  and  16  on the pen body  10 , each of the chips  20  must be precisely aligned with respect to one another and with respect to the nozzle plate during the assembly process. Misalignment may cause improper ink dot placement with respect to one or more colors being printed.  
         [0027]    With reference to FIG. 3, a thin film adhesive in film or paste form, may be used to fixedly attach each chip  20  in one of the chip pockets  12 - 16 . Preferred thin film adhesives include epoxy, cyanate ester and cyanate ester/epoxy adhesives having a thickness ranging from about 0.0005 to about 0.006 inch. Particularly preferred adhesives are available from Bryte Technologies, Inc. of Morgan Hill, Calif. under the trade name BRYTE EX-1522U and from Ablestik Electronic Materials &amp; Adhesives, a subsidiary of National Starch and Chemical Company of Rancho Dominiguez, Calif. under the trade names ABLESTIK 550 and ABLESTIK 561.  
         [0028]    In the case of a center feed chip design for an ink jet pen  10 , the adhesive is preferably provided as a substantially continuous frame  32  having an opening  33 , the frame  32  surrounding or circumscribing slot  22 . In an alternate embodiment (FIG. 3 a ), a frame  32 ′ consisting of a plurality of individual strips or segments  34  is positioned to fully or partially encircle slot  22 . The adhesive frame  32  (or  32 ′) provides a surface on a first side for adhering to the chip cavity and a surface on a second side opposite the first side for adhering to the chip. In the case of an edge feed chip design for an ink jet pen  10 , the adhesive preferably has a substantially continuous solid rectangular configuration rather than being provided as a frame  32  or strips  34 .  
         [0029]    The adhesive frame  34 , strips  34  or rectangle are cut from an adhesive sheet  42  illustrated in FIG. 4. The adhesive sheet  42  includes an adhesive film  80  having a first surface  82  and a second surface  84  opposite the first surface  82 . The adhesive sheet  42  may be tacky or a low tack adhesive may be applied to a release liner or carrier web  86  for attaching the second surface  84  of the adhesive film  80  thereto. The adhesive film  80  preferably has a thickness preferably ranging from about 0.0005 to about 0.006 inch. The release liner or carrier web  86  is preferably substantially thicker than the adhesive film  80  and preferably has a thickness ranging from about 0.01 to about 0.1 inch. As will be appreciated, the release liner or carrier web  86  may be a coated paper or plastic material, which may or may not contain a low tack adhesive layer  85  for attaching the web  86  to an adhesive film  80 . In the case of a non-tacky adhesive film  80 , the frame  32  or strips  34  are simply laid in the chip pockets  12 ,  14  and  16  before placing the chips  20  in the chip/nozzle plate assembly in the chip pockets  12 ,  14  and  16 .  
         [0030]    Once the chip/nozzle plate assembly is attached to the pen body  10 , a flexible circuit or TAB circuit may be attached to the top surface  18  of the pen body  10  using a heat activated or pressure sensitive adhesive. Preferred adhesives include, but are not limited to phenolic butyral adhesives, acrylic based pressure sensitive adhesives such as AEROSET 1848 available from Ashland Chemicals of Ashland, Ky. and phenolic blend adhesives such as SCOTCH WELD 583 available from 3M Corporation of St. Paul, Minn. The adhesive thickness preferably ranges from about 0.001 to about to about 0.005 inch.  
         [0031]    Turning to FIGS.  5 - 8 , there is shown apparatus  40  for simultaneously depositing frames  32  or strips  34  of adhesive onto the surfaces  36 ,  37  and  38  of the chip pockets  12 - 16  of the ink jet pen. The apparatus  40  includes a plurality of assemblies  44 ,  46  and  48 . The assemblies  44 - 48  are aligned with one another and spaced apart from one another corresponding to the locations of the chip pockets  12 - 16 . As explained below, the assemblies  44 - 48  are suitable for positioning the adhesive frames  32  or strips  34  in the chip pockets  12 - 16 , such as to surround the slot  22  of chip pocket  12 . The apparatus  40  may also be used to apply a rectangular adhesive film to the surfaces  36 ,  37  and  38  of chip pockets  12 - 16 .  
         [0032]    The assemblies  44 - 48  are operatively associated in the manner described below with shafts  50 ,  52  and  54 , respectively, mounted on a motorized control assembly  56  for simultaneous operation of the assemblies  44 - 48 . Each assembly  44 - 48  is rigidly connected to the control assembly  56  as by rigid connecting members  58  extending between the assemblies  44 - 48  and the control assembly  56 .  
         [0033]    The control assembly  56  may be of any suitable construction for controlled simultaneous movement of the shafts  50 - 54  of the assemblies  44 - 48 . For example, the control assembly  56  may be mounted to a motor driven, variably positionable support capable of controlled movement towards and away from a work surface, it being understood that the assemblies  44 - 48  move in unison with the control assembly  56  by virtue of the connecting members. In addition, the control assembly  56  contains internal mechanical structure for simultaneous controlled movement of the shafts  50 - 54  either toward or away from the work surface. The structure of a suitable control assembly  56  is considered to be well within the knowledge of one of ordinary skill in the art.  
         [0034]    The assemblies  44 - 48  are preferably identical to one another. Accordingly, only the construction and operation of assembly  44  will be described in detail, and the description applies to the remaining assemblies which are substantially identical thereto.  
         [0035]    As shown in FIGS.  6 - 8 , the assembly  44  includes a substantially rectangular stamping die  60  having substantially continuous side surfaces  61  and  62 , end surfaces  63  and  64 , and top surface  65 . A bottom  66  of the die  60  has a substantially continuous perimeter  67  surrounding a rectangular blind bore  68  and provides a suitable cutting surface for cutting the frame  32  or rectangular portions from the adhesive film  80 , as explained in more detail below. The assembly  44  is preferably constructed of aluminum or a rigid, strong, corrosion resistant material such as stainless steel.  
         [0036]    The blind bore  68  is sized to slidably receive a substantially rectangular and solid insert  69  having sides  70  and  71 , ends  72  and  73 , top  74  and bottom  75 , with depth D of the bore  68  being sufficient to receive both the insert  69  and the adhesive cut from film  80 . Accordingly, when the insert  69  is fully retracted within the bore  68 , the bottom  75  of the insert  69  is withdrawn a distance d within the bore corresponding to the thickness of the adhesive film  80 . The die  60  further includes a bore  76  substantially centrally located on the top surface  65  and extending into the bore  68  for slidably receiving the shaft  50 . A lowermost end of the shaft  50  is attached to the top  74  of the insert  69 .  
         [0037]    A separate die, similar to the die described above may be used to cut the rectangular openings  33  for frame  32  prior to cutting frame  32  from the adhesive film  80 . In the case of a rectangular adhesive film for an edge feed ink jet pen, only one die  60  as described above is required to cut the adhesive film.  
         [0038]    With reference to FIG. 9 a,  the initial step in preparation of one of the frames  32 , strips  34  or rectangular film is to remove a liner (if provided) from the upper surface  82  of the adhesive film  80  and position the assembly  44  so that the perimeter  67  of the assembly  44  rests on the upper surface  82 , it being understood that the adhesive sheet  42  is supported by a suitable work surface, with the carrier web  86  resting on the work surface. The shaft  50  is preferably positioned so that the insert  69  is fully retracted within the bore  68  to provide clearance for the adhesive as it is cut from the adhesive film  80  by downward urging of the perimeter  67 .  
         [0039]    Next (FIG. 9 b ), the assembly  44  is pressed substantially perpendicularly in the direction of the arrows A into the adhesive sheet  42  so that the perimeter  67  cuts through the adhesive film  80  but does not cut into the carrier web  86  or only cuts into the carrier web  86  a minor amount. This renders a cut portion of adhesive corresponding to frame  32 , strips  34  or a rectangular adhesive film, and indicated in FIG. 9 b  using reference numeral  32 . In the case of frame  32 , similar die to die  60  is used to first cut the rectangular opening  33  in frame  32  before cutting the frame  32  from adhesive sheet  42 . The resulting frame  32  or rectangular adhesive film cut from the adhesive sheet  42  remains with the assembly  44  as the assembly  44  is removed from the sheet  42  by pulling it away from the sheet  42  in the direction of the arrows B. As the assembly  44  is withdrawn from sheet  42 , the carrier web  86  is separated from the adhesive film  80 . Throughout the steps represented by FIGS. 9 a - 9   c,  the shaft  50  is preferably maintained such that the insert  69  is fully withdrawn into the bore  38 .  
         [0040]    As shown in FIGS. 10 a - 10   b,  the frame  32  or rectangular adhesive film is installed within the chip pocket  12  by first positioning the assembly  44  adjacent chip pocket  12  (and the other assemblies  46  and  48  being similarly positioned adjacent their respective chip pockets  14  and  16 ) placing the perimeter  67  of the assembly  44  against the surface  36  of the chip pocket  12  and moving the shaft  50  downwardly in the direction of the arrow C thereby urging insert  69  toward the surface  36  of chip pocket  12  and to bear the surface  84 , of the adhesive strip  32  against the chip pocket. As the pressure is exerted on the frame  32  via the shaft  50 , the frame  32  is urged toward surface  36  of the chip. While not required, surface  84  or surface  36  may contain a low-tack adhesive layer for use in attaching frame  32  to the chip pocket  12 . The shaft  50  is then moved in the direction D away from the chip pocket and the frame  32  releases from the surface  75  of the insert  60  and remains in the chip pocket  12 . The assembly  44  is thereafter or simultaneously withdrawn from the chip pocket.  
         [0041]    To facilitate separation of frame  32  from the insert  69 , it is preferred that the surface  75  of the insert  69  have less affinity for the adhesive film  80  as compared to the surface  36  of the chip pocket  12 , but still sufficient adhesion for removing the frame  32  from the material sheet  42 . This may be accomplished, for example, by coating the surface  75  with a low surface energy coating such as a polytetrafluoroethylene coating (PTFE) having a surface energy substantially lower than the surface energy of the surface  36  of the chip pocket  12 . In order to increase the surface energy of surface  36 , a low-tack adhesive layer may be used in the chip pocket  12 . The low tack adhesive should have sufficient tackiness to adhesively secure the frame  32  to the surface  36  of the chip pocket  12  while enabling release of surface  82  of the frame from surface  75  of insert  69 .  
         [0042]    In a preferred fabrication method for an ink jet pen according to the invention, nozzle plates are bonded to semiconductor chips such as chip  20  using well known bonding techniques. The nozzle plate/chip assemblies are then electrically connected to a flexible circuit or TAB circuit. In a separate step, a thermoplastic adhesive is applied to the top surface  18  of the pen body  10 .  
         [0043]    Next, the frames  32  are positioned in the chip pockets  12  of the pen body  10  using the apparatus of FIG. 4 in the manner described above in connection with FIGS. 9 a - 9   c  and  10   a - 10   b.  The nozzle plate/chip/circuit assemblies are then aligned to one another and attached to the pen body  10  by positioning them in their aligned orientation within the chip pockets  12  and pressing them in this orientation against the installed frames to maintain them in the chip pockets in their aligned orientation.  
         [0044]    Finally, the flexible circuits or TAB circuits are heat staked into the thermoplastic adhesive on the surface  18  of the pen body  10  and heat is applied to the exposed surface of the flexible circuits in an amount sufficient to cause the thermoplastic adhesive to flow and encapsulate the edges of the flexible circuits. A preferred thermoplastic adhesive for attaching the flexible circuits or TAB circuits is a flexible polyolefin, non-curing thermoplastic bonding film such as available from Minnesota Mining and Manufacturing Company of Saint Paul, Minn. under the trade name 3M THERMO-BOND 845. Such film has a thickness ranging from about 0.002 to about 0.005 inch and includes a polyolefin based-resin having a softening point in the range of from about 80° to about 150° C.  
         [0045]    As will be appreciated, the invention advantageously enables improved manufacture of ink jet pens using thin film adhesives. Multiple portions of thin film adhesive can be prepared simultaneously and applied simultaneously in the manufacture of ink jet pens, avoiding many of the shortcomings of prior methods and apparatus and the problems inherent in the handling of thin film adhesives.  
         [0046]    Having described various aspects and embodiments of the invention and several advantages thereof, it will be recognized by those of ordinary skills that the invention is susceptible to various modifications, substitutions and revisions within the spirit and scope of the appended claims.