Forming long arrays from short components

Abstract: Process and apparatus for fabricating an extended scanning or printing array in which several smaller scanning or printing chips (5) are bonded end-to-end onto the surface of a glass substrate (10) having an opaque thermally and/or electrically conductive coating (19) thereon, with the coating removed at discrete sites (24) to allow a photocurable adhesive (30) placed at the sites to be cured through exposure to UV light from underneath the substrate, the photocurable adhesive holding the chips in place while a chip-bonding adhesive (38) deposited on the conductive coating where the chips are located is cured to provide a permanent structure.

Description: The invention relates to a process and apparatus for fabricating an extended scanner or printer array, and more particularly to a process and apparatus for locating and bonding small chips onto a substrate to form an extended array without sacrifice in image or print quality. Image sensor arrays for scanning document images, such as charge-coupled devices (CCDs), typically have a row or linear array of photosites together with suitable support circuitry integrated onto silicon. Usually, an array of this type is used to scan line-by-line across the width or length of a document, with the document being moved or stepped in synchronism therewith. Similarly, image marker arrays, such as ink jet printheads typically comprise a row of ink jets on a support structure. In the above, the image or print resolution of the array is proportional to the ratio of the scan width and the number of photosites or printing elements. Because of the difficulty in economically designing and fabricating long or extended arrays, image or print resolution for the typical array commercially available today is relatively low when the array is used to scan or print a full line. While resolution may be improved by various mechanisms, as for example, by interpolating extra image signals, or by interlacing several smaller arrays with one another in a non-collinear fashion and crossing over from one array to the next, manipulations of this type add to both the complexity and the cost of the system. Further, single or multiple array combinations, such as referred to above, usually require more complex and expensive support systems. An extended or full-width scanner or printer array with a large packing of coil near image-reading or-printing elements to ensure high resolution, has been and remains a very desirable but so far unattainable aim. While forming a full-length array by assembling several smaller arrays, referred to as chips herein, together end-to-end has often been postulated, there has nevertheless existed the problem of successfully fabricating the composite array such that the smaller chips that make up the longer array are in precise and exact alignment, with the chip ends in close abutting relation with one another so that distortion of image or print is avoided. US-A-4,523,102; 4,388,128, and 4,661,191, respectively disclose processes for bonding color filters to image sensor chips, in which a heat activated-ultraviolet curable adhesive is used to bond the color filters to the chip. In these known processes; the adhesive is first cured partially by exposing the adhesive to ultraviolet light, with curing completed through the application of heat. These known processes are enabled by virtue of the transparent nature of the filter, allowing the ultraviolet light to pass through the filter and strike the adhesive. US-A-4,698,113 discloses a process for cementing lens elements in which various types of photocurable-heat activated adhesive combinations are provided which are designed to ensure curing of the adhesive where impingement of the ultraviolet rays is prevented by dark bands in the color filter. US-A-4 467 342 discloses a process for fabricating an array of imager chips in which a chip is attached to a temporary glass holder by a wax seal and then bonded to a substrate by UV cured epoxy. EP-A-0 329 004 discloses a chip mounting apparatus featuring a suction head assembly for transferring a set of chips from a template assembly by a printed circuit board. In contrast, the present invention provides a process for fabricating a longitudinal array from several individual chips, the chips being substantially opaque, according to claims 1 and 2. The invention further provides an apparatus for assembling an extended array as is claimed in claim 5. The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a plan view illustrating an extended array comprised of several small chips assembled in end-to-end relation and bonded together using the process and apparatus of the present invention; Figure 2 is an isometric view illustrating a small chip of the type used to make the array shown in Figure 1; Figure 3 is an isometric view depicting the first stage of the process of the present invention in which a transparent substrate, following deposition of a thermal and/or electrically conductive film on the surface thereof, is photopatterned to remove discrete areas of the condutive film and open up bonding windows on the substrate; Figure 4 is an isometric view depicting the substrate following completion of the first stage of the process shown in Figure 3; Figure 5 is an isometric view depicting the second stage of the process of the present invention in which a chip-bonding adhesive is screen-printed onto areas of the surface of the substrate where the chips are to be located; Figure 6 is an isometric view depicting the third stage of the process of the present invention in which chips are placed in aligned and abutting end-to-end relation on the surface of the substrate following deposition of separate chip-bonding and photocurable adhesives thereon; Figure 7 is a bottom view of the substrate illustrating the optical path provided by the bonding windows that permits curing of the photocurable adhesive through exposure to light; Figure 8 is a top view illustrating the assembly apparatus of the present invention, including a base with a suction manifold for holding a row of chips in abutting end-to-end relation, and substrate support fixture in the open loading position; and Figure 9 is a side view in cross section of the apparatus shown in Figure 8, with the substrate support fixture closed and the substrate abutted against the chips. Referring particularly to Figure 1 of the drawings, there is shown an extended, i.e., full-width, scanner array 3 composed of a plurality of smaller sensor chips or arrays 5 assembled end-to-end (specific chips are identified by numerals 5A, 5B, ... 5N) on an elongated rectangular transparent substrate 10. Substrate 10 comprises any suitable transparent material as, for example, glass, having a thermally and/or electrically conductive film 19 on the surface 18 (seen in Figure 3) where chips 5 are to be mounted. Film 19 is substantially opaque. Array 3 is typically used to read or scan a document line-by-line and convert the document image to electrical signals. In that application, array 3 preferably is a full-width array, having an overall length equal to or slightly greater than the width of the largest document to be scanned. As shown in Figure 2, chips 5, which may, for example, be charge-coupled devices (CCDs), comprise a relatively thin silicon die 11 having a generally rectangular shape. A row 14 of photosites 12 parallels the longitudinal axis of the chips. While a single row 14 of photosites 12 is shown, several photosite rows may be used. Other active elements, such as shift registers, gates, pixel clock, etc., are preferably formed integrally with die 11. Chips 5 have suitable external connectors, shown here as bonding pads 16, for electrically coupling the chips to external sources. Chips 5 are opaque. Chips 5 are provided with substantially flat, square ends 15 designed to enable chips 5 to be accurately and tightly abutted together with one another without distortion or other defects. Chips suitable for this purpose may, for example, be formed in the manner described in US-A-4,814,296. When a single chip 5 is used for scanning purposes, the image resolution achieved is a function of the number of photosites 12 that can be fabricated on the chip. Since the number of photosites 12 that can be packed onto a single chip is limited, it is advantageous to assemble several chips together in a longer array, and preferably in a full-width or full-size array. In the present invention, an extended array is fabricated from a plurality of chips 5A, 5B,... 5N secured together in tightly abutting end-to-end relation, the finished array having a continuous and uninterrupted row of photosites with a substantially uniform periodicity. Referring now to Figures 3 and 4, in the present invention, the surface 18 of substrate 10 to which film 19 is applied is exposed through a pattern 20. Pattern 20 consists of a suitable opaque material having a plurality of generally-rectangular transparent areas 22 arranged in a row 26 and in predetermined spaced relation with one another. The number and location of transparent areas 22 are chosen to provide two optically clear bonding windows 24-1 and 24-2 in film 19 (seen in Figure 4) for each chip 5A, 5B, ... 5N to be mounted on substrate 10. Transparent areas 22 of pattern 20 are sized so as to create bonding windows 24 with an area capable of containing a predetermined amount of a photocurable adhesive which is used to initially hold chips 5 initially in place pending completion of the bonding process, as will appear. Because of the delicate nature of bonding items in close proximity (i.e., less than 25 µm″), the advantage of a light-curable adhesive is that minimal thermal expansion results from the curing process. With heat-curable adhesives, there is a risk that the heating may result in non-uniform thermal expansion. While two bonding windows 24-1 and 24-2 for each chip are shown and described, the number of windows 24 per chip may vary from one to any desired number. Further, the size and shape of windows 24 may be different from that shown and described herein. Other suitable processes for forming bonding windows may be contemplated. On exposure of substrate 10 through pattern 20, light, as for example from exposure lamp 23, passing through the transparent areas 22 of pattern 20, exposes the portion of film 19 opposite thereto to delineate the area of the bonding windows 24. As will be understood, the remainder of pattern 22, which is opaque, blocks the transmission of light, leaving the other areas of film 19 unexposed. Following predetermined exposure, surface 18 of substrate 10 is chemically treated to remove pattern 20 and the exposed portions of film 19. As a result, a series of optically-clear bonding windows 24 are created on the surface 18 of substrate 10 where film 19 is removed, as shown in Figure 4. Referring to Figures 5 and 6, a suitable bonding adhesive 38 is dispensed onto the areas of film 19 where chips 5 are to be attached to substrate 10. In order to control deposition of adhesive 38 and prevent application of adhesive 38 to bonding windows 24, a screen 39 having a pattern of opaque areas 40,41 and screened area 42 is used, screen 39 serving to limit application of adhesive 38 to areas of the substrate 10 where chips 5 are to be located. To prevent application of adhesive 38 to bonding windows 24, the opaque areas 41 are approximately the same size and shape as bonding windows 24, with one opaque area 41 being provided as a cover for each of the bonding windows 24. A suitable photocurable adhesive 30 curable by ultra violet (UV) light is separably dispensed onto surface 18 of substrate 10 at each of the bonding windows 24. Other suitable processes for depositing adhesives may be contemplated. Referring to Figures 6 and 7, following deposition of adhesives 30,38 on surface 18 of substrate 10, the chips 5A, 5B, ... 5N that comprise array 3 are placed bottom side down on surface 18 of substrate 10 over adhesives 30,38, with the ends 15 of chips 5 in tight end-to-end abutting relation with one another. A controlled pressure (designated by the arrow 40) is applied to the chips 5 to force the chips 5 tightly against the surface 18 of substrate 10 and into uniform contact with adhesives 30,38. Photocurable adhesive 30 on bonding windows 24 is then exposed by a suitable UV light source 44, light from the source 44 passing through the transparent portion of substrate 10 opposite bonding windows 24 to expose and activate adhesive 30. Exposure of adhesive 30 establishes an initial bond between chips 5 and the substrate 10 which retains the chips 5 in position while adhesive 38 is cured. UV light source 44 may, for example, comprise a UV lamp or scanning UV laser. Following activation of adhesive 30 and initial bonding of chips 5 to substrate 10, adhesive 38 is cured to bond the chips 5 to substrate 10 permanently. Adhesive 38, which typically comprises a thermally-activated adhesive, normally requires removal of the partially processed chip-substrate assembly to a suitable oven where controlled heating of the adhesive is performed. The photocurable adhesive 30 retains the chips in place on substrate 10 while the chip-substrate assembly is moved to the curing site and during the curing process. Referring to Figures 8 and 9 where like numbers refer to like parts, there is shown the assembly apparatus 60 for use in precision fabrication of arrays 3. Apparatus 60 includes a generally-rectangular base 62 with an elongated generally-rectangular suction manifold 64 thereon adjacent one side 63 of base 62, and a pivotable substrate support fixture 66 adjacent the other side 65 of base 62, suction manifold 64 and substrate support fixture 66 being located in predetermined operating relation with one another, as will appear. Suction manifold 64, which serves to retain the row of chips 5A, 5B, ...5N that comprise the array 3 in predetermined end-to-end relation during the fabrication process, has a row of suction holddown openings or ports 68 in the surface thereof for this purpose. Suitable chip registering and locating guides (not shown) may be provided for locating chips 5 in exact aligned and registered position during the assembly process. Individual suction passages 70 in base 60 couple ports 68 with a suitable source of suction (not shown), there being a suitable control valve (not shown) to enable suction to ports 68 to be turned on and off during the array fabrication process. Substrate support fixture 66 comprises a generally-rectangular open frame 72 within which substrate 10 is located in a predetermined fixed position. Sides 74, 75 of frame 72 are extended and are provided with a bore 77 therethrough adjacent the terminal end thereof which, for assembly of substrate support fixture 66 with base 60, aligns with similar bores 78 in spaced-apart mounting brackets 80,81 secured to base 60. Journaling pins 88 fit within bores 77,78 to attach substrate support fixture 66 pivotally to base 60. When mounted in place on base 60, substrate support fixture 66 is pivotally movable through an approximately 180° arc from the retracted position shown in Figure 8 (shown also by dotted lines in Figure 9) to the closed position shown by solid lines in Figure 9. UV light source 44 is suitably supported on base 60 such that light from source 44 impinges on the substrate 10 carried by substrate support fixture 66 when fixture 66 is in the closed position. UV light source 44 is supported so as to not interfere with pivoting movement of substrate support fixture 66. In operation, substrate support fixture 66 is placed in the retracted or open position shown in Figures 8 and 9. Substrate 10 is inserted into the frame 72, with the surface 18 having the previously prepared film 19 with bonding windows 24 formed therein facing outwardly. Photocurable adhesive 30 is applied to bonding windows 24 and chip-bonding adhesive 38 to the remainder of film 19 in the manner described above. Chips 5A, 5B, ... 5N that comprise the array 3 are located in registered end-to-end abutting relation on suction manifold 64, chips 5 being placed face down on manifold 64. Following placing of chips 5 on manifold 64, suction is applied through ports 68 to retain the chips 5 in registered position. Substrate support fixture 66 is pivoted from the dotted-line position to the solid-line position shown in Figure 9 to bring the adhesive-bearing surface of substrate 10 into contact with the row of chips 5 on vacuum manifold 64. With fixture 66 in position, UV lamp 44 is activated and light (radiation) from lamp 44 passes through substrate 10 at the bonding windows 24 to expose and activate photocurable adhesive 30. Activation of adhesive 30 establishes an initial bond between chips 5 and substrate 10. After a preset interval, suction to ports 68 is turned off, freeing chips 5 from suction manifold 64. Substrate support fixture 66 with substrate 10 having chips 5A, 5B, ... 5N bonded thereto is then pivoted in the opposite direction back to the retracted position shown by the dotted lines in Figure 9. There the substrate 10 with chips 5 attached thereto by adhesive 30 is removed and the partially-fabricated chip-substrate assembly removed for curing of adhesive 38. While fabrication of a scanning array 3 and an apparatus for carrying out such fabrication are shown and described, the present invention may be employed to fabricate long or full-width printer arrays using a series of smaller ink jet heads, ionographic heads, etc. which have one or more rows of printing elements.

Claims: A method of fabricating a longitudinal array of individual opaque chips (5) positioned in end-to-end, abutting relation comprising the steps of: a) providing a substrate (10) of transparent material; b) depositing on one surface of the substrate an opaque film (19) of thermally- and/or electrically-conductive material; c) photopatterning the film to remove at least one portion (22) thereof to expose an area (24) of the substrate; d) applying a bonding adhesive (38) to selected areas of the conductive film; e) applying a photocurable adhesive (30) to the areas of exposed substrate; f) placing several of said chips in aligned end-to-end abutting relationship on the substrate surface, with the base of each chip being contacted by both adhesives; g) activating the photocurable adhesive by exposing it to radiant energy through the substrate, to secure each chip in place on the substrate, and h) while the chips are held in place by said photocurable adhesive, curing the bonding adhesive to secure the chips permanently in place. A method of fabricating a longitudinal array of individual opaque chips (5) positioned in end-to-end abutting relation, comprising the steps of: a) providing an substrate (10) of transparent material; b) applying a photocurable adhesive (30) to one surface of the substrate at discrete sites (24) in a predertermined pattern so that there is at least one site for each chip; c) depositing on one surface of the substrate, except for the sites (24), an opaque film (19) of thermally- and/or electrically-conductive material; d) applying a bonding adhesive (38) to the film at locations where chips are to be placed; e) placing several of said chips in aligned end-to-end abutting relationship on the substrate surface, with the base of each chip being contacted by both adhesives; f) activating the photocurable adhesive by exposing it to radiant energy through the substrate, to secure each chip in place on the substrate, and g) while the chips are held in place by said photocurable adhesive, curing said bonding adhesive to secure the chips permanently in place. A fabrication method as claimed in claim 1 or 2, wherein the step of placing several of said chips in aligned end-to-end relationship on the substrate surface comprises : holding the substrate in a fixed location, with one surface thereof exposed; pre-locating the chips in end-to-end relationship with one another at a location separate from the substrate, and bringing the pre-located chips into contact with the exposed surface of the substrate. The method as claimed in claim 3, including the step of holding the chips in position by suction at the separate location and while moving them into contact with the substrate. Apparatus for bonding a longitudinal array of individual chips (5) to a substrate (10) of transparent material having an opaque film of thermally- and/or electrically-conductive material on one surface, the film having in it at least one window (24) for each chip, and a chip-bonding adhesive (38) on the film, and a photocurable adhesive on each window, comprising in combination: a) a member (66) for supporting the substrate releasably in a chosen position in such a way that the transparency of the substrate is preserved; b) a member (64) having a substantially-flat surface (62) for supporting the chips in aligned and end-to-end abutting relationship with each other, with one surface of each chip against the surface; c) means (70) for releasably retaining the chips in their assembled position on the surface of the member (64); d) means (66, 88) for pivotally moving the members relatively to each other until the opposite surfaces of the chips and the substrate are brought together to bring surface areas of each chip into contact with both adhesives, and e) means (44) for directing radiation through the windows on the substrate to activate the photocurable adhesive whereby, on release of the retaining means, the cured adhesive holds the chips in place pending activation of the bonding adhesive. Apparatus as claimed in claim 5, in which the retaining means includes means (70) for holding the chips in place on the support surface by suction.

Inventors: CAMPANELLI MICHAEL R, DRAKE DONALD J, CAMPANELLI, MICHAEL R., DRAKE, DONALD J.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1990
Main classification: H01L25
IPC codes: H01L21, H04N1, H01L27