Method of connecting an integrated circuit chip to a substrate having wiring pattern formed thereon

Abstract: A connecting method of connecting an integrated circuit chip (11) to a wiring substrate (13) having a wiring pattern formed thereon, according to the present invention, is intended to make a connection between fine connecting portions on the substrate and connecting pads (12) on the chip easy and reliable. The connecting method of this invention is featured by connecting a plurality of connecting portions (14) formed on a major surface of a wiring substrate to a plurality of connecting pads (12) formed on a major surface of an integrated circuit chip through metal bumps (15) and adhering portions of the major surface of the wiring substrate which have no connecting portions to portions of the major surface of the integrated circuit chip which have no connecting pads by means of a photothermosetting resin film (16) selectively opened at the connecting portions.

Description: Field of the Invention The present invention relates to a connecting method for connecting an integrated circuit (IC) chip to a substrate having wiring pattern formed thereon. The substrate may be a printed circuit board, a semiconductor wafer or a substrate for a liquid crystal display panel which may be of glass or quartz. The IC chip may be a wafer itself in which an electric circuit is formed. Description of the Prior Art An example of a conventional connecting method will be described with reference to Figs. 1a and 1b which show the steps of the connecting method for connecting an integrated circuit (IC) chip to a substrate. In these figures, an LSI chip 1 has connecting pads 2 on which metal bumps 5 are formed, respectively, and a substrate 3 has terminals 4 which are formed correspondingly in position to the metal bumps 5 on the LSI chip 1. Those terminals 4 are connecting portions of a wiring pattern (not shown) formed on the substrate 3. The LSI chip 1 and the substrate 3 are faced through a thermo-adhesive resin film 6 containing uniformly dispersed electrically conductive particles 7, with the metal bumps 5 on the LSI chip 1 being registered with the terminals 4 on the substrate 3, respectively, as shown in Fig. 1a. Then, as shown in Fig. 1b, the LSI chip 1 is pressed to the substrate 3 while being heated. With this heating, the thermo-adhesive resin film 6 is softened and connects the metal bumps 5 to the terminals 4, respectively, by means of the electrically conductive particles 7 contained therein. By a subsequent cooling of these members, the thermo-adhesive resin film 6 is hardened while keeping this connection between the bumps 5 and the terminals 4, so that the chip 1 and the substrate 3 are fixedly connected. In the conventional connecting method mentioned above, there is a problem of short-circuit or current leakage between adjacent bumps 5 and/or adjacent terminals 4 when an amount of conductive particles 7 dispersed in the resin film 6 forms a connection path between the bumps 5 and the terminals 4. If, in order to avoid such problem, the amount of the conductive particles 7 in the resin film 6 is reduced, resistance between facing bumps 5 and terminals 4 which are to be connected is increased and may become not uniform and, in the worst case, there may be connecting portions produced which are electrically open-circuited. This tendency is becoming more and more important with recent reductions size of connecting portions Further, it is very difficult to press adhering surfaces of the chip and the substrate while keeping them exactly in parallel. If such parallelism is broken, gaps between the bumps 5 and the respective terminals 4 may vary, making the connection therebetween unstable. These problems are sources of malfunction in the device concerned. IBM Technical Disclosure Bulletin, Vol. 26, No. 3a, pages 927-8 discloses a method of joining a chip to a wiring substrate in which a photoresist layer has holes corresponding to metal solder bumps and wiring connector pads. The components are physically joined together only by the solder bumps. US-A-4.749.120 uses adhesive photothermosetting resin to stick together a chip and a wiring substrate. The uncured resin is displaced by metal connection bumps when the components are joined so that electrical contact is made with connector pads. Summary of the Invention The present invention relates to a method for connecting an integrated circuit chip or a semiconductor wafer manufactured as an IC or LSI to a wiring substrate having a wiring pattern formed thereon, such as a printed circuit board, a substrate which may be a semiconductor wafer having a wiring formed thereon or a substrate of a liquid crystal display panel. An electrical connection is made between connecting pads formed on a major surface of an integrated circuit chip and connecting portions of a wiring formed on a major surface of the wiring substrate, through metal bumps. Mechanical adhesion between the chip and the wiring substrate is provided between a portion of the major surface of the chip on which the connecting pads are not formed and a portion of the major surface of the wiring substrate on which the connecting portions are not formed, by means of photothermosetting resin. Thus in one aspect the invention provides a method of joining major a method of connecting a semiconductor chip and a wiring substrate, characterised by comprising the steps of: coating a major surface of a wiring substrate together with a plurality of respective connecting portions formed on said major surface of said wiring substrate with a photothermosetting resin film; selectively removing said photothermosetting resin film from said connecting portions registering, in position, a plurality of connecting pads formed on a major surface of an integrated circuit chip with said connecting portions, the connecting pads having metal bumps; and connecting said connecting portions of the wiring substrate and said metal bumps by heating them while applying a predetermined load thereto to adhere remaining surface portions of said photothermosetting resin film to portions of said major surface of said integrated circuit chip which have no connecting pad. In another aspect the invention provides a method of connecting a semiconductor chip and a wiring substrate characterised by comprising the steps of: coating a major surface of a wiring substrate together with a plurality of metal bumps on respective connecting portions formed on said major surface of said wiring substrate with a photothermosetting resin film; selectively removing said photothermosetting resin film from said metal bumps; registering, in position, a plurality of connecting pads formed on a major surface of an integrated circuit chip with said metal bumps of said wiring substrate; and connecting said connecting pads and said metal bumps of said wiring substrate by heating them while applying a predetermined load thereto to adhere remaining surface portions of said photothermosetting resin film to portions of said major surface of said integrated circuit chip which have no connecting pad. The metal bumps may be indium or an alloy thereof. Preferably, prior to selective removal of the photothermosetting resin film, the film is partially hardened to a first hardness, the subsequent heating of the remaining portion of the film hardening said portions to a second hardness greater than said first hardness. With this invention it is possible to connect fine connecting portions to the connecting pads easily and reliably. Since the electrical connection between the fine connecting portions and the fine connecting pads is made through the bumps of metal such as indium (In) or an alloy of indium, the resultant connection is reliable. Brief Description of the Drawings Figs. 1a and 1b are cross-sections showing the steps of a conventional connecting method; Figs. 2a to 2f are cross-sections showing the steps of connecting method according to a first embodiment of the present invention; and Figs. 3a to 3f are cross-sections showing the steps of connecting method according to a second embodiment of the present invention. Description of the Preferred Embodiments A first embodiment of the present invention is described with reference to a connection of a semiconductor chip and an LCD (liquid crystal display) substrate. As shown in Fig. 2a, an LCD substrate 21 comprising a glass substrate 13 having a major surface 20 on which a plurality of connecting portions 14 are formed is prepared first. The connecting portions 14 are portions of a wiring patterns formed on the major surface of the substrate 13 to act as terminals to be connected to connecting pads formed on an integrated circuit chip. Then, as shown in Fig. 2b, the major surface 20 of the LCD substrate 21 including the connecting portions 14 is pin-coated with photothermosetting resin substantially uniformly. Next, this substrate 21 is pre-baked at 90°C for ten minutes, and a photothermosetting resin film 16 is formed. Constituents of this photothermosetting resin are shown below in weight ratio: epoxy resin: acrylic acid, maleic acid or Triethylene Glycol Dimethacrylate: epoxyacrylate: benzophenone = 100 : 30 to 50 : 10 : 1 to 5 The coating with this photothermosetting resin is performed by a spinner which is a spin coating device. Thereafter, as shown in Fig. 2c, the photothermosetting resin film 16 is selectively exposed with ultraviolet rays 18 through a photo mask 17 having a chromium film 25 patterned to shield the rays to the connecting portions 14, by means of photolighography, so that the photothermosetting resin film 16 except for portions thereof corresponding to the connecting portions 14 is hardened to have the first hardness. Then, as shown in Fig. 2d, the photothermosetting resin film 16 is developed with developer 19. Developer 19 is alkaline aqueous solution (aqueous solution of sodium carbonate or aqueous solution of calcium carbonate) or 1,1,1-Trichloroethane. With this development, the portions of the photothermosetting resin film 16 on the connecting portions 14 are selectively removed. An integrated circuit chip 23 is, as shown in Fig. 2e, prepared by forming a plurality of connecting pads 12 on a major surface 22 of a semiconductor wafer 11 and forming metal bumps 15 on the respective connecting pads 12. The connecting pads 12 constitute a portion of a wiring pattern of an IC or LSI formed on the chip and are also usable as bonding pads. The metal bumps 15 are soft metal bumps of such as indicum (In) or an alloy of indium and lead, which are elastically deformable easily. The metal bumps 15 of the integrated circuit chip 23 and the connecting portions 14 of the LCD substrate 21 are faced to each other. This positioning can be done easily by visually checking the connecting portions 14 and the connecting pads 12 through an opposite surface 24 of the glass substrate 13 to the major surface 20 thereof since the glass substrate 13 and the photothermosetting resin film 16 are transparent or translucent. Then, as shown in Fig. 2f, the integrated circuit chip 23 and the LCD substrate 21 are mated each other with keeping the registration between the metal bumps 15 of the chip and the connecting portions 14 of the substrate 21 and pressed to each other with a load of, for example, 10 Kg/cm 2 . With this load, the metal bumps 15 are elastically deformed to electrically connect the connecting portions 14 and the connecting pads 12 to each other. Keeping this relative position between portions 14 and pads 12, the photothermosetting resin film 16 is kept at 150°C for 10 minutes to have the second hardness which is harder than the first one. Thus, portions of the major surface of the integrated circuit chip 23 which have no connecting pads 12 are adhered to the LCD substrate 21 through the resin film 16 as an adhesive. A second embodiment of the present invention will be described with reference to Figs. 3a to 3f which show the steps of connecting an LCD substrate to a semiconductor chip. First, as shown in Fig. 3a, an LCD substrate 41 is prepared by forming a plurality of connecting portions 34 on a major surface 40 of a glass substrate 33 and then forming metal bumps 35 on the respective connecting portions 34. These connecting portions 34 constitute portions of a wiring pattern and used as terminals to be connected to connecting pads formed on an integrated circuit chip. The metal bumps 35 are soft metal bumps of such as indium (In) or an alloy of indium and lead, which are elastically deformable easily. Then, as shown in Fig. 3b, the major surface 40 of the LCD substrate 41 including the metal burps 35 is spin-coated with photothermosetting resin substantially uniformly. Next, this substrate 41 is pre-baked at 90°C for 10 minutes, and a phothothermosetting resin film 36 is formed. Constituents of this photothermosetting resin are shown below in wheight ratio: epoxy resin: acrylic acid or maleic acid or Triethylene Glycol Dimethacrylate: epoxyacrylate : benzophenone = 100 : 30 to 50 : 10 : 1 to 5 The coating with this photothermosetting resin is performed by a spinner which is a spin coating device. Thereafter, as shown in Fig. 3c, the photothermosetting resin film 36 is selectively exposed with ultraviolet rays 38 through a photo mask 37 having a chromium film 45 patterned to shield rays to the connecting portions 34, by means of photolighography, so that the photothermosetting resin film 36 except for portions thereof corresponding to the connecting portions 34 is hardened to have the first hardness. Then, as shown in Fig. 3d, the photothermosetting resin film 36 is developped with developer 39. Developer 39 is alkaline aqueous solution (aqueous solution of sodium carbonate or aqueous solution calcium carbonate) or 1,1,1-Trichloroethane With this development, the portions of the photothermosetting resin film 36 on the connecting portions 34 are selectively removed. An integrated circuit chip 43 is, as shown in Fig. 3e, prepared by forming a plurality of connecting pads 32 on a major surface 42 of a semiconductor substrate 31. The connecting pads 32 constitute a portion of a wiring pattern of an IC or LSI formed thereon and are also usable as bonding pads. The connecting pads 32 of the integrated circuit chip 43 and the connecting portions 34 of the LCD substrate 41 are registered to each other. The registration can be done easily by visually checking the connecting portions 34 and the connecting pads 32 through an opposite surface 44 of the glass substrate 33 to the major surface 40 thereof since the glass substrate 33 and the photothermosetting resin film 36 are transparent or translucent. Then, as shown in Fig. 3f, the integrated circuit chip 43 and the LCD substrate 41 are mated with maintaining the registration between the connecting pads 32 of the chip and the metal bumps 35 of the substrate 41 and pressed to each other with a load of, for example, 10 Kg/cm 2 . With this load, the metal bumps 35 are elastically deformed to electrically connect the connecting portions 34 and the connecting pads 32 to each other. The photothermosetting resin film 36 is kept at 150°C for 10 minutes to have the second hardness which is harder than the first one. The surface portions of the major surface of the integrated circuit chip 43 are adhered to the LCD substrate 41 through the resin film 36 as an adhesive. It should be noted that the wiring substrate used as an object to be connected according to the present invention is not limited to only a substrate (glass or quartz) of a liquid crystal display panel and it may be a printed circuit board or a semiconductor wafer on which a wiring pattern is formed. Further, the present invention is applicable to any wiring substrate having any configuration so long as it has a portion having a flat surface on which a wiring pattern is formed. In order to perform a registration between a wiring substrate and a semiconductor chip when the wiring substrate is opaque, coordinates of connecting portions on the wiring substrate and coordinates of connecting pads of the integrated circuit chip are preliminarily measured from images of them obtained by a video camera, by using a pattern recognition technique. Then, a relative rotation angle of the connecting portions to the connecting pads is made null by rotating a robot hand fixedly supporting the chip. Thereafter, coordinates at which the connecting portions and the connecting pads can be registered is calculated and the robot hand is moved thereto while detecting a distance to the coordinates in submicron unit by using a laser distance measuring system. Thereafter, the chip is pressed to the wiring substrate with a predetermined load in the same manner as mentioned previously for the case of LCD. Although the integrated circuit chip is usually one of a plurality of chips cut out from a semiconductor wafer, there is an exception that a single wafer bears a single semiconductor device. This invention is also applicable to a connection of such wafer to a wiring substrate. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims.

Claims: A method of connecting a semiconductor chip and a wiring substrate, characterised by comprising the steps of: coating a major surface of a wiring substrate (21) together with a plurality of respective connecting portions (14) formed on said major surface of said wiring substrate with a photothermosetting resin film (16); selectively removing said photothermosetting resin film from said connecting portions (14) registering, in position, a plurality of connecting pads (12) formed on a major surface of an integrated circuit chip (23) with said connecting portions (14), the connecting pads (12) having metal bumps (15); and connecting said connecting portions (14) of the wiring substrate (21) and said metal bumps (15) by heating them while applying a predetermined load thereto to adhere remaining surface portions of said photothermosetting resin film to portions of said major surface of said integrated circuit chip which have no connecting pad. A method of connecting a semiconductor chip and a wiring substrate, characterised by comprising the steps of: coating a major surface of a wiring substrate (41) together with a plurality of metal bumps (35) on respective connecting portions (34) formed on said major surface of said wiring substrate with a photothermosetting resin film (36); selectively removing said photothermosetting resin film from said metal bumps; registering, in position, a plurality of connecting pads (32) formed on a major surface of an integrated circuit chip (43) with said metal bumps of said wiring substrate; and connecting said connecting pads and said metal bumps of said wiring substrate by heating them while applying a predetermined load thereto to adhere remaining surface portions of said photothermosetting resin film to portions of said major surface of said integrated circuit chip which have no connecting pad. A method as claimed in claim 1 or claim 2, wherein the metal bumps are of indium or an alloy thereof. A method as claimed in claim 1, 2 or 3 wherein, prior to selective removal of the photothermosetting resin film (16,36), the film is partially hardened to a first hardness, the subsequent heating of the remaining portion of the film hardening said portions to a second hardness greater than said first hardness.

Inventors: MATSUI KOJI, MATSUI, KOJI, MATSUI, KOJI, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1991
Main classification: H01L21
IPC codes: H01L21, H01L23