Patent Publication Number: US-9426897-B2

Title: Electronic component and method for manufacturing electronic component

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electronic component and a method for manufacturing an electronic component, and in particular, relates to a method for manufacturing an electronic component, including a step of grinding electrical elements or boards, and an electronic component manufactured by the manufacturing method. 
     2. Description of the Related Art 
     Japanese Unexamined Patent Application Publication No. 2006-100587 discloses the following method for manufacturing a solid-state imaging device. First, grooves of a predetermined depth are formed in a wafer having a plurality of solid-state imaging elements formed on a front surface thereof, so as to define each solid-state imaging element. Then, as shown in the left-hand portion of  FIG. 3 , the wafer  60  and a board  50  are joined to each other via spacers  70  which enclose the solid-state imaging elements. After the wafer  60  and the board  50  are joined to each other, the wafer  60  is ground on a back side thereof to form the solid-state imaging elements into individual pieces. Then, the board  50  is diced to produce individual solid-state imaging devices. 
     Japanese Unexamined Patent Application Publication No. 2001-332654 discloses the following method for manufacturing a module including an electrical element. First, an electrical element  81  having an electrical element formed on a front surface thereof is flip-chip bonded onto a wiring board  90  via bumps  82  and sealed with a thermosetting resin  100 . Then, the back surface of the electrical element  81  and the thermosetting resin  100  are ground simultaneously to reduce the height. 
     In the solid-state imaging device manufacturing method disclosed in Japanese Unexamined Patent Application Publication No. 2006-100587, during grinding of the wafer  60 , a physical load is applied from a grinding stone to the wafer  60  not only in the vertical direction but also in the horizontal direction. When the grinding of the wafer  60  progresses and the solid-state imaging elements are divided to define individual pieces, a sufficient retaining force is not applied to each solid-state imaging element in the horizontal direction, and thus the electrical elements are likely to be separated from the spacers  70  due to the horizontal load from the grinding stone, as shown in  FIG. 3  (the right-side diagram). 
     In the electrical element-included module manufacturing method disclosed in Japanese Unexamined Patent Application Publication No. 2001-332654, when the electrical element  81  is ground, not only the electrical element  81  but also the thermosetting resin  100  are ground simultaneously. Thus, due to a horizontal physical load during the grinding, the interface between the side surface of the electrical element  81  and the thermosetting resin  100  is likely to be separated to produce a gap (A in  FIG. 4 ). When a gap is produced between the side surface of the electrical element  81  and the thermosetting resin  100 , moisture and the like enter the gap and hence the weather resistance of the electrical element-included module deteriorates. 
     SUMMARY OF THE INVENTION 
     In view of the problems described above, preferred embodiments of the present invention provide a method for manufacturing an electronic component that prevents separation of an electrical element from a member which retains or seals the electrical element, during manufacturing of the electronic component; and an electronic component manufactured by the manufacturing method, which has excellent mechanical strength and weather resistance. 
     According to a preferred embodiment of the present invention, an electronic component includes an electrical element including first and second principal surfaces opposed to each other, side surfaces connecting the principal surfaces, and a functional portion provided on the first principal surface; a board including first and second principal surfaces opposed to each other and side surfaces connecting the principal surfaces, the first principal surface being arranged so as to face the first principal surface of the electrical element; and a resin interposed between the first principal surface of the electrical element and the first principal surface of the board. The second principal surface of either one of the electrical element or the board is a ground surface which has been subjected to grinding, and the resin includes a joining portion which covers a portion of the side surfaces of either one of the electrical element or the board and which is separated from the ground surface. 
     In a preferred embodiment of the present invention, in the electronic component, the resin includes a hollow portion above the functional portion of the electrical element. 
     In another preferred embodiment of the present invention, in the electronic component, the electrical element is a surface acoustic wave element. 
     According to a further preferred embodiment of the present invention, a method for manufacturing an electronic component includes the steps of preparing a plurality of electrical elements; preparing a base including a plurality of boards on which the plurality of electrical elements are to be mounted, respectively; forming a resin layer on the base; pressing the plurality of electrical elements against the resin layer to join portions of side surfaces of the plurality of electrical elements to the resin layer; grinding the plurality of electrical elements to thin the plurality of electrical elements; and dividing the base to form the plurality of boards into individual pieces. 
     According to another preferred embodiment of the present invention, a method for manufacturing an electronic component includes the steps of preparing a first base on which a plurality of electrical elements are formed; forming a resin layer on the first base; preparing a second base including a plurality of projections on a front surface thereof; pressing the plurality of projections against the resin layer to join portions of side surfaces of the plurality of projections to the resin layer; grinding a back surface of the second base to form the plurality of projections into individual pieces to form a plurality of boards; and dividing the first base to form the plurality of electrical elements into individual pieces. 
     In a preferred embodiment of the present invention, the method further includes the step of providing a plurality of recesses in the resin layer after the resin layer is formed. 
     In another preferred embodiment of the present invention, in the method, the resin layer preferably is a photosensitive resin, for example. 
     According to various preferred embodiments of the present invention, during manufacturing of an electronic component, separation of the electrical element from a member which retains or seals the electrical element is reliably prevented. In addition, an electronic component having excellent mechanical strength and reliability can be realized. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1I  are diagrams showing each step of a method for manufacturing an electronic component according to Preferred Embodiment 1 of the present invention. 
         FIGS. 2A to 2H  are diagrams showing each step of a method for manufacturing an electronic component according to Preferred Embodiment 2 of the present invention. 
         FIG. 3  is a diagram (part  1 ) showing a problem of an existing method for manufacturing an electronic component. 
         FIG. 4  is a diagram (part  2 ) showing a problem of an existing method for manufacturing an electronic component. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described. It should be noted that like or corresponding portions are designated by the same reference characters and the description thereof may not be repeated. 
     It should be noted that in the preferred embodiments described below, when a number, an amount, and the like are mentioned, the scope of the present invention is not necessarily limited to the number, the amount, and the like unless otherwise specified. In addition, in the preferred embodiments described below, each component is not necessarily essential for the present invention unless otherwise specified. 
     Preferred Embodiment 1 
       FIGS. 1A-1I  are diagrams showing each step of a method for manufacturing an electronic component according to Preferred Embodiment 1. Each step will be described with reference to  FIGS. 1A-1I . 
     First, as shown in  FIG. 1A , a wafer  11 A (for example, having a thickness of about 250 μm) is prepared in which functional portions, wires, and pad electrodes of a plurality of electrical elements  11  are formed on a front surface thereof by a thin film microfabrication technique. Next, as shown in  FIG. 1B , stud bumps  12  made of gold (Au) are formed on the pad electrodes of the electrical elements  11 . Further, as shown in  FIG. 1C , the wafer  11 A is diced to divide the electrical elements  11  into individual rectangular chips. 
     Meanwhile, as shown in  FIG. 1D , a base  20 A including a plurality of wiring boards  20  on which the electrical elements  11  are to be mounted is prepared. Next, as shown in  FIG. 1E , a photosensitive resin  21  is applied to a front surface of the base  20 A. Then, a plurality of recesses are formed in the resin  21  by a photolithographic technique. Here, the recesses of the resin  21  are opened such that land electrodes corresponding to the pad electrodes of the electrical elements  11  are exposed. In addition, the openings of the recesses are formed so as to be preferably smaller than the electrical elements  11 . 
     As shown in  FIG. 1F , the electrical elements  11  which are made into the individual pieces in the step shown in  FIG. 1C  are flip-chip bonded (FCB) onto the base  20 A. Specifically, the electrical elements  11  are arranged so as to seal the openings of the recesses of the resin  21  and such that the stud bumps  12  formed on the pad electrodes of the electrical elements  11  are located above the land electrodes of the base  20 A. Then, back surfaces of the electrical elements  11  are pressed toward the base  20 A while ultrasonic vibrations are applied thereto by a bonding tool. By so doing, the pad electrodes of the electrical elements  11  are connected to the land electrodes of the base  20 A via the stud bumps  12 . In addition, the resin  21  is not cured at that time, and thus the electrical elements  11  can be dug into the resin  21 . Thus, the resin  21  moves around to the side surfaces of the electrical elements  11 . 
     Next, as shown in  FIG. 1G , the resin  21  which is also thermosetting is heated at a temperature of about 300° C. to about 400° C., for example, to be cured. By so doing, portions of the electrical elements  11  are joined to the resin  21 , whereby the electrical elements  11  are retained by the resin  21 . Moreover, as shown in  FIG. 1H , the back surfaces of the electrical elements  11  are ground such that the electrical elements  11  are thinned to desired thicknesses, for example, about 150 μm. The thicknesses of the electrical elements  11  are preferably smaller, but the grinding is ended before a grinding stone reaches the resin  21 . Thus, the resin  21  is not ground. 
     Finally, as shown in  FIG. 1I , the base  20 A is diced together with the resin  21  to divide the wiring boards  20  into individual pieces, whereby a plurality of electronic components are completed. 
     Each of the electronic components completed thus preferably includes the electrical element  11  including first and second principal surfaces opposed to each other, side surfaces connecting the principal surfaces, and the functional portion provided on the first principal surface; the wiring board  20  including first and second principal surfaces opposed to each other and side surfaces connecting the principal surfaces, the first principal surface being arranged so as to face the first principal surface of the electrical element  11 ; the resin  21  interposed between the first principal surface of the electrical element  11  and the first principal surface of the wiring board  20 . The second principal surface of the electrical element  11  is a ground surface which has been subjected to grinding. The resin  21  includes a joining portion which covers a portion of the side surfaces of the electrical element  11  and which is separated from the ground surface. In addition, the resin  21  includes a hollow portion which seals the functional portion of the electrical element  11 . 
     It should be noted that each electrical element  11  may be a surface acoustic wave element, a piezoelectric thin-film element, a thin-film circuit element, a semiconductor element, or another element. 
     In this preferred embodiment, as the material of the wiring boards  20 , ceramics such as alumina are typically considered, but monocrystals such as Si, LiTaO3, LiNbO3, and crystal and resins such as glass epoxy resins can also be used. It should be noted that in the present invention, bases for the electrical elements are not limited to the above-described wiring boards, and boards which serve as electrical elements may be used, for example. 
     Further, when, for example, a photosensitive resin such as a photosensitive polyimide resin is used as the resin  21 , patterning accuracy of the recesses is improved, whereby the side surfaces of the electrical elements  11  can more assuredly be protected. However, the resin  21  is not limited to the photosensitive resin, and a material other than the photosensitive resin may be used to form recesses therein by etching or other suitable process, for example. 
     It should be noted that an initial thickness (a state of  FIG. 1E ) of the resin  21  is adjusted such that the height of the resin  21  that moves around to the side surfaces of the electrical elements  11  when the electrical elements  11  are flip-chip bonded onto the boards  20  is lower than the sum of the final thickness of the electrical elements  11  after the grinding and the final height of the stud bumps  12  after the FCB. The initial thickness of the resin  21  is adjusted on the basis of conditions of the viscosity of the resin  21 , the number of rotations of spin application, and the like. 
     Similarly, the conditions of the FCB are adjusted such that the final height of the stud bumps  12  is lower than the initial thickness of the resin  21 . The conditions of the FCB mean the volume of each stud bump  12 , a load of the bonding tool, the ultrasonic wave conditions, and the like. 
     According to the electronic components and the manufacturing method thereof according to this preferred embodiment, the side surfaces of the electrical elements  11 , which are ground members, are retained by the resin  21 , and thus separation of the electrical elements  11  due to a horizontal physical load at grinding can be reliably prevented. 
     Further, the resin  21  retains only a region smaller than the thickness of the electrical elements  11  after grinding, and thus is not ground. Therefore, the interfaces between the electrical elements  11  and the resin  21  are not separated due to a physical load at grinding. 
     Moreover, the hollow portion of the resin  21  is closed, and each electronic component has excellent weather resistance. In particular, this preferred embodiment is suitable for electrical elements  11  that are surface acoustic wave elements in which a hollow portion is needed above an interdigital transducer (IDT) which is a functional portion. 
     A summary of the above description is as follows. Specifically, the method for manufacturing an electronic component according to this preferred embodiment includes a step of preparing a plurality of electrical elements  11  ( FIGS. 1A to 1C ), a step of preparing a base  20 A preferably including a plurality of boards  20  on which the plurality of electrical elements  11  are to be mounted, respectively ( FIG. 1D ), a step of forming a resin  21  as a “resin layer” on the base  20 A ( FIG. 1E ), a step of pressing the plurality of electrical elements  11  against the resin  21  to join portions of the side surfaces of the plurality of electrical elements  11  to the resin  21  ( FIGS. 1F and 1G ), a step of grinding the plurality of electrical elements  11  to thin the plurality of electrical elements  11  ( FIG. 1H ), and a step of dividing the base  20 A to form the plurality of boards  20  into individual pieces ( FIG. 1I ). 
     Preferred Embodiment 2 
       FIGS. 2A to 2H  are diagrams showing each step of a method for manufacturing an electronic component according to Preferred Embodiment 2. Each step will be described with reference to  FIGS. 2A to 2H . 
     First, as shown in  FIG. 2A , a wafer  31 A is prepared in which functional portions, wires, and electrode patterns  32  of a plurality of electrical elements  31 , which electrode patterns  32  are to be pad electrodes, are formed on a front surface thereof by a thin film microfabrication technique. Next, a film type photosensitive resin is adhered to the front surface of the wafer  31 A, and a plurality of recesses are formed in the resin  33  by a photolithographic technique such that the functional portions of the electrical elements  31  are exposed as shown in  FIG. 2B . At the same time, a plurality of grooves are formed in a matrix so as to define the recesses and such that, at least portions of the pad electrodes of the electrical elements  31  are exposed. Since the film type is used as the resin  33  as described above, the thickness of the resin  33  can precisely be controlled. As a film type resin, it is considered to use, for example, polyimide resins, epoxy resins, and the like. 
     Meanwhile, as shown in  FIG. 2C , a cap wafer  40  (for example, having a thickness of about 350 μm) which is to be finally a cap of a package is prepared. Next, as shown in  FIG. 2D , a front surface of the cap wafer  40  is half-cut by dicing to form a plurality of grooves in a matrix. As a result, a plurality of substantially rectangular projections  40 A are formed on the front surface of the cap wafer  40  and defined by the grooves  40 B. Here, the projections  40 A are formed so as to preferably be larger than the openings of the recesses of the resin  33 . It should be noted that the depth of half-cutting preferably is about 125 μm, for example. 
     As shown  FIG. 2E , the wafer  31 A and the cap wafer  40  are stacked to each other at wafer level such that the projections  40 A seal the openings of the recesses of the resin  33 , and are joined to each other via the resin  33  by thermal pressure bonding. At that time, by a load of the pressure bonding, the resin  33  is caused to enter portions of the grooves  40 B of the cap wafer  40 . In other words, the front surface side peripheral portions and side surfaces of the projections  40 A are joined to the resin  33 . 
     Next, as shown in  FIG. 2F , the cap wafer  40  is ground to a thickness of about 100 μm, for example, to form the projections  40 A into individual pieces. By so doing, the projections  40 A become cap boards  40 C which seal the recesses of the resin  33 . 
     Further, as shown in  FIG. 2G , the cap boards  40 C, the resin  33 , and the wafer  31 A are coated with a metal film by a film formation method such as sputtering or plating. Then, a photoresist is applied onto the metal film and is pattern-formed by a photolithographic technique, and then external terminals  50  are formed by an etching technique. Here, the external terminals  50  are connected to at least portions of the pad electrodes which are exposed from the grooves of the resin  33 . 
     Finally, as shown in  FIG. 2H , dicing is performed along the grooves of the resin  33  to divide the wafer  31 A into pieces, whereby a plurality of electronic components are completed. 
     Each of the electronic components thus completed includes the electrical element  31  including first and second principal surfaces opposed to each other, side surfaces connecting the principal surfaces, and the functional portion provided on the first principal surface; the cap board  40 C including first and second principal surfaces opposed to each other and side surfaces connecting the principal surfaces, the first principal surface being arranged so as to face the first principal surface of the electrical element  31 ; and the resin  33  interposed between the first principal surface of the electrical element  31  and the first principal surface of the cap board  40 C. The second principal surface of the cap board  40 C is a ground surface which has been subjected to grinding. The resin  33  includes a joining portion which covers a portion of the side surfaces of the cap board  40 C and which is separated from the ground surface. In addition, the resin  33  includes a hollow portion which seals the functional portion of the electrical element  31 . 
     According to the electronic components and the manufacturing method thereof according to this preferred embodiment, the side surfaces of the projections  40 A of the wafer  40 , which is a ground member, are retained by the resin  33 , and thus separation of the cap boards  40 C (the projections  40 A that are formed into the individual pieces) due to a horizontal physical load at grinding can be prevented. 
     Further, the resin  33  retains only a region smaller than the thickness of the cap boards  40 C, and thus is not ground. Therefore, the interfaces between the cap boards  40 C and the resin  33  are not separated due to a physical load at grinding. 
     To summarize the above contents, the method for manufacturing an electronic component according to this preferred embodiment includes a step of preparing a wafer  31 A as a “first base” in which a plurality of electrical elements  31  are formed ( FIG. 2A ); a step of forming a resin  33  as a “resin layer” on the wafer  31 A ( FIG. 2B ); a step of preparing the wafer  40  as a “second base” including a plurality of projections  40 A on a front surface thereof ( FIGS. 2C and 2D ); a step of pressing the plurality of projections  40 A against the resin  33  to join portions of the side surfaces of the plurality of projections  40 A to the resin  33  ( FIG. 2E ); a step of grinding a back surface of the wafer  40  to form the plurality of projections  40 A into individual pieces to form a plurality of cap boards  40 C ( FIG. 2F ); and a step of dividing the wafer  31 A to form the plurality of electrical elements  31  into individual pieces ( FIG. 2H ). 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the invention. The scope of the present invention, therefore, is to be determined solely by the following claims.