Patent Publication Number: US-2021193612-A1

Title: Method for manufacturing mounting structure for electronic component, mounting structure for electronic component, electronic module, and wiring sheet

Description:
TECHNICAL FIELD 
     The present invention relates to an electronic component mounting technique for mounting an electronic component on a wiring board. 
     BACKGROUND ART 
     A method using an adhesive is known as an example of a method for mounting an electronic component on a wiring board without using heat (for example, soldering). Patent Literature 1 discloses a mounting structure in which an adhesive is used. 
       FIGS. 1A, 1B, and 1C  illustrate the mounting structure disclosed in Patent Literature 1. In this example, a microphone  20  as an electronic component is mounted on a wiring board (referred to as a wiring-attached base material in Patent Literature 1)  10 . The microphone  20  is a micro electro mechanical system (MEMS) microphone manufactured by using a MEMS technique. 
     The wiring board  10  has a structure in which an insulating adhesive layer  12  is formed on one surface  11   a  of a film  11  and further four conductor patterns  13  are formed on the adhesive layer  12 . The adhesive layer  12  is formed on the entire surface of the one surface  11   a  of the film  11 . Lands  13   a  are respectively formed at one ends of four conductor patterns  13  and lands  13   b  are respectively formed at the other ends of the same. 
     The microphone  20  is mounted on the adhesive layer  12  by pressing the microphone  20  onto the adhesive layer  12 . In this state, terminals  21  of the microphone  20  are in contact with the lands  13   a  of the conductor patterns  13  respectively. Part of a bottom surface  20   a  of the microphone  20 , on which the terminals  21  are not formed, adheres to the adhesive layer  12 . Accordingly, the microphone  20  and the adhesive layer  12  are mechanically coupled with each other. Elastic restoring force of the adhesive layer  12  acts as a load in a direction pressing the terminals  21  and the lands  13   a  against each other, being able to provide a favorable and continuous electrical-connection state between the terminals  21  and the lands  13   a.    
     The surface of the wiring board  10  on which the conductor patterns  13  are formed is covered by a cover film  30  other than part on which the microphone  20  is positioned and part on which four lands  13   b  are positioned. In other words, a window  31  and a cutout  32  are formed on the cover film  30 . 
     PRIOR ART LITERATURE 
     Patent Literature 
     Patent Literature 1: Japanese Registered Patent No. 6293938 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     Patent Literature 1 discloses that the conductor patterns are formed by printing. However, forming a conductor pattern on an adhesive layer is not always easy and forming a wiring board accordingly requires a lot of labor and costs. When many conductor patterns need to be formed on an adhesive layer, this problem becomes more remarkable. 
     An object of the present invention is to provide an electronic component mounting technique by which increase in a cost for a wiring board can be avoided even in using an adhesive. 
     Means to Solve the Problems 
     The following technical matters are described simply to facilitate the understanding of the main points of the present invention, not to limit the invention claimed in the claims explicitly or implicitly and not to express the possibility of accepting such a limitation that is imposed by a person other than those who will benefit from the present invention (for example, the applicant and the right holder). 
     According to the present invention, a wiring sheet including an adhesive layer interposes between the electronic component and the wiring board and the electronic component is indirectly mounted on the wiring board. The electronic component is directly mounted on the adhesive layer of the wiring sheet and the adhesive layer of the wiring sheet is directly fitted to the wiring board. Conduction between the electronic component and the wiring board is attained in stages by conduction between the electronic component and the wiring sheet and conduction between the wiring sheet and the wiring board. 
     Effects of the Invention 
     According to the present invention, since an electronic component is locally mounted on a wiring board by using a wiring sheet on which an adhesive layer is formed, increase in a cost for the wiring board can be avoided even in using an adhesive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a plan view of a mounting structure of a related art. 
         FIG. 1B  is a front elevational view of the mounting structure of a related art. 
         FIG. 1C  is a partially enlarged sectional view of the mounting structure of a related art. 
         FIG. 2A  is a plan view of a mounting structure of a first embodiment. 
         FIG. 2B  is a sectional view of the mounting structure of the first embodiment. 
         FIG. 3A  is a front elevational view of an electronic component. 
         FIG. 3B  is a bottom view of the electronic component. 
         FIG. 4A  is a plan view of a wiring sheet. 
         FIG. 4B  is a sectional view of the wiring sheet. 
         FIG. 5A  is a plan view of an electronic module. 
         FIG. 5B  is a sectional view of the electronic module. 
         FIG. 6  is a plan view of a mounting structure of a second embodiment (partially a transparent view). 
         FIG. 7A  is a front elevational view of an electronic component. 
         FIG. 7B  is a bottom view of the electronic component. 
         FIG. 8A  is a plan view of a wiring sheet. 
         FIG. 8B  is a front elevational view of the wiring sheet. 
         FIG. 9  is a plan view of an electronic module (partially a transparent view). 
         FIG. 10  is a plan view of a wiring board. 
         FIG. 11  is a sectional view of a mounting structure of a third embodiment. 
         FIG. 12  illustrates a processing flow of a manufacturing method. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present invention will be described with reference to the accompanying drawings. 
     First Embodiment 
       FIGS. 2A and 2B  illustrate a first embodiment of a mounting structure for electronic component. In this embodiment, an electronic module  50  is first manufactured and the electronic module  50  is then mounted on a wiring board  40  with an adhesive. 
     The electronic module  50  includes a wiring sheet  60  and an electronic component  70  which is mounted on the wiring sheet  60 . The electronic component  70  has a rectangular parallelepiped shape in this example and includes four terminals  71  provided on a bottom surface  70   a  of the electronic component  70  (see  FIGS. 3A and 3B ). 
     The wiring sheet  60  has a structure in which an insulating adhesive layer  62 , which is elastically deformable, is formed on one surface  61   a  of a base  61  and further a conductor pattern  63  is formed on the adhesive layer  62  (see  FIGS. 4A and 4B ). The adhesive layer  62  is formed on the entire surface of the one surface  61   a  of the base  61 . 
     The conductor pattern  63  includes four conductive wires  63   a  in the present embodiment. Two conductive wires  63   a  are arranged on the right half of the wiring sheet  60  having the rectangular parallelepiped shape and the rest two conductive wires  63   a  are arranged on the left half of the same. Inside ends of the four conductive wires  63   a  are parts which directly come into contact with the four terminals  71  of the electronic component  70  respectively. The four conductive wires  63   a  extend in a direction parallel to the long side of the wiring sheet  60 . An outside end of each of the conductive wires  63   a  extends toward the short side of the wiring sheet  60  and is away from the short side by a predetermined distance. 
     In the wiring sheet  60 , the base  61  is a film base member having flexibility. Examples of a material of the film base member include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyimide (PI). 
     Examples of an adhesive for the adhesive layer  62  include polyester based-, polyurethane based-, acrylic based-, epoxy based-, phenolic based-, silicone based-, polyolefin based-, polyimide based-, vinyl based-, and natural polymer based-polymers. Polymer may be composed of one kind of monomer or may be composed of two kinds of monomers. 
     Further, in order to improve an adherence property or a mechanical property, polyester based-, polyurethane based-, acrylic based-, epoxy based-, phenolic based-, silicone based-, polyolefin based-, polyimide based-, and vinyl based-monomers or oligomers, for example, may be mixed with the polymers. 
     The conductor pattern  63  is formed by printing with silver paste (silver ink), for example. Plating may also be employed for forming the conductor pattern  63 . 
       FIGS. 5A and 5B  illustrate the electronic module  50 . The electronic component  70  is pressed onto the adhesive layer  62 , being directly mounted on the wiring sheet  60  (step S 1 ). The four terminals  71  are directly in contact with inside ends of the four conductive wires  63   a , respectively. 
     The terminals  71  of the electronic component  70  directly come into contact with the conductor pattern  63 , being electrically connected with the conductor pattern  63 . Part of the bottom surface  70   a  of the electronic component  70 , on which the terminals  71  are not formed, adheres to the adhesive layer  62 , being mechanically coupled with the adhesive layer  62  (see  FIG. 5B ). That is, the mechanical coupling between the adhesive layer  62  and the electronic component  70  is realized by sticking a part of the surface of the electronic component  70  to a part of the surface of the adhesive layer  62 . 
     Elastic restoring force of the adhesive layer  62  acts as a load in a direction pressing the terminals  71  of the electronic component  70  and the conductor pattern  63  against each other, so that the terminals  71  are reliably and electrically connected with the conductor pattern  63 . 
     In the present embodiment, an electronic component mounting structure in which the electronic component  70  is mounted on the wiring board  40  is manufactured by mounting the electronic module  50  on the wiring board  40 . 
     The wiring board  40  is a common wiring board obtained by forming a conductor pattern on a base  41 . The wiring board  40  is a flexible printed wiring board and a material of the base  41  is a film base material in the present embodiment.  FIGS. 2A and 2B  illustrate only a part of the wiring board  40  on which the electronic component  70  is mounted and omit illustration of an entire shape and a detailed structure of the wiring board  40 . A conductor pattern  42  including four conductive wires  42   a  is formed on part of the wiring board  40  on which the electronic component  70  is mounted. The four conductive wires  42   a  directly come into contact with the four conductive wires  63   a  of the electronic module  50  respectively. 
     Mounting of the electronic module  50  onto the wiring board  40  is performed as follows. 
     A mounting structure is manufactured by directly mounting the electronic module onto the wiring board (step S 2 ). The electronic component  70  of the electronic module  50  is opposed to the surface of the wiring board  40  on which the conductor pattern  42  is formed. The four conductive wires  63   a  of the conductor pattern  63  are set to respectively face the four conductive wires  42   a  of the conductor pattern  42  of the wiring board  40 . The electronic module  50  is pressed against the wiring board  40  by pressing the whole of the electronic module  50 . Part of the wiring sheet  60 , which is positioned around the electronic component  70 , deforms and outside ends of the four conductive wires  63   a  of the conductor pattern  63  directly come into contact with the conductive wires  42   a  of the conductor pattern  42  of the wiring board  40  respectively. Consequently, the wiring sheet  60  is electrically connected with the wiring board  40 . An upper surface  70   b  of the electronic component  70  is directly in contact with the base  41  of the wiring board  40 . 
     The adhesive layer  62  which is brought into direct contact with a board surface of the wiring board  40  by the deformation of the wiring sheet  60  adheres to the wiring board  40  and accordingly, the adhesive layer  62  and the wiring board  40  are mechanically coupled with each other. That is, the mechanical coupling between the adhesive layer  62  and the wiring board  40  is realized by sticking a part of the adhesive layer  62  (specifically, at least part of a surface on which the conductor pattern  63  is not formed and the electronic component  70  is not bonded) to a part of at least one of a surface of the conductor pattern  42  and a surface of the base  41 , on which the conductor pattern  42  is not formed, on the wiring board  40 . The mechanical coupling part between the adhesive layer  62  and the wiring board  40  surrounds the periphery of the electronic component  70 . 
     The elastic restoring force of the adhesive layer  62  acts as a load in a direction pressing the conductor pattern  63  and the conductor pattern  42  of the wiring board  40  against each other, so that the conductor pattern  63  is reliably and electrically connected with the conductor pattern  42 . 
     The first embodiment of the electronic component mounting structure has been described with the method for manufacturing the mounting structure thus far. According to the first embodiment, the following advantageous effects are obtained. 
     (1) Since an adhesive is used, an electronic component can be easily mounted on a wiring board. In the present embodiment, the electronic module  50  is first manufactured by mounting the electronic component  70  on the adhesive layer  62  of the wiring sheet  60  and the adhesive layer  62  of the electronic module  50  is then locally fitted to a fitting part of the wiring board  40 . Thus, there is no need for forming an adhesive layer on the entire surface of a wiring board and, that is, a common wiring board having no adhesive layer can be employed. Accordingly, cost increase for a wiring board can be avoided. 
     (2) An electronic module including an electronic component can be manufactured as a module common to various types of wiring board or as a general-purpose module. Accordingly, improvement of production efficiency can be expected. 
     (3) The mounting structure according to the present embodiment is sandwiched between the wiring board and the wiring sheet which adhere to each other. Especially, employing the structure in which the electronic component is covered by the wiring board and the wiring sheet, more specifically, the structure in which the electronic component is placed in the inside of a closed space, which is formed by a closed loop-shaped adhering portion, between the adhesive layer and the wiring board, the electronic component is not exposed to the outside. That is, waterproofness of the electronic component is ensured. 
     (4) According to the prior art mounting structure (see  FIGS. 1A to 1C ), an adhering area between the electronic component  20  and the adhesive layer  12  is small. If the wiring board  10  is bent so that a surface on which the electronic component is mounted faces outside, there is a possibility occurring a failure in which the terminals  21  of the electronic component  20  separate from the conductor patterns  13  or a failure in which the electronic component  20  drops off. However, the electronic component  70  is sandwiched between the wiring sheet  60  and the wiring board  40  and the adhering area between the adhesive layer  62  of the wiring sheet  60  and the wiring board  40  is largely increased in the present embodiment, being able to prevent occurrence of such failures. Thus, a mounting structure being tolerant to bending and exhibiting high reliability is realized. 
     Second Embodiment 
     A conductor pattern of a wiring sheet serves to relay a terminal of an electronic component and a conductor pattern of a wiring board to each other. In the first embodiment, two conductive wires  63   a  of the conductor pattern  63  extend in parallel at a constant arrangement space on the right side of the electronic component  70  and the rest two conductive wires  63   a  of the conductor pattern  63  extend in parallel at a constant arrangement space on the left side of the electronic component  70  (see  FIG. 4A ). On the other hand, in a second embodiment, a conductor pattern of a wiring sheet includes two or more conductive wires, a space between adjacent two conductive wires of which changing along an extending direction of the adjacent two conductive wires.  FIG. 6  illustrates a mounting structure for electronic component according to the second embodiment. Each drawing illustrates only part of a wiring board  110  on which an electronic component  80  is mounted. 
     The electronic component  80  is a microcomputer chip which can be mounted on a surface of a substrate or the like. On each of four sides of a square bottom surface  80   a  of the electronic component  80 , twelve terminals  81  are arranged (see  FIGS. 7A and 7B ). 
     As is the case with the wiring sheet  60 , an adhesive layer  92  is formed on the whole of one surface  91   a  of a base  91  of a wiring sheet  90  (see  FIG. 8B ). A conductor pattern  93  is formed on the adhesive layer  92 . The conductor pattern  93  is much thinner than the base  91  and the adhesive layer  92 , so that  FIG. 8B  omits illustration of the conductor pattern  93 . The conductor pattern  93  includes forty-eight conductive wires  93   a . From each of four sides of the square wiring sheet  90 , twelve conductive wires  93   a  extend toward the center of the wiring sheet  90 . Inside ends of the forty-eight conductive wires  93   a  directly come into contact with the forty-eight terminals  81  of the electronic component  80  respectively. Outside ends of the forty-eight conductive wires  93   a  are away from edges of the wiring sheet  90  by a predetermined distance. Constituent materials of the base  91  and the adhesive layer  92  are respectively the same as those of the base  61  and the adhesive layer  62  of the first embodiment. 
     Regarding the forty-eight conductive wires  93   a , a space between two adjacent conductive wires  93   a  changes along the extending direction of the two adjacent conductive wires  93   a  (see  FIG. 8A ). Regarding twelve conductive wires  93   a  extending from an upper side of the wiring sheet  90 , a space between inside ends of two adjacent conductive wires  93   a  is narrower than a space between outside ends of the same. Similarly, regarding twelve conductive wires  93   a  extending from a lower side of the wiring sheet  90 , a space between inside ends of two adjacent conductive wires  93   a  is narrower than a space between outside ends of the same. Regarding twelve conductive wires  93   a  extending from a right side of the wiring sheet  90 , a space between inside ends of two adjacent conductive wires  93   a  is wider than a space between outside ends of the same. Similarly, regarding twelve conductive wires  93   a  extending from a left side of the wiring sheet  90 , a space between inside ends of two adjacent conductive wires  93   a  is wider than a space between outside ends of the same. 
     An electronic module  100  illustrated in  FIG. 9  is manufactured by mounting the electronic component  80  on the wiring sheet  90 . 
     The wiring board  110  is a flexible printed wiring board as is the case with the wiring board  40  according to the first embodiment. A predetermined conductor pattern  112  is formed on a base  111 . The conductor pattern  112  includes forty-eight conductive wires  112   a . The forty-eight conductive wires  112   a  of the conductor pattern  112  directly come into contact with the forty-eight conductive wires  93   a  of the conductor pattern  93  respectively. 
     By mounting the electronic module  100  on the wiring board  110 , an electronic component mounting structure in which the electronic component  80  is mounted on the wiring board  110  is manufactured. Mechanical coupling between the adhesive layer  92  and the electronic component  80  and mechanical coupling between the adhesive layer  92  and the wiring board  110  are the same as those of the first embodiment. 
     Third Embodiment 
     The wiring board  40  and the wiring board  110  are flexible printed wiring boards and a material of the base  41  and the base  111  is a film base material having flexibility in the first and second embodiments. However, the material of the base  41  and the base  111  may be a rigid base material having no flexibility. 
     As long as conditions such as the thickness of an adhesive layer are sufficiently satisfied and mechanical coupling by adherence is attained, one or both of the base of the wiring board and the base of the wiring sheet may be made of a rigid base material. 
       FIG. 11  illustrates a mounting structure for an electronic component  150  in which a base  121  of a wiring board  120  and a base  141  of a wiring sheet  140  of an electronic module  130  are made of a rigid base material, as a third embodiment. 
     Even when the base  121  and the base  141  are rigid, the mounting structure for electronic component illustrated in  FIG. 11  can be realized by forming an adhesive layer  142  thicker than an electronic component  150 , which is sufficiently-small and thin chip resistor, for example. In  FIG. 11 , the reference character  143  denotes a conductor pattern of the wiring sheet  140 , the reference character  122  denotes a conductor pattern of the wiring board  120 , and the reference character  151  denotes a terminal of the electronic component  150 . 
     Fourth Embodiment 
     Not illustrated in drawings, in the electronic component  150  provided with the terminal  151  which extends from a bottom surface facing the base  141  to a surface facing the wiring board  120 , the conductor pattern  122  of the wiring board  120  may be not only brought into direct contact with the conductor pattern  143  but also brought into direct contact with a part of the terminal  151  which faces the wiring board  120 . That is, for the mounting of an electronic component provided with a terminal which extends to both of front and back surfaces of the electronic component, a mounting structure may be employed in which the terminal of the electronic component is sandwiched between a conductor pattern of a wiring board and a conductor pattern of a wiring sheet. It goes without saying that such mounting structure can be employed irrespective of whether or not a material of a base of the wiring board or a material of a base of a wiring sheet has flexibility. 
     In the specification and the claims, an ordinal numeral (“the -st/-nd/-rd/-th”, for example, obtained by combining a prefix “the” and a Chinese character figure or an Arabic figure) is not intended to limit an element modified by or coupled to the ordinal numeral by an ordinal position or the amount of the element regardless of a definition of the ordinal numeral, unless otherwise noted. An ordinal numeral is merely used as a convenient expression method to distinguish two or more elements from one another, unless otherwise noted. Thus, for example, the phrase “the first X” and the phrase “the second X” are expressions to distinguish between the two Xs, do not necessarily mean that the total number of Xs is 2, and do not necessarily means that the first X has to come before the second X. 
     In the specification and the claims, the term “include” and inflected forms thereof are used as non-exclusive expressions. For example, the sentence “X includes A and B” does not deny that X includes a component other than A and B (for example, C). If a certain sentence in the specification and the claims includes a phrase in which the term “include” or an inflected form thereof is coupled to a negative word, the sentence only mentions an object thereof. Thus, for example, the sentence “X does not include A and B” admits a possibility that X includes a component other than A and B. Additionally, the term “or” used in the specification and the claims is intended not to mean an exclusive OR. 
     When an article or a part of speech related to an article such as “a”, “an”, and “the” in English are added through translation in the present disclosure, nouns following the part of speech may include the plural form thereof in the present disclosure. 
     The embodiments according to the present invention have been described above, but the present invention is not limited to these embodiments. Various alterations and modifications may be made within a scope of the gist of the present invention. The embodiments that are selected and described are provided for explaining the principle and practical applications of the present invention. The present invention is applied in various embodiments obtained through various alterations or modifications and the various alterations or modifications are determined depending on expected applications. All of such alterations or modifications are intended to be included in the scope of the present invention defined by the accompanied claims, and all of such alterations or modifications are intended to be granted the same protection when they are interpreted in accordance with the scope given fairly, legally, and justly.