Patent Publication Number: US-2022234126-A1

Title: Method of manufacturing mounting substrate and method of manufacturing electronic apparatus

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/270,762, filed May 6, 2014, which claims priority to Japanese Priority Patent Application JP 2013-104225 filed in the Japan Patent Office on May 16, 2013, the disclosures of each of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present application relates to a method of manufacturing a mounting substrate that mounts a device on a substrate by the use of a transfer technique, and a method of manufacturing an electronic apparatus that includes such a mounting substrate. 
     One of technologies for mounting a lightweight and thin or fine device is a transfer technique. In a case where a device is transferred on a substrate utilizing such a transfer technique, when an electrical connection is made between the transferred device and wiring, it is necessary to form a wiring layer after the device is transferred. In this case, for example, the wiring layer may be formed in such a manner that a device is beforehand reduced in thickness to reduce unevenness of a surface that may be caused by a thickness of the device, or the wiring layer may be formed in such a manner that a vacant space between the devices is beforehand buried to flatten a surface on which the wiring layer is formed (see Japanese Unexamined Patent Application Publication Nos. H10-090688, 2004-219964, and 2006-156455). 
     SUMMARY 
     When the transfer technique is used, as described above, it is necessary to form a wiring layer after a device is transferred. As a result, this has posed an issue of involving a lot of processes after a transfer process is completed. 
     It is desirable to provide a method of manufacturing a mounting substrate and a method of manufacturing an electronic apparatus that allow processes in case of use of the transfer technique to be simplified. 
     According to an embodiment of the present application, there is provided a method of manufacturing a mounting substrate that includes following two procedures. 
     (A1) Transferring part or all of a plurality of devices on a device substrate onto a wiring substrate, and temporarily fixing the transferred devices to the wiring substrate with use of a fixing layer having viscosity, the device substrate including a support substrate and the plurality of devices fixed on the support substrate 
     (A2) Performing a reflow process on the wiring substrate to electrically connect the transferred devices with the wiring substrate, and thereby forming the mounting substrate 
     According to an embodiment of the present application, there is provided a method of manufacturing an electronic apparatus that is a method of manufacturing an electronic apparatus provided with a mounting substrate, and that includes following three procedures. 
     (B1) Transferring part or all of a plurality of devices on a device substrate onto a wiring substrate, and temporarily fixing the transferred devices to the wiring substrate with use of a fixing layer having viscosity, the device substrate including a support substrate and the plurality of devices fixed on the support substrate 
     (B2) Performing a reflow process on the wiring substrate to electrically connect the transferred devices with the wiring substrate, and thereby forming the mounting substrate 
     (B3) Electrically connecting the mounting substrate with a control section, and thereby forming an electronic apparatus 
     In the method of manufacturing a mounting substrate and the method of manufacturing an electronic apparatus according to the above-described respective embodiments of the present application, an electrical connection between the transferred device and the wiring substrate is made by performing the reflow process on the wiring substrate in a state where the transferred device is temporarily fixed to the wiring substrate with the use of the fixing layer having viscosity. This makes it possible to omit a step of burying a vacant space between the devices to flatten a surface on which the wiring layer is formed, or a step of forming the wiring layer to make the electrical connection between the device and the wiring. 
     According to the method of manufacturing a mounting substrate and the method of manufacturing an electronic apparatus of the above-described respective embodiments of the present application, an electrical connection between the transferred device and the wiring substrate is made by performing the reflow process on the wiring substrate in a state where the transferred device is temporarily fixed to the wiring substrate with the use of the fixing layer having viscosity. Therefore, it is possible to simplify processes in case of using the transfer technique. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the technology as claimed. 
     Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the specification, serve to explain the principles of the present application. 
         FIG. 1  is a cross-sectional view showing an example of a configuration of a mounting substrate according to a first embodiment of the present application. 
         FIG. 2  is a top view showing an example of a configuration of the mounting substrate illustrated in  FIG. 1 . 
         FIG. 3  is a flowchart showing an example of a manufacturing process of the mounting substrate illustrated in  FIG. 1 . 
         FIG. 4  is a cross-sectional view showing an example of a configuration of a device substrate. 
         FIG. 5  is a cross-sectional view showing an example of a configuration of a wiring substrate. 
         FIG. 6  is a cross-sectional view showing a process following on the process shown in  FIG. 5 . 
         FIG. 7  is a cross-sectional view showing a process following on the process shown in  FIG. 6 . 
         FIG. 8  is a cross-sectional view showing a process following on the process shown in  FIG. 7 . 
         FIG. 9  is a cross-sectional view showing a process following on the process shown in  FIG. 8 . 
         FIG. 10  is a cross-sectional view showing a process following on the process shown in  FIG. 9 . 
         FIG. 11  is a flowchart showing another example of the manufacturing process of the mounting substrate illustrated in  FIG. 1 . 
         FIG. 12  is a cross-sectional view showing a process following on the process shown in  FIG. 4 . 
         FIG. 13  is a cross-sectional view showing a process following on the process shown in  FIG. 12 . 
         FIG. 14  is a cross-sectional view showing a process following on the process shown in  FIG. 13 . 
         FIG. 15  is a cross-sectional view showing a process following on the process shown in  FIG. 14 . 
         FIG. 16  is a cross-sectional view showing a process following on the process shown in  FIG. 15 . 
         FIG. 17A  is a cross-sectional view showing a modification example of the device illustrated in  FIG. 1 . 
         FIG. 17B  is a cross-sectional view showing a modification example of the device illustrated in  FIG. 1 . 
         FIG. 17C  is a cross-sectional view showing a modification example of the device illustrated in  FIG. 1 . 
         FIG. 18A  is a cross-sectional view showing a modification example of the wiring substrate illustrated in  FIG. 1 . 
         FIG. 18B  is a cross-sectional view showing a modification example of the wiring substrate illustrated in  FIG. 1 . 
         FIG. 18C  is a cross-sectional view showing a modification example of the wiring substrate illustrated in  FIG. 1 . 
         FIG. 19  is a cross-sectional view showing an example of a configuration of a mounting substrate according to a second embodiment of the present application. 
         FIG. 20  is a top view showing an example of a configuration of the mounting substrate illustrated in  FIG. 19 . 
         FIG. 21  is a flowchart showing an example of a manufacturing process of the mounting substrate illustrated in  FIG. 19 . 
         FIG. 22  is a cross-sectional view showing an example of a configuration of a device substrate. 
         FIG. 23  is a cross-sectional view showing an example of a configuration of a wiring substrate. 
         FIG. 24  is a cross-sectional view showing a process following on the process shown in  FIG. 23 . 
         FIG. 25  is a cross-sectional view showing a process following on the process shown in  FIG. 24 . 
         FIG. 26  is a cross-sectional view showing a process following on the process shown in  FIG. 25 . 
         FIG. 27  is a cross-sectional view showing a process following on the process shown in  FIG. 26 . 
         FIG. 28  is a cross-sectional view showing a process following on the process shown in  FIG. 27 . 
         FIG. 29  is a flowchart showing another example of the manufacturing process of the mounting substrate illustrated in  FIG. 19 . 
         FIG. 30  is a cross-sectional view showing a process following on the process shown in  FIG. 24 . 
         FIG. 31  is a cross-sectional view showing a process following on the process shown in  FIG. 30 . 
         FIG. 32  is a cross-sectional view showing a process following on the process shown in  FIG. 31 . 
         FIG. 33  is a cross-sectional view showing a process following on the process shown in  FIG. 32 . 
         FIG. 34  is a cross-sectional view showing a process following on the process shown in  FIG. 33 . 
         FIG. 35A  is a cross-sectional view showing a modification example of the device illustrated in  FIG. 19 . 
         FIG. 35B  is a cross-sectional view showing a modification example of the device illustrated in  FIG. 19 . 
         FIG. 35C  is a cross-sectional view showing a modification example of the device illustrated in  FIG. 19 . 
         FIG. 36A  is a cross-sectional view showing a modification example of the wiring substrate illustrated in  FIG. 19 . 
         FIG. 36B  is a cross-sectional view showing a modification example of the wiring substrate illustrated in  FIG. 19 . 
         FIG. 36C  is a cross-sectional view showing a modification example of the wiring substrate illustrated in  FIG. 19 . 
         FIG. 37  is a cross-sectional view showing an example of a configuration of a mounting substrate according to a third embodiment of the present application. 
         FIG. 38  is a flowchart showing an example of a manufacturing process of the mounting substrate illustrated in  FIG. 37 . 
         FIG. 39  is a cross-sectional view showing an example of a configuration of a device substrate. 
         FIG. 40  is a cross-sectional view showing an example of a configuration of a wiring substrate. 
         FIG. 41  is a cross-sectional view showing a process following on the process shown in  FIG. 40 . 
         FIG. 42  is a cross-sectional view showing a process following on the process shown in  FIG. 41 . 
         FIG. 43  is a cross-sectional view showing a process following on the process shown in  FIG. 42 . 
         FIG. 44  is a schematic diagram showing an example of a configuration of an electronic apparatus according to a fourth embodiment of the present application. 
         FIG. 45  is a cross-sectional view showing an example of a chip-shaped material. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, some embodiments of the present application are described in details with reference to the drawings. It is to be noted that the descriptions are provided in the order given below. 
     1. First Embodiment (Mounting Substrate) 
     An example where a device includes a bump, and a fixing layer is provided on a wiring substrate side 
     2. Modification Example of First Embodiment (Mounting Substrate) 
     An example where a device includes a bump, and a fixing layer is provided on a device substrate side 
     A variation of an electrical connection part 3. Second Embodiment (Mounting Substrate) 
     An example where a wiring substrate includes a bump, and a fixing layer is provided on a device substrate side 
     4. Modification Example of Second Embodiment (Mounting Substrate) 
     An example where a wiring substrate includes a bump, and a fixing layer is provided on a wiring substrate side 
     A variation of an electrical connection part 
     5. Third Embodiment (Mounting Substrate) 
     An example where a device and a support substrate include no bump, and a fixing layer is provided on a support substrate side 
     6. Fourth Embodiment (Electronic Apparatus) 
     1. First Embodiment 
     [Configuration] 
     First, description is provided on a mounting substrate  1  according to a first embodiment of the present application.  FIG. 1  shows an example of a cross-sectional configuration of the mounting substrate  1 .  FIG. 2  shows an example of a top surface configuration of the mounting substrate  1 .  FIG. 1  corresponds to a cross-sectional configuration in the direction shown with an arrow A-A in  FIG. 2 . The mounting substrate  1  is a substrate where a plurality of devices  20  are mounted on a wiring substrate  10 . The wiring substrate  10  and each of the devices  20  are electrically connected with each other. 
     The wiring substrate  10  may include, for example, a support substrate  11 , an insulating layer  12 , and a metallic layer  13 . Also, the wiring substrate  10  may include, for example, a plurality of wires that are electrically connected with one or more metallic layers  13  in the insulating layer  12 . The support substrate  11  supports the plurality of devices  20 , and may be configured of, for example, a silicon substrate, a glass substrate, a resin substrate, and/or the like. The insulating layer  12  is a layer for insulating the plurality of above-described wires from one another, and serves as an interlayer insulating film. The insulating layer  12  may be configured of, for example, an insulating inorganic material such as SiO 2 . The top surface of the insulating layer  12  has a role as a mounting surface on which each of the devices  20  is mounted. A wiring layer is formed of the insulating layer  12  and the plurality of above-described wires. 
     The metallic layer  13  electrically connects the device  20  with the above-described wires, and is electrically connected with the above-described wires in the insulating layer  12 . The metallic layer  13  may be configured to include, for example, UBM (Under Bump Metal) that serves as a foundation for a solder bump. The UBM may be configured of a material such as Ni, and serves as a solder diffusion suppression layer. In the metallic layer  13 , for example, the side surface thereof may be buried in the insulating layer  12 , and the top surface thereof may be exposed. The metallic layer  13  is arranged in such a manner that, for example, the top surface of the metallic layer  13  may be in the same plane as the top surface of the insulating layer  12 . It is to be noted that it is not necessary that all of the metallic layers  13  be electrically connected with the wires in the insulating layer  12 . For example, some metallic layers  13  out of the plurality of metallic layers  13  that are provided in correspondence with the respective devices  20  may be those that are joined with metallic protrusions that are provided on the respective devices  20  to assure the stability of the devices  20 . 
     As detailed hereinafter, each of the devices  20  on the wiring substrate  10  is transferred on the wiring substrate  10  from a device substrate  30  using a transfer technique. The respective devices  20  are arranged to be away from one another in a plane. The device  20  may be, for example, a submillimeter-sized chip. It is to be noted that the device  20  may be larger in size than a submillimeter size. The device  20  is an individual component in a chip-shaped form to be used as a constituent part for an apparatus or an electronic circuit. Examples of the device  20  may include a light-emitting device (such as an LED (Light-Emitting Diode), an LD (Laser Diode), an organic EL), a light receiving device (such as a photodiode, a photodetector, a CCD (Charge-Coupled Device), and a CMOS (Complementary Metal-Oxide Semiconductor)), and a circuit device (such as a capacitor, a transistor, a resistor, an IC (Integrated Circuit), and an LSI (Large-Scale Integrated Circuit)). Alternatively, the device  20  may be a device that includes at least two out of the above-described light-emitting devices, light receiving devices, and circuit devices, for example. 
     For example, as shown in  FIG. 1 , the device  20  may have a function section  21 , and a metallic layer  22  and a solder bump  23  that are provided on the undersurface of the function section  21 . The function section  21  is a part having the functions of the device  20  that is exemplified in the above, and may be configured to include, for example, an LED, an LD, an organic EL, a photodiode, a photodetector, a CCD, a CMOS, a capacitor, a transistor, a resistor, an IC, an LSI, and/or the like. The metallic layer  22  makes a connection between the function section  21  and the metallic layer  13  via the solder bumps  23 , and is electrically or capacitively connected with the function section  21 . It is to be noted that, when each of the devices  20  is provided with the plurality of metallic layers  22 , a part of these metallic layers  22  may be a dummy that is not useful for the functions of the function section  21 . In this case, a portion that is configured of the dummy metallic layer  13  and the solder bump  23  that is provided on such a dummy metallic layer  13  serves as a metallic protrusion that is provided on the device  20  to assure the stability of the device  20 . 
     The metallic layer  22  and the solder bump  23  are laminated in this order on the undersurface of the function section  21 . The metallic layer  22  and the solder bump  23  are projecting toward the wiring substrate  10  side on the undersurface of the function section  21 , and configure a protrusion standing out from a surrounding area. In other words, each of the devices  20  has an electrically-conductive protrusion that is made up of the metallic layer  22  and the solder bump  23 . For example, as shown in  FIG. 1 , the electrically-conductive protrusion may be configured of a block-like metal member. It is to be noted that the conductive protrusion may be alternatively configured of, for example, a wedge-like metal member. Further, it is to be noted that the solder bump  23  may not necessarily be in a spherical shape from the beginning. The solder bump  23  may take a shape such as cylinder, circular cone, inverted circular cone, mushroom form, quadrangular pyramid, quadrangular prism, prismatic column, pyramid, polygonal pyramid, and polygonal column. The solder bump  23  is transformed into an almost spherical shape by surface tension of a solder in a state of being in the form of a liquid with a temperature above the solder melting point. 
     It is to be noted that  FIG. 1  illustrates by an example a case where each of the devices  20  has two electrically-conductive protrusions on the undersurface of the function section  21 . However, each of the devices  20  may have one or three or more electrically-conductive protrusions alternatively. The electrically-conductive protrusion may be, for example, in a shape of a rectangle, square, circle, or ellipse when viewed from a direction of a normal to the undersurface of the function section  21 . The number of the electrically-conductive protrusions may be desirably three or more in consideration of the stability of the device  20 . When the number of the electrically-conductive protrusions is one or two, the electrically-conductive protrusion may be desirably in a shape of a rectangle or ellipse in consideration of the stability of the device  20 . 
     The metallic layer  22  may be configured to include the UBM, for example. In the metallic layer  22 , for example, a part of the side surfaces thereof may be exposed from the function section  21 , and the undersurface thereof may be exposed. The solder bump  23  may be configured of, for example, alloy containing lead or tin as a primary component, and may be formed in a manner of, for example, electrolytic plating, imprinting of a solder paste, and/or the like. 
     [Manufacturing Method] 
     Next, the description is provided on an example of a method of manufacturing the mounting substrate  1 . 
       FIG. 3  shows an example of a manufacturing process for the mounting substrate  1  using a flowchart. Each of  FIG. 4  to  FIG. 10  shows an example of a manufacturing process for the mounting substrate  1  using a cross-sectional view. First, the device substrate  30  and the wiring substrate  10  are prepared (step S 101 ,  FIG. 4  and  FIG. 5 ). 
     For example, as shown in  FIG. 4 , the device substrate  30  may have a support substrate  31 , a fixing layer  32 , and the plurality of devices  20 . Each of the devices  20  is arranged on the support substrate  31  with the metallic layer  22  directed upward (that is, with the metallic layer  22  directed toward the opposite side, of the function section  21 , from the support substrate  31 ). The support substrate  31  supports the plurality of devices  20 , and may be configured of, for example, a silicon substrate, a glass substrate, a resin substrate, and/or the like. The fixing layer  32  fixes each of the devices  20  on the support substrate  31 , and peels off each of the devices  20  from the support substrate  31  at the time of a transfer process. When a transfer is carried out by a laser ablation method, the fixing layer  32  may be configured of, for example, a material that absorbs light at laser oscillation wavelength band. The fixing layer  32  may be formed, for example, over a whole area of the top surface of the support substrate  31 . For example, as shown in  FIG. 4 , the fixing layer  32  may be formed only at a gap between the support substrate  31  and each of the devices  20 . Considering the transfer performance, as shown in  FIG. 4 , the fixing layer  32  may be preferably formed for each of the devices  20 . Further, considering the simplicity of the process, the fixing layer  32  may be preferably formed over a whole area of the top surface of the support substrate  31 . The fixing layer  32  may come in direct contact with the support substrate  31 . It is to be noted that an adhesion layer, an insulating layer, a metallic layer, and/or the like may be interposed between the fixing layer  32  and the support substrate  31 . 
     Next, a fixing layer  41  is formed over a whole area of the top surface of the wiring substrate  10  (step S 102 ,  FIG. 6 ). The fixing layer  41  accepts each of the devices  20  at the time of a transfer process, and holds one or more of the transferred devices  20  using an adhesive force. The fixing layer  41  is in the form of a liquid having viscosity or a gel, and may be configured of, for example, a flux. The flux is mainly made of resin and solvent. The flux is a so-called solder flux, and is a material in the form of a liquid or a paste that has a function of reducing oxides on the metal surface or includes an activator to have a reduction action. The above-described activator may be molten salt, acid, or the like having the reducing characteristics. The above-described molten salt may be a halide, such as chloride and fluoride. Examples of the above-described acid may include orthophosphoric acid, organic acid, amines, hydrohalic acid amine salt, and the like. In some instances, any other additive agent may be added to the flux as appropriate. 
     By the use of a method such as spin coating, spray method, doctor blade method, printing, transfer method, and imprinting method, the flux is coated with a small and uniform thickness over a whole area of the top surface of the wiring substrate  10 . Therefore, at this time, the flux has a low degree of viscosity suitable for coating. 
     Subsequently, the degree of the viscosity of the fixing layer  41  on the wiring substrate  10  is changed (step S 103 ). For example, using at least one method of heating, decompression, light irradiation, and addition of curing agent, a process is carried out that raises the degree of the viscosity of the flux applied on the top surface of the wiring substrate  10 . The degree of the viscosity of the fixing layer  41  is changed after the fixing layer  41  is formed on the top surface of the wiring substrate  10  and before a transfer process to be hereinafter described is performed. One reason for this is that the optimum degree of viscosity desired for the fixing layer  41  when the fixing layer  41  is applied on the top surface of the wiring substrate  10  is different from that when the fixing layer  41  accepts each of the devices  20  at the time of the transfer process. More specifically, when the fixing layer  41  is formed on the top surface of the wiring substrate  10 , the degree of the viscosity of the fixing layer  41  may be preferably relatively low, and may be preferably relatively high at the time of the transfer process. 
     When heating is used for changing the degree of viscosity, a solvent contained in the flux is volatized by heating the wiring substrate  10  using, for example, a hot plate, an atmosphere furnace, an infrared heating furnace, and/or the like to change the viscosity of the flux. When a decompression furnace is used for changing the viscosity, the wiring substrate  10  coated with the flux is placed in the decompression furnace to be in a decompression state slowly. This volatizes the solvent contained in the flux to change the degree of the viscosity of the flux. In a case where the light irradiation is used for changing the degree of the viscosity, and when photosensitive resin is used as resin to be contained in the flux, the photosensitive resin is modified in composition in such a manner that the flux is irradiated with optical energy rays such as ultraviolet rays, to change the degree of the viscosity of the flux. When a curing agent is used for changing the degree of the viscosity, the curing agent having a curing function is sprayed onto the flux applied on the top surface of the wiring substrate  10  to change the degree of the viscosity of the flux. 
     Thereafter, part or all of the plurality of devices  20  on the device substrate  30  are transferred on the wiring substrate  10  (step S 104 ). First, the device substrate  30  and the wiring substrate  10  are attached to a transfer apparatus. Next, the device substrate  30  and the wiring substrate  10  are arranged in opposition to each other with a predetermined vacant space  42  interposed between (that is, with them placed away from each other) ( FIG. 7 ) or with them closely-attached to each other ( FIG. 8 ). Subsequently, one or more of the plurality of devices  20  on the device substrate  30  are transferred on the wiring substrate  10  using, for example, a laser ablation method ( FIG. 9 ). This temporarily fixes the transferred device(s)  20  (or solder bumps  23 ) on the wiring substrate  10  with the use of the fixing layer  41 . It is to be noted that such a transfer process may be carried out in a method other than the laser ablation. 
     At the time of the transfer process, an electrically-conductive protrusion that is configured of the metallic layer  22  and the solder bump  23  sticks into the fixing layer  41  to serve as an anchor. At this time, a height of the electrically-conductive protrusion that is configured of the metallic layer  22  and the solder bump  23  (to be exact, a distance between the undersurface of the function section  21  and a tip end of the solder bump  23 ) may be larger (longer) or smaller (shorter) than a thickness of the fixing layer  41 . 
     After the transfer process, the whole metallic layer  22  or a part thereof and the metallic layer  13  are opposed to each other with the solder bump  23  in between. Further, when viewed from a direction of a normal to the mounting surface of the wiring substrate  10 , it is enough that a portion where the metallic layer  22  and the metallic layer  13  are opposed to each other has an area at least about a half as large as the area of the metallic layer  22 . Therefore, it is enough that this transfer process has the accuracy that allows such a transfer to be achieved. 
     Afterward, the degree of the viscosity of the fixing layer  41  on the wiring substrate  10  is changed (step S 105 ). For example, by heating (post-baking), a process is carried out that raises the degree of the viscosity of the flux applied on the top surface of the wiring substrate  10 . The degree of the viscosity of the fixing layer  41  is changed after the transfer is completed and before a reflow process to be hereinafter described is performed. One reason for this is that the optimum degree of viscosity desired for the fixing layer  41  when the fixing layer  41  accepts each of the devices  20  at the time of the transfer process is slightly different from that when the reflow process is performed. More specifically, when the reflow process is carried out, the degree of the viscosity of the fixing layer  41  may be desirably higher than that at the time of the transfer process. A specific method of changing the degree of viscosity is similar to the above-described method. It is to be noted that this step is intended to prevent each of the transferred devices  20  from shifting during a period of time before the reflow process is performed or during the reflow process. Therefore, this step may be omitted when there is not concern about such a possibility. 
     Subsequently, a reflow process is carried out for the wiring substrate  10  (step S 106 ,  FIG. 10 ). At this time, the solder bump  23  is melted or softened, and thus the metallic layer  22  and the metallic layer  13  are opposed to each other or are exactly face to face with each other due to a self-alignment function of the solder bump  23 . Further, an electrical connection between the transferred device  20  (or the metallic layer  22 ) and the wiring substrate  10  (or the metallic layer  13 ) is made as a consequence of melting or softening of the solder bump  23 . In other words, the transferred device  20  (or the metallic layer  22 ) and the wiring substrate  10  (or the metallic layer  13 ) are electrically connected with each other via the electrically-conductive protrusion (the solder bump  23 ). After the reflow process, the solder bump  23  is solidified, and accordingly, each of the devices  20  is fixed with high accuracy at a predetermined position on the support substrate  11 . 
     Finally, the fixing layer  41  is removed (cleaned) (step S 107 ). Here, it is sufficient that the flux used as the fixing layer  41  is dissolved, and any residual material is eliminated. A cleaning agent suitable for the flux may be used. At this time, it is possible to clear away any material (dirt) attached on the mounting surface of the wiring substrate  10 , such as a residue that may be generated from the laser ablation, in conjunction with the cleaning of the flux. It is to be noted that when the flux is a non-cleaning type, removal of the fixing layer  41  may be omitted. 
     [Effects] 
     Next, description is provided on the effects of the method of manufacturing the mounting substrate  1 . 
     In this embodiment of the present application, the electrical connection between the transferred device  20  and the wiring substrate  10  is made by performing a reflow process on the wiring substrate  10  in a state where the transferred device  20  is temporarily fixed to the wiring substrate  10  with the use of the fixing layer  41 . This makes it possible to omit a step of burying a vacant space between the devices  20  to flatten a surface on which the wiring layer is formed, or a step of forming the wiring layer, in order to make the electrical connection between the device  20  and the wiring. As a result, this allows steps following on the transfer process to be simplified. 
     Further, as shown in  FIG. 7 , when a non-contact transfer (proximity transfer) is carried out, each of the devices  20  remaining on the device substrate  30  without being transferred (hereinafter referred to as a “non-transferred device”) does not come in contact with the fixing layer  41 . Therefore, a part of the fixing layer  41  or a residue that may be generated from the laser ablation is not attached to the non-transferred device. Consequently, there is no concern about the possibility of deterioration in the transfer performance of the non-transferred device. In addition, in the proximity transfer, there is no necessity for moving the device substrate  30  up and down before or after the transfer process, which allows the transfer processing time to be shortened. Moreover, in the proximity transfer, the device substrate  30  and the wiring substrate  10  do not come in contact with each other. As a result, when there is slight unevenness on the surface (mounting surface) of the wiring substrate  10 , or there is slight waviness on the device substrate  30  and/or the wiring substrate  10 , it is possible to avoid damage to each of the devices  20  that could be caused by contact transfer. 
     In addition, as shown in  FIG. 10 , when the reflow process is carried out, it is possible to improve the alignment accuracy due to the self-alignment function of a solder. Therefore, there is no necessity for preparing a high-level adjusting apparatus for improving the alignment accuracy during the transfer process. As a result, it is possible to simplify steps during the transfer process, as well as to perform the transfer using inexpensive manufacturing facility. Further, when the electrical connection between the device  20  and the wiring substrate  10  is made using the reflow process, even if a defect in the device  20  is found later, it is possible to take out the defective device  20  with ease. In an existing method in which the device  20  is embedded to form the wiring layer, it is difficult to take out the defective device  20  with ease. 
     Moreover, in this embodiment of the present application, the degree of the viscosity of the fixing layer  41  is changed after the fixing layer  41  is applied on the top surface of the wiring substrate  10  and before the transfer process is performed. This makes it possible to reduce the possibility that a positional shift will occur in each of the devices  20  after the transfer. Further, in this embodiment of the present application, the degree of the viscosity of the fixing layer  41  is changed after the transfer process is performed and before the reflow process is performed. Also, this makes it possible to reduce the possibility that a positional shift will occur in each of the devices  20  immediately before or in the middle of the reflow process. 
     2. Modification Examples of First Embodiment 
     Modification Example 1 
     Next, description is provided on a modification example of the method of manufacturing the mounting substrate  1  according to the above-described embodiment of the present application.  FIG. 11  shows another example of the manufacturing process for the mounting substrate  1  using a flowchart. Each of  FIG. 12  to  FIG. 16  shows another example of the manufacturing process for the mounting substrate  1  using a cross-sectional view. In this modification example, a fixing layer  43  is used instead of the fixing layer  41 . This fixing layer  43  is applied on the device substrate  30 . 
     First, the device substrate  30  and the wiring substrate  10  are prepared (step S 201 ,  FIG. 4  and  FIG. 5 ). Next, the fixing layer  43  is formed on the undersurface of each of the devices  20  (step S 202 ,  FIG. 12 ). In concrete terms, the fixing layer  43  is formed on a top end of the electrically-conductive protrusion that is configured of the metallic layer  22  and the solder bump  23 . It is to be noted that the fixing layer  43  may be formed only on the undersurface of the device  20  to be transferred among the plurality of devices  20  on the device substrate  30 . The fixing layer  43  accepts each of the devices  20  at the time of the transfer process, while holding one or more of the transferred devices  20  using an adhesive force. More specifically, the fixing layer  43  is a flux. The flux is the same as the flux of the fixing layer  41  that is used in the above-described embodiment of the present application. 
     For example, by the use of a method such as a dip method, a spray method, and printing, the flux is applied with a small and uniform thickness on the top end of the electrically-conductive protrusion. Therefore, at this time, the flux has a low degree of viscosity suitable for coating. 
     Subsequently, the degree of the viscosity of the fixing layer  43  on the device substrate  30  is changed (step S 203 ). For example, using at least one method of heating, decompression, light irradiation, and addition of curing agent, a process is carried out that raises the degree of the viscosity of the flux applied on the top surface of the device substrate  30 . The degree of the viscosity of the fixing layer  43  is changed after the fixing layer  43  is formed on the device substrate  30  and before the transfer process to be hereinafter described is performed. One reason for this is that the optimum degree of viscosity desired for the fixing layer  43  when the fixing layer  43  is applied on the device substrate  30  is different from that when the fixing layer  43  accepts each of the devices  20  at the time of the transfer process. More specifically, when the fixing layer  43  is formed on the device substrate  30 , the degree of the viscosity of the fixing layer  43  may be preferably relatively low, and may be preferably relatively high at the time of the transfer process. A specific method of changing the degree of viscosity is similar to the above-described method. It is to be noted that, in an embodiment where the optimum degree of viscosity desired for the fixing layer  43  when the fixing layer  43  is applied on the device substrate  30  is not significantly different from that when the fixing layer  43  accepts each of the devices  20  at the time of the transfer process, when the fixing layer  43  is applied on the device substrate  30 , this step may be omitted. 
     Thereafter, part or all of the plurality of devices  20  on the device substrate  30  are transferred on the wiring substrate  10  (step S 204 ). First, the device substrate  30  and the wiring substrate  10  are attached to a transfer apparatus. Next, the device substrate  30  and the wiring substrate  10  are arranged in opposition to each other with a predetermined vacant space  42  interposed between (that is, with them placed away from each other) ( FIG. 13 ) or with them closely-attached to each other ( FIG. 14 ). Subsequently, one or more of the plurality of devices  20  on the device substrate  30  are transferred on the wiring substrate  10  using, for example, a laser ablation method ( FIG. 15 ). This temporarily fixes the transferred device(s)  20  (or the solder bump(s)  23 ) on the wiring substrate  10  with the use of the fixing layer  43 . It is to be noted that such a transfer process may be carried out in a method other than the laser ablation. 
     At the time of the transfer process, an electrically-conductive protrusion that is configured of the metallic layer  22  and the solder bump  23  sticks into the fixing layer  43  to function as an anchor. At this time, it is important that a height of the electrically-conductive protrusion that is configured of the metallic layer  22  and the solder bump  23  (to be exact, a distance between the undersurface of the function section  21  and a tip end of the solder bump  23 ) is larger (longer) than a thickness of the fixing layer  43 , in terms of an anchor effect. 
     After the transfer process, the whole metallic layer  22  or a part thereof and the metallic layer  13  are opposed to each other with the solder bump  23  in between. Further, when viewed from a direction of a normal to the mounting surface of the wiring substrate  10 , it is enough that a portion where the metallic layer  22  and the metallic layer  13  are opposed to each other has an area at least about a half as large as the area of the metallic layer  22 . Therefore, it is enough that this transfer process has the accuracy that allows such a transfer to be achieved. 
     Afterward, the degree of the viscosity of the fixing layer  43  on the wiring substrate  10  is changed (step S 205 ). For example, by heating (post-baking), a process is carried out that raises the degree of the viscosity of the flux on the wiring substrate  10 . The degree of the viscosity of the fixing layer  43  is changed after the transfer is completed and before the reflow process to be hereinafter described is performed. One reason for this is that the optimum degree of viscosity desired for the fixing layer  43  when the fixing layer  43  accepts each of the devices  20  at the time of the transfer process is slightly different from that when the reflow process is performed. More specifically, when the reflow process is carried out, the degree of the viscosity of the fixing layer  43  may be preferably higher than that at the time of the transfer process. A specific method of changing the degree of viscosity is similar to the above-described method. It is to be noted that this step is intended to prevent each of the transferred devices  20  from shifting during a period of time before the reflow process is performed or during the reflow process. Therefore, this step may be omitted when there is no such a possibility. 
     Subsequently, a reflow process is carried out for the wiring substrate  10  (step S 206 ,  FIG. 16 ). At this time, the solder bump  23  is melted or softened, and thus the metallic layer  22  and the metallic layer  13  are opposed to each other or are exactly face to face with each other due to a self-alignment function of the solder bump  23 . Further, an electrical connection between the transferred device  20  (or the metallic layer  22 ) and the wiring substrate  10  (or the metallic layer  13 ) is made as a consequence of melting or softening of the solder bump  23 . In other words, the transferred device  20  (or the metallic layer  22 ) and the wiring substrate  10  (or the metallic layer  13 ) are electrically connected with each other via the electrically-conductive protrusion (the solder bump  23 ). After the reflow process, the solder bump  23  is solidified, and accordingly, each of the devices  20  is fixed with high accuracy at a predetermined position on the support substrate  11 . 
     Finally, the fixing layer  43  is removed (cleaned) (step S 207 ). Here, it is sufficient that the flux used as the fixing layer  43  is dissolved, and any residual material is eliminated. A cleaning agent suitable for the flux may be used. At this time, it is possible to remove any material (dirt) attached on the mounting surface of the wiring substrate  10 , such as a residue that may be generated from the laser ablation, in conjunction with the cleaning of the flux. It is to be noted that when the flux is a non-cleaning type, removal of the fixing layer  43  may be omitted. 
     Next, description is provided on the effects of the method of manufacturing the mounting substrate  1  in this modification example. 
     In this modification example, the electrical connection between the transferred device  20  and the wiring substrate  10  is made by performing a reflow on the wiring substrate  10  in a state where the transferred device  20  is temporarily fixed to the wiring substrate  10  with the use of the fixing layer  43 . This makes it possible to omit a step of burying a vacant space between the devices  20  to flatten a surface on which the wiring layer is formed, or a step of forming the wiring layer, in order to make the electrical connection between the device  20  and the wiring. As a result, it is possible to simplify steps following on the transfer process. 
     Further, as shown in  FIG. 13 , when a non-contact transfer (proximity transfer) is carried out, the non-transferred device does not come in contact with the fixing layer  43 . Therefore, a part of the fixing layer  43  or a residue that may be generated from the laser ablation is not attached to the non-transferred device. Consequently, there may be no possibility of deterioration in the transfer performance of the non-transferred device. In addition, in the proximity transfer, there is no necessity for moving the device substrate  30  up and down before or after the transfer process, which allows the transfer processing time to be shortened. Moreover, in the proximity transfer, the device substrate  30  and the wiring substrate  10  do not come in contact with each other. As a result, when there is slight unevenness on the surface (mounting surface) of the wiring substrate  10 , or there is slight waviness on the device substrate  30 , the wiring substrate  10  and/or the like, it is possible to avoid damage to each of the devices  20  that could be caused by a contact transfer. 
     In addition, as shown in  FIG. 16 , when the reflow is carried out, it is possible to improve the alignment accuracy due to the self-alignment function of a solder. Therefore, there may be no necessity for preparing a high-level adjusting apparatus for improving the alignment accuracy during the transfer process. As a result, it is possible to simplify steps during the transfer process, as well as to perform the transfer using inexpensive manufacturing facility. Further, when the electrical connection between the device  20  and the wiring substrate  10  is made using the reflow process, even if a defect in the device  20  is found later, it is possible to take out the defective device  20  with ease. In an existing method in which the device  20  is embedded to form the wiring layer, it is difficult to take out the defective device  20  with ease. 
     Modification Example 2 
     Next, description is provided on another modification example of the mounting substrate  1  according to the above-described embodiment and modification example thereof. In the above-described embodiment and modification example thereof, as shown in an example in  FIG. 17A , the metallic layer  22  is provided on the undersurface of the function section  21 , and the whole side surfaces or a part thereof of the metallic layer  22  and the undersurface of the metallic layer  22  are exposed to the outside without being covered by the function section  21 . However, for example, as shown in  FIG. 17B , the metallic layer  22  may be arranged in such a manner that the undersurface of the metallic layer  22  is in the same or almost the same plane as the undersurface of the function section  21 . Alternatively, for example, as shown in  FIG. 17C , the metallic layer  22  may be arranged in such a manner that the undersurface of the metallic layer  22  is located at a position recessed from the undersurface of the function section  21 . It is to be noted that, in  FIG. 17C , a depression is formed on the undersurface of the function section  21  in correspondence with the metallic layer  22 , and the undersurface of the metallic layer  22  is exposed at the bottom of the depression. 
     Further, in the above-described embodiment and modification example thereof, as shown in an example in  FIG. 18A , the metallic layer  13  is arranged in such a manner that the top surface of the metallic layer  13  is in the same or almost the same plane as the mounting surface of the wiring substrate  10  (the top surface of the insulating layer  12 ). However, for example, as shown in  FIG. 18B , the metallic layer  13  may be arranged in such a manner that the top surface of the metallic layer  13  is located at a position recessed from the mounting surface of the wiring substrate  10  (the top surface of the insulating layer  12 ). It is to be noted that, in  FIG. 18B , a depression is formed on the mounting surface of the wiring substrate  10  (the top surface of the insulating layer  12 ) in correspondence with the metallic layer  13 , and the top surface of the metallic layer  13  is exposed at the bottom of the depression. Alternatively, for example, as shown in  FIG. 18C , the metallic layer  13  may be provided on the mounting surface of the wiring substrate  10  (the top surface of the insulating layer  12 ), and the whole side surfaces or a part thereof of the metallic layer  13  and the top surface of the metallic layer  13  may be exposed to the outside without being covered by the insulating layer  12 . At this time, the metallic layer  13  becomes an electrically-conductive protrusion standing out from a surrounding area on the mounting surface of the wiring substrate  10  (the top surface of the insulating layer  12 ). 
     Moreover, in this modification example, the viscosity of the fixing layer  43  is changed after the fixing layer  43  is applied on the top surface of the device substrate  30  and before the transfer process is performed. This makes it possible to reduce the possibility that a positional shift will occur in each of the devices  20  after the transfer. Further, in this embodiment of the present application, the degree of the viscosity of the fixing layer  43  is changed after the transfer process is performed and before the reflow process is performed. Also, this makes it possible to reduce the possibility that a positional shift will occur in each of the devices  20  immediately before or in the middle of the reflow process. 
     3. Second Embodiment 
     [Configuration] 
     Next, description is provided on a mounting substrate  2  according to a second embodiment of the present application.  FIG. 19  shows an example of a cross-sectional configuration of the mounting substrate  2 .  FIG. 20  shows an example of a top surface configuration of the mounting substrate  2 .  FIG. 19  corresponds to a cross-sectional configuration in the direction shown with an arrow A-A in  FIG. 20 . The mounting substrate  2  is a substrate where a plurality of devices  60  are mounted on a wiring substrate  50 . The wiring substrate  50  and each of the devices  60  are electrically connected with each other. 
     The wiring substrate  50  may include, for example, a support substrate  11 , an insulating layer  12 , a metallic layer  13 , and a solder bump  51 . The wiring substrate  50  is equivalent to a substrate in which the solder bump  51  is provided on the wiring substrate  10  in the above-described first embodiment of the present application. The solder bump  51  may be configured of, for example, alloy containing lead or tin as a primary component, and may be formed in a manner of, for example, electrolytic plating, imprinting of a solder paste, and/or the like. It is to be noted that it is not necessary that the solder bump  51  be in a spherical shape from the beginning. The solder bump  51  may take a shape, such as cylinder, circular cone, inverted circular cone, mushroom form, quadrangular pyramid, quadrangular prism, prismatic column, pyramid, polygonal pyramid, and polygonal column. The solder bump  51  is transformed into an almost spherical shape by surface tension of a solder in a state of being in the form of a liquid with a temperature above the solder melting point. The solder bump  51  is projecting toward the device  60  side on the mounting surface of the wiring substrate  50  (the top surface of the insulating layer  12 ), and configures a protrusion standing out from a surrounding area. For example, as shown in  FIG. 19 , such an electrically-conductive protrusion may be configured of a block-like (or spherical) metal member. It is to be noted that the electrically-conductive protrusion may be alternatively configured of, for example, a wedge-like metal member. 
     It is to be noted that  FIG. 19  illustrates by an example a case where the wiring substrate  50  has two electrically-conductive protrusions in correspondence with each of the devices  60 . However, the wiring substrate  50  may have one or three or more electrically-conductive protrusions alternatively. The electrically-conductive protrusion may be, for example, in a shape of a rectangle, square, circle, or ellipse when viewed from a direction of a normal to the mounting surface of the wiring substrate  50  (the top surface of the insulating layer  12 ). The number of the electrically-conductive protrusion may be preferably three or more in consideration of the stability of the device  60 . When the number of the electrically-conductive protrusion is one or two, the electrically-conductive protrusion may be preferably in a shape of a rectangle or ellipse in consideration of the stability of the device  60 . 
     As detailed hereinafter, each of the devices  60  on the wiring substrate  50  is transferred on the wiring substrate  50  from a device substrate  70  using a transfer technique. The respective devices  60  are arranged to be away from one another in a plane. The device  60  may be, for example, a submillimeter-sized chip. It is to be noted that the device  60  may be larger in size than a submillimeter size. The device  60  is an individual component to be used as a constituent part for an apparatus or an electronic circuit in a chip-shaped form. Examples of the device  60  may include a light-emitting device (such as an LED, an LD, and an organic EL), a light receiving device (such as a PD), and a circuit device (such as a capacitor, a transistor, a resistor, an IC, and an LSI). Alternatively, the device  60  may be a device that includes at least two out of the above-described light-emitting devices, light receiving devices, and circuit devices, for example. 
     For example, as shown in  FIG. 19 , the device  60  may include a function section  21 , and a metallic layer  22  that is provided on the undersurface of the function section  21 . In other words, the device  60  is equivalent to a device in which the solder bump  23  is removed in the device  20  in the above-described first embodiment. 
     [Manufacturing Method] 
     Next, description is provided on an example of a method of manufacturing the mounting substrate  2 . 
       FIG. 21  shows an example of a manufacturing process for the mounting substrate  2  using a flowchart. Each of  FIG. 22  to  FIG. 28  shows an example of a manufacturing process for the mounting substrate  2  using a cross-sectional view. First, the device substrate  70  and the wiring substrate  50  are prepared (step S 301 ,  FIG. 22  and  FIG. 23 ). 
     For example, as shown in  FIG. 22 , the device substrate  70  may include a support substrate  31 , a fixing layer  32 , and the plurality of devices  60 . The device  60  is equivalent to a device in which the solder bump  23  is removed in the device  20  in the above-described first embodiment. Therefore, the device substrate  70  is equivalent to a substrate in which the solder bump  23  is removed in the device substrate  30  in the above-described first embodiment. 
     Next, a fixing layer  44  is formed on the undersurface of each of the devices  60  (step S 302 ,  FIG. 24 ). In concrete terms, the fixing layer  44  is formed on a top end of the electrically-conductive protrusion that is configured of the metallic layer  22 . It is to be noted that the fixing layer  44  may be formed only on the undersurface of the device  60  to be transferred among the plurality of devices  60  on the device substrate  70 . The fixing layer  44  accepts each of the devices  60  at the time of the transfer process, while holding one or more of the transferred devices  60  using an adhesive force. More specifically, the fixing layer  44  is a flux. The flux is the same as the flux of the fixing layer  43  that is used in the modification example of the above-described first embodiment. 
     For example, by the use of a method such as a dip method, a spray method, and printing, the flux is applied with a small and uniform thickness on the top end of the electrically-conductive protrusion. Therefore, at this time, the flux has a low degree of viscosity suitable for coating. 
     Subsequently, the degree of viscosity of the fixing layer  44  on the device substrate  70  is changed (step S 303 ). For example, using at least one method of heating, decompression, light irradiation, and addition of curing agent, a process is carried out that raises the degree of viscosity of the flux applied on the top surface of the device substrate  70 . The degree of the viscosity of the fixing layer  44  is changed after the fixing layer  44  is formed on the device substrate  70  and before the transfer process to be hereinafter described is performed. One reason for this is that the optimum degree of viscosity desired for the fixing layer  44  when the fixing layer  44  is applied on the device substrate  70  is different from that when the fixing layer  44  accepts each of the devices  60  at the time of the transfer process. More specifically, when the fixing layer  44  is formed on the device substrate  70 , the degree of the viscosity of the fixing layer  44  may be preferably relatively low, and may be preferably relatively high at the time of the transfer process. A specific method of changing the degree of viscosity is similar to the above-described method. It is to be noted that, in an embodiment where the optimum degree of viscosity desired for the fixing layer  44  when the fixing layer  44  is applied on the device substrate  70  is not significantly different from that when the fixing layer  44  accepts each of the devices  60  at the time of the transfer process, when the fixing layer  44  is applied on the device substrate  70 , this step may be omitted. 
     Thereafter, part or all of the plurality of devices  60  on the device substrate  70  are transferred on the wiring substrate  50  (step S 304 ). First, the device substrate  70  and the wiring substrate  50  are attached to a transfer apparatus. Next, the device substrate  70  and the wiring substrate  50  are arranged in opposition to each other with a predetermined vacant space  53  interposed between (that is, with them placed away from each other) ( FIG. 25 ) or with them closely-attached to each other ( FIG. 26 ). This temporarily fixes the transferred devices  60  on the wiring substrate  50  with the use of the fixing layer  44 . At this time, the fixing layer  44  that is provided on the device  60  to be not transferred may not be preferably in contact with the mounting surface of the wiring substrate  50  (the top surface of the insulating layer  12 ). It is to be noted that, when the fixing layer  44  is formed only on the undersurface of the device  60  to be transferred among the plurality of devices  60  on the device substrate  70 , only the fixing layer  44  that is provided on the device  60  to be transferred comes in contact with the mounting surface of the wiring substrate  50  (the top surface of the insulating layer  12 ). Subsequently, one or more of the plurality of devices  60  on the device substrate  70  are transferred on the wiring substrate  50  using, for example, a laser ablation method ( FIG. 27 ). It is to be noted that such a transfer process may be carried out in a method other than the laser ablation. 
     After the transfer process, the whole metallic layer  22  or a part thereof and the metallic layer  13  are opposed to each other with the solder bump  23  in between. Further, when viewed from a direction of a normal to the mounting surface of the wiring substrate  50 , it is enough that a portion where the metallic layer  22  and the metallic layer  13  are opposed to each other has an area at least about a half as large as the area of the metallic layer  22 . Therefore, it is enough that this transfer process has the accuracy that allows such a transfer to be achieved. 
     Afterward, the degree of the viscosity of the fixing layer  44  on the wiring substrate  50  is changed (step S 305 ). For example, by heating (post-baking), a process is carried out that raises the degree of viscosity of the flux on the wiring substrate  50 . The degree of the viscosity of the fixing layer  44  is changed after the transfer is completed and before the reflow process to be hereinafter described is performed. One reason for this is that the optimum degree of viscosity desired for the fixing layer  44  when the fixing layer  44  accepts each of the devices  60  at the time of the transfer process is slightly different from that when the reflow process is performed. More specifically, when the reflow process is carried out, the degree of the viscosity of the fixing layer  44  may be preferably higher than that at the time of the transfer process. A specific method of changing the degree of viscosity is similar to the above-described method. It is to be noted that this step is intended to prevent each of the transferred devices  60  from shifting during a period of time before the reflow process is performed or during the reflow process. Therefore, this step may be omitted when there is no such a possibility. 
     Subsequently, a reflow process is carried out for the wiring substrate  50  (step S 306 ,  FIG. 28 ). At this time, the solder bump  23  is melted or softened, and thus the metallic layer  22  and the metallic layer  13  are opposed to each other or are exactly face to face with each other due to a self-alignment function of the solder bump  23 . Further, an electrical connection between the transferred device  60  (or the metallic layer  22 ) and the wiring substrate  50  (or the metallic layer  13 ) is made as a consequence of melting or softening of the solder bump  23 . In other words, the transferred device  60  (or the metallic layer  22 ) and the wiring substrate  50  (or the metallic layer  13 ) are electrically connected with each other via the electrically-conductive protrusion (the solder bump  23 ). After the reflow process, the solder bump  23  is solidified, and accordingly, each of the devices  60  is fixed with high accuracy at a predetermined position on the support substrate  11 . 
     Finally, the fixing layer  44  is removed (cleaned) (step S 307 ). Here, it is sufficient that the flux used as the fixing layer  44  is dissolved, and any residual material is eliminated. A cleaning agent suitable for the flux may be used. At this time, it is possible to remove any material (dirt) attached on the mounting surface of the wiring substrate  50 , such as a residue that may be generated from the laser ablation, in conjunction with the cleaning of the flux. It is to be noted that, when the flux is a non-cleaning type, removal of the fixing layer  44  may be omitted. 
     Next, description is provided on the effects of the method of manufacturing the mounting substrate  2 . 
     In this embodiment of the present application, the electrical connection between the transferred device  60  and the wiring substrate  50  is made by performing a reflow process on the wiring substrate  50  in a state where the transferred device  60  is temporarily fixed to the wiring substrate  50  with the use of the fixing layer  44 . This makes it possible to omit a step of burying a vacant space between the devices  60  to flatten a surface on which the wiring layer is formed, or a step of forming the wiring layer, in order to make the electrical connection between the device  60  and the wiring. As a result, it is possible to simplify steps following on the transfer process. 
     Further, as shown in  FIG. 25 , when a non-contact transfer (proximity transfer) is carried out, the non-transferred device does not come in contact with the fixing layer  44 . Therefore, a part of the fixing layer  44  or a residue that may be generated from the laser ablation is not attached to the non-transferred device. Consequently, there may be no possibility of deterioration in the transfer performance of the non-transferred device. In addition, in the proximity transfer, there may be no necessity for moving the device substrate  70  up and down before or after the transfer process, which allows the transfer processing time to be shortened. Moreover, in the proximity transfer, the device substrate  70  and the wiring substrate  50  do not come in contact with each other. As a result, when there is slight unevenness on the surface (mounting surface) of the wiring substrate  50 , or there is slight waviness on the device substrate  70 , the wiring substrate  50 , and/or the like, it is possible to avoid damage to each of the devices  60  that could be caused by a contact transfer. 
     In addition, as shown in  FIG. 28 , when the reflow process is carried out, it is possible to improve the alignment accuracy due to the self-alignment function of a solder. Therefore, there may be no necessity for preparing a high-level adjusting apparatus for improving the alignment accuracy during the transfer process. As a result, this makes it possible to simplify steps during the transfer process, as well as to perform the transfer using inexpensive manufacturing facility. Further, when the electrical connection between the device  60  and the wiring substrate  50  is made using the reflow process, even if a defect in the device  60  is found later, it is possible to take out the defective device  60  with ease. In an existing method of embedding the device  60 , it is difficult to take out the defective device  60  with ease. 
     Moreover, in this embodiment of the present application, the degree of the viscosity of the fixing layer  44  is changed after the fixing layer  44  is applied on the top surface of the device substrate  70  and before the transfer process is performed. This makes it possible to reduce the possibility that a positional shift will occur in each of the devices  60  after the transfer. Further, in this embodiment of the present application, the degree of the viscosity of the fixing layer  44  is changed after the transfer process is performed and before the reflow process is performed. This makes it possible to reduce the possibility that a positional shift will occur in each of the devices  60  immediately before or in the middle of the reflow process. 
     4. Modification Examples of Second Embodiment 
     Modification Example 1 
     Next, description is provided on a modification example of a method of manufacturing the mounting substrate  2  according to the above-described second embodiment of the present application.  FIG. 29  shows another example of a manufacturing process for the mounting substrate  2  using a flowchart. Each of  FIG. 30  to  FIG. 34  shows another example of a manufacturing process for the mounting substrate  2  using a cross-sectional view. In this modification example, a fixing layer  45  is used instead of the fixing layer  44 . This fixing layer  45  is applied on the wiring substrate  50 . 
     First, the device substrate  70  and the wiring substrate  50  are prepared (step S 401 ,  FIG. 22  and  FIG. 23 ). Next, the fixing layer  45  is formed over a whole area of the top surface of the wiring substrate  50  (step S 402 ,  FIG. 30 ). It is to be noted that the fixing layer  45  may be alternatively formed only on the top surface of the solder bump  51  or only over a whole surface of the solder bump  51 . The fixing layer  45  accepts each of the devices  60  at the time of the transfer process, while holding one or more of the transferred devices  60  using an adhesive force. More specifically, the fixing layer  45  is a flux. The flux is the same as the flux of the fixing layer  41  that is used in the above-described first embodiment of the present application. 
     For example, by the use of a method such as spin coating, a spray method, a doctor blade method, printing, a transfer method, and an imprinting method, the flux is applied with a small and uniform thickness over a whole area of the top surface of the wiring substrate  50 . Therefore, at this time, the flux has a low degree of viscosity suitable for coating. 
     Subsequently, the degree of the viscosity of the fixing layer  45  on the wiring substrate  50  is changed (step S 403 ). For example, using at least one method of heating, decompression, light irradiation, and addition of curing agent, a process is carried out that raises the degree of viscosity of the flux applied on the device substrate  70 . The degree of the viscosity of the fixing layer  45  is changed after the fixing layer  45  is formed on the wiring substrate  50  and before the transfer process to be hereinafter described is performed. One reason for this is that the optimum degree of viscosity desired for the fixing layer  45  when the fixing layer  45  is applied on the top surface of the wiring substrate  50  is different from that when the fixing layer  45  accepts each of the devices  60  at the time of the transfer process. More specifically, when the fixing layer  45  is formed on the wiring substrate  50 , the degree of the viscosity of the fixing layer  45  may be preferably relatively low, and may be preferably relatively high at the time of the transfer process. A specific method of changing the degree of viscosity is similar to the above-described method. 
     Thereafter, part or all of the plurality of devices  60  on the device substrate  70  are transferred on the wiring substrate  50  (step S 404 ). First, the device substrate  70  and the wiring substrate  50  are attached to a transfer apparatus. Next, the device substrate  70  and the wiring substrate  50  are arranged in opposition to each other with a predetermined vacant space  53  interposed between (that is, with them placed away from each other) ( FIG. 31 ) or with them closely-attached to each other ( FIG. 32 ). Subsequently, one or more of the plurality of devices  60  on the device substrate  70  are transferred on the wiring substrate  50  using, for example, a laser ablation method ( FIG. 33 ). This temporarily fixes the transferred device(s)  60  on the wiring substrate  50  with the use of the fixing layer  45 . It is to be noted that such a transfer process may be carried out in a method other than the laser ablation. 
     After the transfer process, the whole metallic layer  22  or a part thereof and the metallic layer  13  are opposed to each other with the solder bump  23  in between. Further, when viewed from a direction of a normal to the mounting surface of the wiring substrate  50 , it is enough that a portion where the metallic layer  22  and the metallic layer  13  are opposed to each other has an area at least about a half as large as the area of the metallic layer  22 . Therefore, it is enough that this transfer process has the accuracy that allows such a transfer to be achieved. 
     Afterward, the degree of the viscosity of the fixing layer  45  on the wiring substrate  50  is changed (step S 405 ). For example, by heating (post-baking), a process is carried out that raises the degree of viscosity of the flux coated on the wiring substrate  50 . The degree of the viscosity of the fixing layer  45  is changed after the transfer is completed and before the reflow process to be hereinafter described is performed. One reason for this is that the optimum degree of viscosity desired for the fixing layer  45  when the fixing layer  45  accepts each of the devices  60  at the time of the transfer process is slightly different from that when the reflow process is performed. More specifically, when the reflow process is carried out, the degree of the viscosity of the fixing layer  45  may be preferably higher than that at the time of the transfer process. A specific method of changing the degree of viscosity is similar to the above-described method. It is to be noted that this step is intended to prevent each of the transferred devices  60  from shifting during a period of time before the reflow process is performed or during the reflow process. Therefore, this step may be omitted when there is no such a possibility. 
     Subsequently, a reflow process is carried out for the wiring substrate  50  (step S 406 ,  FIG. 34 ). At this time, the solder bump  23  is melted or softened, and thus the metallic layer  22  and the metallic layer  13  are opposed to each other or are exactly face to face with each other due to a self-alignment function of the solder bump  23 . Further, an electrical connection between the transferred device  60  (or the metallic layer  22 ) and the wiring substrate  50  (or the metallic layer  13 ) is made as a consequence of melting or softening of the solder bump  23 . In other words, the transferred device  60  (or the metallic layer  22 ) and the wiring substrate  50  (or the metallic layer  13 ) are electrically connected with each other via the electrically-conductive protrusion (the solder bump  23 ). After the reflow process, the solder bump  23  is solidified, and accordingly, each of the devices  60  is fixed with high accuracy at a predetermined position on the support substrate  11 . 
     Finally, the fixing layer  45  is removed (cleaned) (step S 407 ). Here, it is sufficient that the flux used as the fixing layer  45  is dissolved, and any residual material is eliminated. A cleaning agent suitable for the flux may be used. At this time, it is possible to remove any material (dirt) attached on the mounting surface of the wiring substrate  50 , such as a residue that may be generated from the laser ablation, in conjunction with the cleaning of the flux. It is to be noted that, when the flux is a non-cleaning type, removal of the fixing layer  45  may be omitted. 
     Next, description is provided on the effects of the method of manufacturing the mounting substrate  2  according to this modification example. 
     In this modification example, the electrical connection between the transferred device  60  and the wiring substrate  50  is made by performing a reflow process for the wiring substrate  50  in a state where the transferred device  60  is temporarily fixed to the wiring substrate  50  with the use of the fixing layer  45 . This makes it possible to omit a step of burying a vacant space between the devices  60  to flatten a surface on which the wiring layer is formed, or a step of forming the wiring layer, in order to make the electrical connection between the device  60  and the wiring. As a result, it is possible to simplify steps following on the transfer process. 
     Further, as shown in  FIG. 31 , when a non-contact transfer (proximity transfer) is carried out, the non-transferred device does not come in contact with the fixing layer  45 . Therefore, a part of the fixing layer  45  or a residue that may be generated from the laser ablation is not attached to the non-transferred device. Consequently, there may be no possibility of deterioration in the transfer performance of the non-transferred device. In addition, in the proximity transfer, there may be no necessity for moving the device substrate  70  up and down before or after the transfer process, which allows the transfer processing time to be shortened. Moreover, in the proximity transfer, the device substrate  70  and the wiring substrate  50  do not come in contact with each other. As a result, when there is slight unevenness on the surface (the mounting surface) of the wiring substrate  50 , or there is slight waviness on the device substrate  70 , the wiring substrate  50 , and/or the like, it is possible to avoid damage to each of the devices  60  that could be caused by a contact transfer. 
     In addition, as shown in  FIG. 34 , when the reflow process is carried out, it is possible to improve the alignment accuracy due to the self-alignment function of a solder. Therefore, there may be no necessity for preparing a high-level adjusting apparatus for improving the alignment accuracy during the transfer process. As a result, it is possible to simplify steps during the transfer process, as well as to perform the transfer using inexpensive manufacturing facility. Further, when the electrical connection between the device  60  and the wiring substrate  50  is made using the reflow process, even if a defect in the device  60  is found later, it is possible to take out the defective device  60  with ease. In an existing method of embedding the device  60 , it is difficult to take out the defective device  60  with ease. 
     Moreover, in this modification example, the degree of the viscosity of the fixing layer  45  is changed after the fixing layer  45  is applied on the top surface of the wiring substrate  50  and before the transfer process is performed. This makes it possible to reduce the possibility that a positional shift will occur in each of the devices  60  after the transfer. Further, in this modification example, the degree of the viscosity of the fixing layer  45  is changed after the transfer process is performed and before the reflow process is performed. This makes it possible to reduce the possibility that a positional shift will occur in each of the devices  60  immediately before or in the middle of the reflow process. 
     Modification Example 2 
     Next, description is provided on another modification example of the mounting substrate  2  according to the above-described second embodiment and modification example thereof. In the above-described second embodiment and modification example thereof, for example, as shown in  FIG. 35A , the metallic layer  22  is provided on the undersurface of the function section  21 , and the whole side surfaces or a part thereof of the metallic layer  22  and the undersurface of the metallic layer  22  are exposed to the outside without being covered by the function section  21 . However, for example, as shown in  FIG. 35B , the metallic layer  22  may be arranged in such a manner that the undersurface of the metallic layer  22  is in the same or almost the same plane as the undersurface of the function section  21 . Further, for example, as shown in  FIG. 35C , the metallic layer  22  may be arranged in such a manner that the undersurface of the metallic layer  22  is located at a position recessed from the undersurface of the function section  21 . It is to be noted that, in  FIG. 35C , a depression is formed on the undersurface of the function section  21  in correspondence with the metallic layer  22 , and the undersurface of the metallic layer  22  is exposed at the bottom of the depression. 
     Further, in the above-described embodiment and modification example thereof, as shown in an example in  FIG. 36A , the metallic layer  13  is arranged in such a manner that the top surface of the metallic layer  13  is in the same or almost the same plane as the mounting surface of the wiring substrate  50  (the top surface of the insulating layer  12 ). However, for example, as shown in  FIG. 36B , the metallic layer  13  may be arranged in such a manner that the top surface of the metallic layer  13  is located at a position recessed from the mounting surface of the wiring substrate  50  (the top surface of the insulating layer  12 ). It is to be noted that, in  FIG. 36B , a depression is formed on the mounting surface of the wiring substrate  50  (the top surface of the insulating layer  12 ) in correspondence with the metallic layer  13 , and the top surface of the metallic layer  13  is exposed at the bottom of the depression. Alternatively, for example, as shown in  FIG. 36C , the metallic layer  13  may be provided on the mounting surface of the wiring substrate  50  (the top surface of the insulating layer  12 ), and the whole side surface or a part thereof of the metallic layer  13  and the top surfaces of the metallic layer  13  may be exposed to the outside without being covered by the insulating layer  12 . 
     5. Third Embodiment 
     [Configuration] 
     Next, the description is provided on a mounting substrate  3  according to a third embodiment of the present application.  FIG. 37  shows an example of a cross-sectional configuration of the mounting substrate  3 . The mounting substrate  3  is a substrate where a plurality of devices  60  are mounted on a support substrate  80  with a fixing layer  81  in between. The support substrate  80  and each of the devices  60  are electrically separated from each other by the fixing layer  81 . 
     For example, as shown in  FIG. 37 , the mounting substrate  3  may include the support substrate  80 , the fixing layer  81 , an insulating layer  82 , the plurality of devices  60 , a plurality of wires  83 , and a plurality of wires  84 . The support substrate  80  supports the plurality of devices  60 , and may be configured of, for example, a silicon substrate, a glass substrate, a resin substrate, or the like. In the support substrate  80 , the surface on the device  60  side is a flat surface. That is, the mounting surface of the support substrate  80  is a flat surface. The fixing layer  81  fixes each of the devices  60  on the support substrate  80 . It is to be noted that the fixing layer  81  also accepts each of the devices  60  at the time of the transfer process, and holds one or more of the transferred devices  60  using an adhesive force. The fixing layer  81  may be configured of, for example either an adhesive material or a sticking material. The insulating layer  82  is a layer for burying each of the devices  60  therein and for forming a flat surface on the top surface of the mounting substrate  3 , and serves as an interlayer insulating film as well. The insulating layer  82  may be configured of, for example, an insulating material such as polyimide. The wires  83  and  84  are configured to make an electrical connection between each of the devices  60  and an external circuit, and are electrically connected with the metallic layer  22  on each of the devices  60 . Each of the devices  60  is arranged on the support substrate  80  with the metallic layer  22  directed upward (that is, with the metallic layer  22  directed toward the opposite side, of the function section  21 , from the support substrate  80 ). Therefore, in each of the devices  60 , the function section  21  is connected with the fixing layer  81 . 
     [Manufacturing Method] 
     Next, description is provided on an example of a method of manufacturing the mounting substrate  3 . 
       FIG. 38  shows an example of a manufacturing process for the mounting substrate  3  using a flowchart. Each of  FIG. 39  to  FIG. 43  shows an example of a manufacturing process for the mounting substrate  3  using a cross-sectional view. First, a device substrate  100  and the support substrate  80  are prepared (step S 501 ,  FIG. 39  and  FIG. 40 ). 
     For example, as shown in  FIG. 39 , the device substrate  100  may include a support substrate  101 , a fixing layer  102 , and the plurality of devices  60 . Each of the devices  60  is arranged on the support substrate  101  with the metallic layer  22  directed downward (that is, with the metallic layer  22  directed toward the support substrate  101  side in relationship with the function section  21 ). Therefore, in each of the devices  60 , the metallic layer  22  is in contact with the fixing layer  102 . The support substrate  101  supports the plurality of devices  60 , and may be configured of, for example, a silicon substrate, a glass substrate, a resin substrate, or the like. The fixing layer  102  fixes each of the devices  60  on the support substrate  101 , and peels off each of the devices  60  from the support substrate  101  at the time of the transfer process. When a transfer is carried out in a laser ablation method, the fixing layer  102  may be configured of, for example, a material that absorbs light at laser oscillation wavelength band. The fixing layer  102  may be formed, for example, over a whole area of the top surface of the support substrate  101 . For example, as shown in  FIG. 39 , the fixing layer  102  may be formed only at a gap between the support substrate  101  and each of the devices  60 . Considering the transfer characteristics, as shown in  FIG. 39 , the fixing layer  102  may be preferably formed for each of the devices  60 . Further, considering the simplicity of the process, the fixing layer  102  may be preferably formed over a whole area of the top surface of the support substrate  101 . The fixing layer  102  may come in direct contact with the support substrate  101 . It is to be noted that an adhesion layer, an insulating layer, a metallic layer, and/or the like may be interposed between the fixing layer  102  and the support substrate  101 . 
     Next, a fixing layer  81  is formed over a whole area of the top surface of the support substrate  80  (step S 502 ,  FIG. 41 ). The fixing layer  81  accepts each of the devices  60  at the time of the transfer process, while holding one or more of the transferred devices  60  using an adhesive force. More specifically, the fixing layer  81  is either an adhesive material or a sticking material. Subsequently, the degree of the viscosity of the fixing layer  81  on the support substrate  80  is changed (step S 503 ). For example, using a heating treatment, a process is carried out that raises the degree of viscosity of an adhesive material or a sticking material that is applied on the top surface of the support substrate  80 . The degree of the viscosity of the fixing layer  81  is changed after the fixing layer  81  is formed on the top surface of the support substrate  80  and before the transfer process to be hereinafter described is performed. One reason for this is that the optimum degree of viscosity desired for the fixing layer  81  when the fixing layer  81  is applied on the top surface of the support substrate  80  is different from that when the fixing layer  81  accepts each of the devices  60  at the time of the transfer process. More specifically, when the fixing layer  81  is formed on the top surface of the support substrate  80 , the degree of the viscosity of the fixing layer  81  may be preferably relatively low, and may be preferably relatively high at the time of the transfer process. When heating is used for changing the degree of viscosity, a solvent contained in the adhesive material or the sticking material is volatized by heating the support substrate  80  using, for example, a hot plate, an atmosphere furnace, an infrared heating furnace, and/or the like to change the degree of viscosity of the adhesive material or the sticking material. 
     Thereafter, part or all of the plurality of devices  60  on the device substrate  100  are transferred on the support substrate  80  (step S 504 ). First, the device substrate  100  and the support substrate  80  are attached to a transfer apparatus. Next, the device substrate  100  and the support substrate  80  are arranged in opposition to each other with them closely-attached to each other ( FIG. 42 ). Subsequently, one or more of the plurality of devices  60  on the device substrate  100  are transferred on the support substrate  80  using, for example, a laser ablation method ( FIG. 43 ). This temporarily fixes the transferred device(s)  60  on the support substrate  80  with the use of the fixing layer  81 . It is to be noted that such a transfer process may be carried out in a method other than the laser ablation. 
     Afterward, the degree of the viscosity of the fixing layer  81  on the support substrate  80  is changed (step S 505 ). For example, using a heating treatment, a process is carried out that raises the degree of viscosity of the adhesive material or the sticking adhesive material that is applied on the top surface of the support substrate  80 . The degree of the viscosity of the fixing layer  81  is changed after the transfer is completed and before embedding to be hereinafter described is performed. One reason for this is that the optimum degree of viscosity desired for the fixing layer  81  when the fixing layer  81  accepts each of the devices  60  at the time of the transfer process is slightly different from that when the embedding is performed. More specifically, when the embedding is carried out, the degree of the viscosity of the fixing layer  81  may be preferably higher than that at the time of the transfer process. A specific method of changing the degree of viscosity is similar to the above-described method. It is to be noted that this step is intended to prevent each of the transferred devices  60  from shifting during a period of time before the embedding is performed or during the embedding process. Therefore, this step may be omitted when there is no such a possibility. Finally, each of the devices  60  is embedded to form the insulating layer  82 , as well as the wires  83  and  84 . 
     [Effects] 
     Next, description is provided on the effects of the method of manufacturing the mounting substrate  3 . 
     In this embodiment of the present application, the degree of the viscosity of the fixing layer  81  is changed after the fixing layer  81  is coated on the top surface of the support substrate  80  and before the transfer process is performed. This makes it possible to reduce the possibility that a positional shift will occur in each of the devices  60  after the transfer. Further, in this embodiment, the degree of the viscosity of the fixing layer  81  is changed after the transfer process is performed and before each of the devices  60  is embedded. This makes it possible to reduce the possibility that a positional shift will occur in each of the devices  60  immediately before or in the middle of the embedding. 
     6. Fourth Embodiment 
     [Configuration] 
     Next, description is provided on an electronic apparatus  4  according to a fourth embodiment of the present application.  FIG. 44  shows an example of a simplified configuration of the electronic apparatus  4 . The electronic apparatus  4  includes any one of the mounting substrates  1 ,  2 , and  3 , and a control section  5  that is electrically connected with the mounting substrate  1 ,  2 , or  3 . The control section  5  may be, for example, a circuit that applies a voltage or a current to the mounting substrate  1 ,  2 , or  3 , or receives an output from the mounting substrate  1 ,  2 , or  3 . In the electronic apparatus  4 , the mounting substrate  1 ,  2 , or  3  may serve as, for example, a light-emitting panel, a display panel, or a light-receiving panel due to application of a voltage or a current by the control section  5  to the mounting substrate  1 ,  2 , or  3 . 
     [Manufacturing Method] 
     Subsequently, description is provided on an example of a method of manufacturing the electronic apparatus  4  including any one of the mounting substrates  1 ,  2 , and  3 . First, using any of the methods described in the above-described embodiments and modification examples thereof, the mounting substrate  1 ,  2 , or  3  is formed (for example, see  FIG. 3 ,  FIG. 11 ,  FIG. 21 ,  FIG. 29 , and  FIG. 38 ). Next, the control section  5  is prepared, and thereafter, the mounting substrate  1 ,  2 , or  3  and the control section  5  are electrically connected with each other. Thus, the electronic apparatus  4  is formed. 
     [Effects] 
     Next, description is provided on the effects of the method of manufacturing the electronic apparatus  4 . 
     In this embodiment of the present application, using any of the methods described in the above-described embodiments and modification examples thereof, any one of the mounting substrates  1 ,  2 , and  3  is formed. This makes it possible to use a more inexpensive and easier-to-repair mounting substrate for the electronic apparatus  4  as compared with a mounting substrate that is formed using an existing method. 
     The present application is described thus far with reference to some embodiments and modification examples thereof. However, the present application is not limited to the above-described embodiments and the like, and various modifications may be made. 
     For example, in the above-described third embodiment, a chip-shaped material may be transferred instead of the device  60 . More specifically, in the present application, the device may not necessarily have unique function by itself, and may be configured of, for example, a chip-shaped material. On this occasion, in the device, the surface on the support substrate  81  side may be a flat surface. Further, on this occasion, in the support substrate  81 , the mounting surface thereof may be a flat surface. Further, when the device is configured of a chip-shaped material, the device may have one or more protrusions on the surface on the support substrate  81  side. This protrusion has a role (a role as an anchor) that is similar to that of the protrusion in the above-described first embodiment. For example, as shown in  FIG. 45 , a chip-shaped material  110  may have a plurality of protrusions  111  on the underside thereof (a surface on the support substrate  81  side). In this case, each of the protrusions  111  has a role as an anchor. 
     Further, for example, it is possible to achieve at least the following configurations from the above-described example embodiments and the modifications of the present application. 
     (1) A method of manufacturing a mounting substrate, the method including: 
     transferring part or all of a plurality of devices on a device substrate onto a wiring substrate, and temporarily fixing the transferred devices to the wiring substrate with use of a fixing layer having viscosity, the device substrate including a support substrate and the plurality of devices fixed on the support substrate; and performing a reflow process on the wiring substrate to electrically connect the transferred devices with the wiring substrate, and thereby forming the mounting substrate. 
     (2) The method according to (1), wherein 
     each of the devices has one or more first metallic parts on a surface of the device, 
     the wiring substrate has one or more second metallic parts on a surface of the wiring substrate, 
     either or both of the first metallic part and the second metallic part has an electrically-conductive protrusion standing out from a surrounding area, and 
     the first metallic part is electrically connected with the second metallic part via the protrusion through the performing of the reflow process. 
     (3) The method according to (2), wherein the protrusion includes one or both of a solder bump and a solder diffusion suppression layer.
 
(4) The method according to (2) or (3), wherein
 
     the first metallic part has the protrusion, and 
     the first metallic part includes a solder bump serving as the protrusion. 
     (5) The method according to (4), wherein 
     the second metallic part also has the protrusion, and 
     the second metallic part includes a solder diffusion suppression layer serving as the protrusion. 
     (6) The method according to (4), wherein the second metallic part has no the protrusion, and is provided at a position that is same or lower in height as compared with the surrounding area.
 
(7) The method according to any one of (1) to (6), further including removing the fixing layer after the reflow process is performed.
 
(8) The method according to any one of (1) to (7), further including performing a process of raising a degree of viscosity of the fixing layer before the transferring is performed.
 
(9) The method according to (8), further including performing a process of raising the degree of the viscosity of the fixing layer after the transferring is performed and before the reflow process is performed.
 
(10) The method according to (8), further including performing the process of raising the degree of the viscosity of the fixing layer by one or more methods out of heating, decompression, light irradiation, and addition of a curing agent.
 
(11) A method of manufacturing an electronic apparatus, the method including:
 
     transferring part or all of a plurality of devices on a device substrate onto a wiring substrate, and temporarily fixing the transferred devices to the wiring substrate with use of a fixing layer having viscosity, the device substrate including a support substrate and the plurality of devices fixed on the support substrate; 
     performing a reflow process on the wiring substrate to electrically connect the transferred devices with the wiring substrate, and thereby forming the mounting substrate; and 
     electrically connecting the mounting substrate with a control section, and thereby forming an electronic apparatus. 
     Also, for example, it is possible to achieve at least the following configurations from the above-described example embodiments and the modifications of the present application. 
     (12) A method of manufacturing a mounting substrate, the method of manufacturing a mounting substrate where a plurality of devices are mounted on a transfer substrate including: 
     performing a process of raising a degree of viscosity of a fixing layer having viscosity after coating the fixing layer on a surface of the transfer substrate; and 
     transferring some or all of the plurality of devices on a device substrate where the plurality of devices are fixed on a support substrate on the transfer substrate. 
     (13) The method according to (12), further including: 
     performing a process of raising a degree of viscosity of the fixing layer using at least one method of heating, decompression, light irradiation, and addition of curing agent. 
     (14) The method according to (12) or (13), wherein the fixing layer is any one of a flux, an adhesive material, and a pressure-sensitive adhesive material.
 
(15) The method according to (12) or (13), wherein the fixing layer is either an adhesive material or a pressure-sensitive adhesive material.
 
(16) The method according to (12), (13), or (15), wherein
 
     in each of the devices, a surface of the transfer substrate is a flat surface, and 
     in the transfer substrate, a mounting surface for each of the devices is a flat surface. 
     (17) The method according to (16), wherein each of the devices has one or more first metallic parts on a surface on the opposite side of a surface on the transfer substrate side.
 
(18) A method of manufacturing an electronic apparatus, the method of manufacturing an electronic apparatus provided with a mounting substrate where a plurality of devices are mounted on a transfer substrate including:
 
     performing a process of raising a degree of viscosity of a fixing layer having viscosity after coating the fixing layer on a surface of the transfer substrate; and 
     transferring some or all of the plurality of devices on a device substrate where the plurality of devices are fixed on a support substrate on the transfer substrate. 
     It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.