Patent Publication Number: US-2022238463-A1

Title: Substrate, electronic device, and method for manufacturing substrate

Description:
TECHNICAL FIELD 
     The present technique relates a substrate. More specifically, the present technique relates to a substrate on which a semiconductor chip is mounted, an electronic device, and a method for manufacturing a substrate. 
     BACKGROUND ART 
     In recent years, the performance of electronic devices has improved, and along with this, an amount of heat generated by electronic devices during operation has tended to increase. As the amount of heat generated increases, there is an increasing likelihood that adverse effects such as thermal runaway of a mounted circuit and warpage of a substrate will occur. Thus, for example, an electronic device in which an area of a conductive pattern, which is a wiring pattern on a substrate, is increased, and the conductive pattern is caused to function as a heat sink has been proposed (see, for example, PTL 1). 
     CITATION LIST 
     Patent Literature 
     [PTL 1] 
     
         
         JP 2014-049604 A 
       
    
     SUMMARY 
     Technical Problem 
     In the above-mentioned conventional technique, heat dissipation performance is improved by increasing the area of the conductive pattern. However, when the area of the conductive pattern (wiring) is increased, an amount of metal constituting the wiring may be increased, and power consumption and a weight of the device may be increased due to the increase in the amount of metal. If the amount of metal is reduced in order to inhibit the increase in power consumption and weight, the heat dissipation performance will be degraded. As described above, in the above-mentioned device, it is difficult to improve the heat dissipation performance while inhibiting increase in the amount of metal. 
     The present technique has been devised in view of such circumstances and an object thereof is to improve heat dissipation performance while inhibiting an increase in an amount of metal in a wired substrate. 
     Solution to Problem 
     The present technique has been made to solve the above-mentioned problems, and a first aspect thereof is a substrate including: a transmission line configured to transmit a predetermined electrical signal from a semiconductor chip; an insulating material to which the transmission line is wired; and a heat storage material that has a higher thermal conductivity than the insulating material and accumulates latent heat accompanying phase transition that occurs within an operating temperature range of the semiconductor chip. This causes the effect that the heat generated by the semiconductor chip is absorbed by the heat storage material. 
     Also, in the first aspect, the substrate may include a flexible substrate, the transmission line may be wired to a base layer, and the base layer may include the insulating material. This causes the effect that the heat generated by the semiconductor chip mounted on the flexible substrate is absorbed by the heat storage material. 
     Also, in the first aspect, the substrate may include a rigid substrate, and the transmission line may be wired to a wiring layer in which a core material and a prepreg are disposed. This causes the effect that the heat generated by the semiconductor chip mounted on the rigid substrate is absorbed by the heat storage material. 
     Also, in the first aspect, the heat storage material may further be disposed on the wiring layer, and the core material and the prepreg may include the insulating material. This causes the effect that the heat is absorbed in the heat storage material that is disposed separately from the core material and the prepreg. 
     Also, in the first aspect, the prepreg may include the insulating material and the heat storage material. This causes the effect that the heat is absorbed in the prepreg. 
     Also, in the first aspect, the core material may include the insulating material and the heat storage material. This causes the effect that the heat is absorbed in the core material. 
     Also, in the first aspect, a solder resist configured to cover a surface of the substrate may further be provided, and the solder resist may include the heat storage material. This causes the effect that the heat is absorbed in the solder resist. 
     Also, a second aspect of the present technique is an electronic device including: a semiconductor chip; a transmission line configured to transmit a predetermined electrical signal from the semiconductor chip; an insulating material to which the transmission line is wired; and a heat storage material that has a higher thermal conductivity than the insulating material and accumulates latent heat accompanying phase transition that occurs within an operating temperature range of the semiconductor chip. This causes the effect that the heat generated by the semiconductor chip mounted on the substrate is absorbed by the heat storage material. 
     Also, a third aspect of the present technique is a method for manufacturing a substrate, the method including: a heat storage material disposing procedure of disposing a heat storage material that has a higher thermal conductivity than an insulating material and accompanies phase transition that occurs within an operating temperature range of a semiconductor chip; and a wiring procedure of wiring a transmission line configured to transmit a predetermined electrical signal from the semiconductor chip to the insulating material. This causes the effect that the substrate on which the heat storage material that absorbs the heat generated by the semiconductor chip is disposed is manufactured. 
     Also, in the third aspect, in the wiring procedure, the transmission line may be wired to a wiring layer in which a core material and a prepreg are disposed, and in the heat storage material disposing procedure, the heat storage material may further be disposed on the wiring layer. This causes the effect that the heat is absorbed in the heat storage material that is disposed separately from the core material and the prepreg. 
     Also, in the third aspect, a coating procedure of coating a surface of the substrate with a solder resist may further be provided, at least one of the solder resist, the core material, and the prepreg may include the heat storage material, the core material and the prepreg may include the insulating material, and in the heat storage material disposing procedure, at least one of the solder resist, the core material, and the prepreg may be disposed, and in the wiring procedure, the transmission line may be wired to the wiring layer in which the core material and the prepreg are disposed. This causes the effect that the heat is absorbed in at least one of the core material, the prepreg, and the solder resist. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing a configuration example of an electronic device according to a first embodiment of the present technique. 
         FIG. 2  is an example of a cross-sectional view of the electronic device according to the first embodiment of the present technique. 
         FIG. 3  is an example of a cross-sectional view of a wiring layer according to the first embodiment of the present technique. 
         FIG. 4  is a diagram for explaining heat dissipation performance of the first embodiment of the present technique. 
         FIG. 5  is a diagram for explaining a process until desmearing according to the first embodiment of the present technique. 
         FIG. 6  is a diagram for explaining a process until visual inspection according to the first embodiment of the present technique. 
         FIG. 7  is a flowchart showing an example of a method for manufacturing a mounting substrate according to the first embodiment of the present technique. 
         FIG. 8  is an example of a cross-sectional view of a mounting substrate according to a second embodiment of the present technique. 
         FIG. 9  is an example of a cross-sectional view of an electronic device according to a third embodiment of the present technique. 
         FIG. 10  is a diagram for explaining a method for manufacturing a glass cloth according to the third embodiment of the present technique. 
         FIG. 11  is a diagram for explaining a method of manufacturing a mounting substrate according to the third embodiment of the present technique. 
         FIG. 12  is a diagram for explaining a process until formation of through holes according to the third embodiment of the present technique. 
         FIG. 13  is a diagram for explaining a process until visual inspection according to the third embodiment of the present technique. 
         FIG. 14  is a diagram showing an example of a composition of a solder resist according to the third embodiment of the present technique. 
         FIG. 15  is a flowchart showing an example of a method for manufacturing a mounting substrate according to the third embodiment of the present technique. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, aspects for implementing the present technique (hereinafter referred to as embodiments) will be described. The description will be made in the following order. 
     1. First embodiment (example in which heat storage material is disposed in rigid substrate) 
     2. Second embodiment (example in which heat storage material is disposed in flexible substrate) 
     3. Third embodiment (example in which core material or the like including heat storage material is disposed in rigid substrate) 
     1. First Embodiment 
     [Configuration Example of Electronic Device] 
       FIG. 1  is a diagram showing a configuration example of an electronic device  100  according to a first embodiment of the present technique. This electronic device  100  includes a semiconductor chip  110  and a mounting substrate  200 . 
     The semiconductor chip  110  includes a solid-state imaging element  111 , external terminals (not shown), and the like. The solid-state imaging element  111  captures image data by photoelectric conversion. For the solid-state imaging element  111 , for example, a complementary metal oxide semiconductor (CMOS) imaging element or the like is used. Also, although the solid-state imaging element  111  is disposed in the semiconductor chip  110 , the present technique is not limited to this configuration, and a semiconductor integrated circuit other than the solid-state imaging element  111  can be disposed. 
     The mounting substrate  200  is a rigid substrate on which the semiconductor chip  110  is mounted and includes various circuits such as a digital signal processor  210 . The digital signal processor  210  performs predetermined signal processing on the image data. This digital signal processor  210  exchanges the image data and control signals with the solid-state imaging element  111  via a signal line  109 . Also, although the digital signal processor  210  is disposed in the mounting substrate  200 , the present technique is not limited to this configuration, and a circuit other than the digital signal processor  210  can be disposed. 
       FIG. 2  is an example of a cross-sectional view of the electronic device  100  according to the first embodiment of the present technique. The semiconductor chip  110  is mounted on one of both surfaces of the mounting substrate  200  by wire bonding. Hereinafter, a surface on which the semiconductor chip  110  is mounted is referred to as a “front surface,” and a surface on which the semiconductor chip  110  is not mounted is referred to as a “back surface.” Also, mounting of the semiconductor chip  110  is not limited to the wire bonding, and for example, flip chip mounting can also be used. In addition, components other than the semiconductor chip  110  can further be mounted. 
     Further, a predetermined direction parallel to the front surface of the mounting substrate is defined as an “X direction,” and a direction perpendicular to the front surface is defined as a “Z direction.” A direction perpendicular to the X and Z directions is defined as a “Y direction.” The figure is a cross-sectional view seen in the Y direction. 
     Also, the front surface of the mounting substrate  200  is coated with a solder resist  221  and the back surface of the mounting substrate  200  is coated with a solder resist  222 . 
     Further, the mounting substrate  200  includes a wiring layer  230  to which a signal line  240  is wired. The wiring layer  230  includes a core material  231 , prepregs  232  and  233 , the signal line  240 , heat storage materials  251  to  259 , and copper foils  271  to  274 . 
     The core material  231  is a member disposed in the vicinity of a center of the mounting substrate  200  and includes an insulating material. The copper foils  272  and  273  are laminated on both surfaces of the core material  231 . 
     The prepregs  232  and  233  are members for connecting copper foils such as the copper foils  271  to  274  and include insulating materials. For the prepregs  232  and  233 , for example, members obtained by impregnating a glass cloth, which is a covering made of glass, with a resin called resin and covering its top and bottom with a thin resin are used. The prepreg  232  is disposed between the copper foil  271  and the copper foil  272  above the core material  231  with a direction toward the front surface of the mounting substrate  200  set as an upward direction. On the other hand, the prepreg  233  is disposed between the copper foil  273  and the copper foil  274  below the core material  231 . 
     As described above, in the mounting substrate  200 , the solder resist  221 , the copper foil  271 , the prepreg  232 , the copper foil  272 , the core material  231 , the copper foil  273 , the prepreg  233 , the copper foil  274 , and the solder resist  222  are laminated in order from a top thereof. The substrate in which copper foils are applied to a laminated board on which prepregs are stacked in this way is called a copper-clad laminated board. 
     Further, the signal line  240  is connected to the semiconductor chip  110  via the signal line  109 , and is also connected to the copper foil  271  or the like. In addition, a portion of the signal line  240  extending in the Z direction is called a via. This signal line  240  and the copper foils  271  to  274  are used as a transmission line for transmitting a predetermined electrical signal (image data or the like) from the semiconductor chip  110 . Various circuits such as the digital signal processor  210  are formed by this transmission line. Also, the signal line  240  and the copper foils  271  to  274  are an example of the transmission line described in the claims. 
     Further, the heat storage materials  251  to  259  are embedded in the wiring layer  230 . These heat storage materials  251  to  259  are members that have higher thermal conductivities than the insulating materials constituting the core material  231  and the prepregs  232  and  233  and accumulate latent heat accompanying phase transition that occurs within an operating temperature range of the semiconductor chip  110 . The heat storage material that accumulates latent heat in this way is called a latent heat storage material. 
     Here, the latent heat is thermal energy generated or absorbed when phase transition of an object occurs without change in temperature of the object. In addition, the phase transition also means, in addition to a change of state between a gas, a liquid and a solid, a change of physical properties (crystal structure, density, magnetism, etc.) or a change of ground state of a substance in the same phase. This phase transition is also called a phase change. 
     Further, shapes and sizes of the heat storage materials  251  to  259  are arbitrary. The heat storage material  251  is disposed directly below the solder resist  221  and the heat storage material  259  is disposed directly above the solder resist  222 . The heat storage materials  252  to  258  are disposed in a region in which at least some of the heat storage materials  252  to  258  comes into contact with the transmission line (signal line  240  or the like). Further, a part of the heat storage material  254  is filled into a through hole extending in the Z direction. This part can be called a thermal via. 
     For the heat storage material  251  and the like, vanadium oxides, paraffin-based heat storage materials, phase change material (PCM) sheets, or the like are used. Their thermal conductivities are, for example, 10 to 250 watts per meter Kelvin (W/m·K). Also, the latent heat is, for example, 50 to 510 joules per gram (J/g). The heat storage materials such as vanadium oxides are used for heating and cooling houses and for keeping warm and cold during transportation. 
     Vanadium oxides are solid at room temperature, are relatively easy to handle if powdered, and have greater latent heat than a paraffin-based heat storage material. On the other hand, vanadium oxides have a higher density than a paraffin-based heat storage material, and in a case in which they is disposed on the mounting substrate  200 , insulation is required depending on a location. Further, the paraffin-based heat storage material changes from a solid to a gel state at a high temperature such as 80° C. or higher, but if it is encapsulated in microcapsules, it can be easily handled. In addition, the paraffin-based heat storage material encapsulated in a microcapsule is also called a thermomemory. 
     Further, a material of the transmission line (the signal line  240 , the copper foil  271 , etc.) is a metal such as copper, and a material of the insulating materials constituting the core material  231  and the prepregs  232  and  233  is glass or a resin. These metals, glass, and resin do not undergo phase transition within a general operating temperature range of the semiconductor chip  110 , and within that temperature range, sensible heat is generated instead of latent heat. Sensible heat is thermal energy generated or absorbed when a temperature of an object changes without phase transition. 
     In summary of the above-mentioned configuration, in the mounting substrate  200  which is a rigid substrate, the transmission line such as the signal line  240  and the copper foil  271  are wired in the wiring layer  230  in which the prepreg  232  and the core material  231  including the insulating materials are disposed. This transmission line transmits an electrical signal from the semiconductor chip  110 . Further, the heat storage materials  251  to  259  that have higher thermal conductivities than the insulating materials and accumulate latent heat accompanying phase transition that occurs within the operating temperature range of the semiconductor chip  110  are further disposed in the wiring layer  230 . With this configuration, the heat generated in the semiconductor chip  110  is conducted to the heat storage material  251  and the like via the transmission line and absorbed. 
       FIG. 3  is an example of a cross-sectional view of the wiring layer according to the first embodiment of the present technique.  FIG. 3  is an example of a cross-sectional view of the wiring layer  230  taken along line segment X 1 -X 2  in  FIG. 2  and viewed in the Z direction. As illustrated in  FIG. 3 , in the prepreg  232  and the like, a via that functions as the signal line  240  is wired, and the heat storage material  254  is embedded in a region in which at least a part is in contact with the signal line  240  (for example, a region surrounding the signal line  240 ). 
       FIG. 4  is a diagram for explaining heat dissipation performance of the first embodiment of the present technique. Arrows in the figure indicate directions in which heat conducts. As illustrated in the figure, when heat is generated in the semiconductor chip  110 , the transmission line such as the signal line  240  conducts the heat. As described above, the thermal conductivity of the heat storage material ( 251 , etc.) is higher than those of the insulating materials. For this reason, most of the heat is conducted from the transmission line to the heat storage materials. 
     Further, the heat storage materials undergo phase transition within the operating temperature range of the semiconductor chip  110 , and the latent heat accompanying the phase transition is accumulated. In other words, the heat storage materials absorb thermal energy corresponding to the latent heat. Also, the thermal energy absorbed by the heat storage materials is released to the back surface side of the mounting substrate  200  via the transmission line with the elapse of time. 
     As described above, the heat generated in the semiconductor chip  110  is conducted from the transmission line to the heat storage materials, and the heat storage materials absorb the heat during the phase transition, and thus an amount of heat radiated from the semiconductor chip  110  increases as compared with a case in which the heat storage materials are not provided. As a result, it is possible to inhibit a temperature rise of the semiconductor chip  110  and prevent thermal runaway of the semiconductor chip  110  due to the temperature rise. 
     Also, since the heat storage materials absorb the heat during the phase transition without the temperature being raised, a temperature rise of the mounting substrate  200  can be inhibited as compared with the case in which the heat storage materials are not provided. Further, by disposing the heat storage materials in a dispersed manner in the mounting substrate  200 , a heat distribution of the mounting substrate  200  can be made uniform and an internal stress can be relaxed at the time of thermal expansion. By inhibiting the temperature rise and making the heat distribution uniform, it is possible to prevent the mounting substrate  200  from being warped due to the temperature rise. By preventing warpage, deterioration of imaging characteristics of the solid-state imaging element  111  can be inhibited. In particular, as a size of the solid-state imaging element  111  increases, the effect of inhibiting deterioration of imaging characteristics increases. 
     By increasing a volume and an area of a metal (copper or the like) transmission line (signal line  240  or the like), an amount of heat dissipated from the semiconductor chip  110  can also be increased. However, as an amount of metal constituting the transmission line increases, a leakage current increases, which may increase power consumption and weight. For this reason, it is not preferable to increase the number of transmission lines. 
     The heat storage materials are thinner and lighter than the metal constituting the transmission line, and thus by improving the heat dissipation performance with the heat storage materials, it is possible to easily reduce a density of the wiring, and a size and a weight of the imaging element. 
     [Method for Manufacturing Mounting Substrate] 
       FIG. 5  is a diagram for explaining a process until desmearing according to the first embodiment of the present technique. In the figure, a is a diagram for explaining a process of forming through holes, and in the figure, b is a diagram for explaining processes of copper-plating and forming an inner layer circuit. In the figure, c is a diagram for explaining processes of forming the heat storage materials and lamination pressing, and in the figure, d is a diagram for explaining a process from drilling to desmearing. 
     As illustrated in a of the figure, a manufacturing system forms through holes for conduction in an inner layer (that is, the core material  231 ) by drilling or laser machining. 
     Next, as illustrated in b of the figure, the manufacturing system performs copper-plating on an inner wall of the through hole and a front surface of the core material  231  to form an inner layer circuit. 
     Subsequently, as illustrated in c of the figure, the prepregs  232  and  233  are laminated, and the heat storage material  252  and the like are disposed inside them, on upper surfaces and lower surfaces thereof. Then, the manufacturing system melts and cures the laminated resins of the prepregs  232  and  233  by thermocompression bonding to prepare a multilayer substrate. 
     Here, as a method for forming the heat storage materials, an appropriate method is selected in accordance with a type of the heat storage materials. In the case of using vanadium oxides or paraffin-based heat storage materials, the manufacturing system mixes their microcapsules and powders with an epoxy resin or the like, prints and applies it to a circuit surface, the prepreg  232 , or the like with a screen printing machine or a dispenser, and cures the resin. In addition to applying and printing, when a lay-up is performed at the time of laminating the prepregs  232  and  233 , the heat storage materials are sandwiched between the prepreg  232  and the like, or overlapped on the upper and lower surfaces thereof, and thus they can be formed at arbitrary positions. In this case, the manufacturing system may prepare a flexible PCM sheet as a heat storage material, cut it into an arbitrary shape using a cutter, a hollow, or the like, and dispose it on the circuit surface, above, below and in the middle of the prepreg  232  and the like in the lay-up of the laminating process. 
     Then, as illustrated in d of the figure, the manufacturing system forms through holes and non-through holes in the laminated substrate by drilling or laser processing. The manufacturing system cleans the inside of the holes by performing a process of dissolving and removing unnecessary deposits (that is, desmearing) such as a resin remaining inside the holes formed in the laminated substrate with a plasma, a chemical solution, or the like. 
       FIG. 6  is a diagram for explaining a process until visual inspection according to the first embodiment of the present technique. In the figure, a is a diagram for explaining a process from formation of an outer layer circuit to formation of the heat storage materials, and in the figure, b is a diagram for explaining a process from formation of the solder resists to visual inspection. 
     As illustrated in a of the figure, the manufacturing system performs copper-plating on the holes formed in the laminated substrate and outer layers (the prepregs  232  and  233 , etc.) of the laminated substrate and electrically connects the copper-plated portions to the inner layer circuit. Then, the manufacturing system wires the signal line  240  to the outer layer by etching or an additive method to form the outer layer circuit. Subsequently, the manufacturing system disposes the heat storage material  257  and the like on the holes formed in the laminated substrate and the outer layer circuit. In a case in which the heat storage materials are formed, an appropriate method is selected in accordance with a type of the heat storage materials, and coating, printing, or the like is used. When they are disposed directly below or directly above the solder resists  221  and  222 , coating, printing, laminating, pasting, or the like is used. 
     Then, as illustrated in b of the figure, the manufacturing system forms the solder resists  221  and  222  on the front surface and the back surface of the outer layer circuit. For a method for forming the solder resists  221  and  222 , screen printing, roll coating, spray coating, or the like is used. In addition, the manufacturing system cures solder resist ink by thermosetting, ultra-violet (UV) curing, or the like. 
     The manufacturing system performs gold-plating on necessary lands for the purposes of wire bonding, soldering, formation of contacts and terminals, or the like. Also, if the purpose of wire bonding or the like can be achieved, processing other than gold-plating can be performed. Then, the manufacturing system performs outer shape processing on the laminated substrate to have a predetermined shape by router processing, outer shape pressing, or the like. In addition, the manufacturing system electrically inspects whether or not connections electrically necessary for circuits and conduction holes are performed, and whether there is a breakage or a short-circuit in the circuits. Finally, the manufacturing system visually inspects, using an inspection machine or the like, whether or not an appearance of the mounting substrate  200  is finished in accordance with standards. This visual inspection may be performed visually by an operator. 
       FIG. 7  is a flowchart showing an example of a method for manufacturing the mounting substrate  200  according to the first embodiment of the present technique. The manufacturing system forms the through holes for conduction in the inner layer (step S 901 ). The manufacturing system performs copper-plating (step S 902 ) to form the inner layer circuit (step S 903 ). Then, the manufacturing system forms the heat storage materials (step S 904 ), melts and cures the resins of the prepregs  232  and  233  by thermocompression bonding, and prepares the multilayer substrate (step S 905 ). 
     Next, the manufacturing system forms the through holes and the non-through holes in the laminated substrate (steps S 906  and S 907 ) and performs desmearing (step S 908 ). The manufacturing system performs copper-plating on the holes formed in the laminated substrate and the outer layer of the laminated substrate are (step S 909 ) to form the outer layer circuit (step S 910 ). 
     Subsequently, the manufacturing system forms the heat storage material  257  and the like on the holes formed in the laminated substrate and the outer layer circuit (step S 911 ). The manufacturing system forms the solder resists  221  and  222  on the front and back surfaces of the outer layer circuit (step S 912 ) and performs gold-plating on necessary lands (step S 913 ). Also, if the purpose of wire bonding or the like can be achieved, processing other than gold-plating can be performed. Then, the manufacturing system performs outer shape processing on the laminated substrate (step S 914 ). Further, the manufacturing system performs an electrical inspection (step S 915 ) and a visual inspection (step S 916 ). After step S 916 , the manufacturing system ends the manufacturing of the mounting substrate  200 . Also, some of these manufacturing processes can be performed by an operator instead of the manufacturing system. 
     As described above, according to the first embodiment of the present technique, the heat storage material  251  and the like, which have higher thermal conductivities than the insulating materials and accumulate the latent heat accompanying the phase transition are disposed, and thus the heat generated in the semiconductor chip  110  can be conducted and absorbed by the heat storage material  251  and the like. As a result, the heat dissipation performance of the electronic device  100  can be improved while an increase in the amount of metal is inhibited. 
     2. Second Embodiment 
     In the first embodiment described above, a rigid substrate is used for the mounting substrate  200 , but since the rigid substrate cannot be bent, three-dimensional wiring in the device may be difficult. The electronic device  100  of a second embodiment is different from that of the first embodiment in that the heat storage materials are disposed on a flexible substrate. 
       FIG. 8  is an example of a cross-sectional view of a mounting substrate  201  according to the second embodiment of the present technique. In the electronic device  100  of the second embodiment, the mounting substrate  201  is disposed instead of the mounting substrate  200 . For the mounting substrate  201 , a flexible substrate is used. 
     The mounting substrate  201  includes a cover lay  225 , a heat storage material  251 , a signal line  240 , and a base layer  280 . Also, although components such as the semiconductor chip  110  are mounted on the mounting substrate  201 , the semiconductor chip  110  is omitted in the figure. 
     The base layer  280  is a thin film-shaped insulating material, and polyimide or the like is used. The base layer  280  is also called a base film. In the base layer  280 , a signal line  240  is wired and a heat storage material  251  is disposed. A front surface of the base layer  280  is covered with the cover lay  225 . 
     At the time of manufacturing the substrate, the manufacturing system forms a circuit formed by the signal line  240  on the base layer  280  and disposes the heat storage material  251  by pasting, printing or coating. Then, the manufacturing system performs thermocompression bonding of the cover lay  225 . Further, a solder resist can be disposed instead of the cover lay  225 . 
     Since the heat storage material  251  absorbs latent heat, it is possible to improve heat dissipation performance of components mounted on the mounting substrate  201  (that is, the flexible substrate) as in the first embodiment. 
     Also, although a flexible substrate is used for the mounting substrate  201 , the present technique is not limited to this configuration. A flex rigid substrate formed by combining a flexible substrate with a rigid substrate can also be used for the mounting substrate. In the case of a flex rigid substrate, for example, the semiconductor chip  110  is mounted on the rigid substrate, and the heat storage material  251  and the signal line  240  are disposed on the flex substrate or the rigid substrate. 
     As described above, according to the second embodiment of the present technique, the heat storage material  251  is disposed on the flexible substrate, and thus when three-dimensional wiring is performed with the flexible substrate, heat dissipation performance of the substrate can be improved. 
     3. Third Embodiment 
     In the first embodiment described above, the manufacturing system has disposed the heat storage materials  251  to  259  in the wiring layer  230 , but it is necessary to further carry out a process of disposing the heat storage material  251  and the like as compared with the case in which they are not disposed. A mounting substrate of a third embodiment is different from that of the first embodiment in that a process of forming the heat storage material is unnecessary. 
       FIG. 9  is an example of a cross-sectional view of the electronic device  100  according to the third embodiment of the present technique. The electronic device  100  of the third embodiment is different from that of the first embodiment in that a mounting substrate  202  is provided instead of the mounting substrate  200 . 
     The mounting substrate  202  includes solder resists  223  and  224  instead of the solder resists  221  and  222 . Also, the mounting substrate  202  includes a core material  235  instead of the core material  231  and prepregs  236  and  237  instead of the prepregs  232  and  233 . 
     The solder resists  223  and  224  are obtained by mixing a heat storage material with solder resist ink or the like. Further, the core material  235  and the prepregs  236  and  237  are obtained by mixing a heat storage material with an insulating material such as a varnish or a silane coupling material. That is, the solder resists  223  and  224 , the core material  235 , and the prepregs  236  and  237  further include a heat storage material in addition to the insulating material and the solder resist ink. 
     The solder resist ink used for the solder resists  223  and  224  includes a two-component type in which a main agent and a curing agent are mixed immediately before use and a one-component type in which the main agent and curing agent are already mixed by an ink manufacturer. Examples of a method for applying the solder resists  223  and  224  include screen printing, roll coating, spraying, and curtain coating. A viscosity of the ink is adjusted in accordance with the coating method. Specifically, the manufacturing system uses a stirrer to put the solder resist ink in a container and stirs the container while rotating the container with a spatula or the like in the container. In this case, microcapsules and powder of a heat storage material such as paraffin or vanadium oxide are added at the same time and mixed with the solder resist ink. As a result, the solder resists  223  and  224  having a heat storage function can be formed by using a normal solder resist manufacturing process. 
     The heat storage material mixed with the solder resist  223  and the like or the core material  235  and the like in the second embodiment has the same function as that of the first embodiment. That is, the heat storage material has a higher thermal conductivity than the insulating material and accumulates latent heat accompanying phase transition. For this reason, even in the second embodiment, the heat dissipation performance can be improved as in the first embodiment. 
       FIG. 10  is a diagram for explaining a method for manufacturing a glass cloth according to the third embodiment of the present technique. The manufacturing system performs processes of warping and gluing, drawing, weaving and heat cleaning. These processes are omitted in the figure. Details of these processes are described in, for example, “ Seizo hoho  (Manufacturing method),” [online], Nitto Boseki Co., Ltd., [Search on Apr. 2, 2019], Internet (URL: https://www.nittobo.co.jp/business/glassfiber/about/process.htm).” 
     As illustrated in the figure, after heat cleaning, the manufacturing system performs secondary degreasing, transports glass fibers using an accumulator  311 , and immerses them in a surface processing solution tank  312  containing a silane coupling material. Then, the manufacturing system heats the glass fibers in a heating furnace  313 , transports them using an accumulator  314 , and performs a processing to complete the glass cloth. In this process, the manufacturing system can mix the heat storage material with the silane coupling material in the surface processing solution tank  312 . 
       FIG. 11  is a diagram for explaining a method for manufacturing the mounting substrate  202  according to the third embodiment of the present technique. In the figure, a is a diagram for explaining a manufacturing process of a varnish, and in the figure, b is a diagram for explaining a manufacturing process of prepregs. In the figure, c is a diagram for explaining a process of laminating copper foils, and in the figure, d is a diagram for explaining a process of heating and pressing using a pressing machine. In the figure, e is a diagram showing an example of a copper-clad laminate. 
     As illustrated in a of the figure, the manufacturing system manufactures the varnish by stirring a resin, a curing agent, or the like with a stirrer  321  or the like. In this process, the manufacturing system can further mix the heat storage material in addition to the resin and the like. 
     Next, as illustrated in b of the figure, the manufacturing system applies the varnish to the glass cloth, immerses it in an impregnated pad  322 , and dries it with a heater  323 . Then, the manufacturing system cuts the glass cloth into a sheet shape using a cutter  324  and laminates them. As a result, the prepregs  236  and  237  are manufactured. In this process, the manufacturing system can form the heat storage material on surfaces of the prepregs by roll coating, printing, or the like. 
     Subsequently, as illustrated in c of the figure, the manufacturing system superimposes the copper foils  271  and  272  on both surfaces of the prepregs. 
     As illustrated in d of the figure, the manufacturing system heats and pressurizes the prepregs on which the copper foils are laminated by the pressing machine  326 . As a result, a copper-clad laminate can be manufactured as illustrated in e of the figure. 
     As illustrated in  FIGS. 10 and 11 , the prepregs can be manufactured by mixing the heat storage material with the insulating material. Specifically, as illustrated in  FIG. 10 , the heat storage material can be mixed with the silane coupling material. Also, as illustrated in a of  FIG. 11 , the heat storage material can be mixed with the varnish. As illustrated in b of  FIG. 11 , the heat storage material can also be applied to surfaces of the dried prepregs. All of these three methods can be used, or only one or two can be used. Further, the core material can also be manufactured by the same method as that of the prepregs. 
     Also, the manufacturing system mixes the heat storage material with all of the core material, the prepregs, and the solder resists, but it is also possible to mix the heat storage material with only one or two of these. 
       FIG. 12  is a diagram for explaining a process until formation of the through holes according to the third embodiment of the present technique. In the figure, a is a diagram for explaining a process of forming the through holes, and in the figure, b is a diagram for explaining processes of copper plating and forming the inner layer circuit. In the figure, c is a diagram for explaining a process from formation of the heat storage material and lamination pressing to via processing. 
     As illustrated in a of the figure, the manufacturing system forms the through holes for conduction in the inner layer (core material  235 ) by drilling or laser machining. 
     Next, as illustrated in b of the figure, the manufacturing system performs copper-plating on inner walls of the through holes and a surface of the core material  235  to form the inner layer circuit. 
     Subsequently, as illustrated in c of the figure, the prepregs  236  and  237  are laminated, melted and cured by thermocompression bonding to prepare the multilayer substrate. Then, the manufacturing system forms the through holes and the non-through holes in the laminated substrate by drilling or laser machining. 
     The core material  235 , the prepreg  236 , and the like in the figure are manufactured by the manufacturing methods illustrated in  FIGS. 10 and 11 , and the heat storage material is mixed. 
       FIG. 13  is a diagram for explaining a process until visual inspection of the third embodiment of the present technique. In the figure, a is a diagram for explaining a process from desmearing to formation of the outer layer circuit, and in the figure, b is a diagram for explaining a process from formation of the solder resists  223  and  224  to visual inspection. 
     As illustrated in a of the figure, the manufacturing system cleans the inside of the holes by performing a process of dissolving and removing unnecessary deposits (desmearing) such as a resin remaining inside the holes formed in the laminated substrate with a plasma, a chemical solution, or the like. Then, the manufacturing system performs copper-plating on the holes formed in the laminated substrate and the outer layer of the laminated substrate and electrically connects copper-plated portions to the inner layer circuit. Then, the manufacturing system wires the signal line  240  to the outer layer by etching or an additive method to form the outer layer circuit. 
     Next, as illustrated in b of the figure, the manufacturing system forms the solder resists  223  and  224  on the front surface and the back surface of the outer layer circuit. The manufacturing system performs gold-plating on necessary lands for the purposes of wire bonding, soldering, formation of contacts and terminals, or the like. Also, if the purpose of wire bonding or the like can be achieved, processing other than gold-plating can be performed. Then, the manufacturing system performs outer shape processing on the laminated substrate to have a predetermined shape by router processing, outer shape pressing, or the like. In addition, the manufacturing system electrically inspects whether or not connections electrically necessary for circuits and conduction holes are performed. Finally, the manufacturing system inspects whether or not an appearance of the mounting substrate  202  is finished in accordance with standards using an inspection machine or the like. 
       FIG. 14  is a diagram showing an example of a composition of the solder resist according to the third embodiment of the present technique. As illustrated in the figure, the solder resist includes, for example, a resin, a filler, a color pigment, a catalyst, an additive, and a solvent. A proportion of a weight of the filler among these is about 20 to 25%. By adding microcapsules or powder of the heat storage material such as paraffin or vanadium oxide to the filler component, the solder resist ink itself can be imparted with a heat storage function. This makes it possible to manufacture the solder resists  223  and  224  that can store heat. Also, a particle size of the heat storage material added to the solder resist ink is preferably 2 micrometers (μm) or less. 
       FIG. 15  is a flowchart showing an example of a method for manufacturing the mounting substrate  202  according to the third embodiment of the present technique. The manufacturing method of the third embodiment is different from the first embodiment in that the processes of forming the heat storage material (steps S 904  and S 911 ) are not executed. In the third embodiment, since the solder resist  223  and the like including the heat storage material are used, the processes of forming the heat storage material (step S 904  or the like) can be reduced as compared with the first embodiment. 
     As described above, in the third embodiment of the present technique, the solder resist  223  and the like including the heat storage material, the core material  235  and the prepreg  236  and the like are disposed, and thus when the mounting substrate  202  is manufactured, the process of disposing the heat storage material becomes unnecessary. This makes it possible to simplify the manufacturing process of the mounting substrate  202 . 
     Also, the above-described embodiments show examples for embodying the present technique, and matters in the embodiments and matters specifying the invention in the claims have a corresponding relationship with each other. Similarly, the matters specifying the invention in the claims and the matters in the embodiments of the present technique having the same name have a corresponding relationship with each other. However, the present technique is not limited to the embodiments and can be embodied by applying various modifications to the embodiments without departing from the gist thereof. 
     In addition, the effects described in the present specification are merely examples and are not intended as limiting, and other effects may be obtained. 
     Further, the present technique can have the following configurations. 
     (1) A substrate including: 
     a transmission line configured to transmit a predetermined electrical signal from a semiconductor chip; 
     an insulating material to which the transmission line is wired; and 
     a heat storage material that has a higher thermal conductivity than the insulating material and accumulates latent heat accompanying phase transition that occurs within an operating temperature range of the semiconductor chip. 
     (2) The substrate according to the above (1), 
     wherein the substrate includes a flexible substrate, 
     the transmission line is wired to a base layer, and 
     the base layer includes the insulating material. 
     (3) The substrate according to the above (1) or (2), 
     wherein the substrate includes a rigid substrate, and 
     the transmission line is wired to a wiring layer in which a core material and a prepreg are disposed. 
     (4) The substrate according to the above (3), 
     wherein the heat storage material is further disposed on the wiring layer, and the core material and the prepreg include the insulating material. 
     (5) The substrate according to the above (3) or (4), wherein the prepreg includes the insulating material and the heat storage material. 
     (6) The substrate according to one of the above (3) to (5), wherein the core material includes the insulating material and the heat storage material. 
     (7) The substrate according to one of the above (3) to (6), further including a solder resist configured to cover a surface of the substrate, wherein the solder resist includes the heat storage material. 
     (8) An electronic device including: 
     a semiconductor chip; 
     a transmission line configured to transmit a predetermined electrical signal from the semiconductor chip; 
     an insulating material to which the transmission line is wired; and 
     a heat storage material that has a higher thermal conductivity than the insulating material and accumulates latent heat accompanying phase transition that occurs within an operating temperature range of the semiconductor chip. 
     (9) A method for manufacturing a substrate, the method including: 
     disposing a heat storage material that has a higher thermal conductivity than an insulating material and accompanies phase transition that occurs within an operating temperature range of a semiconductor chip; and 
     wiring a transmission line configured to transmit a predetermined electrical signal from the semiconductor chip to the insulating material. 
     (10) The method for manufacturing a substrate according to the above (9), 
     wherein in the wiring, the transmission line is wired to a wiring layer in which a core material and a prepreg are disposed, and 
     in the disposing of the heat storage material, the heat storage material is further disposed on the wiring layer. 
     (11) The method for manufacturing a substrate according to the above (9), further including coating a surface of the substrate with a solder resist, 
     wherein at least one of the solder resist, the core material, and the prepreg contains the heat storage material, 
     the core material and the prepreg include the insulating material, 
     in the disposing of the heat storage material, at least one of the solder resist, the core material, and the prepreg is disposed, and 
     in the wiring, the transmission line is wired to the wiring layer in which the core material and the prepreg are disposed. 
     REFERENCE SIGNS LIST 
     
         
           100  Electronic device 
           109 ,  240  Signal line 
           110  Semiconductor chip 
           111  Solid-state imaging element 
           200 ,  201 ,  202  Mounting substrate 
           210  Digital signal processor 
           221  to  224  Solder resist 
           225  Cover lay 
           230  Wiring layer 
           231 ,  235  Core material 
           232 ,  233 ,  236 ,  237  Prepreg 
           251  to  259  Heat storage material 
           271  to  274  Copper foil 
           280  Base layer 
           311 ,  314  Accumulator 
           312  Surface processing solution tank 
           313  Heating furnace 
           321  Stirrer 
           322  Impregnated pad 
           323  Heater 
           324  Cutter 
           326  Press machine