Patent Publication Number: US-2021168966-A1

Title: Composite substrate

Description:
TECHNICAL FIELD 
     The present invention relates to a composite substrate including a heat dissipation plate. 
     BACKGROUND ART 
     High-output semiconductors such as high-brightness LEDs (Light Emitting Diodes) are used in devices requiring a high-brightness light source such as a head-up display mounted on a vehicle (for example, see Patent Document 1). In the case of high-brightness LEDs, since heat affects light output, dealing with the heat is an issue. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Japanese Unexamined Patent Application Publication No. 2016-218259 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     For example, for heat dissipation from the LED, it is conceivable to provide, on a substrate, a heat dissipation plate made of a material having excellent thermal conductivity different from the material of the substrate on which the LED is mounted, and mount the LED on the heat dissipation plate. However, the adhesive that bonds the LED and the substrate, and the wiring that crosses over the LED and the substrate may be broken or disconnected at or near the interface due to a difference in the linear expansion coefficient (thermal expansion coefficient) between different materials. 
     The present invention has been made in view of such circumstances, and an object thereof is to provide a composite substrate capable of reducing the influence by the difference in linear expansion coefficient between materials. 
     Solution to Problem 
     To solve the above-described problems, a composite substrate according to the present invention includes a quadrangular heat dissipation plate that has a corner part, the quadrangular heat dissipation plate including a surface on which an electronic component is provided, a substrate in a shape of a quadrangle that has a corner part, the substrate including an opening in which the heat dissipation plate is arranged, and an adhesive member bonding the heat dissipation plate and the substrate, in the composite substrate, the heat dissipation plate is arranged such that the corner part of the heat dissipation plate is rotated with respect to the corner part of the substrate. 
     Effect of the Invention 
     In the composite substrate according to the present invention, it is possible to reduce the influence by the difference in the linear expansion coefficient between materials. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an explanatory diagram illustrating a configuration of an optical system of a head-up display using a composite substrate according to the present embodiment. 
         FIG. 2  is a configuration diagram of a projection display device. 
         FIG. 3  is an explanatory diagram illustrating a configuration of an optical system of the projection display device. 
         FIG. 4  is a configuration diagram of an LED substrate of the projection display device. 
         FIG. 5  is an enlarged view for explaining an attachment structure for attaching the LED substrate to a housing. 
         FIG. 6  is a cross-sectional view along a thickness direction of the LED substrate. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     An embodiment of a composite substrate according to the present invention will be described with reference to the accompanying drawings. In the present embodiment, explanation will be provided by using an example in which the composite substrate according to the present invention is used as an LED substrate of a head-up display mounted on an automobile. 
       FIG. 1  is an explanatory diagram illustrating a configuration of an optical system of a head-up display using the composite substrate according to the present embodiment. 
     The head-up display  1  (hereinafter, referred to as HUD 1 ) is arranged in an instrument panel of an automobile. The HUD  1  mainly includes a projection display device  10 , a first plane mirror  13 , a second plane mirror  14 , a screen  15 , a first concave mirror  16 , a second concave mirror  17 , and a case  18 . The HUD  1  reflects display light L representing a display image displayed by the projection display device  10 , on the first and the second plane mirrors  13  and  14  and the first and the second concave mirrors  16  and  17  forming a relay optical system, and emits the display light L toward a windshield  2  of an automobile, which is an example of a transmission-reflection unit. By placing a viewpoint  4  in an eye box  3  being an image visible region generated by the HUD  1 , a viewer (mainly a driver) can visually recognize a virtual image V of the display image, which is superimposed on the scene (real scene) in front of the vehicle. 
     The projection display device  10  (display device  10 ) generates the display light L relating to the display image. The display device  10  will be described in detail below. The first plane mirror  13  reflects the display light L generated and emitted by the display device  10 . The second plane mirror  14  further reflects the display light L reflected by the first plane mirror  13 . The screen  15  receives the display light L reflected by the second plane mirror  14  and displays an image (real image). The first concave mirror  16  reflects the display light L emitted from the screen  15 . The second concave mirror  17  reflects the display light L reflected by the first concave mirror  16  toward the windshield  2 . The case  18  houses the display device  10 , the first and the second plane mirrors  13  and  14 , the screen  15 , and the first and the second concave mirrors  16  and  17 . The case  18  has an opening  18   a  at a portion facing the windshield  2 . The opening  18   a  is covered by a light transmissive cover  19  that is light transmissive. The display light L reflected by the second concave mirror  17  passes through the light transmissive cover  19  and is emitted from the HUD  1 . 
       FIG. 2  is a configuration diagram of the display device  10 . 
       FIG. 3  is an explanatory diagram illustrating a configuration of the optical system of the display device  10 . 
     The projection display device  10  includes a housing  21 , an LED substrate  22 , an optical member  23 , a light modulation element  24 , a light modulation element control substrate  26 , and a main control substrate  27 . 
     The housing  21  houses the optical member  23 . The housing  21  has a structure for attaching the light modulation element  24  and each of the substrates  22 ,  26 , and  27 . In particular, the housing  21  includes a plurality of protruding units for preventing erroneous assembly  31   a ,  31   b , and  31   c  (housing-side attachment units) (see  FIG. 5 ) for attaching the LED substrate  22 . 
     The LED (Light Emitting Diode) substrate  22  includes a first substrate  22   a , a second substrate  22   b , and a third substrate  22   c , each of which includes a different light source mounted thereon. A red light source  62   a  that emits a red light beam R is mounted on the first substrate  22   a . A green light source  62   b  that emits a green light beam G is mounted on the second substrate  22   b . A blue light source  62   c  that emits a blue light beam B is mounted on the third substrate  22   c . In the description below, in a context in which the first to third substrates  22   a ,  22   b , and  22   c  are not distinguished, they are simply referred to as the LED substrate  22 . In a context in which the red light source  62   a , the green light source  62   b , and the blue light source  62   c  are not distinguished, they are simply referred to as the light sources  62 . The details of the LED substrate  22  will be described below. 
     As illustrated in  FIG. 3 , the optical member  23  includes a mirror  41 , dichroic mirrors  42  and  43 , a reflection mirror  44 , a convex lens  45 , a prism  46 , and a light projecting lens  47 . 
     The red light beam R emitted from the red light source  62   a  is reflected by the mirror  41  and passes through the dichroic mirrors  42  and  43 . The green light beam G emitted from the green light source  62   b  is reflected by the dichroic mirror  42  and passes through the dichroic mirror  43 . The blue light beam B emitted from the blue light source  62   c  is reflected by the dichroic mirror  43 . The light beams R, G, and B are reflected by the reflection mirror  44 , distributed by the convex lens  45 , and transmitted through the prism  46 . The transmitted light beams R, G, and B are converted to the display light L by the light modulation element  24 . The display light L is reflected by the prism  46 , transmitted through the light projecting lens  47 , and projected (emitted). 
     The light modulation element  24  is, for example, a reflective display element such as a DMD (Digital Mirror Device) or an LCOS (Liquid Crystal On Silicon). 
     The light modulation element control substrate  26  is connected to the light modulation element  24  and controls the light modulation element  24 . 
     The main control substrate  27  is connected to the LED substrate  22  via a wiring  51  and controls the LED substrate  22 . Further, the main control substrate  27  is connected to the light modulation element control substrate  26  via a wiring  52  and controls the light modulation element control substrate  26 . 
       FIG. 4  is a configuration diagram of the LED substrate  22  of the display device  10 . 
     The LED substrate  22  is a glass epoxy substrate in which FR4 (Flame Retardant Type 4) material is used as a base material, for example. Due to the manufacturing process, the LED substrate  22  has, as fiber directions, a lengthwise direction and a crosswise direction orthogonal to the lengthwise direction. The fiber directions are substantially coincident with the directions of the orthogonal sides (Xs-Ys) of the LED substrate  22 . The LED substrate  22  is substantially rectangular (quadrangular) and includes a notch for preventing erroneous assembly  55  ( 55   a ,  55   b , and  55   c ) (substrate-side attachment units), and a screwing notch  56  ( 56   a ,  56   b , and  56   c ). The notches for preventing erroneous assembly  55  are used to position the housing  21 , and form pairs with the protruding units for preventing erroneous assembly  31   a ,  31   b , and  31   c  of the housing  21 . Moreover, the screwing notch  56  ( 56   a ,  56   b ,  56   c ) is used at the time of screwing to the housing  21 , and forms a pair with the screw hole (not illustrated) of the housing  21 . 
     Here,  FIG. 5  is an enlarged view for explaining an attachment structure for attaching the LED substrate  22  to the housing  21 . 
     The LED substrate  22  is positioned to an attachment wall  32  of the housing  21  and then fixed with screws  35 . The notches for preventing erroneous assembly  55   a ,  55   b , and  55   c  of the first to the third substrates  22   a ,  22   b , and  22   c  are provided at different positions on sides  57   a ,  57   b , and  57   c  of the rectangles, respectively. Further, the protruding units for preventing erroneous assembly  31   a ,  31   b , and  31   c  of the housing  21  are provided at different positions corresponding to the positions of the notches for preventing erroneous assembly  55   a ,  55   b , and  55   c . That is, the pair of protruding unit  31   a  and notch  55   a , the pair of protruding unit  31   b  and notch  55   b , and the pair of protruding unit  31   c  and notch  55   c  are provided at different positions. Thus, if an attempt is made to attach the LED substrate  22  at an incorrect position, the LED substrate will not fit. For this reason, upon attaching the LED substrate  22  to the housing  21 , it is possible to prevent erroneous attachment of the LED substrate  22 . 
     As illustrated in  FIG. 4 , the LED substrate  22  includes a heat dissipation plate  61 , an adhesive  68 , the light source  62 , a thermistor  63 , a connector  64 , and wirings  65   a  to  65   d.    
     The heat dissipation plate  61  is substantially square (quadrangular) in a plan view. The heat dissipation plate  61  includes the light source  62  (electronic component) on the surface thereof, and dissipates the heat from the light source  62 . The heat dissipation plate  61  is made of a material having good thermal conductivity and insulating properties, for example, aluminum nitride (AlN) (ceramics). From the viewpoint of thermal characteristics and the viewpoint of temperature detection by the thermistor  63 , the heat dissipation plate  61  is preferably made of the same material as the material of a base  75  of the light source  62 . Here,  FIG. 6  is a cross-sectional view along the thickness direction of the LED substrate  22 . The LED substrate  22  includes an opening  72  in which the heat dissipation plate  61  is arranged. The adhesive  68  (adhesive member) is, for example, an epoxy resin, and bonds the heat dissipation plate  61  and the LED substrate  22 . 
     The light source  62  is a surface-mounted electronic component connected to the wirings  65   a  and  65   b , and is substantially quadrangular in a plan view. Since the light source  62  emits heat during driving, the light source  62  is provided on the heat dissipation plate  61 . The light source  62  includes an LED element  74  and the base  75 . The base  75  is made of aluminum nitride, for example. 
     The thermistor  63  (electronic component) is an electronic component connected to the wirings  65   c  and  65   d , and is provided on the heat dissipation plate  61  to detect the temperature. Information about the temperature of the heat dissipation plate  61  detected by the thermistor  63  is output to the main control substrate  27  as the temperature of the light source  62  and is used for controlling the light source  62  and the like. 
     The connector  64  includes terminals  81   a  to  81   d . Moreover, the wirings  65   a  to  65   d  connect the light source  62  and the connector  64  (component on the substrate). The connector  64  supplies power to the light source  62  by connecting the LED substrate  22  and a power supply (not illustrated) at the terminal  81   a  via the wiring  65   a . The connector  64  connects the light source  62  and the ground (not illustrated) at the terminal  81   b  via the wiring  65   b . The connector  64  supplies power to the thermistor  63  by connecting the thermistor  63  and a power supply (not illustrated) at the terminal  81   c  via the wiring  65   c . The connector  64  supplies a signal output from the thermistor  63  to the main control substrate  27  by connecting the thermistor  63  and the main control substrate  27  via the wiring  65   d  at the terminal  81   d . Among the terminals  81   a  to  81   d , the terminals  81   a  and  81   b  are arranged on an outer side. Among the terminals  81   a  to  81   d , the terminals  81   c  and  81   d  are arranged on an inner side. 
     Each of the wirings  65   a  to  65   d  includes a reinforcement unit  66  in a part of the wiring extending from an interface  73   a  between the heat dissipation plate  61  and the adhesive  68  to an interface  73   b  between the LED substrate  22  and the adhesive  68 , and the reinforcement unit  66  has a larger line width than the other parts of the wiring. 
     Next, the arrangement of components on the LED substrate  22  will be described. 
     As illustrated in  FIG. 4 , the light source  62  is arranged substantially at the center of the heat dissipation plate  61 . 
     The heat dissipation plate  61  is arranged such that a corner part  91  of the heat dissipation plate  61  is rotated with respect to a corner part  92  of the LED substrate  22  by about 45 degrees. In other words, if the heat dissipation plate  61  and the LED substrate  22  are in a shape of a quadrangle having two orthogonal sides, the orthogonal axes Xh-Yh defining the directions of the two orthogonal sides of the heat dissipation plate  61  are rotated by about 45 degrees with respect to the orthogonal axes Xs-Ys defining the directions of the two orthogonal sides of the LED substrate  22 . 
     Here, if the light source  62  emits heat, the heat is transmitted to the LED substrate  22  via the heat dissipation plate  61 . As described above, the LED substrate  22  has fiber directions, and as is known, the density is different between the lengthwise direction and the crosswise direction, resulting in differences in various characteristics such as the linear expansion coefficient. Thus, the LED substrate  22  affected by the heat of the light source  62  has different expansion coefficients in the lengthwise and crosswise directions. Specifically, the expansion coefficient is smaller in the lengthwise direction than in the crosswise direction. Further, when the lengthwise direction and the crosswise direction are compared, a difference in the linear expansion coefficient with respect to the heat dissipation plate  61  is larger in the crosswise direction. Thus, the interface orthogonal to the crosswise direction is more largely expanded or contracted, and affected than the interface in the lengthwise direction, which may lead to breakage of the bonded site. 
     On the other hand, in the LED substrate  22  in the present embodiment, the heat dissipation plate  61  is inclined by about 45 degrees with respect to the fiber directions (Xs-Ys directions). As a result, as a whole, the interfaces  73   a  and  73   b  are not orthogonal to the crosswise direction, and the influence of the thermal expansion in the crosswise direction having the largest linear expansion coefficient can be reduced. 
     Further, in consideration of the influence of expansion and contraction at the interface, the part of the wiring extending from the interface  73   a  to the interface  73   b  is preferably designed to extend in a direction coinciding with the lengthwise direction. However, limiting the wiring direction to the lengthwise direction reduces the degree of freedom of the design. That is, if wiring is not formed in the direction coinciding with the crosswise direction, the direction in which the wiring can be led out from the heat dissipation plate  61  is limited. 
     In the LED substrate  22  in the present embodiment, the heat dissipation plate  61  is inclined by about 45 degrees with respect to the fiber directions (the orthogonal sides of the LED substrate  22 ). As a result, there is no difference in linear expansion due to the lengthwise and crosswise relationship, between the heat dissipation plate  61  and the LED substrate  22 , in any of the sides of the heat dissipation plate  61 , which results in a similar (uniform) expansion or contraction. Thus, there is no side on which the effect of large thermal expansion is exerted, and so it is possible to reduce the effect of large (maximum) expansion and contraction due to heat in any of the wirings  65   a  to  65   d , and thus reduce the breakage (disconnection) of the wiring. 
     Further, the wirings  65   a  to  65   d  are provided with the reinforcement unit  66 . Thus, even if the wirings  65   a  to  65   d  are affected by the expansion and contraction due to heat, it is possible to prevent the wirings  65   a  to  65   d  from disconnecting. 
     Although some embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof. 
     For example, the amount of rotation of the corner part  91  of the heat dissipation plate  61  with respect to the corner part  92  of the LED substrate  22  and a corner part  93  of the light source  62  is not limited to 45 degrees. Further, the heat dissipation plate  61 , the LED substrate  22 , and the light source  62  are not limited to a quadrangular shape having two orthogonal sides, and may be diamond-shaped having two sides that are not orthogonal. 
     An example of the LED substrate  22  in which the expansion coefficient in the lengthwise direction is smaller than that in the crosswise direction has been described, but the lengthwise direction and crosswise direction may have the reverse relationship. Further, an example in which the fiber directions (lengthwise direction, crosswise direction) are substantially coincident with the directions of the orthogonal sides of the LED substrate  22  (Xs-Ys directions) has been described, but the present invention is not limited thereto. That is, since the orthogonal axes Xh-Yh of the heat dissipation plate is inclined with respect to the orthogonal axes Xs-Ys of the LED substrate  22 , it is not necessary to take the fiber directions into consideration when the LED substrate  22  is taken from a worksheet. 
     The materials of heat dissipation plate  61  and the base  75  are not limited to aluminum nitride (AlN). For example, the material of the base  75  may be selected from aluminum (Al), gallium nitride (GaN), copper (Cu), and the like. If the heat dissipation plate  61  is made of a conductive material, an insulating layer and a copper foil pattern are laminated, and the light source (LED) is mounted thereon. The difference in the thermal expansion coefficient between the heat dissipation plate  61  and the base  75  is preferably less than 1 (10−6/K). Most preferably, the heat dissipation plate  61  are made of the same material as the base  75  to eliminate difference in thermal expansion coefficient. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
         
           
               1  Head-up display (HUD) 
               2  Windshield 
               3  Eye box 
               4  Viewpoint 
               10  Projection display device (display device) 
               13  First plane mirror 
               14  Second plane mirror 
               15  Screen 
               16  First concave mirror 
               17  Second concave mirror 
               18  Case 
               18   a  Opening 
               19  Light transmissive cover 
               21  Housing 
               22  LED substrate 
               22   a  First substrate 
               22   b  Second substrate 
               22   c  Third substrate 
               23  Optical member 
               24  Light modulation element 
               26  Light modulation element control substrate 
               27  Main control substrate 
               31   a ,  31   b ,  31   c  Protruding unit for preventing erroneous assembly 
               32  Attachment wall 
               41  Mirror 
               42 ,  43  Dichroic mirror 
               44  Reflection mirror 
               45  Convex lens 
               46  Prism 
               47  Light projecting lens 
               51 ,  52  Wiring 
               55 ,  55   a ,  55   b ,  55   c  Notch for preventing erroneous assembly 
               61  Heat dissipation plate 
               62  Light source 
               62   a  Red light source 
               62   b  Green light source 
               62   c  Blue light source 
               63  Thermistor 
               64  Connector 
               65   a ,  65   b ,  65   c ,  65   d  Wiring 
               66  Reinforcement unit 
               68  Adhesive 
               71 ,  75  Base 
               72  Opening 
               73   a ,  73   b  Interface 
               74  LED element 
               81   a ,  81   b ,  81   c ,  81   d  Terminal 
               91 ,  92 ,  93  Corner part