JP2006128512A - Ceramic substrate for light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic substrate for a light emitting element which has a cooling function of high efficiency and, as a result, can effectively suppress the temperature rise of the element or a substrate even when it is used for illuminating, etc. <P>SOLUTION: The ceramic substrate 1 for the light emitting element includes a substrate body 1M in which a ceramic layer 15 and metal layers 24, 25 and 26 are alternately laminated. A metal pad 16 for carrying the element in which the energizing terminal of a light emitting element chip 4 to be carried is electrically connected is exposed and formed to the first main surface side of the substrate body 1M. And, metal surface conductors 24 and 25 for heat dissipation which function as a heat dissipation path within the light emitting chip 4 carried on the metal pad 16 for carrying the element are embedded at the position in the middle of the thickness direction of the substrate body 1M so that the surface shape state along the plate surface of the substrate body 1M is formed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ceramic substrate for a light emitting element and an illumination module using the same.

JP 2003-243717 A Japanese Patent Laid-Open No. 2002-246652 JP 2001-223388 A Japanese Patent Laid-Open No. 2004-22895 JP 2003-347600 A

  Conventional semiconductor light emitting devices have been mainly used for small devices such as displays, but semiconductor devices have high light conversion efficiency, little heat generation, and mercury is not used like fluorescent lamps. It is also attracting attention as a light source for illumination because it is desirable from the viewpoint of environmental protection. In particular, in response to the realization of high-luminance blue light-emitting elements using InGaAlN-based compounds, various combinations of light-emitting elements that output red, green, and blue monochromatic light corresponding to the three primary colors of light are combined. Many light emitting elements capable of emitting light of color (for example, white) have been developed and put into practical use for illumination.

  Conventionally, a printed circuit board having an insulating layer made of a polymer material is often used as a mounting substrate for a light emitting element. However, when a light-emitting element is used for illumination, the energization current level is very high compared to a general light-emitting element for display, etc. Become. In particular, an automobile headlight that needs to illuminate a distant place with a small-sized light source has a problem that current concentration on the light source is remarkably high and the temperature around the light source tends to be very high during use. Therefore, in consideration of high heat generation for illumination, it has been studied to use a ceramic substrate (Patent Documents 1 to 5).

  In order to ensure a long life for illumination, it is essential to improve the heat dissipation of the substrate on which the light emitting element is mounted. The thermal conductivity of ceramic is not so good, and even if a ceramic with relatively high thermal conductivity such as alumina is used, there is a limit to improving the heat dissipation characteristics. The above patent document discloses a structure in which the surface of the ceramic substrate is covered with a thin metal layer that also serves as a current path of the light emitting element to enhance the heat dissipation effect. However, the heat in the thickness direction of the ceramic substrate main body with low thermal conductivity is disclosed. Since the conduction improvement is neglected, the heat conduction path is biased to the thin metal layer forming the surface layer of the substrate, so that the thermal resistance increases and a sufficient heat radiation effect cannot be expected.

  An object of the present invention is to provide a ceramic substrate for a light emitting device that has a highly efficient cooling function and can effectively suppress an increase in temperature of the device and the substrate even when used for illumination.

Means for Solving the Problems and Effects of the Invention

  In order to solve the above-described problems, a ceramic substrate for a light-emitting element according to the present invention is formed so as to be exposed on the first main surface side of a plate-shaped substrate body made of ceramic, and mounted on the substrate. The element mounting metal pad to which either the anode or the cathode of the element chip is electrically connected and a planar shape along the plate surface of the substrate body are embedded in the middle of the substrate body in the thickness direction. And a metal heat dissipating surface conductor that functions as an in-plane heat dissipating path of the light emitting element chip mounted on the element mounting metal pad.

  The illumination module of the present invention includes the above-described ceramic substrate for a light-emitting element of the present invention, and a light-emitting element that constitutes a light source for illumination mounted on an element mounting metal pad of the ceramic substrate for a light-emitting element. Features.

  According to the ceramic substrate for a light emitting device of the present invention, the metal heat dissipating surface conductor is embedded in the middle of the thickness direction of the substrate body made of ceramic. Since the substrate body is made of ceramic, the thermal conductivity is small, but by interposing a metal heat dissipation surface conductor in the middle of the thickness direction, the substrate body made of ceramic is divided into a plurality of layers by the heat dissipation surface conductor, Individual layers have a reduced thermal diffusion distance in the thickness direction. If the heat flux reaches the buried heat dissipating surface conductor, the thermal conductivity of the metal is very good, so that in-plane heat diffusion can proceed quickly. As a result, heat generated from the light emitting element is promoted in the in-plane direction heat diffusion by the heat dissipating surface conductor located in the middle of the substrate body, and the individual ceramic layers having a small thickness are sequentially separated in the thickness direction. By diffusing into the substrate, uniform and good heat dissipation characteristics can be realized over the entire substrate body. In particular, if this is applied to a lighting module that generates a particularly large amount of heat generated by light emission driving, the temperature rise of the light emitting element as a light source can be effectively suppressed and the life can be improved even if the lighting is kept on for a long time. Can do.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of an illumination module using the ceramic substrate for light-emitting elements of the present invention, and FIG. 2 is a schematic plan view. The light emitting element ceramic substrate 1 that forms a main part of the illumination module 301 includes a substrate body 1M in which ceramic layers 15 and metal layers 24, 25, and 26 are alternately stacked. The ceramic layer 15 is made of aluminum oxide or aluminum nitride having a relatively good thermal conductivity. On the other hand, the metal layers 24, 25, and 26 (and 16) are made of a refractory metal such as W or Mo that can be fired simultaneously with these ceramics. However, the materials are not limited to these.

  On the first main surface side of the substrate body 1M, an element mounting metal pad 16 to which an energization terminal of the mounted light emitting element chip 4 is electrically connected is exposed. And in the middle of the thickness direction of the substrate body 1M, a planar shape is formed along the plate surface of the substrate body 1M, and in-plane heat dissipation of the light emitting element chip 4 mounted on the element mounting metal pad 16 is achieved. Heat dissipating surface conductors 24 and 25 made of metal functioning as a path are embedded. Since the substrate body 1M is made of ceramic, the thermal conductivity is relatively small. However, the heat dissipating surface conductors 24 and 25 made of metal intervene in the middle of the thickness direction so that a plurality of ceramics can be obtained. Divided into layers 15, the thermal diffusion distance in the thickness direction of each layer 15 is reduced. The heat generated from the light emitting element chip 4 is accelerated in the in-plane direction by the heat dissipating surface conductors 24 and 25 located in the middle of the substrate body 1M in the thickness direction, and has a thickness separated therefrom. The thin ceramic layers 15 are sequentially diffused in the thickness direction, so that uniform and good heat dissipation characteristics can be realized over the entire substrate body 1M, and the light emitting element chip that becomes a light source even when lighting is continued for a long time The temperature rise of 4 can be effectively suppressed and the life can be improved.

This will be described in more detail below.
The substrate body 1M has a back side conductor 26 disposed so as to cover the second main surface, and electrically connects the element mounting metal pad 16 and the back side conductor 26 so as to penetrate the substrate body 1M in the thickness direction. In addition, a heat radiation via conductor 27 that functions as a heat radiation path in the thickness direction of the light emitting element chip 4 mounted on the element mounting metal pad 16 is formed. The element mounting metal pad 16 for mounting the light emitting element chip 4 serving as a heat generating source is directly connected to the back surface side conductor 26 by the heat radiating via conductor 27, so that the ceramic substrate body 1M has a thickness direction. The heat dissipation efficiency is further improved.

  In this structure, the light-emitting element chip 4 is formed on one of the anode and the cathode on the first main surface and the other on the second main surface, and mounted on the element mounting metal pad 16 on the second main surface. Is particularly effective. With this structure, the light emitting element chip 4 is energized in the normal direction of the chip main surface, and it becomes easier to obtain a sink current for light emission driving, which is advantageous for large current surface light emission driving for illumination. In the above structure, the heat dissipation via conductor 27 that forms the energization path is arranged so as to coincide with the direction of the large sink current, so that the effect of reducing the excessive resistance heat generation in the substrate is also added. Despite the flow of heat, the temperature rise due to heat generation becomes even less likely to occur. In order to enhance the above effect, it is effective to dispose the heat dissipation via conductors 27 immediately below the light emitting element chip 4 or to dispose a plurality of heat dissipating via conductors 27 so as to surround the light emitting element chip 4.

  In FIG. 1, the first main surface of the light emitting element chip 4 is a light extraction surface, and a light extraction side electrode 19 serving as an anode or a cathode is formed so as to cover a partial region thereof. On the other hand, the entire surface of the second main surface of the light emitting element chip 4 is covered with the back electrode 20, and is adhered onto the element mounting metal pad 16 with a conductive adhesive 18 such as Ag paste. In addition, a conductive path forming via 8 is disposed so as to penetrate the substrate body 1M in the thickness direction, and the light extraction side electrode 19 is provided to the pad 8a integrated at the end portion on the first main surface side of the substrate. They are connected via a current-carrying wire W. In the conductive path forming via 8, connection pads 8 b are arranged corresponding to the boundary positions between the ceramic layers 15, and are insulated from the surface conductors 24, 25, and 26 by gaps 9 h. With the above structure, on the second main surface side of the substrate body 1M, the back surface side of the light emitting element chip 4 is electrically connected to the back surface conductor 26, and the light extraction surface side is electrically connected to the terminal pad 8c of the conductive path forming via 8. . The light emitting element chip 4 is covered with a transparent resin mold 1c made of an epoxy resin or the like together with the first main surface of the substrate body 1M.

  In FIG. 1, the heat dissipating surface conductor includes a first type heat dissipating surface conductor 25 embedded so as to be located on the second main surface side of the substrate body 1M with respect to the element mounting metal pad 16. By embedding the first type heat radiation surface conductor 25 at a position deeper than the element mounting metal pad 16 in the thickness direction of the substrate body 1M, a plurality of substrate body portions positioned below the light emitting element chip 4 are provided. The ceramic layers 15 and 15 are further divided to further enhance the heat dissipation effect in the substrate thickness direction. As shown in FIG. 2, the effect is that the first type heat radiation surface conductor 25 includes the projection area of the light emitting element chip 4 mounted on the element mounting metal pad 16. It is remarkable when it is formed in a larger area than 4. In FIG. 1, only one layer of the first type heat radiation surface conductor 25 is provided, but a plurality of layers may be provided.

  In the embodiment of FIG. 1, the first type heat radiation surface conductor 25 and the element mounting metal pad 16 are connected by the heat radiation via conductor 27 described above. With this structure, the in-plane heat diffusion effect by the first type heat radiation surface conductor 25 and the heat diffusion effect in the thickness direction by the heat radiation via conductor 27 are combined, and heat radiation proceeds three-dimensionally, and the light emitting element chip 4 and the temperature rise of the board | substrate 1 can be suppressed very effectively. In the present embodiment, the element mounting metal pad 16 is formed in a larger area than the light emitting element chip 4, and the first type heat radiation surface conductor 25 is formed in a larger area than the element mounting metal pad 16. By forming the element mounting metal pad 16 in a larger area than the light emitting element chip 4, it becomes easier to mount the light emitting element chip 4 on the element mounting metal pad 16 (using a conductive adhesive). Further, the in-plane thermal diffusion effect by the element mounting metal pad 16 itself on the mounting surface of the light emitting element chip 4 is enhanced, and further, it works advantageously in considering a structure in which a plurality of heat dissipation via conductors 27 are arranged. .

  Next, in the ceramic substrate 1 of FIG. 1, the element mounting notch portion 14 is opened to the first main surface of the substrate body 1M and the bottom surface is located in the middle of the substrate body 1M in the thickness direction. The element mounting metal pad 16 is formed on the bottom surface of the element mounting notch 14. By mounting the light emitting element chip 4 on the bottom surface of the element mounting notch portion 14, the luminous flux directed toward the side surface of the light emitting element chip 4 can be reflected by the inner side surface of the element mounting notch portion 14. The directivity of the illumination light to the side can be increased. In this case, when the reflective metal portion 6 having a reflective surface with a diameter reduced from the opening portion toward the bottom surface is formed along the inner peripheral edge of the element mounting notch portion 14, this effect is particularly remarkable.

  By providing the element mounting notch 14 as described above, the heat dissipating surface conductor is a second type heat dissipating material embedded on the extension of the bottom surface around the element mounting notch 14 with respect to the board body 1M. It may have a surface conductor 24. Thereby, the thermal diffusion effect within the mounting surface of the light emitting element chip 4 can be enhanced.

  In the embodiment of FIG. 1, a bottom metallized layer 24P that covers the outer periphery of the bottom surface of the element mounting notch 14 and a side metallized layer 7 that covers the inner surface of the element mounting notch 14 are formed. A brazing filler fillet portion (for example, composed of an Ag-based brazing material or a Cu-based brazing material, and Ag plating for increasing the reflectance is applied to the surface) 6 straddling the bottom surface metallization layer 24P and the side surface metallization layer 7 Can be formed. In this case, the reflective metal portion 6 can be easily formed by pouring the brazing material along the edge of the concave portion formed by the bottom surface metallized layer 24P and the side surface metallized layer 7. Further, the inner peripheral surface of the fillet forming the reflective metal portion 6 becomes a tapered surface (or a concave R surface), and the effect of reflecting the emitted light beam emitted from the side surface of the light emitting element chip 4 in the normal direction of the substrate main surface is enhanced. The directivity of the illumination light is further improved.

  As shown in FIG. 2, on the bottom surface of the element mounting notch 14, the brazing filler metal stop gap is formed between the element mounting metal pad 16 and the bottom metallized layer 24P so as to expose the ceramic layer as a base. A portion 17 is formed. When the brazing material is poured into the concave portion formed by the bottom surface metallization layer 24P and the side surface metallization layer 7, the brazing material stop gap portion 17 prevents the brazing material from flowing into the element mounting metal pad 16 side, thereby reflecting metal. It plays the role of defining the angle θ of the fillet forming part 6. The effect of reflecting the luminous flux emitted from the side surface of the light emitting element chip 4 in the normal direction of the main surface of the substrate is remarkable when the angle θ is adjusted to 30 ° or more and 60 ° or less (for example, 45 °). .

  In addition, the inner edge part of the above-described second type heat radiation surface conductor 24 can be extended inward from the side surface of the element mounting notch part 14. Thereby, the bottom metallized layer 24P can be formed by the extended portion, and the second-type heat radiation surface conductor 24 and the bottom metallized layer 24P can be collectively formed, which contributes to simplification of the process. Further, on the bottom metallized layer 24P, a reflective metal portion 6 (fillet) having a large heat capacity and high thermal conductivity is mounted, and this is directly connected to the second type heat radiation surface conductor 24 that carries the in-plane heat diffusion path. It also contributes to the improvement of heat dissipation effect. Moreover, in the structure of the ceramic substrate 1 of FIG. 1, as a result, both the 1st type heat radiation surface conductor 25 and the 2nd type heat radiation surface conductor 24 are provided, and the heat radiation effect is further enhanced.

  FIG. 3 shows an example of a manufacturing process of the illumination module 301 of FIG. First, as shown in step 1, a ceramic green sheet 115 to be the ceramic layer 15 (FIG. 1) is prepared. The ceramic green sheet 115 is prepared by adding a solvent (acetone, methyl ethyl ketone, diacetone, methyl isobutyl ketone, benzene, bromochloromethane, ethanol, butanol, propanol, toluene, xylene, etc.), binder (acrylic) to the raw ceramic powder of the ceramic dielectric layer. Resin (for example, polyacrylic acid ester, polymethyl methacrylate), cellulose acetate butyrate, polyethylene, polyvinyl alcohol, polyvinyl butyral, etc.), plasticizer (butyl benzyl phthalate, dibutyl phthalate, dimethyl phthalate, phthalic acid ester, polyethylene glycol derivative) , Tricresol phosphate, etc.), peptizer (fatty acid (glycerin trioleate, etc.), surfactant (benzenesulfonic acid, etc.), wet Additives such as (alkyl allyl polyether alcohol, polyethylene glycol ethyl ether, nithyl phenyl glycol, polyoxyethylene ester, etc.) are blended and kneaded, and formed into a sheet by a known doctor blade method or the like. In the ceramic green sheet 115, through holes 108h and 127h for arranging via conductors are formed in advance by drilling, punching or laser drilling.

  First, as shown in step 1, the through holes 108h and 127h are filled with a metal paste to form a via conductor pattern 127. Then, as shown in step 2, the metal patterns 126 and 108c to be the back side conductor 26 and the terminal pad 8c are formed on the second main surface of the ceramic green sheet 115 described above. The wiring layer metal pattern 126 is formed by a known screen printing method using a metal powder paste. The metal powder paste is prepared by blending and adjusting a metal powder with an organic binder such as ethyl cellulose and an organic solvent such as butyl carbitol so as to obtain an appropriate viscosity. Further, the second main heat dissipating surface conductor 25 (and the bottom metallized layer 24P) and the metal patterns 125 (124P) and 108b to be the connection pads 8b are formed on the first main surface of the ceramic green sheet 115 by printing. The printing order of the first main surface and the second main surface of the ceramic green sheet 115 can be reversed.

  Next, as shown in step 3, another ceramic green sheet 115 is overlaid thereon, and the metal patterns 124 and 16 to be the first type heat radiation surface conductor 24 and the element mounting metal pad 16 are similarly printed and formed. . Then, as shown in step 4, a further ceramic green sheet 115 is formed with a through hole 107 to be the element mounting notch 14 and a metal pattern 107 to be the side metallized layer 7 on the inner surface. In addition, a metal pattern 108a to be the pad 8a is also formed, and is superposed so as to be the uppermost layer of the stacked body. After firing the green laminate, a reflective metal portion 6 is further formed. And after mounting the light emitting element chip | tip 4 and bonding the wire W, the resin mold 1c is formed and the illumination module 301 of FIG. 1 is completed.

  Hereinafter, various modifications of the ceramic substrate for a light emitting device of the present invention will be described. In addition, the same code | symbol is provided to a common part with the ceramic substrate 1 for light emitting elements of FIG. 1, and detailed description is abbreviate | omitted. First, the ceramic substrate 50 of FIG. 4 corresponds to the ceramic substrate 1 of FIG. 1 in which the second type heat radiation surface conductor 24 is omitted (in contrast, the first type heat radiation surface conductor 25 is omitted). Can also).

  The ceramic substrate 51 of FIG. 5 has an overlapping region formed between the first type heat radiation surface conductor 25 and the second type heat radiation surface conductor 24 in the projection relationship in the thickness direction of the substrate body 1M. An auxiliary heat radiation via conductor 227 that connects the first type heat radiation surface conductor 25 and the second type heat radiation surface conductor 24 is formed in the overlapping region. The auxiliary heat radiation via conductor 227 forms a heat radiation path in the thickness direction that connects the first type heat radiation surface conductor 25 and the second type heat radiation surface conductor 24, thereby enhancing the heat radiation effect of the entire substrate. In FIG. 5, the heat radiating via conductor 27 that connects the element mounting metal pad 16 and the first type heat radiating surface conductor 25 is omitted, but as shown by a one-dot chain line (the same arrangement form as FIG. 2). Further, the heat radiating via conductor 27 can be provided together. In this case, the heat radiation effect in the thickness direction of the substrate is further enhanced. The overlapping region of the first type heat radiation surface conductor 25 and the second type heat radiation surface conductor 24 is formed outside the element mounting metal pad 16.

  The ceramic substrate 52 shown in FIG. 6 is made of a ceramic made of different materials in the ceramic layer 215 adjacent to the first main surface side and the ceramic layer 15 adjacent to the second main surface side with respect to the heat dissipating surface conductor 224. The surface conductor 224 is a brazing material layer for brazing and joining these different ceramic layers 215 and 15. When a plurality of ceramic layers 215 and 15 forming the ceramic substrate 52 are made of different materials, it is generally difficult to perform simultaneous firing because different ceramics have different firing temperatures and shrinkage rates. Thus, as described above, the ceramic layers 215 and 15 of different materials are separately fired with the heat radiation surface conductor 224 as a boundary, and then bonded together with a brazing material 224s as shown in FIG. By using the heat dissipating surface conductor 224 as the layer, the ceramic substrate 52 including the ceramic layers 215 and 15 of different materials can be easily realized.

  In this case, one of the ceramic layers 215, 15 of different materials is disposed adjacent to the second main surface side of the element mounting metal pad 16, and the ceramic layer 15 is a ceramic having a higher thermal conductivity than the other ceramic layers ( For example, when the ceramic layer 215 is made of aluminum oxide and the ceramic layer 15 is made of aluminum nitride, the heat dissipation effect of the entire substrate can be further enhanced, and the entire substrate is made of expensive aluminum nitride. Rather than doing so, material costs can be reduced.

  The ceramic substrate 53 of FIG. 8 is premised on mounting a light emitting element chip 204 having a structure different from that of the ceramic substrate 1 of FIG. The light emitting element chip 204 has a structure in which no electrode is formed on the first main surface of the chip, and an anode terminal 204A and a cathode terminal 204C are formed on the second main surface side. The anode terminal 204A and the cathode terminal 204C are surface-mounted by soldering or the like on the element mounting metal pad 16 and the auxiliary pad 8t electrically insulated from the element mounting metal pad 16, respectively.

  Specifically, as shown in FIG. 9, a part of the element mounting metal pad 16 is cut out, and a pad 8a conducting to the conductive path forming via 8 is formed in the cutout portion 8i, and the pad 8a. A lead portion 8l is formed in which one end is conductive and the other end is formed with an auxiliary pad 8t. In addition, no element mounting notch is formed in the substrate body 1M, and the entire flat first main surface is covered with a surface conductor forming the element mounting metal pad 16. A reflecting mirror 150 that reflects the luminous flux from the light emitting element chip 204 is separately assembled to the substrate body 1M.

  The illumination module 301 using the ceramic substrates 50 to 53 as described above can be used as a light source of an automobile headlamp.

The cross-sectional schematic diagram which shows 1st embodiment of the ceramic substrate for light emitting elements of this invention. The top view of FIG. Process explanatory drawing which shows the manufacturing method of the ceramic substrate for light emitting elements of FIG. The cross-sectional schematic diagram which shows 2nd embodiment of the ceramic substrate for light emitting elements of this invention. The cross-sectional schematic diagram which shows 3rd embodiment of the ceramic substrate for light emitting elements of this invention. The cross-sectional schematic diagram which shows 4th embodiment of the ceramic substrate for light emitting elements of this invention. Process explanatory drawing which shows the manufacturing method of the ceramic substrate for light emitting elements of FIG. The cross-sectional schematic diagram which shows 5th embodiment of the ceramic substrate for light emitting elements of this invention. The top view of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,50-53 Ceramic substrate for light emitting elements 1M Substrate body 4 Light emitting element chip 6 Reflective metal part 7 Side metallization layer 14 Element mounting notch part 15,215 Ceramic layer 16 Metal pad for element mounting 17 Brazing material stop gap part 24, 25 Radiation surface conductor 25 Type 1 radiation surface conductor 24 Type 2 radiation surface conductor 24P Bottom metallization layer 26 Back side conductor 27 Radiation via conductor

Claims (2)

A plate-like substrate body made of ceramic, and an element mounting metal pad formed so as to be exposed on the first main surface side of the substrate body, and electrically connected to energization terminals of light emitting element chips mounted on the substrate And forming a planar shape along the plate surface of the substrate body, embedded in a position in the middle of the thickness of the substrate body, and the light emitting element chip mounted on the element mounting metal pad A ceramic substrate for a light emitting device, comprising: a metal heat dissipating surface conductor that functions as an in-plane heat dissipation path. A back side conductor is disposed so as to cover the second main surface of the substrate body, and the element mounting metal pad and the back side conductor are electrically connected so as to penetrate the substrate body in the thickness direction. The ceramic substrate for light emitting elements according to claim 1, wherein a heat dissipation via conductor functioning as a heat dissipation path in the thickness direction of the light emitting element chip mounted on the element mounting metal pad is formed.

Images