JP2011176106A - Substrate for mounting light-emitting element, and light-emitting device using the substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate for mounting a light-emitting element, which can prevent corrosion of a reflection layer, and can be baked at about 500-700°C; and to provide a light-emitting device using this substrate. <P>SOLUTION: The substrate has: a substrate body having a mounting surface on which the light-emitting element is mounted; the reflection layer which is formed on a part of the mounting surface of the substrate body, reflects light emitted from the light-emitting element and contains silver; and a glass insulating layer formed on the reflection layer. The glass insulating layer is formed of low melting point glass containing by mole percent on the oxide basis, 30-60% B<SB>2</SB>O<SB>3</SB>, 0-50% SiO<SB>2</SB>, 2-40% ZnO and 5-15% Li<SB>2</SB>O+Na<SB>2</SB>O+K<SB>2</SB>O. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a light-emitting element mounting substrate and a light-emitting device using the same, and more particularly to a light-emitting element mounting substrate capable of preventing a decrease in reflectance and a light-emitting device using the same.

  2. Description of the Related Art In recent years, light emitting devices using light emitting elements have been used as lighting, various displays, backlights for large liquid crystal televisions, and the like with the increase in brightness and whiteness of light emitting diode elements (light emitting elements). In general, a light emitting element mounting substrate on which a light emitting element is mounted is required to have high reflectivity for efficiently reflecting light emitted from the element.

  For this reason, conventionally, an attempt has been made to apply a reflective layer to the substrate surface for the purpose of reflecting light emitted from the light emitting element as far forward as possible. As such a reflective layer, there is a silver reflective layer having a high reflectance.

However, silver is easily corroded, and if left as it is, a compound such as Ag ₂ S is generated on the surface and the light reflectance is likely to be lowered. As a countermeasure, a method has been proposed in which the surface of silver is coated with a resin such as a silicone resin, an acrylic resin, an epoxy resin, or a urethane resin (see Patent Document 1). However, in this method, moisture or corrosive gas enters the resin or from the interface between the silver conductor layer and the resin, and the silver conductor layer is corroded over time. Therefore, it can be applied to products that require long-term reliability. was difficult.

  Moreover, in order to prevent corrosion of a silver conductor layer, the method of coat | covering the surface of silver with a glass layer is also proposed (refer patent document 2). In Patent Document 2, a silver conductor paste is formed on a ceramic (alumina) substrate manufactured by firing to form a silver wiring conductor, and further, a glass paste is applied onto this wiring conductor and fired. A method for coating the surface of silver with a glass layer is described. However, in the method disclosed in Patent Document 2, it is necessary to repeat the firing step in forming the silver conductor layer and the glass layer.

  In order to efficiently manufacture a package with a silver conductor layer, an LTCC substrate using a low temperature co-fired ceramic (hereinafter referred to as LTCC) technology that can be sintered simultaneously with the silver conductor layer is used. It is useful. Conventionally, the LTCC substrate is generally fired at 800 to 900 ° C. However, in recent years, silver conductor materials that can be fired at a lower temperature than conventional products have also been developed.

JP 2007-0671116 JP 2009-231440 A

  However, the glass transition point Tg of the glass contained in the glass paste described in Patent Document 2 (product name: AP5700, manufactured by Asahi Glass Co.) is about 660 ° C., and the softening point Ts is about 805 ° C. For this reason, even if this glass paste is used on a low temperature LTCC substrate of about 500 to 700 ° C., since the firing temperature is lower than Ts of glass, the glass does not sufficiently soften and flow and a dense glass layer is formed. I can't do it. Moreover, when it used for the normal LTCC board | substrate baked at 800-900 degreeC, and it co-fired, the board | substrate warped and it was difficult to apply to a product. This glass paste has a crystallization temperature Tc of about 880 ° C., and when baked at 800 to 900 ° C., the glass layer is crystallized. For this reason, it is thought that the cause of the warp is that the shrinkage of the substrate during firing and the shrinkage of the glass layer differ greatly.

  An object of the present invention is to provide a light-emitting element mounting substrate that prevents corrosion of a reflective layer and can be fired at a temperature of about 500 to 700 ° C. It is another object of the present invention to provide a light emitting device using this light emitting element mounting substrate.

The present invention relates to a substrate for mounting a light emitting element, a substrate body having a mounting surface on which the light emitting element is mounted, a reflective layer containing silver formed on a part of the mounting surface of the substrate body, and on the reflective layer and a vitreous insulating layer formed, the vitreous insulating layer 2 as represented by mol% based on _oxides, B 2 _{O 3} 30-60%, the SiO ₂ 0 to 50%, a ZnO It is formed of low-melting glass containing 40% and 5 to 15% of Li ₂ O + Na ₂ O + K ₂ O. In addition to the glass, the glassy insulating layer may contain a ceramic filler.

  Further, the light emitting device includes the light emitting element mounting substrate, a light emitting element mounted on the mounting surface of the substrate body, and a phosphor layer covering the light emitting element.

In the light-emitting element mounting substrate of the present invention, the reflective layer containing silver is covered with the vitreous insulating layer, so that the reflective layer can be prevented from corrosion such as oxidation and sulfidation. . Moreover, since the glass contained in the vitreous insulating layer is excellent in fluidity at low temperatures, it has good reflection characteristics even at a baking temperature of 500 to 700 ° C.
Further, according to the light emitting device of the present invention, the reflection layer can be prevented from corroding for a long period of time, so that the state of high reflectance can be maintained for a long period.

It is an example of sectional drawing of the board | substrate used for this invention. It is an example of sectional drawing which has arrange | positioned the light emitting element to the board | substrate used for this invention. It is an example of sectional drawing of the light-emitting device of this invention.

The light emitting element mounting substrate of the present invention is formed on a substrate body having a mounting surface on which the light emitting element is mounted, a reflective layer containing silver formed on a part of the mounting surface of the substrate body, and the reflective layer. It is and a vitreous insulating layer, the vitreous insulating layer is to, by mol% based on _oxides, B 2 _{O 3} 30-60%, the SiO ₂ 0 to 50%, the ZnO 2 to 40 %, Li ₂ O + Na ₂ O + K ₂ O is formed of a low melting point glass containing 5 to 15%.

  The substrate body is a flat plate member as shown in FIG. 1 or a member formed with a recess so that the light emitting element mounting surface is positioned one step lower as shown in FIG. The material constituting the substrate is preferably an inorganic material (alumina ceramics, aluminum nitride, LTCC, etc.) for baking the reflective layer and the insulating layer. In particular, in the case of LTCC, the substrate body, the reflective layer, and the insulating layer can be formed by simultaneous firing, and the load on the process when manufacturing the light emitting element mounting substrate can be reduced. Furthermore, in the case of using an LTCC in which a plurality of layers are laminated, an internal wiring layer for feeding can be fired at the same time.

  Silver is used for the reflective layer because of its high reflectance. This silver is processed into a paste to facilitate application on the substrate body. Here, conventionally used silver paste has been difficult to form a film having high reflectivity unless it is baked at a temperature of about 800 to 900 ° C., but in recent years, it has a temperature lower than the melting point (962 ° C.). A silver paste for low-temperature firing using nano-sized silver powder or the like that can be sintered at (around 600 ° C.) has been developed. Further, a silver paste that can be sintered at a low temperature (around 600 ° C.) by making silver particles into spherical fine particles and improving the filling property at the time of coating has been developed. In the present invention, this low-temperature sinterable silver paste can be used. Further, there may be a case where a silver paste that cannot be sufficiently sintered unless it is usually fired at a temperature of about 800 to 900 ° C. may be used. This is because the low melting point glass contained in the vitreous insulating layer promotes the sintering of the reflective layer.

  The glassy insulating layer is a layer for protecting the lower reflective layer from corrosion (especially, oxidation or sulfidation of silver) and the like, and is a layer of low melting point glass or a mixed layer of low melting point glass and ceramic filler (glass -It is preferable to be comprised by a ceramic layer. The low melting point glass is preferably colorless so as not to reduce the reflectance of the vitreous insulating layer.

  It is preferable that the low melting point glass can be fired simultaneously with the conductor containing silver forming the reflective layer. And what does not produce defects, such as an open pore, does not react with silver when fired simultaneously with a silver conductor. Furthermore, it is preferable that the vitreous insulating layer can be sintered and densified at a firing temperature of 500 to 700 ° C.

  In general, the reaction during firing of silver and glass tends to increase as the softening point of the glass is lower. Conventionally, even glass that can be fired simultaneously with silver has to use a material with a higher softening point. .

  Further, when the low melting point glass contained in the vitreous insulating layer is crystallized during firing, the substrate is warped, and sufficient performance as a light emitting element mounting substrate cannot be exhibited. Therefore, it is desirable that the low-melting glass used for the vitreous insulating layer is difficult to crystallize during firing, and has a transition point Tg of 380-620 ° C., a softening point Ts of 500-700 ° C., and a crystallization point Tc of 700 ° C. or higher. A glass with thermal properties was considered suitable.

  However, as described above, the reaction during firing of silver and glass generally tends to increase as the softening point of the glass decreases. Therefore, simply using a glass that softens and flows at a low temperature makes silver in the glass. There was a risk that the ions would diffuse and colloid to develop a yellow or red color.

  In the present invention, when a glass that can be used at 500 to 700 ° C., which is lower than the prior art, has been intensively studied, there is a range in which the glass can flow and become dense at the time of firing and the reaction with silver can be suppressed. I found out.

  In the light emitting device of the present invention, examples of the light emitting element include an LED element. More specifically, there is one that excites a phosphor with emitted light to emit visible light, and examples include a blue light emitting type LED element and an ultraviolet light emitting type LED element. However, the light-emitting element is not limited thereto, and various light-emitting elements can be used depending on the use of the light-emitting device, the target light emission color, or the like as long as the light-emitting element can excite the phosphor and emit visible light. Can be used.

  The light emitting device of the present invention is preferably provided with a phosphor layer. The phosphor is excited by the light emitted from the light emitting element to emit visible light, and the visible light or the visible light itself emitted from the phosphor by color mixture of the visible light and the light emitted from the light emitting element. As a light emitting device, a desired light emission color is obtained by mixing the colors. The type of the phosphor is not particularly limited, and is appropriately selected according to the target emission color, light emitted from the light emitting element, and the like.

  The light emitting device of the present invention is preferably provided with a phosphor layer (see FIG. 3) covering the light emitting element. This phosphor layer is obtained by mixing and dispersing phosphors in a transparent resin such as a silicone resin or an epoxy resin. The phosphor is excited by the light emitted from the light emitting element to emit visible light, and the visible light or the visible light itself emitted from the phosphor by color mixture of the visible light and the light emitted from the light emitting element. As a light emitting device, a desired light emission color is obtained by mixing the colors. The type of the phosphor is not particularly limited, and is appropriately selected according to the target emission color, light emitted from the light emitting element, and the like.

  In addition, the phosphor layer can be separately provided on a coating layer formed so as to directly cover the light emitting element. That is, the phosphor layer is preferably formed on the uppermost layer on the side where the light emitting element of the light emitting device is formed.

  The light emitting device of the present invention typically has a terminal portion for electrically connecting the LED element on the surface of the substrate, and a region excluding the terminal portion is covered with an overcoat layer. In this case, for example, the LED element is mounted on the substrate with an epoxy resin or silicone resin (die bond), and the electrode on the upper surface of the chip is connected to the pad portion of the substrate through a bonding wire such as a gold wire. Or a bump electrode such as a solder bump, an Au bump, or an Au—Sn eutectic bump provided on the back surface of the LED chip is flip-chip connected to a lead terminal or a pad portion of the substrate.

  The substrate body is not particularly limited as long as it can be provided with a reflective layer and a glassy insulating layer that protects the reflective layer. Hereinafter, a case where the substrate body is an LTCC substrate will be described.

  The LTCC substrate is a substrate manufactured by baking a mixture of glass powder and ceramic filler such as alumina powder, and can be manufactured by baking simultaneously with a silver conductor.

  Ceramic fillers such as glass powder and alumina powder used for the LTCC substrate are usually used as green sheets. For example, first, glass powder and alumina powder are mixed with a resin such as polyvinyl butyral or acrylic resin and, if necessary, a plasticizer such as dibutyl phthalate, dioctyl phthalate, or butyl benzyl phthalate. Next, a solvent such as toluene, xylene, or butanol is added to form a slurry, and this slurry is formed into a sheet on a film of polyethylene terephthalate or the like by a doctor blade method or the like. Finally, the sheet formed into a sheet is dried to remove the solvent to obtain a green sheet. On these green sheets, wiring patterns, vias, and the like are formed by screen printing using a silver paste as necessary.

  The green sheet is processed into a desired shape after firing to form a substrate. In this case, the body to be fired is a laminate of one or more green sheets. The firing is typically performed by holding at 500 to 700 ° C. for 20 to 60 minutes. A more typical firing temperature is 550 to 600 ° C.

  In addition, it is preferable that the reflective layer containing silver formed on the substrate surface does not contain other inorganic components from the viewpoint of reflectance. The reflective layer mainly reflects light emitted from the light emitting element mounted on the substrate body.

Next, the vitreous insulating layer will be described.
The glassy insulating layer is preferably a single layer of low-melting glass or a layer containing low-melting glass and a ceramic filler.

  The thickness of the glassy insulating layer is typically 5 to 30 μm. If it is less than 5 μm, the covering property may be insufficient, so that it is preferably 5 μm or more. If it exceeds 30 μm, the heat dissipation of the light emitting element may be hindered and the light emission efficiency may be reduced.

  The method for forming the glassy insulating layer is not particularly limited as long as a layer having a thickness of 5 to 30 μm can be formed flat. Typically, a low melting point glass alone or a mixture of a low melting point glass and a ceramic filler is used. It is formed by pasting, screen printing, and baking.

  In the present invention, the glassy insulating layer preferably contains 50% or more of low melting point glass in volume%. If the content is less than 50%, the sintering at the time of firing becomes insufficient, and the covering property may be impaired. In order to improve sinterability, it is more preferable to contain 70% or more. Further, it contains 50% or less of ceramic filler. The ceramic filler content is typically 5% or more. By containing a ceramic filler, the strength of the vitreous insulating layer may be increased. Moreover, the heat dissipation of a glassy insulating layer may be able to be made high.

  The ceramic filler is exemplified by alumina and silica, but is not limited as long as it does not cause absorption that impairs the reflectance (white or transparent).

  The glass of the vitreous insulating layer preferably has a Tg of 380 to 620 ° C. For example, Tg can be observed as the temperature of the shoulder of the first bent portion when differential thermal analysis measurement is performed at a temperature rising rate of 10 ° C./min.

  The glass of the vitreous insulating layer preferably has a Ts of 500 to 700 ° C. Here, Ts can be observed as the temperature of the fourth bent portion when differential thermal analysis measurement is performed up to 1000 ° C. under a temperature rising rate of 10 ° C./min.

  The glass of the vitreous insulating layer is preferably one that does not crystallize in the firing step. Those having Tc of 700 ° C. or higher or those in which Tc cannot be observed are preferred. If the Tc is less than 700 ° C., the vitreous insulating layer is easily crystallized in the firing step, which may cause the substrate to warp. Here, Tc refers to the temperature of an exothermic peak observed at a temperature higher than Tg when differential thermal analysis measurement is performed up to 1000 ° C. under a temperature rising rate of 10 ° C./min.

  Next, the composition of the glass that can be used in the present invention will be described.

Low melting point containing 30 to 60% B ₂ O ₃ , 0 to 50% SiO ₂ , ₂ to 40% ZnO, and 5 to 15% Li ₂ O + Na ₂ O + K ₂ O in terms of mol% based on oxide. It is glass.

B ₂ O ₃ is a glass network-forming oxide, an essential component that lowers Tg, and is contained in an amount of 30% or more. If it is less than 30%, the glass becomes unstable. Or Tg or Ts may be too high. If it exceeds 60%, the water resistance and chemical durability of the glass are lowered, and the function as a protective film for the silver conductor may be insufficient. Preferably it is 50% or less.

Although SiO ₂ is not an essential component, it is a component that increases the stability of the glass and is preferably contained in an amount of 5% or more. If it is less than 5%, the water resistance may be insufficient, or the glass may be easily crystallized. In order to suppress silver coloring, the content is preferably 10% or more, and more preferably 20% or more. If the SiO ₂ content exceeds 50%, Ts may be too high.

  ZnO is an essential component and has the effect of increasing the fluidity of the glass and lowering Tg and Ts, and is preferably contained in an amount of 2% or more. When the ZnO content is more than 40%, color tends to develop when fired simultaneously with the silver conductor. Preferably it is 20% or less.

Each component and mixture of Li ₂ O, Na ₂ O and K ₂ O has an effect of lowering Ts, and is preferably contained in a total amount of 5% or more. On the other hand, if the content of the mixture exceeds 15%, silver ions may diffuse into the glass and colloids may be formed. Preferably, it is 10% or less.

Al ₂ O ₃ is not an essential component but can be contained in a small amount to increase the stability of the glass. However, when Al ₂ O ₃ is excessive, color tends to develop when fired simultaneously with the silver conductor. The content of Al ₂ O ₃ is preferably 2% or less.

  If the glass containing the above components as a main component has a crystallization temperature of 900 ° C. or higher, it can also be applied to a general LTCC that is fired at 800 to 900 ° C.

  The glass that can be used in the present invention essentially contains the above-mentioned components as main components, but may contain other components as long as the object of the present invention is not impaired. When such components are contained, the total content of these components is preferably 10% or less. However, lead oxide is not contained.

  The reflectance of the light emitting element mounting substrate on which the vitreous insulating layer of the present invention is formed is preferably 80% or more, more preferably 85% or more, and further preferably 88% or more.

  A glass raw material was prepared and mixed so as to have a composition shown in mol% for Examples 1 to 4 shown in Table 1, and the mixed raw material was put in a platinum crucible and melted at 1200 to 1500 ° C. for 60 minutes, and then the molten glass was mixed. Sink out and cool. The obtained glass was pulverized and classified for 10 to 60 hours with water as an auxiliary in an alumina ball mill to obtain glass powder. Examples 1-3 are the glass of an Example, Example 4 is the glass of a comparative example. Example 3 is an example in which an alumina filler (AA-2 manufactured by Sumitomo Chemical) was added to the glass powder of Example 1. The volume ratio of glass to alumina is shown in the glass column and alumina column in the table.

The average particle diameter D ₅₀ (unit: μm) of each glass powder was measured using a SALD2100 manufactured by Shimadzu Corporation, which is a laser diffraction / scattering particle size distribution measuring apparatus. Were each in the range of _D 50 = 1 to 3 [mu] m. The softening point Ts (unit: ° C.) was measured up to 1000 ° C. at a temperature rising rate of 10 ° C./min using a thermal analyzer TG-DTA2000 manufactured by Bruker AXS. In any of Examples 1 to 4, no crystal peak was observed during Ts measurement.

  For Examples 1, 2 and 4, only for each glass powder, for Example 3, a mixed powder obtained by adding an alumina filler to a glass powder is 70% by mass%, and a vehicle component obtained by melting a resin in a solvent is 30%. The mixture was kneaded for 1 hour in a porcelain mortar, and further dispersed three times with three rolls to prepare a glass paste.

  The silver paste is prepared by blending conductive powder (manufactured by Daiken Chemical Industry Co., Ltd.) having an average particle size of about 2.5 μm, a small particle size distribution and a spherical shape, and ethyl cellulose at a mass ratio of 85:15. After being dispersed in a solvent (α terpineol) at a mass% display concentration of 85%, the mixture was kneaded in a porcelain mortar for 1 hour and further dispersed three times with a three roll.

  A silver paste was printed on an alumina substrate, and after drying, a glass paste was printed on the silver paste, and this was held at 600 and 700 ° C. for 30 minutes for firing. The reflectance of the surface of the obtained substrate was measured. The reflectance was measured using a spectroscope USB2000 and a small integrating sphere ISP-RF manufactured by Ocean Optics, and the average value of 400 to 800 nm in the visible light region was calculated as the reflectance (unit:%). The results are shown in Table 1.

  Reflectance is based on the correlation between the result of measuring the amount of light and mounting the light emitting element on the actual package and the reflectance measured by this method. If the reflectance is less than 80%, the light from the light emitting element is reflected efficiently. Since it was not possible, it was considered unpreferable as an insulating layer. As can be seen from the results in Table 1, there is a tendency that the reflectance is improved by increasing the firing temperature.

  It can be used for backlights of mobile phones and large LCD TVs.

1: LTCC substrate 2: Conductor layer (reflection layer)
3: Overcoat layer 4: Via conductor 5: Sealing resin (phosphor layer)
6: Light emitting element 7: Bonding wire 8: Gold plating layer

Claims (6)

A substrate body having a mounting surface on which the light emitting element is mounted; a reflective layer containing silver formed on a part of the mounting surface of the substrate body; and a vitreous insulating layer formed on the reflective layer. The glassy insulating layer is expressed in terms of mol% based on oxide, and B ₂ O ₃ is 30 to 60%, SiO ₂ is 0 to 50%, ZnO is 2 to 40%, Li ₂ O + Na ₂ O + K ₂ O. A substrate for mounting a light-emitting element, characterized by being formed of a low-melting glass containing 5 to 15%.   The low melting point glass contained in the glassy insulating layer is a glass having thermal characteristics having a transition point of 380 to 620 ° C, a softening point of 500 to 700 ° C, and a crystallization point of 700 ° C or higher. Light emitting element mounting substrate.   The light emitting element mounting substrate according to claim 1, wherein the glassy insulating layer contains a ceramic filler in addition to the low melting point glass.   The light emitting element mounting substrate according to claim 1, wherein a terminal portion for the light emitting element is formed on the substrate body, and the insulating layer is formed in a region excluding the terminal portion.   The light emitting element mounting substrate according to any one of claims 1 to 4, wherein the substrate body has a recess, and the bottom surface of the recess is a light emitting element mounting surface.   A light-emitting device having a phosphor layer on which a light-emitting element is mounted on the glassy insulating layer of the light-emitting element mounting substrate according to claim 1.

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