JP2011238819A - Light-emitting device and package - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting device and a package wherein reaction between a connection terminal of a circuit pattern provided on a mounting substrate and gas in an external atmosphere can be suppressed.SOLUTION: A light-emitting device 1 includes: a mounting substrate 3 made of an inorganic material in which a circuit pattern 4 mounted with an LED element 2 is provided; an external connection electrode 44 of the circuit pattern 4; and a protection film 5 which is provided so as to cover the outer edge of the exposed surface of the external connection electrode 44 and is made of an inorganic material.

Description

  The present invention relates to a light emitting device and a package provided with a protective film for protecting an electrode provided on a mounting substrate.

  Conventionally, in a light emitting device provided with a protective film for protecting an electrode provided on a mounting substrate, a light emitting device in which a resin resist layer is formed as a protective film is known (for example, see Patent Document 1). The light-emitting device described in Patent Document 1 has electrodes provided on at least one of the front and back surfaces of a ceramic mounting substrate, and the electrodes are formed larger than the diameter of solder balls to be joined. A resin resist is formed on at least a portion of the surface of the electrode excluding the joint portion and the surface of the ceramic mounting substrate that straddles the outer edge of the electrode. Since the resin resist is formed in a portion that straddles the outer edge of the electrode, cracks starting from the outer edge portion of the electrode due to thermal shock are unlikely to occur.

JP-A-2005-244100

  By the way, although the resin resist of the light emitting device described in Patent Document 1 can suppress the generation of cracks based on the outer edge portion of the electrode by protecting the outer edge portion of the electrode, it is an organic material, so Permeate sulfur-containing gas. As a result, the permeated gas reaches the electrode, and the electrode and the gas react to deteriorate to become a weakened portion.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a light emitting device and a package capable of suppressing a reaction between an electrode provided on a mounting substrate and a gas in an external atmosphere. There is to do.

  In order to achieve the above object, in the present invention, a light emitting element is mounted, a mounting substrate made of an inorganic material, an electrode provided on the back surface of the mounting substrate, and a back surface of the mounting substrate so as to cover an outer edge of the electrode. A light-emitting device having a protective film made of an inorganic material is provided.

  The light emitting device may include a conductive bonding material used for electrical connection between the electrode and the outside, and the protective film may cover all of the electrode other than a bonding region with the conductive bonding material.

  In the light emitting device, the light emitting element may be sealed with a sealing material made of an inorganic material.

  The wiring board which has the said light-emitting device, the external electrode joined to the said electrically conductive joining material, and the protective film which consists of inorganic materials which cover those external electrodes other than the joining area | region with the said electrically conductive joining material may be provided. .

  According to the present invention, the reaction between the electrode provided on the mounting substrate and the gas in the external atmosphere can be suppressed.

FIG. 1 is a schematic longitudinal sectional view of a light emitting device according to a first embodiment of the present invention. FIG. 2 is a plan view showing the back surface of the mounting substrate of the light emitting device according to the first embodiment of the present invention. FIG. 3 is a schematic longitudinal sectional view of the LED element according to the first embodiment of the present invention. 4A to 4E are schematic longitudinal sectional views for explaining a manufacturing process of the light emitting device according to the first embodiment of the invention. FIG. 5 is a schematic longitudinal sectional view of a package in which the light emitting device according to the first modification of the present invention is mounted. FIG. 6 is a schematic longitudinal sectional view of a light emitting device according to the second embodiment of the present invention. FIG. 7 is a plan view showing the back surface of the mounting substrate of the light emitting device according to the second embodiment of the present invention.

[First Embodiment]
1 is a schematic longitudinal sectional view of a light emitting device according to a first embodiment of the present invention, FIG. 2 is a plan view showing a back surface of a mounting substrate of the light emitting device, and FIG. 3 is a schematic longitudinal sectional view of an LED element. FIG.

  As shown in FIG. 1, the light emitting device 1 includes an LED element 2 made of a flip-chip GaN-based semiconductor material, a mounting substrate 3 on which the LED element 2 is mounted, and a tungsten (W)- A circuit pattern 4 made of nickel (Ni) -gold (Au), a protective film 5 that protects the back pattern 42 of the circuit pattern 4, and a glass that seals the LED element 2 and is bonded to the mounting substrate 3. And a sealing portion 6. Further, a hollow portion 7 in which the glass does not surround is formed between the LED element 2 and the mounting substrate 3. In the present embodiment, the mounting board 3 and the circuit pattern 4 constitute a mounting board for mounting the LED element 2 and supplying power to the LED element 2.

As shown in FIG. 3, the LED element 2 as a light-emitting element is formed by epitaxially growing a group III nitride semiconductor on the surface of a growth substrate 20 made of sapphire (Al ₂ O ₃ ). The mold layer 22, the MQW layer 23, and the p-type layer 24 are formed in this order. This LED element 2 is epitaxially grown at 700 ° C. or higher, and its heat-resistant temperature is 600 ° C. or higher, and is stable with respect to the processing temperature in sealing processing using low-melting glass described later. The LED element 2 includes a p-side electrode 25 provided on the surface of the p-type layer 24 and a p-side pad electrode 26 formed on the p-side electrode 25, and the p-type layer 24 to the n-type layer. 22 has an n-side electrode 27 formed on the n-type layer 22 exposed by etching a part thereof. Au bumps 28 are formed on the p-side pad electrode 26 and the n-side electrode 27, respectively.

  The p-side electrode 25 is made of, for example, silver (Ag), and functions as a light reflecting layer that reflects light emitted from the MQW layer 23 as a light emitting layer toward the growth substrate 20. The material of the p-side electrode 25 can be changed as appropriate. In the present embodiment, two p-side pad electrodes 26 are formed on the p-side electrode 25, and an Au bump 28 is formed on each p-side pad electrode 26. The number of p-side pad electrodes 26 may be three, for example, and the number of p-side pad electrodes 26 formed on the p-side electrode 25 can be changed as appropriate.

  In the n-side electrode 27, a contact layer and a pad layer are formed in the same area. As shown in FIG. 3, the n-side electrode 27 is formed of an Al layer 27a, a thin film Ni layer 27b covering the upper surface of the Al layer 27a, and an Au layer 27c covering the upper surface of the Ni layer 27b. Note that the material of the n-side electrode 27 can be changed as appropriate. In the present embodiment, the n-side electrode 27 is formed at the corner of the LED element 2 and the p-side electrode 25 is formed almost entirely except for the formation region of the n-side electrode 27 in plan view. .

The LED element 2 has a thickness of 100 μm and a 346 μm square, and has a thermal expansion coefficient of 7 × 10 ⁻⁶ / ° C. Here, although the thermal expansion coefficient of the GaN layer of the LED element 2 is 5 × 10 ⁻⁶ / ° C., the thermal expansion coefficient of the growth substrate 20 made of sapphire occupying most is 7 × 10 ⁻⁶ / ° C. The thermal expansion coefficient of the LED element 2 main body is equal to the thermal expansion coefficient of the growth substrate 20. In addition, in each figure, in order to clarify the structure of each part of the LED element 2, each part is shown by the size different from an actual size.

The mounting substrate 3 as a mounting substrate is made of a polycrystalline sintered material of alumina (Al ₂ O ₃ ), is formed in a 1.0 mm square with a thickness of 0.25 mm, and has a thermal expansion coefficient α of 7 × 10 ^{−. 6} / ° C. As shown in FIG. 1, the circuit pattern 4 of the mounting substrate 3 includes a surface pattern 41 formed on the substrate surface and electrically connected to the LED element 2, and a back surface formed on the substrate back surface and connectable to an external terminal. And a pattern 42. The surface pattern 41 includes a W layer 4a patterned according to the electrode shape of the LED element 2, a thin film Ni layer 4b covering the surface of the W layer 4a, and a thin film Au layer covering the surface of the Ni layer 4b. 4c. The back surface pattern 42 includes a W layer 4a patterned according to an external connection electrode 44 described later, a thin film Ni layer 4b covering the surface of the W layer 4a, and a thin film Au layer covering the surface of the Ni layer 4b. 4c. The front surface pattern 41 and the back surface pattern 42 are electrically connected by a via pattern 43 made of W provided in a via hole 3 a penetrating the mounting substrate 3 in the thickness direction. One external connection electrode 44 is provided on each of the anode side and the cathode side. Each external connection electrode 44 is diagonally arranged on the mounting substrate 3 in plan view.

The protective film 5 is made of an inorganic material such as SiO _{2 and} is continuously formed from the back surface of the mounting substrate 3 to the outer edge portion of the external connection electrode 44 as shown in FIG. Protect. The inorganic material that can be used for the protective film 5 is not limited to SiO ₂ but may be Al ₂ O ₃ , TiO ₂ or the like. The protective film 5 has an opening 50 for connecting the external connection electrode 44 to a conductive bonding material 8 described later.

Glass sealing part 6 _is made of glass of _ZnO-B 2 O 3 -SiO ₂ based inorganic material. The composition of the glass is not limited to this. For example, the glass may contain Nb ₂ O ₅ for a high refractive index, or Na ₂ O, Li ₂ O, etc. for lowering the melting point. May be contained. Furthermore, ZrO ₂ , TiO ₂ or the like may be included as an optional component. This glass has a glass transition temperature (Tg) of 490 ° C., a yield point (At) of 520 ° C., and the formation temperature at the time of epitaxial growth in the light emitting layer of the LED element 2 (MQW layer 23 in the present embodiment), The glass transition temperature (Tg) is sufficiently low. In the present embodiment, the glass transition temperature (Tg) is lower by 200 ° C. or more than the epitaxial growth temperature of the light emitting layer. Moreover, the thermal expansion coefficient ((alpha)) in 100 to 300 degreeC of glass is 6x10 < ^-6 > / ^degreeC . When the thermal expansion coefficient (α) exceeds the glass transition temperature (Tg), a larger numerical value is obtained. Thereby, the glass is bonded to the mounting substrate 3 at about 600 ° C., and hot pressing is possible. Moreover, the refractive index of the glass of the glass sealing part 6 is 1.7.

  As shown in FIG. 1, the glass sealing part 6 has a lens-shaped surface, covers the LED element 2 and the mounting substrate 3 entirely, and has a thickness of 0.5 mm.

  In the light emitting device 1 configured as described above, when a voltage is applied to the LED element 2 through the circuit pattern 4, blue light is emitted from the LED element 2. Blue light emitted from the LED element 2 is radiated to the outside through the lens-shaped surface of the glass sealing portion 6.

  The light emitting device 1 is manufactured through the following steps.

  4A to 4E are schematic longitudinal sectional views for explaining a manufacturing process of the light emitting device according to the first embodiment of the invention. Hereinafter, the manufacturing process of the external connection electrode 44 on the back surface of the mounting substrate 3 will be described in particular.

  First, a green sheet 30 forming the mounting substrate 3 is prepared, and the via hole 3a is formed by a press die or the like. Then, as shown in FIG. 4A, the W paste 40 is screen-printed on the back surface according to the circuit pattern. Next, as shown in FIG. 4B, the green sheet 30 on which the W paste 40 is printed is baked by heat-treating at 1000 ° C. or more to form a mounting substrate 3 made of alumina, and the W layer 4 a is formed on the mounting substrate 3. Bake.

  Further, as shown in FIG. 4C, Ni plating is performed on the W layer 4a to form the Ni layer 4b, and as shown in FIG. 4D, Au plating is applied on the Ni layer 4b. The Au layer 4c is formed, and the circuit pattern 4 is formed (pattern formation process). The Au layer 4c is preferably formed so as to cover the surface and the outer edge of the Ni layer 4b in order to protect the Ni layer 4b that is more reactive with the gas in the external atmosphere than Au.

  In forming the circuit pattern 4, a metal such as Cr or Ti is vapor-deposited on the fired ceramic, and Ni plating and Au plating are performed. Can be applied.

Next, as shown in FIG. 4E, a protective film 5 made of SiO _{2 is} formed by a sol-gel method. The protective film 5 is formed so as to protect the back surface of the mounting substrate 3 and the outer edge portion of the external connection electrode 44 (protective film forming step).

  On the other hand, the oxide powder of the glass component is heated to 1200 ° C. and stirred in a molten state. And after solidifying glass, it slices so that it may correspond to the thickness of the glass sealing part 6, and processes glass before sealing in a spherical shape. Thereafter, a lens-shaped surface having a lens shape, a bonding surface to be bonded to the mounting substrate 3, and a concave portion corresponding to the LED element 2 provided on the bonding surface are formed on the pre-sealing glass using a mold (sealing). Stop member preparation step).

  Next, the pre-sealing glass prepared in the sealing member preparation step is disposed so that the concave portion faces the LED element 2 and hot-pressed on the mounting substrate 3 by a mold. By hot pressing, the concave portion of the glass before sealing is deformed along the LED element 2 and is bonded to the surface of the mounting substrate to seal the LED element 2 and the surface pattern 41 (sealing process). In addition, you may perform the sealing member preparation process and the sealing process before a protective film formation process.

  According to the first embodiment, the outer edge portion of the external connection electrode 44 is protected by the protective film 5 made of an inorganic material having low gas permeability in the external atmosphere, and the Au layer 4c having low reactivity with the gas is formed. Since the structure is exposed from the opening 50, the reaction between the external connection electrode 44 and the gas in the external atmosphere can be suppressed.

  In addition, since the outer edge portion of the external connection electrode 44 is protected by the protective film 5, it is possible to suppress the occurrence of cracks originating from the outer edge portion of the external connection electrode 44, peeling of the external connection electrode 44, and the like.

[First Modification]
FIG. 5 is a schematic longitudinal sectional view of a package in which the light emitting device is mounted. In the first modification, the light emitting element 1 according to the first embodiment is mounted on a wiring board 9.

The package 10 includes the light emitting element 1 described above, a conductive bonding material 8 made of a paste containing metal fine particles, and a wiring substrate 9 made of an inorganic material having a circuit pattern 90 provided on the surface thereof. Further, the circuit pattern 90 of the wiring substrate 9 is protected by a protective film 91 in a region other than the bonding surface with the conductive bonding material 8 on the surface. As the protective film 91, SiO ₂ or the like is used similarly to the protective film 5.

  The conductive bonding material 8 may be provided on at least one of the external connection electrode 44 of the light emitting element 1 or the surface of the circuit pattern 90 of the wiring board 9. For the conductive bonding material 8, for example, a gold tin (AuSn) solder layer or a paste containing metal fine particles such as gold, silver, platinum, and palladium may be used.

  In addition, the conductive bonding material 8 is bonded so as to cover the entire area of the external connection electrode 44 exposed to the opening 50 of the protective film 5 in a state where the light emitting element 1 and the wiring substrate 9 are mounted. The Similarly, bonding is performed so as to cover all areas of the circuit pattern 90 that are not protected by the protective film 91.

  Further, when a paste containing metal fine particles is used as the conductive bonding material 8, the gap formed between the metal fine particles allows movement and deformation of the metal fine particles and the metal fine particles fused by pressure bonding, so that the light emitting element 1 and The stress caused by the difference in thermal expansion / shrinkage between the wiring board 9 and the like is relieved, and the light emitting element 1 is prevented from being peeled off from the wiring board 9.

  When a paste containing metal fine particles is used as the conductive bonding material 8, a metal layer made of the same kind of metal as the metal fine particles is provided on both the bonding surface of the external connection electrode 44 and the bonding surface of the circuit pattern 90. It is preferable. This is because a part of the metal fine particles penetrates into the metal layer provided on each joining surface at the time of pressure bonding, so that the joining property is improved.

  According to the first modification, when the light emitting element 1 is mounted on the wiring board 9, the external connection electrode 44 and the circuit pattern 90 are not exposed, and the protective film 5 and the protective film 91 of the inorganic material and the conductive bonding material 8 are not exposed. Therefore, a package in which the reaction between the external connection electrode 44 and the circuit pattern 90 and the gas in the external atmosphere is suppressed can be manufactured.

[Second Embodiment]
FIG. 6 is a schematic longitudinal sectional view of the light emitting device according to the second embodiment of the present invention, and FIG. 7 is a plan view showing the back surface of the mounting substrate of the light emitting device. The second embodiment differs from the first embodiment in that an Au layer is further provided on the protective film 5.

  As shown in FIGS. 6 and 7, the external connection electrode 45 covers the opening 50 on the Au layer 4 c of the light emitting device 1 according to the first embodiment and the protective film 5 covering the outer edge of the Au layer 4 c. Further, the Au layer 51 is formed by further performing Au plating, and protects the back pattern 42 and the protective film 5 from the external atmosphere.

  According to the second embodiment, the back pattern 42 and the protective film 5 are covered with the Au layer 51 to expose the Au layer 51 having low reactivity with the gas in the external atmosphere. Reaction with the gas in the external atmosphere can be suppressed.

  Further, since the opening 50 of the protective film 5 is protected by the Au layer 51, it is possible to suppress the occurrence of peeling or the like based on the opening 50 of the protective film 5.

  When mounting the light emitting element 1A on the wiring board 9 described above, in addition to using the conductive bonding material 8 described above, a gold plating layer is provided on both the bonding surface of the external connection electrode 45 and the bonding surface of the circuit pattern 90. The gold plating layers may be joined at normal temperature by irradiating both gold plating layers with plasma and activating them.

  Moreover, in the said embodiment, although the light-emitting device using an LED element as a light emitting element was demonstrated, a light emitting element is not limited to an LED element. Furthermore, the glass sealing portion 6 is not limited to having a lens-shaped surface, and may be composed of a plurality of planes, and other specific details such as a detailed structure can be appropriately changed. Of course.

DESCRIPTION OF SYMBOLS 1 Light emitting element 1A Light emitting element 2 LED element 3 Mounting board 3a Via hole 4 Circuit pattern 4a Au layer 4b Ni layer 4c W layer 5 Protective film 6 Glass sealing part 7 Hollow part 8 Conductive bonding material 9 Wiring board 10 Package 20 Growth board 21 Buffer layer 22 n-type layer 23 MQW layer 24 p-type layer 25 p-side electrode 26 p-side pad electrode 27 n-side electrode 27a Au layer 27b Ni layer 27c W layer 28 Bump 30 Green sheet 40 W paste 41 Surface pattern 42 Back surface pattern 43 Via pattern 44 External connection electrode 45 External connection electrode 50 Opening 51 Au layer 90 Circuit pattern 91 Protective film

Claims (4)

A mounting substrate on which a light emitting element is mounted and made of an inorganic material;
An electrode provided on the back surface of the mounting substrate;
A light emitting device having a protective film made of an inorganic material provided on a back surface of the mounting substrate so as to cover an outer edge of the electrode. A conductive bonding material used for electrical connection between the electrode and the outside;
The light-emitting device according to claim 1, wherein the protective film covers all of the electrodes except for a bonding region with the conductive bonding material.   The light emitting device according to claim 2, wherein the light emitting element is sealed with a sealing material made of an inorganic material. A light emitting device according to claim 2 or 3,
A package comprising: an external electrode that is bonded to the conductive bonding material; and a wiring board that includes a protective film made of an inorganic material that covers a portion of the external electrode other than a bonding region with the conductive bonding material.

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