Patent Application
20150084080
The present invention relates to a light-emitting device and a method for manufacturing the light-emitting device. More particularly, the present invention relates to a light-emitting device with a mounted light-emitting element, and a method for manufacturing such device.
Recently, LEDs serving as a light source are used for various purposes in terms of their longer life and energy saving. Especially during recent years, luminous efficiency of the LEDs for the high-light use is improving and thus the LEDs are becoming to be used for a lighting purpose.
In a case of a white LED used for the lighting purpose, the light quantity can be increased by applying a larger current to the LED. However, a performance of the LED can be degraded under such a severe condition that the large current is applied. Therefore, it is concerned that the LED package and a LED module cannot have a longer life and a high reliability. For example, when an electric current flowing through the LED is increased, the heat attributed to the LED increases. Accordingly, the temperature tends to rise in the LED module for lighting and a system thereof, which can cause a deterioration of the LED module and the system. In this regard, only about 25% of the electric power to be consumed in the white LED is converted into the visible light and the rest of the electric power is directly converted into the heat. Therefore, it is required to release the heat from the LED package and the LED module. For example, various types of heat sinks are used to release the heat, wherein the heat sink may be mounted to a bottom surface of a package substrate in order to improve the heat release.
In general, the LED does not have a high resistance property against a static electricity, and thus the designs or measures for protecting the LED from such stress attributed to the static electricity may be employed (see, Patent Literature 1). For example, a Zener diode may be provided in electrically parallel connection with the LED. This can reduce the stress of the LED upon the applying of the overvoltage or overcurrent to the LED. However, in a case of a surface-mounted type LED package 200 as illustrated in
Moreover, the recent LED requires not only its downsizing but also an improvement of light use efficiency. That is, higher brightness of the LED is required.
The present invention has been created in view of the above circumstances. In other words, in light of a need for a compact LED package with a satisfactory heat-releasing performance and brightness, an object of the present invention is to provide a light-emitting device which suitably satisfies the above need, and also provide a method for such device.
In order to achieve the above object, the present invention provides a light-emitting device comprising a light-emitting element and a substrate for light-emitting element,
wherein the light-emitting element is in a mounted state on a mounting surface of the substrate, the mounting surface being one of two opposed main surfaces of the substrate,
wherein the substrate is provided with a protection element for the light-emitting element, the protection element comprising a voltage-dependent resistive layer embedded in the substrate, and also comprising a first electrode and a second electrode each of which is in connection with the voltage-dependent resistive layer,
wherein the mounted light-emitting element is in an overlapping relation with the voltage-dependent resistive layer, and
wherein a reflective layer is provided on at least one of the substrate and the voltage-dependent resistive layer such that the reflective layer is located adjacent to the first electrode which is in contact with a substrate exposure surface of the voltage-dependent resistive layer.
In the light emitting device of the present invention, not only the voltage-dependent resistive layer of the protection element is in an embedded state within the substrate to be positioned in the overlapping relation with the light-emitting element, but also the reflective layer is provided on at least one of the substrate and the voltage-dependent resistive layer to be located adjacent to the first electrode which is in contact with the substrate exposure surface of the voltage-dependent resistive layer. In other words, one of the features regarding the light emitting device is that not only the voltage-dependent resistive layer of the protection element is embedded in the mounting area for the light-emitting element, but also the reflective layer is positioned in a particular region adjacent to the electrode of the protection element, the electrode being on the mounting surface of the substrate for light-emitting element.
The term “light-emitting element” used in the present description substantially means an element capable of emitting light. Examples of the light-emitting element include a light-emitting diode (LED) and an electronic component equipped therewith. Accordingly, the term “light-emitting element” in the present invention means not only a “bare chip type LED (i.e., LED chip)” but also a “discrete type light-emitting element wherein a molding of the LED chip is provided for an easy packaging thereof with respect to the substrate”. The LED chip may also be a semiconductor laser chip.
The term “light-emitting device” used in the present description substantially means a light-emitting element package (especially “LED package”). This term (i.e., “light-emitting device”) also means “product with a plurality of LEDs arranged in a form of array”. In a case where the light-emitting element is a LED chip equipped with a positive electrode and a negative electrode on its surface which is opposed to a light-emitting surface of the LED chip, the LED chip may be in a mounted state on the mounting surface of the substrate in a manner of flip-chip. The term “voltage-dependent resistive layer” used in the present description substantially means a layer capable of changing its resistive property according to a voltage to be applied thereto. The voltage-dependent resistive layer may be one in which the high electrical resistance is provided in the range of the low voltage applied across the electrodes disposed on both sides thereof, whereas the electrical resistances sharply drops if the higher voltage is applied. This means that the voltage-dependent resistive layer can have a nonlinearity relationship between the applied voltage and the resistance value. In an embodiment according to the present invention, the voltage-dependent resistive layer may be in the form of “single layer”.
The term “substrate” used in the present description substantially means a member to be used as a platform for mounting the light-emitting element. Therefore, the examples of the substrate for light-emitting element include not only a “plate member having a substantially flat form” but also a “member having a recessed portion in its main surface to accommodate the LED chip and the like therein”.
Furthermore, the present invention also provides a method for manufacturing the above-described device. More specifically, the present invention provides the method for manufacturing the light-emitting device comprising a substrate for light-emitting element and a light-emitting element mounted on the substrate, the substrate including a varistor element comprising a voltage-dependent resistive layer embedded in the substrate and first and second electrodes each of which is in connection with the voltage-dependent resistive layer, the method comprising the steps of:
(A) forming a second electrode precursor layer on a main surface of a green sheet;
(B) pressing the second electrode precursor layer into the green sheet from above by means of a convex-shaped die, and thereby forming a recessed portion in the green sheet with the second electrode precursor layer disposed on a bottom surface of the recessed portion;
(C) disposing the voltage-dependent resistive layer in the recessed portion;
(D) sintering the green sheet with the voltage-dependent resistive layer and the second electrode precursor layer disposed in the recessed portion of the green sheet, and thereby producing a substrate with the voltage-dependent resistive layer and the second electrode embedded in the substrate;
(E) forming a reflective layer on the substrate and/or the voltage-dependent resistive layer; and
(F) forming the first electrode on the substrate except for a forming region for the reflective layer, the first electrode being in contact with the voltage-dependent resistive layer.
The manufacturing method according to the present invention is characterized at least in that the reflective layer is formed on the substrate and/or the voltage-dependent resistive layer, and that the first electrode is formed on the substrate except for a forming region for the reflective layer to bring the first electrode into contact with the voltage-dependent resistive layer. One of other features regarding the method is that the substrate for light-emitting element is prepared by the voltage-dependent resistive layer which has been beforehand formed, and then the light-emitting device is manufactured by the use of such substrate.
(Improved Utilization Efficiency of Light)
In the light emitting device of the present invention, a light reflection efficiency can be additionally improved because the reflective layer is located beneath the light-emitting element such that they are adjacent to each other. Specifically, the downward light emitted from the light-emitting diode can be reflected by the reflective layer, and thus such emitted light can be utilized without a substantial loss. In particular, the reflective layer can not only contribute to an improvement of the luminous efficiency, but also serve to protect the voltage-dependent resistive layer (“protection function of voltage-dependent resistive layer” will be described below). The light-emitting device of the present invention makes it possible to suitably downsize the device due to the voltage-dependent resistive layer embedded in the substrate. This makes it possible to realize a LED product having a higher luminous efficiency and a higher brightness while having its smaller size (“smaller size” and “higher brightness” will be described below).
(Protection Function of Reflective and Protective Layer)
In accordance with the present invention, the reflective layer can be used as a protective layer with respect to the voltage-dependent resistive layer. For example, the reflective layer can be used for protecting the voltage-dependent resistive layer from its damage occurred during the formation of the electrode of the protection element. By way of example, in a case where a foundation layer is formed on the substrate by a sputtering process, and then the first electrode is formed thereon by a plating process, the reflective layer can be used for protecting the voltage-dependent resistive layer from a reagent used for such processes, e.g., acid, alkari or plating reagent. Such usage of the reflective layer makes it possible to keep the initial properties of the voltage-dependent resistive layer due to the fact that the voltage-dependent resistive layer is not impaired. This can ensure that the device has a desired performance of the protection element (i.e., varistor element), which leads to an achievement of the desired LED product its higher quality (i.e., higher reliability of the protection element).
(Compact Sizing and Improved Heat Releasing)
The light-emitting device according to the present invention is configured such that the voltage-dependent resistive layer of the protective element is embedded in an overlapping relation with the mounting surface for the light-emitting element to be mounted. This leads to an achievement of a compact-sizing of the device as a whole. Accordingly, the light-emitting device of the present invention is suitable as the packaging device in various purposes (e.g., in the lighting use), and it can effectively contribute to the down-sizing of an end product.
Further, the light-emitting device according to the present invention has such a configuration that the protection element (especially, voltage-dependent resistive layer and one of the electrodes, occupying a larger volume in the protection element) is substantially eliminated from the surface of the substrate. This makes it possible to save a space for the other components disposed on the surface of the substrate. For example, there can be formed the spaces for the electrodes and metal patterns to be provided on the mounting surface of the substrate for light-emitting element. The electrodes and the metal patterns are connected with the light-emitting element which generates the heat, and they are made of a material with a high thermal conductivity (e.g., copper), which effectively contributes to the heat releasing from the light-emitting element product. In accordance with the present invention, the space formed due to the “embedding” of the protection element can contribute to larger size and thicker dimension of the electrodes and the metal patterns capable of releasing the heat, and thereby the heat-releasing performance can be effectively improved in the light-emitting element product.
Particularly in a case where the reflective layer is made of resin component so that it has insulating properties, an electrical short can be effectively prevented. This makes it possible to narrow the distance between the divided two pieces of the first electrode, which leads to an achievement of an enlarged first electrode while the substrate is not enlarged. This means that the reflective layer can indirectly contribute to an improvement of the heat releasing performance of the device.
Moreover, in accordance with the present invention, the substrate with satisfactory heat-resisting and heat-releasing properties can be used (for example, ceramic substrate can be used) as the light-emitting element substrate with the voltage-dependent resistive layer embedded therein. This also makes it possible to improve the heat-releasing performance of the device.
The light-emitting device according to the present invention is configured such that the protection element is embedded without increasing of the thickness of the substrate. The reason for this is that, under the condition of the embedding of the protection element (more specifically, the voltage-dependent resistive layer and the one of the electrodes of the varistor element) in the substrate, the voltage-dependent resistive layer can be in a form of a single layer. Therefore, a thinning of the light-emitting element substrate with the protection element accommodated therein is achieved, and thereby the heat from the light-emitting element can be released to the outside, which leads to an improvement of the heat releasing performance in the light-emitting element product.
In general, the luminous efficiency (i.e., a ratio of the driving current being converted into the light) of the light-emitting element (especially, the LED) tends to be decreased with increased temperature, and thus the brightness of the light-emitting element becomes lowered when the temperature rises. In this regard, according to the present invention, the substrate with the improved luminous efficiency and brightness can be provided since it has an excellent performance of the heat releasing. Moreover, the device according to the present invention has such an excellent heat releasing performance that an operation life of the LED can be prolonged and also the degradation and/or color change of a sealing resin, which may be attributed to the heat, can be effectively prevented.
A light-emitting device according to the present invention will be hereinafter described in more detail. It should be noted that various components or elements are schematically shown in the drawings wherein their dimensional proportions and their appearances are not necessarily real ones, and are merely for the purpose of making it easy to understand the present invention.
As shown in
In the substrate 10 for light-emitting element, a voltage-dependent resistive layer 50 of a protection element is in an embedded state in a substrate region in an overlapping relation with the light-emitting element. More specifically, as illustrated in
As shown in
The first and second electrodes 60, 70 of the protection element substantially serve as external electrodes of the protection element, and thus they can contribute to a parallel electrical connection between the protection element and the light-emitting element. In order to allow the parallel electrical connection between the protection element and the light-emitting element to provide a protective function, the first electrode and the second electrode are directly connected to the electrodes of the light-emitting element, respectively, or are electrically connected to wiring patterns (i.e., patterned metal layers) disposed in the substrate. In other words, the first electrode and the second electrode of the protection element, as required, may be in an electrical connection with the wiring patterns (i.e., patterned metal layers) and the like of the substrate to form a typical circuit diagram as illustrated in
As shown in
The reflective layer 55 serves as a protective layer for protecting the voltage-dependent resistive layer 50. This means that the reflective layer 55 not only serves to reflect the light from the light-emitting element 20, but also preferably serves to protect the voltage-dependent resistive layer 50. More specifically, the reflective layer 55 is used for protecting the voltage-dependent resistive layer from the outside during the formation of the first electrode. The reflective layer can be used for protecting the voltage-dependent resistive layer from a reagent (e.g., acid, alkali, plating reagent or combination thereof) used for the formation of the first electrode wherein a foundation layer is formed on the substrate by a sputtering process and then the first electrode is formed thereon by a plating process. Such usage of the reflective layer makes it possible to keep the initial properties of the voltage-dependent resistive layer due to the fact that the voltage-dependent resistive layer is not impaired by the reagent. This can ensure that the device has a desired performance of the protection element (i.e., varistor element).
The thickness of the reflective layer 55, which may depend on the kinds of the material to be used, is preferably in the approximate range of 1 um to 20 um. When the reflective layer has the thickness of more than 20 um, the device may have the insufficient reflectivity. On the other hand, when the reflective layer has the thickness of less than 20 um, the device may have the insufficient function of protecting the voltage-dependent resistive layer. It is more preferred that the thickness of the reflective layer 55 may be in the approximate range of 5 um to 15 um.
Since the reflective layer preferably has the insulating properties, the distance between the divided two pieces of the first electrode can be narrowed. In other words, in a case where the reflective layer serves as a insulating layer made of the resin component, the electrical short can be more effectively prevented, which makes it possible to narrow the distance between the divided two pieces of the first electrode. More specifically, it is possible to narrow the distance between the first sub-electrode 60a and first sub-electrode 60b (see
The light-emitting device of the present invention can be practically provided as a LED package 150 as illustrated in
The light-emitting device (i.e., LED package) according to the present invention has the protection element suitably incorporated in the substrate. Thus, the LED in the light-emitting device can be protected from the static electricity and the surge voltage while keeping the inherent characteristic of the LED chip, and also an erroneous action of the LED can be prevented in the light-emitting device.
As illustrated in
The LED package 150 illustrated in
As seen from the embodiment of
As illustrated in
Now, the substrate 10 for light-emitting element will be described in more detail. The body 10 of the substrate for light-emitting element may be made of any materials, i.e., may be made of a material which can be used for a substrate of a general LED package. However, in view of an improvement of the heat releasing performance in the light-emitting device, it is preferred that the substrate is made of a material having the desired heat conductivity. Examples of the material having the desired heat conductivity include a metal, a ceramic, a composite material and a thermally conductive filler-containing resin. Among those, the ceramic is particularly suitable material for the substrate on which the light-emitting element generating the heat is mounted, since it has the higher heat conductivity and the less thermal expansion coefficient. Further in light of the fact that the ceramic substrate (e.g., LTCC substrate) can be obtained with ease by sintering the green sheet, the ceramic is suitable material for the substrate in the present invention.
In the light-emitting device of the present invention, a size of the substrate is relatively small since the voltage-dependent resistive layer of the protection element has not been disposed on the surface of the substrate, but embedded within the body of the substrate (specifically, at the mounting region for the light-emitting element). For example in a case of producing an LED package 150 as illustrated in
According to the present invention, a thin substrate is provided as the light-emitting element substrate in which the protection element is accommodated. For example in a case of the LED package 150 of
A voltage-dependent resistive layer 50 of the protection element, which is in an embedded in the substrate, may be made of any material as long as the resistance of the layer 50 varies according to a voltage applied thereto. In a case where the protection element is a varistor element, it is typical that the voltage-dependent resistive layer 50 is a layer made of a varistor material. In this regard, the voltage-dependent resistive layer 50, which is made of the varistor material, may be in a form of singular layer as illustrated in
The size of the voltage-dependent resistive layer is not particularly limited as long as it is smaller than that of the substrate. In other words, it is preferred that the horizontal width dimensions of the voltage-dependent resistive layer are smaller than those of the main surface of the substrate. For example, a width dimension “w” of the voltage-dependent resistive layer 50 as illustrated in
In the substrate 10 for light-emitting element, a surface of the voltage-dependent resistive layer 50 is preferably positioned in the same plane as the surface of the substrate as illustrated in
In the present invention, the voltage-dependent resistive layer 50 is in an exposed state at the surface of the substrate wherein the size of the exposed surface of the resistive layer is relatively small. Preferably, the exposed surface of the voltage-dependent resistive layer 50 has a smaller area than that of the mounting region 25 of the light-emitting element (see,
The material for each of the first electrode and the second electrode of the protection element is not particularly limited, and thus may be typical one used for the conventional protection element. For example in a case where the protection element is a varistor element, any typical material used for the varistor electrode can be used for the first electrode and the second electrode of the varistor element. For example, at least one of metal materials selected from the group consisting of silver (Ag), copper (Cu), palladium (Pd), platinum (Pt) and nickel (Ni) can be used as a main material of the first electrode and the second electrode of the varistor element.
The first electrode 60 may be one formed through a plating process (e.g., dry plating process and/wet plating process). For example, the first electrode 60 may be one formed by sputtering and electroplating processes. In this regard, the first electrode 60 may be composed of a sputtering film layer as a foundation layer, and a thick plating layer formed thereon.
Each size of the first electrode 60 and the second electrode 70 of the protection element is not largely limited. In other words, as illustrated in
The substrate 10 for light-emitting element has such a configuration that the protection element (especially, voltage-dependent resistive layer and the second electrode which occupy a larger volume) is substantially eliminated from the surface of the substrate, making it possible to give a space for other components. Therefore, the present invention can make the first electrode 60 thicker. For example, the thickness of the first electrode can be preferably in the range of about 50 μm to about 200 μm, more preferably in the range of about 60 μm to about 150 μm, most preferably in the range of about 70 μm to about 125 μm. Since the first electrode effectively contributes to the heat releasing because of its high thermal conductivity, the thicker first electrode can effectively improve the heat-releasing effect in the product with the light-emitting element provided therein. Similarly, the present invention can make the larger thickness of the wiring pattern (i.e., patterned metal layer) and the like provided on the mounting surface of the substrate. For example, the thickness of the wiring patter or the like can be in the range of about 50 μm to about 200 μm, preferably in the range of about 60 μm and about 150 μm, and more preferably in the range of about 70 μm to about 100 μm.
In a case where the protection element is the varistor element, the substrate 10 for light-emitting element can be configured to have “double-varistor structure” as illustrated in
The light-emitting device of the preset invention can be realized as LED package products according to various modified embodiments. The detailed explanation about this will be described.
(Disposition in Recessed-Portion)
With respect to the embodiment “disposition in recessed-portion”, a configuration of
The following embodiments are also possible in the present invention.
(Built-in Multilayer Varistor)
(Embedding of Second Electrode in the Interior of Voltage-Dependent Resistive Layer)
Next, a method for manufacturing the light-emitting device according to the present invention will be described.
The manufacturing method described below is based on “method for manufacturing a substrate for light-emitting element, the substrate being equipped with a varistor element comprising a voltage-dependent resistive layer and first and second electrodes electrically connected to the voltage-dependent resistive layer”. Firstly, as illustrated in
Subsequent to the sintering, the reflective layer is disposed on the substrate 10 and the voltage-dependent resistive layer 50. More specifically, as shown in
The formation of the reflective layer 55 may be performed by any suitable processes as long as they can produce the reflective layer 55 locally at region adjacent to the forming region for the first electrode. The reflective layer 55 can be formed by applying a raw material therefor on the entire surface of the substrate 10, followed by a mask exposure process and a subsequent development process (see
In a case of the formation of the reflective layer made of the resin component with the oxide ceramic component therein, such a resin material that contains the oxide ceramic powder (e.g., titanium oxide powder and/or alumina powder) therein may be applied, followed by being subjected to a curing treatment (for example, heat curing or photo curing treatment). In another case of the formation of the reflective layer made of the glass component with the oxide ceramic component therein, such a glass paste material (e.g., glass paste made of a vehicle and glass powder such as SiO2 and B2O3 powder) that contains the oxide ceramic powder (e.g., titanium oxide powder and/or alumina powder) therein may be applied, followed by being subjected to a heat treatment.
It is preferred that the thickness of the formed reflective layer 55 is in the approximate range of 1 um to 20 um in terms of “improved reflectivity” and “protection of voltage-dependent resistive layer”.
Subsequent to the formation of the reflective layer, the first electrode 60 and the wiring pattern 90 are formed. For example, the metal layer 90′ is formed on the main surface of the substrate 10 as illustrated in
The first electrode can be formed through the plating process as described below, in which process the reflective layer can serve to protect the voltage-dependent resistive layer 50 from the forming process of the first electrode.
With respect to the obtained substrate 10, a light-emitting element (e.g., LED chip) is mounted. Specifically, the LED chip is mounted on the substrate to be electrically connected to the substrate element such as the first electrode and the wiring pattern. Preferably, the mounting of the LED chip is performed by a GGI technology. The GGI (Gold-to-Gold Interconnection) technology corresponds to a flip-chip mounting process in which a gold bump provided on a gold pad of the LED chip is connected to a gold pad provided on the substrate by a thermo-compression bonding. The GGI technology provides an advantageous effect in that no reflow and no flux cleaning is performed due to no use of solder bump, and also a satisfactory reliability can be obtained even at high temperature. In the GGI technology, a gold melting may be performed for example by using an ultrasonic wave in addition to the load and heat. After the mounting of the LED chip is completed, the necessary components (e.g., phosphor layer) are formed, followed by the encapsulating of the light-emitting element, the phosphor layer, the wirings and the like with a sealing resin. As a result, there can be obtained the light-emitting device, i.e., LED package 150 as illustrated in
As for the manufacturing of the substrate 10 for light-emitting element, the sintered voltage-dependent resistive layer can be used. More specifically, a voltage-dependent resistive layer which has been preliminarily subjected to the sintering process can be used as the voltage-dependent resistive layer 50 to be carried by the carrier film 47. Therefore, the voltage-dependent resistive layer 50 is not adversely affected by the subsequent sintering of the green sheet (specifically, the voltage-dependent resistive layer 50 is not chemically adversely influenced from the green sheet 10′ upon the sintering thereof), and thereby a high performance of the varistor element can be still provided. Typical examples of the material for the voltage-dependent resistive layer include a zinc oxide type varistor material. The zinc oxide type varistor material can be obtained by adding bismuth oxide, antimony oxide, cobalt oxide and/or manganese oxide by about 0.5 mol % to about 1.0 mol % to the zinc oxide as a main composition, followed by the sintering thereof. In this case, a typical sintering temperature is in the range of about 1200° C. to about 1350° C. While on the other hand, the low-temperature co-fired glass ceramic substrate (LTCC) is obtained by the sintering at a temperature of about 900° C. In the light of this, it can be understood that the manufacturing method of the present invention (wherein the sintered voltage-dependent resistive layer is used and the sintering process of the green sheet for forming the LTCC is performed at about 900° C.) allows the voltage-dependent resistive layer to be hardly influenced by the LTCC sintering, making it possible to keep the high varistor performance. The term “high varistor performance” as used herein specifically means that “clamping voltage characteristic is excellent” and “less electric current is leaked to the varistor upon the driving of the LED”. Incidentally, the phrase “clamping voltage characteristic is excellent” specifically means that the voltage-dependent resistive layer is stable with respect to the voltage to be continuously applied and the fluctuation thereof, and that a possible surge voltage can be reduced to a level equal to or less than a withstand voltage of the LED.
With respect to the carrier film 47 with the voltage-dependent resistive layer 50 disposed thereon, the manufacturing process thereof is illustrated in
Various modified embodiments may be possible with respect to the manufacturing method of the present invention. The detailed explanation about this will be described.
(Sintered Substrate with Recessed-Portion)
The manufacturing process as illustrated in
It should be noted that the present invention as described above includes the following aspects:
The First Aspect:
A light-emitting device comprising a light-emitting element and a substrate for light-emitting element,
wherein the light-emitting element is in a mounted state on a mounting surface of the substrate, the mounting surface being one of two opposed main surfaces of the substrate,
wherein the substrate is provided with a protection element for the light-emitting element, the protection element comprising a voltage-dependent resistive layer embedded in the substrate, and also comprising a first electrode and a second electrode each of which is in connection with the voltage-dependent resistive layer,
wherein the mounted light-emitting element is in an overlapping relation with the voltage-dependent resistive layer, and
wherein a reflective layer is provided on at least one of the substrate and the voltage-dependent resistive layer such that the reflective layer is located adjacent to the first electrode which is in contact with a substrate exposure surface of the voltage-dependent resistive layer.
The Second Aspect:
The light-emitting device according to the first aspect, wherein the reflective layer is “insulating layer comprising a resin component and an oxide ceramic component” or “insulating layer comprising a glass component and an oxide ceramic component”.
The Third Aspect:
The light-emitting device according to the first or second aspect, wherein the reflective layer serves as a protective layer for protecting the voltage-dependent resistive layer. In this aspect, the reflective layer is preferably provided as the protective layer for protecting the voltage-dependent resistive layer during the manufacturing of the light-emitting device.
The Fourth Aspect:
The light-emitting device according to any one of the first to third aspects, wherein the first electrode has a divided form wherein the divided two pieces of the first electrode are positioned on the surface of the voltage-dependent resistive layer. In other words, the divided two pieces of the first electrode are positioned on the surface of the substrate, the surface including “substrate exposure surface of the voltage-dependent resistive layer” or “mounting surface of the substrate”. Since the reflective layer preferably has the insulating properties, the distance between the divided two pieces of the first electrode can be narrowed. For example, in a case where the first electrode has such a divided form that the divided two pieces of the first electrode are positioned on the substrate exposure surface of the voltage-dependent resistive layer, the reflective layer, which is located between the divided two pieces of the first electrode, can have the narrowed width dimension of about 20 μm to about 100 μm.
The Fifth Aspect:
The light-emitting device according to any one of the first to fourth aspects, wherein the reflective layer has a layer thickness of 1 μm to 20 μm. In light of suitable properties of the layer, i.e., not only the reflective property but also the protective property of the layer, the thickness of the reflective layer is preferably in the range of about 1 μm to about 20 μm.
The Sixth Aspect:
The light-emitting device according to any one of the first to fifth aspects, wherein the second electrode is positioned in an opposed relation to the first electrode such that the second electrode is in contact with a substrate embedment surface of the voltage-dependent resistive layer or is accommodated in the interior of the voltage-dependent resistive layer. Preferably in the light-emitting device according to the sixth aspect, the first electrode of the protection element is located on the surface of the substrate such that the first electrode is in contact with the light-emitting element, whereas the second electrode of the protection element is located within the body of the substrate in an opposed relation to the first electrode such that the second electrode is in partial or whole contact with the voltage-dependent resistive layer. For example, the first electrode of the protection element is positioned on the surface of the substrate in contact with the protection element, whereas the second electrode of the protection element, which is opposed to the first electrode, is positioned within the substrate in an overlapping relation with the voltage-dependent resistive layer. Alternatively, the first electrode of the protection element is positioned on the surface of the substrate in contact with the protection element, whereas the second electrode of the protection element, which is opposed to the first electrode, is positioned within the substrate such that the second electrode is included in the interior of the voltage-dependent resistive layer. In this case, the second electrode, which is included in the interior of the voltage-dependent resistive layer, not necessarily have a form of single layer, but may have a form of a plurality of layers.
The Seventh Aspect:
The light-emitting device according to any one of the first to sixth aspects, wherein a surface of the voltage-dependent resistive layer is in the same plane as the one of the two opposed main surfaces of the substrate, and thereby the surface of the voltage-dependent resistive layer forms a part of the mounting surface. In the light-emitting device according to the seventh aspect, the upper surface of the voltage-dependent resistive layer of the protection element is substantially flush with the mounting surface of the substrate. Alternatively, the surface of the voltage-dependent resistive layer may be in the same plane as the other of the two opposed main surfaces of the substrate. This means that the lower surface of the voltage-dependent resistive layer of the protection element may be substantially flush with the back surface of the substrate.
The Eighth Aspect:
The light-emitting device according to any one of the first to seventh aspects, wherein the second electrode is in connection with an electrode or metal layer (or wiring pattern in an electrical communication with such electrode) provided on the one or the other of the two opposed main surfaces (i.e., the mounting surface and back surface opposed thereto) by a via hole which extends in the body of the substrate between the voltage-dependent resistive layer and the one or the other of the two opposed main surfaces. The eighth aspect can correspond to an embodiment wherein the second electrode has a form of “Through Electrode”.
The Ninth Aspect:
The light-emitting device according to any one of the first to eighth aspects, wherein the protection element is a varistor element. It is preferred in the light-emitting device according to the ninth aspect that the second electrode is positioned in an opposed relation to the first electrode such that the second electrode is in contact with a substrate embedment surface of the voltage-dependent resistive layer, and that the varistor element is composed of serially-connected two varistor elements which share the second electrode provided on the substrate embedment surface of the voltage-dependent resistive layer. As for the preferred embodiment wherein the protection element is the varistor element, the first electrode of the varistor element has a divided form wherein the divided two pieces of the first electrode are positioned on the surface of the voltage-dependent resistive layer (i.e., “substrate exposure surface of the voltage-dependent resistive layer” or “mounting surface of the substrate”), and the serially-connected two varistor elements share the second electrode provided on the substrate embedment surface of the voltage-dependent resistive layer. This means that the varistor element is composed of a sub-varistor A and a sub-varistor B wherein a first electrode A corresponding to one of the two electrodes of the sub-varistor A and a first electrode B corresponding to one of the two electrodes of the sub-varistor B are positioned on the mounting surface of the substrate. While on the other hand, a second electrode A corresponding to the other of the two electrodes of the sub-varistor A and a second electrode B corresponding to the other of the two electrodes of the sub-varistor B are electrically interconnected in the embedded state within the substrate (it is particularly preferred that the second electrode A of the sub-varistor A and the second electrode B of the sub-varistor B integrally form a single layer). The above structure of the varistor can be referred to as “double-varistor structure” since two of the varistor elements are provided as a component of the substrate. In such “double-varistor structure”, a positive electrode of the light-emitting element is to be in connection with one of the divided two pieces of the first electrode, whereas a negative electrode of the light-emitting element is to be in connection with the other of the divided two pieces of the first electrode. Consequently, the two pieces of varistor elements serially connected to each other (i.e., the sub-varistor element A and the sub-varistor element B) are in an electrically parallel connection with the light-emitting element. In one preferred embodiment, the protection element for the light-emitting element is a multilayer varistor. Even in this embodiment, the voltage-dependent resistive layer of the multilayer varistor is preferably in an embedded state at the substrate mounting area for the light-emitting element. It is preferred that a surface of the voltage-dependent resistive layer of the multilayer varistor is in the same plane as the one of the two opposed main surfaces of the substrate, and thereby the surface of such voltage-dependent resistive layer forms a part of the mounting surface in the substrate. This means that, preferably, the upper surface of the voltage-dependent resistive layer of the multilayer varistor is substantially flush with the mounting surface of the substrate.
The Tenth Aspect:
The light-emitting device according to any one of the first to ninth aspects, wherein the substrate has a two-layered structure composed of an upper layer and a lower layer made of different materials from each other. It is preferred in this aspect that the upper layer provides the substrate with the mounting surface, and also has the voltage-dependent resistive layer embedded therein. It is preferred that the upper layer and the lower layer made of different materials from each other have different heat conductivities from each other. In light of the heat releasing from the substrate, it is preferred that the heat conductivity of the lower layer is higher that the heat conductivity of the upper layer. For example, the material for the upper layer of the substrate may be a glass ceramic, whereas the material for the lower layer of the substrate may be an alumina. Alternatively, the material for the upper layer of the substrate may be a glass ceramic, whereas the material for the lower layer of the substrate may be an aluminum nitride.
The Eleventh Aspect:
A method for manufacturing a light-emitting device comprising a substrate for light-emitting element and a light-emitting element mounted on the substrate, the substrate including a varistor element comprising a voltage-dependent resistive layer embedded in the substrate and first and second electrodes each of which is in connection with the voltage-dependent resistive layer, the method comprising the steps of:
(A) forming a second electrode precursor layer on a main surface of a green sheet;
(B) pressing the second electrode precursor layer into the green sheet from above by means of a convex-shaped die, and thereby forming a recessed portion in the green sheet with the second electrode precursor layer disposed on a bottom surface of the recessed portion;
(C) disposing the voltage-dependent resistive layer in the recessed portion;
(D) sintering the green sheet with the voltage-dependent resistive layer and the second electrode precursor layer disposed in the recessed portion of the green sheet, and thereby producing a substrate with the voltage-dependent resistive layer and the second electrode embedded in the substrate;
(E) forming a reflective layer on the substrate and/or the voltage-dependent resistive layer; and
(F) forming the first electrode on the substrate except for a forming region for the reflective layer, the first electrode being in contact with the voltage-dependent resistive layer.
The Twelfth Aspect:
The method according to the eleventh aspect, wherein the reflective layer formed by the step (E) is used for protecting the voltage-dependent resistive layer from the outside during the formation of the first electrode in the step (F).
The Thirteenth Aspect:
The method according to the eleventh or twelfth aspect, wherein the formation of the first electrode in the step (F) is performed by a plating processing in which the reflective layer is used for protecting the voltage-dependent resistive layer from a reagent used for the formation of the first electrode. In other words, in a case where the first electrode is formed through a plating treatment in the step (F), the reflective layer formed by the step (E) is used for the protection of the voltage-dependent resistive layer from a reagent used for such formation of the first electrode. By way of an example, the reflective layer is used for protecting the voltage-dependent resistive layer from an acid liquid (e.g., sulfuric acid or hydrochloric acid) which has been used for removing the impurities or unnecessary matters after the plating treatment (e.g., the residual palladium catalyst of the electroless plating treatment). Such usage of the reflective layer enables the initial properties of the voltage-dependent resistive layer to be maintained due to the fact that the voltage-dependent resistive layer is not impaired during the formation of the first electrode.
The Fourteenth Aspect:
The method according to any one of the eleventh to thirteenth aspect, wherein the first electrode is formed to be in contact with a substrate exposure surface of the voltage-dependent resistive layer in the step (F), and the reflective layer is formed at a region adjacent to a forming region for the first electrode in the step (E). According to this aspect, not only the downward light emitted from the light-emitting element can be effectively reoriented upwardly by the reflective layer, but also the voltage-dependent resistive layer can be suitably protected during the formation of the first electrode by the reflective layer.
The Fifteenth Aspect:
The method according to any one of the eleventh to fourteenth aspect, wherein, instead of the steps (A) and (B), another step is performed wherein a recessed portion is formed in a main surface of a green sheet by means of a convex-shaped die by pushing the die into the green sheet; and
wherein, in the step (C), the voltage-dependent resistive layer having a second electrode precursor layer formed on a lower surface of the voltage-dependent resistive layer is disposed in the recessed portion of the green sheet.
The Sixteenth Aspect:
The method according to any one of the eleventh to fourteenth aspect, wherein, instead of the steps (B) and (C), another step is performed wherein the voltage-dependent resistive layer is pressed into the green sheet via the second electrode precursor layer, and thereby forming a recessed portion in the green sheet while disposing the voltage-dependent resistive layer and the second electrode precursor layer in the recessed portion. In this aspect, the voltage-dependent resistive layer located above the second electrode precursor layer is pressed into the green sheet, and thereby the voltage-dependent resistive layer and the second electrode precursor layer are embedded into the green sheet.
The Seventeenth Aspect:
The method according to any one of the eleventh to fourteenth aspect, wherein, instead of the steps (A) to (C), another step is performed wherein the voltage-dependent resistive layer having a second electrode precursor layer formed thereon is pressed into a green sheet under such a condition that the second electrode precursor layer is positioned beneath the voltage-dependent resistive layer, and thereby forming a recessed portion in the green sheet while disposing the voltage-dependent resistive layer and the second electrode precursor layer in the recessed portion. In this aspect, the voltage-dependent resistive layer provided with the second electrode precursor layer therebeneath is pressed into the green sheet from above, and thereby the voltage-dependent resistive layer and the second electrode precursor layer are embedded into the green sheet.
The Eighteenth Aspect:
The method according to any one of the eleventh to fourteenth aspect, wherein, instead of the steps (A) to (C), another step is performed wherein the voltage-dependent resistive layer accommodating the second electrode in an interior thereof is disposed on a main surfaces of a green sheet, and then the voltage-dependent resistive layer is pressed into the green sheet from above by means of a convex-shaped die, and thereby forming a recessed portion in the green sheet with the voltage-dependent resistive layer accommodating the second electrode in the interior thereof disposed in a bottom surface of the recessed portion. In the step (D), the green sheet with the voltage-dependent resistive layer accommodating the second electrode in the interior thereof disposed in the bottom surface of the recessed portion is sintered to produce the substrate with the voltage-dependent resistive layer and the second electrode embedded therein.
While some embodiments of the present invention have been hereinbefore described, they are merely the typical embodiments. It will be readily appreciated by those skilled in the art that the present invention is not limited to the above embodiments, and that various modifications are possible without departing from the scope of the present invention.
The embodiment of the present invention has been hereinbefore described wherein the voltage-dependent resistive layer disposed in the carrier film is in a form of singular layer. The present invention, however, is not limited to that. For example, an embodiment as illustrated in
The embodiment of the present invention has been hereinbefore described wherein the voltage-dependent resistive layer, which is in an embedded state within the substrate, is positioned beneath the light-emitting element to be mounted. The present invention, however, is not limited to that. For example, the voltage-dependent resistive layer may be in an embedded state such that at least the part of the layer is in an overlapping relation with the mounting region for the light-emitting element. In this case, the thermal via can be provided immediately below the light-emitting element generating the heat, which leads to an improved heat-releasing performance of the substrate.
The embodiment of the present invention has been hereinbefore described wherein the substrate may have the two-layered structure composed of an upper layer and a lower layer with respect to the case of the heterogeneous ceramic substrate. The present invention, however, is not limited to that. Specifically, the substrate of the present invention may be composed of more than two layers of different materials. For example, the substrate may be three-layered structure or four-layered structure, which also leads to an improved heat-releasing performance of the substrate.
Finally, by exemplifying the LED package as illustrated in
The LED equipped the substrate for light-emitting element according to the present invention can be suitably available for various lighting uses since it has an improved brightness and a compacted size. Such LED according to the present invention can also be suitably available for wide range of applications, for example, a backlight source application (for LCD images), camera flash application, vehicle installation application.
The present application claims the right of priority of Japan patent application No. 2012-030741 (filing date: Feb. 15, 2012, title of the invention: LIGHT-EMITTING DEVICE AND METHOD FOR MANUFACTURING THE SAME), the whole contents of which are incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-030741 | Feb 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/000818 | 2/14/2013 | WO | 00 |
