This application claims priority under 35 U.S.C. Section 119 to Japanese Patent Application No. 2012-145450 filed on Jun. 28, 2012, which are herein incorporated by references.
1. Field of the Invention
The present invention relates to a method of manufacturing an LED.
2. Description of the Related Art
Generally, an LED includes a substrate and a light emitting element formed on the substrate. In order to enhance the brightness, in some cases, the LED includes a reflective layer formed on a surface of the substrate on aside opposite to the light emitting element (for example, Japanese Patent Application Laid-open No. 2001-085746). The reflective layer is formed by, for example, a vapor deposition method such as a MOCVD method and an ion assisted electron beam deposition method. In the case of the MOCVD method, after an LED wafer is placed on a table with the reflective layer forming side up (that is, with the outer side of the substrate up), an outer surface of the substrate is subjected to vapor deposition processing. Further, in the case of the ion assisted electron beam deposition method, the LED wafer is covered with a lid from a side opposite to the reflective layer forming side (that is, the light emitting element side), and a reflective layer forming surface (that is, the outer surface of the substrate) is exposed. The exposed surface is subjected to vapor deposition processing. However, in such conventional manufacturing methods, the following problem may arise. A metal enters a space between the surface of the LED wafer on the side opposite to the reflective layer forming surface (that is, the surface on the light emitting element side) and the table or the lid, and thus a metal layer is also formed on the outer side of the light emitting element. Thus, the brightness of the LED is negatively affected. Such a problem becomes more conspicuous when the LED wafer to be subjected to the forming of the reflective layer is warped, and when the LED wafer is warped during the reflective layer formation.
The present invention has been made to solve the above-mentioned conventional problem, and has an object to provide a method of manufacturing an LED, which is capable of preventing a metal layer from being formed on an outer side of a light emitting element.
A method of manufacturing an LED according to an embodiment of the present invention includes:
forming a reflective layer on an outer side of a substrate of an LED wafer including the substrate and a light emitting element on one surface of the substrate; and
attaching, prior to the forming a reflective layer, a heat-resistant pressure-sensitive adhesive sheet onto an outer side of the light emitting element.
In an embodiment of the present invention, the heat-resistant pressure-sensitive adhesive sheet includes a hard base member and a pressure-sensitive adhesive layer.
According to the present invention, the method includes the forming of the reflective layer on the outer side of the substrate of the LED wafer including the substrate and the light emitting element on the one surface of the substrate. Prior to the forming of the reflective layer, the heat-resistant pressure-sensitive adhesive sheet is attached onto the outer side of the light emitting element. In this manner, the metal layer may be prevented from being formed on the outer side of the light emitting element. Further, the heat-resistant pressure-sensitive adhesive sheet also has a function of protecting the LED wafer, and hence according to the present invention, before and after the forming of the reflective layer, the damage to the LED wafer may be prevented to manufacture the LED with high yields.
In the accompanying drawings:
In a manufacturing method of the present invention, an LED wafer that has been appropriately processed in the pre-process is subjected to a reflective layer forming step.
As the heat-resistant pressure-sensitive adhesive sheet 20, any appropriate pressure-sensitive adhesive sheet may be used as long as the effect of the present invention may be obtained. It is preferred to use a heat-resistant pressure-sensitive adhesive sheet which does not melt and generate a gas and can maintain its adhesion even when the heat-resistant pressure-sensitive adhesive sheet is exposed under high temperature (for example, 135° C. to 200° C.) at the time of vapor deposition processing in the reflective layer forming step of the post-process.
The heat-resistant pressure-sensitive adhesive sheet 20 includes, for example, a base member and a pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer may be provided on one surface of the base member, or may be provided on each of both surfaces thereof.
As a material for constituting the base member, any appropriate material may be used as long as the effect of the present invention may be obtained. Examples of the material for constituting the base member include resins such as polyimide and polyethylene naphthalate. With use of such resins, a heat-resistant pressure-sensitive adhesive sheet excellent in heat-resisting performance can be obtained.
When the base member is made of a resin, the thickness of the base member is preferably 10 μm to 1,000 μm, more preferably 25 μm to 700 μm.
According to the embodiment, the base member is a hard base member. In this specification, the hard base member refers to a base member made of an inorganic material having a Young's modulus of 70 GPa or more at 25° C. With use of the heat-resistant pressure-sensitive adhesive sheet including the hard base member, the reflective layer forming step can be performed after the warpage of the LED wafer is corrected, and further, the warpage can be prevented from occurring during the reflective layer forming step. As a result, the effect of the present invention that the metal layer is prevented from being formed on the outer side of the light emitting element 12 becomes more conspicuous.
As a material for constituting the hard base member, there may be given, for example: silicon; glass; metal such as stainless steel; and a ceramic.
When the base member is the hard base member, the thickness of the hard base member is preferably 0.2 mm to 50 mm, more preferably 0.3 mm to 10 mm.
As a pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer, any appropriate pressure-sensitive adhesive may be used. It is preferred to use a pressure-sensitive adhesive which does not melt and generate a gas and can maintain its adhesion even under high temperature (for example, 135° C. to 200° C.) at the time of vapor deposition. Further, the pressure-sensitive adhesive is preferred to be peeled off without adhesive residue even after heating. Examples of the pressure-sensitive adhesive include an acrylic pressure-sensitive adhesive, a silicone-based pressure-sensitive adhesive, and a polyimide-based pressure-sensitive adhesive. Examples of the polyimide-based pressure-sensitive adhesives include a polyimide-based resin obtained by imidizing a polyamic acid obtained by a reaction of an acid anhydride and a diamine having an ester structure. It is preferred that the mixing ratio of the diamine having the ether structure when the acid anhydride is reacted with the diamine having the ether structure be 5 parts by weight to 90 parts by weight with respect to 100 parts by weight of the acid anhydride.
Further, a foaming agent may be added to the pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer having the foaming agent added thereto exhibits a peel property by heating. Specifically, in the pressure-sensitive adhesive layer having the foaming agent added thereto, the foaming agent is foamed or expanded by heating, and thus the adhesion is reduced or lost. A heat-resistant pressure-sensitive adhesive sheet including such a pressure-sensitive adhesive layer can be adhered tightly to the LED wafer, and can be easily released when it is removed from LED wafer. With use of such a heat-resistant pressure-sensitive adhesive sheet, the damage to the LED wafer can be markedly prevented during releasing the heat-resistant pressure-sensitive adhesive sheet. Further, automated steps can be easily designed. Any appropriate foaming agent may be used as the foaming agent. Examples of the foaming agent include: inorganic foaming agents such as ammonium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium boron hydride, and an azide; and organic foaming agents such as an alkane chloride fluoride, an azo-based compound, a hydrazine-based compound, a semicarbazide-based compound, a triazole-based compound, and an N-nitroso-based compound. Details of the pressure-sensitive adhesive layer containing the foaming agent as described above are described in Japanese Patent Application Laid-open Nos. Hei 5-043851, Hei 2-305878, and Sho 63-33487, the contents of which are hereby incorporated by reference into this specification.
The thickness of the pressure-sensitive adhesive layer is preferably 1 μm to 100 μm, more preferably 3 μm to 60 μm.
The LED wafer with the heat-resistant pressure-sensitive adhesive sheet is placed on a table 100 via the heat-resistant pressure-sensitive adhesive sheet 20, and a reflective layer 30 is formed on the outer side of the substrate 11 of the LED wafer 10 (
As a material for constituting the reflective layer 30, any appropriate material may be used as long as the light from the light emitting element 12 may be satisfactorily reflected. Examples of the material for constituting the reflective layer 30 include metals such as aluminum, silver, gold, palladium, platinum, rhodium, and ruthenium. The reflective layer 30 made of a metal may be formed by, for example, a vapor deposition method (for example, as in the illustrated example, a MOCVD method). It is preferred that an underlayer made of, for example, SiO2, TiO2, ZrO2, and/or MgF2 be formed on the outer side of the substrate 11 of the LED wafer 10, and then the reflective layer 30 made of a metal be formed by a vapor deposition method. According to the present invention, the LED wafer 10 having the heat-resistant pressure-sensitive adhesive sheet 20 attached to the outer side of the light emitting element 12 is subjected to the reflective layer forming step. Therefore, the heat-resistant pressure-sensitive adhesive sheet 20 plays a role as a so-called masking sheet, and hence the metal may be prevented from entering behind the LED wafer 10 and depositing on the light emitting element 12. Further, as described above, when the hard base member is used as the base member of the heat-resistant pressure-sensitive adhesive sheet, the warpage of the LED wafer can be corrected, and hence it is possible to provide a manufacturing method having high reliability in terms of preventing the metal from depositing on the light emitting element 12. According to the manufacturing method of the present invention, a metal layer is hardly formed on the light emitting element 12, and hence an LED having high brightness can be obtained.
In the present invention, the method of forming the reflective layer 30 is not limited to the MOCVD method, and any other appropriate methods may be employed. Examples of the other appropriate methods include an ion assisted electron beam deposition method. In the ion assisted electron beam deposition method, generally, the LED wafer is covered with a lid from a side opposite to the reflective layer forming side (that is, from the light emitting element side) , and a reflective layer forming surface (that is, the outer surface of the substrate) is exposed. The exposed surface is subjected to vapor deposition processing. According to the present invention, by attaching the heat-resistant pressure-sensitive adhesive sheet on the outer side of the light emitting element, also in the case of employing the ion assisted electron beam deposition method, the metal may be prevented from entering behind the LED wafer and depositing on the light emitting element.
As described above, the LED wafer 10 having the reflective layer 30 formed thereon can be obtained (
The method of manufacturing an LED of the present invention may further include any other appropriate steps. Examples of the other appropriate steps include a step of cutting the LED wafer 10 to singulate small element pieces (dicing step).
Referring to
In the embodiments illustrated in
Number | Date | Country | Kind |
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2012-145450 | Jun 2012 | JP | national |