The present application relates to a method of forming a wiring of a light emitting device, a substrate for mounting a light emitting device, a display, a back light and an electronic appliance, particularly suitable for a substrate for mounting a light emitting device in which a minute light emitting device, for example, a light emitting diode is mounted on the substrate and then a wiring is formed thereon, and a display, a back light and an electronic appliance using the substrate for mounting a light emitting device.
As a light emitting device, for example, a light emitting diode, there are a light emitting diode in which a p-side electrode and an n-side electrode are formed on one side, and a light emitting diode in which a p-side electrode and an n-side electrode are separately formed on a light emission surface (the surface to take out light) and on a surface on the opposite side thereof (the back side). An example of the former light emitting diode is shown in FIGS. 14a and 14B, and an example of the latter light emitting diode is shown in FIGS. 15A and 15B. Here, FIGS. 14A and 14B show a plan view and a cross section, respectively. In addition, FIGS. 15A and 15B show a cross section and a bottom view, respectively.
In the light emitting diode shown in FIGS. 14A and 14B, the structure of a light emitting diode is formed of an n-type semiconductor layer 101, a light emitting layer (an active layer) 102 and a p-type semiconductor layer 103, in which a p-side electrode 104 is formed on the p-type semiconductor layer 103, and an n-side electrode 105 is formed on the n-type semiconductor layer 101. Connecting conductive materials 106 and 107 are formed on the p-side electrode 104 and the n-side electrode 105, respectively. In this case, the back side of the n-type semiconductor layer 101 is the light emission surface. A protective insulating resin 108 is formed so as to cover the surfaces except the light emission surface and the connecting conductive materials 106 and 107 in the light emitting diode.
In the light emitting diode shown in FIGS. 15A and 15B, the structure of a light emitting diode is formed of an n-type semiconductor layer 101, a light emitting layer 102 and a p-type semiconductor layer 103, in which a p-side electrode 104 is formed on the p-type semiconductor layer 103, and an n-side electrode 105 in a linear shape is formed on one side of the back side of the n-type semiconductor layer 101 that is the light emission surface. A connecting conductive material 106 is formed on the p-side electrode 104. A protective insulating resin 108 is formed so as to cover the surfaces except the light emission surface and the connecting conductive material 106 in the light emitting diode.
FIGS. 16A and 16B show the state in which the light emitting diode shown in FIGS. 14A and 14B is mounted on a substrate and wirings are formed thereon. Here, FIGS. 16A and 16B show a plan view and a cross section, respectively. As shown in FIGS. 16A and 16B, in this example, the light emitting diode is mounted on a transparent substrate 201 as the n-type semiconductor layer 101 is turned down, an insulating resin 202 is buried so that the connecting conductive materials 106 and 107 are exposed around the light emitting diode, and then a wiring 203 which is connected to the connecting conductive material 106 and a wiring 204 which is connected to the connecting conductive material 107 are formed on the insulating resin 202. In this case, the wirings 203 and 204 are lead to the opposite sides to each other.
FIGS. 17A and 17B show the state in which the light emitting diode shown in FIGS. 15A and 15B is mounted on a substrate and wirings are formed. Here, FIGS. 17A and 17B show a plan view and a cross section, respectively. As shown in FIGS. 17A and 17B, in this example, the light emitting diode is mounted on a wiring 203 which is formed in advance on a substrate 201 as the connecting conductive material 106 is turned down, an insulating resin 202 is buried so that the light emission surface is exposed around the light emitting diode, and then a wiring 204 which is connected to the n-side electrode 105 is formed on the insulating resin 202 as the wiring 204 is lead to the opposite side of the wiring 203.
In addition, in a light emitting diode array having a center electrode type light emitting diode part in which an ohmic contact layer is disposed at the center of a light emission surface and light emission surfaces on both sides thereof emit light, such a technique is proposed that the ohmic contact layer is configured of a base part which passes through the center of the light emission surface and branch parts which are extended in the direction crossing the direction in which a bonding electrode is led from the base part, and ohmic electrodes are provided on the ohmic contact layer as tracing the shapes of the base part and the branch part (see Patent Reference 1 (JP-A-2004-14676)). However, this technique is greatly different in technical principles from the light emitting device according an embodiment in which an electrode on the light emission surface is formed nearly in a linear shape having the width narrower than that of the light emission surface, a wiring connected to the electrode is formed nearly in a linear shape having the width narrower than that of the light emission surface, and the wiring is crossed to the electrode.
From the viewpoint of easiness to form a wiring after mounted, as compared with the light emitting diode shown in FIGS. 14A and 14B in which the p-side electrode 104 and the n-side electrode 105 are formed on one side, the light emitting diode shown in FIGS. 15A and 15B is more preferable in which the n-side electrode 105 and the p-side electrode 104 are separately formed on the light emission surface and on the surface on the opposite side thereof. In the light emitting diode shown in FIGS. 15A and 15B, it is desirable that the n-side electrode 105 to be formed on the light emission surface is as small as possible in order to suppress the light blocking against the light emission surface due to the n-side electrode 105. In addition, in the case in which the light emitting diode is mounted and then the wiring 204 is formed which is connected to the n-side electrode 105 on the light emission surface, it is necessary to form the wiring 204 as well not to block light against the light emission surface as much as possible. Moreover, the light blocking area on the light emission surface is greatly changed in the cases in which the position is shifted in mounting the light emitting diode on the substrate 201 and in which the position is shifted in forming the wiring 204, causing the brightness is varied, which has to be prevented. However, in practice, it is actually difficult to satisfy all of these demands.
Then, a method shown in FIGS. 18A and 18B is proposed by the inventor as a method of forming a wiring that satisfies these demands. Here, FIGS. 18A and 18B show a plan view and a cross section, respectively. As shown in FIGS. 18A and 18B, in the method, a transparent electrode 205 formed of ITO (indium tin oxide) is formed to cover the entire light emission surface so that an n-side electrode 105 formed on the back side of an n-type semiconductor layer 101 that is the light emission surface is connected to a wiring 204 formed on an insulating resin 202.
However, in the method of forming a wiring shown in FIGS. 18A and 18B, in practice, it is difficult to connect the n-side electrode 105 on the light emission surface to the wiring 204 formed on the insulating resin 202 with no breaks of the transparent electrode 205, and materials for use in forming the transparent electrode 205 are relatively expensive, causing a problem that fabrication costs for a mounting substrate are increased.