1. Field of the Invention
The present invention relates to a surface-mountable glass-sealed light-emitting diode including a glass-sealed LED bare chip.
2. Description of the Related Art
In a conventional glass-sealed light-emitting diode (LED), for example, a pair of leads 33 are connected to anode and cathode electrodes of an LED bare chip 31, respectively, as shown in FIG. 4. A glass seal 32 is employed to integrally cover connections between the LED bare chip 31 and electrodes and the leads 33 for hermetic sealing. In the light-emitting diode 30 thus configured, when power is supplied through the leads 33 to the LED bare chip 31, an active region thereof emits light, which is guided from the side of the LED bare chip 31 through the glass seal 32 and output to external. There is an incident light that is emitted from the active region in the LED bare chip 31 and arrives at an interface between the LED bare chip 31 and the glass seal 32. This incident light has an angle (incident angle) from the normal to the interface at the incident point. If the incident angle is smaller than a critical angle, the light arrived at the interface is output from the LED bare chip 31 into the glass seal 32. If it is larger than the critical angle, the light is reflected back to the LED bare chip 31 and can not be output into the glass seal 32. In comparison of glass with air as materials that form interfaces with the LED bare chip, glass has a relatively larger refractive index and therefore a relatively larger critical angle. This means that a light can be output from the LED bare chip without being reflected at a larger incident angle from the interface with glass compared to air. When glass is selected as a material that adjoins the LED bare chip because it has a larger refractive index compared to air, a ratio of light output from the LED bare chip 31 can be increased relative to the total light emitted from the active region in the LED bare chip 31. This is effective to improve the external quantum efficiency (light-extraction efficiency). (For example, see Patent Document 1: Japanese Patent Application Laid-Open No. 61-67971, page 2, FIG. 1).
The above-described glass-sealed light-emitting diode includes leads for supplying power from external to drive the light-emitting diode. The leads extend outward from both sides of the light-emitting diode. When such the light-emitting diode is implemented on a printed circuit board, the leads are inserted into through-holes in a double-sided through-hole printed-circuit board and soldered to achieve fixation and electrical conduction. Recently, as electronic instruments are downsized and light-weighted, it is also intensively promoted to address downsizing and surface mounting of electronic components. In order to make the conventional glass-sealed light-emitting diode support surface mounting, it is required to mount surface mounting components other than the light-emitting diode on the double-sided through-hole printed-circuit board by a method of reflow or dip soldering and then the light-emitting diode by a method of manual soldering. Alternatively, it is required to use a high-temperature solder to solder the surface mounting components and then use a lower melting point solder to solder the light-emitting diode by a method of dip soldering. When these methods are employed to implement the conventional light-emitting diode on the same substrate together with the surface mounting components, they cause the following problems:
(1) When only the surface mounting components are implemented, a single-sided board with circuits formed only on one side functions sufficiently. In contrast, when the conventional light-emitting diode is mixed together, a double-sided through-hole board with circuits formed on both sides is required, which increases the cost of the printed circuit board.
(2) After the surface mounting components are implemented on the printed circuit board, it is required to solder the conventional light-emitting diode additionally. This requirement increases the number of processes for mounting components on the printed circuit board and elevates the production cost.
(3) When a high-temperature solder is used to solder the surface mounting components and then a lower melting point solder is used to solder the light-emitting diode by the method of dip soldering, the second soldering may impart stress to the surface mounting components and badly influences on the reliability.
The present invention has been made in consideration of the above problems and has an object to provide a glass-sealed light-emitting diode capable of achieving a high reliability and a high external quantum efficiency as an optical semiconductor component, and a high reliability and a low cost as for a components-implemented printed-circuit board.