1. Technical Field
The present invention relates to an optical semiconductor device and a manufacturing method thereof, and more particularly to an optical semiconductor device including a semiconductor device which emits a light beam and a manufacturing method thereof.
2. Description of the Related Art
A package for an optical semiconductor device such as a surface-mounted LED, is formed by inserting an electrically conductive lead in a thermoplastic resin. Japanese Patent Publication (kokai) No. 2000-183407 discloses such a package. FIG. 5 is a vertical section of a package 100 for an optical semiconductor device. Package 100 is provided with a conductive lead 101 and a base 102. Base 102 includes an indentation 102a provided on an upper surface 101a of lead 101. A light emitting element 104 is positioned on lead 101. Indentation 102a is filled with translucent resin to form a translucent part 103. A wire 105 made of gold, electrically connects emitting element 104 and lead 101. A light beam emitted from light emitting element 104 radiates from package 100 through translucent part 103.
Package 100 is manufactured as described next. First, lead 101 is inserted into a die. Then, injection molding is carried out by filling the die with thermoplastic resin to form base 102. After a conductive adhesive is applied on one electrode of lead 101, light emitting element 104 is positioned on the applied conductive adhesive. Wire 105 is bonded to the other electrode of lead 101 to complete a conductive connection to light emitting element 104. Then, after filling into indentation 102a, translucent resin is cured under a certain curing condition to form translucent part 103. As a result, package 100 is produced.
A light beam emitted from element 104 radiates through translucent part 103. The angle of the beam spread ranges from 100-degree to 120-degree. Therefore, it is difficult to focus the light beam outputted from package 100 without a focusing lens or a light reflector. Consequently, package 100 is not suited for illuminating a specific limited region.
In order to illuminate a specific region, some packages have a wall for reflecting a light beam to control a directivity thereof. FIG. 6 is a vertical section of a package 200 for an optical semiconductor device as one example of such packages. Package 200 includes a lead 201 and an outer envelope 202. Outer envelope 202 includes a first indentation part 202a and a second indentation part 202b which surrounds first indentation part 202a. A translucent part 203 is formed by filling first indentation 202a with phosphor mixed silicon resin. An inner wall of second indentation part 202b serves as a reflecting wall 204 to reflect a light beam emitted from light emitting element 205. A wire 206 made of gold electrically connects a light emitting element 205 and one of electrodes of lead 201. Q in FIG. 6 designates light rays of the light beam emitted from light emitting element 205.
FIG. 7 illustrates a problem that may be experienced with package 200 having reflection wall 204 and translucent part 203 which is made by filling sealing resin. As shown in FIG. 7, phosphor mixed silicon resin creeps up reflection wall 204 in the process of filling and curing the resin. As a result, the area of reflection wall 204 is substantially reduced. Further, a surface shape of translucent part 203 differs from a desired designed shape. Consequently, reflection wall 204 does not perform as expected. Moreover, the phosphor mixed silicon resin creeping up reflection wall 204 also results in translucent part 203 being concave. As a result, an optical path of a light ray passing through the center of translucent part 203 is shorter than that of a light ray passing through the periphery of translucent part 203. This causes a different excitation and luminescence of the phosphor between a center and a peripheral part of translucent part 203. Consequently, color tone deteriorates.