1. Field of the Invention
The present invention relates to a shield case for a semiconductor optical device. More specifically, the invention relates to a shield case to be mounted onto a circuit board with a semiconductor light-emitting or light-receiving device (may be hereinafter referred to as a "semiconductor optical device" as a general term inclusive for both the semiconductor light-emitting and light-receiving devices) placed therein shielded electromagnetically.
2. Description of the Prior Art
In a semiconductor optical device of this kind, a semiconductor light-emitting or light-receiving element (maybe hereinafter referred to as a "semiconductor optical device") is wire-bonded through metal wires to a plurality of lead terminals and then encapsulated by a mold resin into an encapsulated body in a rectangular parallelepiped form. This encapsulated body has, at a top surface, a transparent (or semi-transparent) semi-spherical lens formed of a synthetic resin covering over the semiconductor optical device. That is, the semiconductor optical device of this kind is generally in rectangular parallelepiped form having lead terminals extending outward through one surface of the encapsulated body.
There are cases that such a semiconductor optical device is mounted on a circuit board through using the lead terminals. In such cases, there encounters a problem that the mount stability becomes poor due to insufficiency in mechanical strength of the lead terminals and the affection of noises caused by the absence of a shield structure for prevention against electromagnetism.
Under such circumstances, a shield case formed by a magnetic metal plate, e.g., iron plate, having high magnetic permeability has been conventionally used, wherein the magnetic metal plate is blanked generally in a rectangular shape having opposite mount legs so that the magnetic metal plate is bent into an arch form having a top plate and opposite side plates. In the conventional shield case, the top plate has an opening through which a light-receiving/light-emitting surface of the semiconductor optical device is exposed while the side plates retain the semiconductor optical device therebetween. That is, the conventional shield case provides electromagnetic shield for the semiconductor optical device at three faces in total, i.e., the light-receiving/light-emitting surface except for a region of the opening plus opposite side surfaces. Due to this, the semiconductor optical device can be shielded from electromagnetism with enhanced mount stability.
However, the conventional shield case involved a problem to be dissolved. That is, where utilizing the conventional shield case, the semiconductor optical device has been held by providing inward projections from the side plates or otherwise by attaching a separate fixing member to the inward of the side plates. In the former case, there has been a problem that there is difficulty in stably holding the semiconductor optical device. On the other hand, in the latter case the structure is complicated and hence cost is expensive.
Moreover, because the conventional shield case is in the arch form, the semiconductor optical device is shielded at only three surfaces among six surfaces but the remaining three surfaces are left open, thus insufficiency in the effect of shield.