Semiconductor module

An image sensor module is composed of a base, a CCD image sensor, a glass plate, and a frame-shaped moisture permeable member. The base has a depressed chip chamber, in which the CCD image sensor is contained. Top and under surfaces of the moisture permeable member are provided with adhesive layers. The base and the glass plate are attached above and below the moisture permeable member through the adhesive layers, and the chip chamber is sealed. The moisture permeable member has the property to block liquid water while transmit water vapor, and releases the water vapor produced by the heat of the CCD image sensor from the inside to the outside of the chip chamber.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor module with a semiconductor chip contained in a package, and more particularly to the semiconductor module capable of preventing dew condensation in the package.

2. Description Related to the Prior Art

Digital cameras and Camera phones are provided with image sensor modules. The image sensor module has a package which contains an image sensor chip so as to protect a light receiving surface of the image sensor chip from dusts. Generally, the package is made of either plastic, metals, or ceramic, and the plastic is often used in these days because of ease of process and low cost.

The package has a package body and a cover. Formed in the package body is a chip chamber, in which the image sensor is contained. The transparent cover is placed on the package body and bonded thereto with an adhesive agent such as an epoxy resin. In this manner, the chip chamber is sealed for the protection from dusts.

The semiconductor chips such as the image sensors are often made of an epoxy resin because of cost concerns. The epoxy resin, nevertheless, absorbs moisture when left in a damp place for a long time, and sometimes causes dew condensation in the chip chamber that contains the semiconductor chip. The Japanese patent laid-open publication No. 2004-331920 then discloses the semiconductor chip package made of a waterproof, low water absorption material.

Even with such waterproof package, however, if water vapor happens to be trapped in the chip chamber when the semiconductor chip is sealed, there is no method for releasing the water vapor from the chip chamber. As a result, when the ambient temperature goes lower than the temperature inside the chip chamber, dew condensation occurs in the chip chamber. In this case, the dew drops may fall on the semiconductor chip and cause a short circuit in the semiconductor chip. Furthermore, if the semiconductor chip is the image sensor chip, a light receiving surface of the image sensor may have the dew condensation, and the quality of images may therefore be degraded.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of the present invention is to provide a semiconductor module capable of preventing dew condensation in a chip chamber.

To achieve the above and other objects, the semiconductor module according to the present invention is provided with a frame-shaped moisture permeable member attached to a top surface of a package body. The package body has a depressed chip chamber for containing a semiconductor chip, and the moisture permeable member encloses this chip chamber. A cover is then attached to the top surface of the moisture permeable member, so that the chip chamber is sealed tightly. Preferably, the moisture permeable member is made of a high polymer material having a lot of pores.

The semiconductor chip can be an image sensor chip that has a light receiving surface. In this case, the cover is made of a transparent material.

According to the semiconductor module of the present invention, the water vapor inside the chip chamber is released to the outside through the moisture permeable member. Dew condensation in the chip chamber is therefore prevented, and so does a short circuit of the semiconductor chip. A simple structure that has the moisture permeable member inserted between the package body and the cover enables the package to release the water vapor to the outside. It is also possible, if the semiconductor chip is the image sensor chip, to prevent the dew condensation on the light receiving surface. Therefore, the high image quality can be maintained.

DESCRIPTION OF THE PREFFERED EMBODIMENTS

Referring toFIG. 1, an image sensor module2, i.e. a semiconductor module, includes a package3and a CCD image sensor8that is a semiconductor chip. The package3is composed of a base6as a package body, a glass plate10as a cover, and a moisture permeable member11. The base6has a depressed chip chamber12defined by a mounting area6ato which the CCD image sensor8is attached, a surrounding wall6bthat surrounds the mounting area6a, and an opening6c. The CCD image sensor8has a light receiving surface8a. The moisture permeable member11is formed into a frame shape whose inner periphery is almost the same size as the opening6c, and attached on the base6to enclose the opening6c. On a top surface of the moisture permeable member11, the glass plate10is attached. Incidentally, the base6is made of either an epoxy resin, a plastic resin such as a polyimide resin, or ceramic.

As shown inFIG. 2, the transparent glass plate10transmits light that goes to the light receiving surface8aof the CCD image sensor8. Disposed around the light receiving surface8aare plural electrodes (not shown), which output the electric signals which the CCD image sensor8generates relative to the intensity of incident light. The base6is provided with a wiring layer18, whose one end is connected to the electrodes of the CCD image sensor8through bonding wires14. The other end of the wiring layer18is exposed on the top surface of the base6, and connected through a lead wire to a signal processing circuit that processes the output signals of the CCD image sensor8.

Between the base6and the glass plate10, the moisture permeable member11is inserted tightly. The moisture permeable member11is formed of a high polymer material having a lot of pores, which block liquid water (liquid) and transmit water vapor (gas). On the top and under surfaces of the moisture permeable member11, adhesive layers20are provided. The base6and the glass plate10are attached to the moisture permeable member11through the adhesive layers20, and thereby the chip chamber12is sealed. The inside surface of the moisture permeable member11is exposed in the chip chamber12, while the outside surface thereof is exposed outside the image sensor module2. This structure allows the water vapor in the chip chamber12to be released to the outside. Accordingly, neither the CCD image sensor8nor the glass plate10has dew condensation, and the high image quality is maintained. Preferably, the moisture permeable member11is made of Gore-Tex (registered trademark) or ENTRANT (registered trademark).

The operation of the present invention is now described. Firstly, the CCD image sensor8is placed in the chip chamber12. Then, the electrodes of the CCD image sensor8are connected to the wiring layer18of the base6through the bonding wires14, and the glass plate10is attached to the base6through the moisture permeable member11. The moisture permeable member11is made of the Gore-Tex, and allows the passage of water vapor from the chip chamber12to the outside. Therefore, the chip chamber12hardly has the dew condensation even when, for example, the ambient temperature is lower than the temperature inside the chip chamber12.

Although the semiconductor chip is the image sensor chip in the above embodiment, the semiconductor chip is not limited to this. The semiconductor chip may have transistors or thyristors formed therein, for example.

In the above embodiment, the moisture permeable member11is formed into a frame shape and attached around the opening6cthrough the adhesive layer20. Instead of this structure, it is possible to incorporate the moisture permeable member into a part of the surrounding wall of the chip chamber. This constitution also ensures adequate release of the water vapor from the chip chamber, and the dew condensation is prevented.

As described so far, the present invention is not to be limited to the above embodiments, and all matter contained herein is illustrative and does not limit the scope of the present invention. Thus, obvious modifications may be made within the spirit and scope of the appended claims.