Surface mount type semiconductor device and lead frame structure thereof

A surface mount type semiconductor device can be configured to include a pair of lead frames that are butted to each other with a spacing such that ends of the lead frames are opposite to each other. A bare chip can be mounted on a chip mount portion on one end side of one of the lead frames, and wire-bonded to a connection portion on an end side of the other lead frame. A housing can be insert-molded to an end side of both of the lead frames, and the lead frames can be shaped such that they extend along the side and bottom surfaces of the housing and form surface mounting terminal portions. The lead frames are preferably formed to be thin at least at the regions that are to be bent, and other regions thereof are preferably formed to be thick to improve heat radiating effect.

This invention claims the benefit of Japanese patent application No. 2004-000042, filed on Jan. 5, 2004, which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a surface mount type semiconductor device. More specifically, this invention relates to a surface mount type semiconductor device that can include a bare chip mounted on a lead frame arranged on a substrate, and to a lead frame structure thereof.

DESCRIPTION OF THE RELATED ART

A surface mount type semiconductor device such as a surface mount type LED has conventionally been configured as shown inFIGS. 4 to 6. InFIGS. 4 and 5, a surface mount type LED1includes a pair of lead frames2and3, an LED chip4mounted on the lead frame2, a hollow lamphouse5insert-molded to the lead frames2and3and a sealing resin6filled into a hollow portion5aof the lamphouse5.

The lead frames2and3, are each made of a conductive material such as iron- or copper-based metal, and are provided with surface mounting terminal portions2aand3athat are exposed on the bottom and side surfaces of the lamphouse5.

The lead frame2is further provided with a chip mount portion2bexposed inside the hollow portion5aat the center region of the lamphouse5, whereas the lead frame3is provided with a connection portion3badjacent to the chip mount portion2band exposed inside the hollow portion5aof the lamphouse5.

It is to be noted that the chip mount portion2band the connection portion3bof the lead frames2and3are adjacent to each other such that they are opposite to each other with a spacing, for example, of approximately 0.2 mm or less. The terminal portions2aand3aare respectively formed continuously from the chip mount portion2band the connection portion3b.

The LED chip4has its bottom surface die-bonded to the chip mount portion2bof the lead frame2and its front surface (top surface inFIG. 4) wire-bonded to the connection portion3bof the adjacent lead frame3via a gold wire4a.

The lamphouse5is insert-molded to the lead frames2and3by, for example, resin, and is provided with the hollow portion5athat is open upward. This allows the inner surface of the hollow portion5aof the lamphouse5to constitute a reflecting frame for the LED chip4.

Within the hollow portion5a, the chip mount portion2bof the lead frame2and the connection portion3bof the lead frame3are exposed. The sealing resin6, made of a silicon-based thermosetting resin, etc., is filled into the hollow portion5aof the lamphouse5and hardened.

It is to be noted that the lead frames2and3are subjected to forming after the sealing resin6is filled and hardened, thus forming the terminal portions2aand3a.

The lead frames2and3have complex shapes as shown inFIG. 5partly to take as many of the lead frames2and3as possible from a flat plate material in the manufacture of the chip LED1thus configured. For this reason, the individual lead frames2and3are not set in a mold for insert-molding of the lamphouse5. Instead, the mutually and integrally molded lead frames2and3are set in a mold for insert-molding of the lamphouse5.

This eliminates the need to accurately position each of the lead frames2and3within the mold. In addition, positioning the integral lead frames2and3within the mold allows accurate positioning of the lead frames2and3relative to each other.

According to the chip LED1thus manufactured, when a drive voltage is applied to the LED chip4from the terminal portions2aand3aof the lead frames2and3, the LED chip4emits light. This light is reflected by the inner surface of the hollow portion5aof the lamphouse5and is simultaneously emitted externally through the sealing resin6, thus being radiated upward.

For the chip LED1having such a configuration, incidentally, after the product size is determined, the areas of the lead frames2and3can be roughly determined, and it is preferred that the areas of the lead frames2and3be as small as possible in consideration of adhesion between the sealing resin6and the lamphouse5.

To improve the heat radiating property of the lead frames2and3, therefore, the volumes of the lead frames2and3could be increased by increasing their thicknesses as shown inFIG. 6without increasing their areas.

However, increasing the thicknesses of the lead frames2and3leads to a relatively large stress acting on the lamphouse5during forming of the lead frames2and3, which can possibly crack or otherwise damage the lamphouse5under certain circumstances.

In addition, the spacing between the mutually-opposing end surfaces of the lead frames2and3must be wider than the thicknesses of the lead frames2and3for lead frame manufacturing reasons, resulting in a large-sized package for the LED1.

Such problems are not limited to the aforementioned surface mount type LED. The same problems are apparent in other surface mount type semiconductor devices such as devices that generate heat during operation, namely, semiconductor laser devices, various ICs, etc.

SUMMARY OF THE INVENTION

In accordance with one of several aspects of the present invention, a simple configuration is provided for a surface mount type semiconductor device and lead frame structure thereof for, among other reasons, improving the heat radiating property of the lead frames and reducing stress during forming of the lead frames. The surface mount type semiconductor device can include a pair of lead frames that are butted to each other with a spacing such that one end of the lead frames are opposite to each other. A bare chip can be mounted on a chip mount portion on one end side of one of the lead frames and wire-bonded to a connection portion on one end side of the other lead frame. A housing is preferably insert-molded to one end sides of both of the lead frames. The lead frames can be shaped by forming so as to extend along the side and bottom surfaces of the housing and to form surface mounting terminal portions. The lead frames are also preferably formed such that they are thin at least at the regions to be bent during forming, with other regions thereof formed to be thick to improve heat radiating effect.

In the surface mount type semiconductor device of the present invention it is preferred that the lead frames be thinly formed at the regions of the mutually-opposing end surfaces on the rear surface side. In addition, the lead frames are preferably provided with stepped portions at the regions of the mutually-opposing end surfaces on the rear surface side. Further, the lead frames are preferably provided with sloped portions at the regions of the mutually-opposing end surfaces on the rear surface side.

According to another aspect of the present invention a lead frame structure of a surface mount type semiconductor device can include a pair of lead frames that are butted to each other with a spacing such that one end of the lead frames are opposite to each other. A bare chip can be mounted on a chip mount portion on one end side of one of the lead frames and wire-bonded to a connection portion on one end side of the other lead frame. A housing can be insert-molded to one end side of both of the lead frames, wherein the lead frames can be shaped by forming so as to extend along the side and bottom surfaces of the housing and to form surface mounting terminal portions. The lead frames are preferably formed such that they are thin at least at the regions to be bent during forming, with other regions thereof formed such that they are thick to improve heat radiating effect.

It is preferred that the lead frames be thinly formed at the regions of the mutually-opposing end surfaces on the rear surface side. The lead frames are preferably provided with stepped portions at the regions of the mutually-opposing end surfaces on the rear surface side. The lead frames are also preferably provided with sloped portions at the regions of the mutually-opposing end surfaces on the rear surface side.

The exposed portions on the side and bottom surfaces of the housing of the lead frames can be connected to the connection land on the mount substrate by surface mounting the semiconductor device. The bare chip can be powered from both lead frames, thus putting the bare chip into operation.

In this case, the individual lead frames can be formed to be thick as a whole, thus boosting their volumes. This can secure a sufficient volume for the individual lead frames even if the semiconductor package is small in size, and therefore the lead frames can be relatively small in area. This can lead to improvements in heat radiating effect of the lead frames, thus efficiently radiating heat generated during the operation of the bare chip mounted on the chip mount portion of one of the lead frames.

The lead frames can be thinly formed at the regions that are to be bent during forming, keeping stress that occurs during forming relatively small and considerably reducing the likelihood of cracking or otherwise damaging the housing that is molded to the lead frames.

If the lead frames are thinly formed at the regions of the mutually-opposing end surfaces on the rear surface side and, more specifically, if the lead frames are provided with stepped or sloped portions at the regions of the mutually-opposing end surfaces on the rear surface, the butt thickness of the lead frames at the mutually-opposing end surfaces will diminish. Thus, it is possible, even when a spacing that is wider than the butt thickness is secured, to reduce the spacing between the mutually-opposing end surfaces of the lead frames and further downsize the package of the surface mount type semiconductor device. Thus, the lead frames can be formed to be thick as a whole, boosting the volumes of the lead frames and improving their heat radiating property.

According to another aspect of the invention, A surface mount type semiconductor device can include a pair of lead frames having a first end and a second end that are spaced from each other and that are butted opposite to each other, the first end having a chip mount portion and the second end having a connection portion. A chip can be mounted on the chip mount portion and wire-bonded to the connection portion. A housing is preferably molded to the lead frames, wherein the lead frames are shaped such that they extend along a bottom surface of the housing and form surface mounting terminal portions. The lead frames can be thinner at least at regions that are bent, and are relatively thicker at other regions.

According to yet another aspect of the invention, a lead frame structure can include a pair of lead frames that have a first end and a second end and that are butted to each other with a spacing such that the first and second ends of the lead frames are located opposite to each other. The lead frames can include a chip mount portion located at the first end of the lead frames, and a connection portion located at the second end of the lead frames. A chip can be mounted on the chip mount portion and wire-bonded to the connection portion. A housing can be located adjacent to the lead frames, wherein the lead frames include bent regions such that the lead frames extend along a bottom surface of the housing and include surface mounting terminal portions. The lead frames can be thinner at least at the bent regions of the lead frames and can be relatively thicker at other regions of the lead frames.

DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described below in detail with reference toFIGS. 1 to 3.

It is to be noted that while the embodiments described below are preferred specific examples of the present invention and therefore have various technically preferred features, the present invention is not limited thereto.

FIGS. 1 to 3show the configuration of various embodiments of a surface mount type LED made in accordance with the principle of the present invention.

InFIG. 1, a surface mount type LED10can include a pair of lead frames11and12, an LED chip13mounted on the lead frame11, a hollow lamphouse14configured as a housing19that is preferably insert-molded to the lead frames11and12. A sealing resin15can be filled into a hollow portion14aof the lamphouse14.

The lead frames11and12, can each be made of a conductive material such as iron- or copper-based metal, and can be provided with surface mounting terminal portions11aand12athat can be exposed on the bottom and side surfaces of the lamphouse14.

The lead frame11is preferably provided with a chip mount portion11bthat is exposed inside the hollow portion14aat the center region of the lamphouse14. The lead frame12is preferably provided with a connection portion12bthat is adjacent to the chip mount portion11band exposed inside the hollow portion14aof the lamphouse14. The terminal portions11aand12acan be formed respectively from the chip mount portion11band the connection portion12b.

The LED chip13can have its bottom surface die-bonded to the chip mount portion11bof the lead frame11and its front surface (top surface inFIG. 1) wire-bonded to the connection portion12bof the adjacent other lead frame12via a gold wire13a.

The lamphouse14can be insert-molded to the lead frames11and12, for example, by resin, and can be provided with a hollow portion14athat is open upward. This allows the inner surface of the hollow portion14aof the lamphouse14to constitute a reflecting frame for the LED chip13.

Within the hollow portion14a, the chip mount portion11bof the lead frame11and the connection portion12bof the lead frame12can be partially exposed. The sealing resin15, preferably made of a silicon-based thermosetting resin, etc., is filled into the hollow portion14aof the lamphouse14and hardened. The lead frames11and12are preferably subjected to forming after filling and hardening of the sealing resin15, thus forming the terminal portions11aand12a.

The surface mount type LED10according to the above described embodiment of the invention includes lead frames11and12that can be made thicker as a whole as compared to conventional lead frames (except for the regions to be bent during forming).

When a drive voltage is applied to the LED chip13from the terminal portions11aand12aof the lead frames11and12, the LED chip13emits light. This light can be reflected by the inner surface of the hollow portion14aof the lamphouse14and simultaneously emitted externally through the sealing resin15, thus being radiated upward.

The individual lead frames11and12can be formed thick as a whole, thus boosting their volumes. This secures a sufficient volume for the individual lead frames11and12even if the semiconductor package of the surface mount type LED10is small in size (and therefore the lead frames11and12are relatively small in area).

The above-described structures can in some instances lead to improved heat radiating effect for the lead frames11and12. Efficient radiation of heat generated during the operation of the LED chip13mounted on the chip mount portion11bof the lead frame11can also be achieved.

The lead frames11and12can be thinly formed at the regions that are to be bent during the forming process, thus keeping stress that occurs during forming relatively small and considerably reducing the likelihood of cracking or otherwise damaging the lamphouse14that is molded to the lead frames11and12.

FIG. 2shows a configuration of another embodiment of a surface mount type LED made in accordance with the principles of the present invention. InFIG. 2, the surface mount type LED20is similar in configuration to the surface mount type LED10shown inFIG. 1in some aspects, and accordingly the same elements are assigned the same symbols, and explanation of similar or identical elements will be omitted.

The surface mount type LED20can include lead frames11and12that are provided with stepped portions11cand12cat the regions of the mutually-opposing end surfaces and on the rear surface of the mutually-opposing end surfaces. The stepped portions allow these regions to be further thinned.

The surface mount type LED20thus configured can function in approximately the same manner as the surface mount type LED10shown inFIG. 1. The lead frames11and12can be formed thinner at the mutually-opposing end surfaces due to the stepped portions11cand12c, thus possibly reducing the spacing therebetween close to the thin thickness of the stepped portions11cand12c. This makes it possible to further downsize the overall package of the surface mount type LED20.

FIG. 3shows the configuration of yet another embodiment of a surface mount type LED made in accordance with the principles of the present invention. InFIG. 3, the surface mount type LED30is similar to the surface mount type LED20shown inFIG. 2in some aspects, and accordingly the same elements are assigned the same symbols, and explanation of the same or similar elements will be omitted.

The surface mount type LED30can include lead frames11and12that are provided with sloped portions11dand12dinstead of the stepped portions11cand12cat the regions of the mutually-opposing end surfaces and on the rear surface of the mutually-opposing end surfaces. Thus, these regions can be formed to be thin. The surface mount type LED30thus configured can function in the same manner as the surface mount type LED10shown inFIG. 1, and the lead frames11and12can be formed such that they are thin at the mutually-opposing end surfaces due to the sloped portions11dand12d, possibly reducing the spacing therebetween. This makes it possible to further downsize the overall package of the surface mount type LED30.

While the above description relates to embodiments in which the present invention is applied to the surface mount type LEDs10,20and30, the present invention is not limited thereto. It should be apparent that the present invention is applicable to other semiconductor devices such as ICs and other devices, especially devices that generate heat during operation.

Improved heat radiating effect can be achieved in a semiconductor device even as its volume is increased by forming the lead frames thick except for the regions to be bent during forming procedures, even if the area remains unchanged. The lead frames can be formed to be thin at the regions that are to be bent during the forming procedure, thus reducing stress occurring during forming, and preventing damage such as cracking to the housing that is molded to the lead frames. The invention is applicable to various semiconductor devices, including those that incorporate elements such as IC's, lasers, diodes or bare chips and other devices that generate heat during operation.

While illustrative and presently preferred embodiments of the present invention have been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art. For example, the stepped portion and the sloped portion can be differently configured to provide a narrowing or thinner portion at the lead frame ends. Specifically, other shapes, such as a curved or zig-zag shapes can be used to effect the narrowing of either the ends of the lead frames or the generally thinner portions. In addition, different methods of manufacture can be used to make the device and frame structure, such as insert molding, resin molding, and other processes. In addition, the ends of the lead frames do not have to be butted exactly in orientation with each other, but can be butted opposite to each other such that there is some play in alignment, provided the alignment does not disturb manufacturability of the device.