1. Field of the Invention
The present invention relates to a method of making packaged electronic devices.
2. Description of the Related Art
To provide a semiconductor device of a surface-mount type, conductors as a terminal may be partially exposed in the bottom surface of a resin package. As is known, such a semiconductor device can be produced collectively using a leadframe. A leadframe may be provided with a number of semiconductor device-forming regions, in each of which a semiconductor chip is placed. The respective semiconductor chips are subjected to wire-bonding, and then the chips are resin-packaged. Finally, cuts are made between the semiconductor device-forming regions by using cutting means such as a punch press or a rotary blade, to provide separate resin-packaged semiconductor devices.
As shown in FIG. 16, for example, the resin-packaging may be performed so as to enclose a plurality of semiconductor chips 90 by a common resin coating layer 91. To obtain semiconductor devices as the final products, both the coating layer 91 and the frame 93 need to be cut by a cutting tool 92. In this manner, however, many burrs will be produced when the coating layer 91 is cut. In addition, the production cost tends to become unduly high since resin material needs to be supplied not only to the portions for forming the final resin packages but also to the other wasted portions.
Alternatively, as shown in FIG. 17, the resin-packaging may be performed in a manner such that the semiconductor chips 90 are enclosed individually by separate resin packages 91A. In this case, the cutting tool 92 does not need to cut the resin packages 91A, and the resin material for forming the package is supplied only to the non-wasted portions. Thus, the above-mentioned problems regarding the burrs and the increased production cost do not arise. By this method, however, the following problems will arise.
In order to make compact the semiconductor device, the cutting for the frame 93 should be performed at a position as adjacent to the resin package 91A as possible. For proper processing, as shown in FIG. 17, the frame 93 needs to be pressed against the die 94 by a guide presser (stripper) 95, so that no external force is exerted on the semiconductor chips 90 and that the frame 93 is not detached from the resin packages 91A. As seen from the figure, the guide presser 95 is provided with a recess to accommodate the resin package 91A and a tapering wall to be brought into contact with the frame 93. The presser 95 needs to be made strong enough to permit the frame 93 to be pressed against the die 94 with an appropriate force. To this end, the presser 95 cannot be too thin, particularly in the tapering wall. In the presence of such dimensional requirements, the gap between the cutting tool 92 and the resin package 91A becomes greater than desired due to the intervention of the tapering wall, which is disadvantageous to the downsizing of the semiconductor device.
Further, the method illustrated in FIG. 17 will produce burrs B on the bottom surface of the frame 93 since the frame 93 is cut by a non-stop downward movement of the cutting tool 92. Disadvantageously, the burrs B may be mixed in the solder material applied between the semiconductor device and a circuit board, thereby making the connection less stable.
The present invention has been proposed under the circumstances described above. It is, therefore, an object of the present invention to provide a method of making a non-defective electronic device with a resin package from which terminal conductors project slightly.
According to the present invention, an electronic device is made in the following manner. First, a leadframe including a first conductive member and a second conductive member is prepared. A first electronic element is connected to the first conductive member, and a second electronic element is connected to the second conductive member. A first resin package is formed for enclosing the first electronic element in a manner allowing exposure of a part of the first conductive member, while a second resin package is formed for enclosing the second electronic element which is spaced apart from the first resin package. Then, the exposed part of the first conductive member is cut. In this cutting procedure, a first tool is used for forming an indentation in the above-mentioned exposed part on a first side of the exposed part, while a second tool is used for making a full cut in the exposed part on a second side opposite to the first side. The full-cut is continued until the resultant cut is linked with the indentation.
By the above method, a preliminary indentation is formed when the conductive member is to be cut. When a full cut is made in the conductive member in a manner such that the full cut extends to be linked with the indentation, the desired cutting for the conductive member can be performed without exerting an unduly great force on the cutting tool (and hence on the conductive member).
Preferably, the indentation may be formed adjacent to the first resin package.
Preferably, the full cut may be formed at a position which is farther from the first resin package than the indentation is, so that the above-mentioned exposed part has a stepped edge.
Preferably, the indentation and the first resin package may be spaced apart from each other by a distance ranging from 10 xcexcm to 100 xcexcm.
Preferably, the first resin package may include a bottom surface brought into contact with a circuit board and also include a side surface extending upward from the bottom surface, the above-mentioned exposed part projecting from the side surface.
Preferably, the indentation formed in the first conductive member may be disposed on the side of the bottom surface of the first resin package.
Preferably, the first conductive member may also be exposed in the bottom surface of the first resin package.
Preferably, the indentation may comprise an upright surface and another surface, the upright surface being closer to the side surface of the first resin package than said another surface is.
Preferably, the indentation may comprise a notch having a V-shaped cross section.
Preferably, each of the first tool and the second tool may comprise a punch.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.