Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame – With structure for mounting semiconductor chip to lead frame
Patent
1992-06-29
1995-08-08
James, Andrew J.
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
With structure for mounting semiconductor chip to lead frame
257666, H01L 2348, H01L 2944, H01L 2952, H01L 2960
Patent
active
054401704
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a semiconductor device and its manufacturing method, and particularly to a semiconductor device which employs a lead frame and is hermetically sealed by resin, and a method of manufacturing such a semiconductor device.
DESCRIPTION OF THE RELATED ART
FIG. 1 is a side cross-sectional view showing an example of conventional semiconductor devices which employ lead frames and sealed by resin.
In FIG. 1, 11 represents a semiconductor chip, 12 a resin package, 13 wires, 14 a die pad, 15 leads, 16 a support bar.
The semiconductor chip 11 is fixed on the die pad 14, which has a flat plate shape, and is connected to the leads 15 through the wires 13 by wire-bonding. The leads 15 make external connection with circuits formed onto the semiconductor chip 15.
The resin package 12 seals the semiconductor chip 11 and its periphery, and protects the semiconductor chip 11 and its periphery from the environment. The periphery includes the die pad 14, the wires 13 and those parts of the leads 15 attached to the semiconductor 11.
A semiconductor device, as described above, is generally called a resin-sealed semiconductor device. Such a semiconductor device is manufactured by using the die pad 14 and a lead frame having the leads 15 disposed outside the die pad 14. The semiconductor chip 11 is mounted onto the die pad 14 (and the wires 13 are connected). Then, the resin package 12 is formed by means of resin molding.
The lead frame used in the manufacture practiced in the prior art is formed by cutting it from a metal plate by press working or etching in a pattern such that the leads 15 and the support bar 16 are connected, after providing the support bar 16 in an arrangement such that it is placed, as a support for the die pad 14, in alignment with the leads 15 and extends from the die pad 14. Excess parts from that operation are cut off after the resin package 12 is formed.
Recently, shifts toward downsizing of semiconductor devices, and toward using surface packaging, has brought about a serious problem in which either spontaneous moisture absorption of the resin package 2, or thermal stress at the time of the printed board packaging cause the destructive crack on the resin package 12 to start at an edge of the die pad 14 as shown in FIG. 2A. This results from the fact that the outermost edge of the die pad 14 is sharp.
This has been conventionally dealt with by chamfering the edge of the die pad 14, on the lead frame, by press working. This, however, can easily create a burr 18 during chamfering, making it impossible to fully prevent a crack 7 from resulting due to this burr 18.
The present inventor attempted, as a simple means of performing chamfering of the die pad, an etching in which the entire lead frame is soaked in a chemical. The following problems arose, however, resulting in the lead frame not performing the function expected of it. Etching developed extensively on the leads and other narrow parts before the desired chamfer of the die pad was obtained, rendering etched parts out of shape, and resulting in an irregular thickness of the lead frame, and in inaccuracy, when feeding the lead frame, at the time a semiconductor chip was mounted on it. An extremely high number of resin burrs was created in the resin molding process for forming the resin package. Following the resin package forming, the dimension of bending became unstable in the lead bending.
Japanese Laid-Open Patent Application No. 1-251747 describes a process in which resist is applied to the die pad of the lead frame and the edge of the die pad is chamfered by means of etching.
However, applying resist to the formed lead frame makes it difficult to ensure high precision due to a deformation of the lead frame. Thus the process has been accompanied by the difficulty and inpracticability of chamfering the edge even if it is etched.
SUMMARY OF THE INVENTION
Accordingly, a general object of the present invention is to provide a novel and useful semiconductor device, and a method of manufacturin
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Kasai Junichi
Tsuji Kazuto
Yoneda Yoshiyuki
Clark S. V.
Fujitsu Limited
James Andrew J.
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