Active solid-state devices (e.g. – transistors – solid-state diode – Combined with electrical contact or lead – Ball or nail head type contact – lead – or bond
Reexamination Certificate
2000-06-29
2002-11-05
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Combined with electrical contact or lead
Ball or nail head type contact, lead, or bond
C257S737000, C257S773000, C257S778000, C438S615000, C361S779000
Reexamination Certificate
active
06476503
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a semiconductor device having columnar electrodes, and to a method for manufacturing a semiconductor device having pin wires.
2. Description of the Related Art
Hitherto, there have been known semiconductor packages each having a resin-sealed semiconductor chip. Semiconductor packages are becoming increasingly smaller. Recently, a semiconductor package having nearly the same size as a semiconductor chip has emerged. Such a semiconductor package is called, for example, a CSP (Chip Size Package).
One method for manufacturing CSPs consists of the steps of forming integrated circuits and electrode pads on a wafer, and then forming columnar electrodes connected to the electrode pads on the wafer, and subsequently sealing the surface of the wafer and the columnar electrodes with resin, and upon completion of the sealing, dicing the wafer to thereby separate semiconductor packages, which include semiconductor chips, from the wafer (see, for instance, Japanese Unexamined Patent Publication (Kokai) No. 9-64049).
A resin layer is formed in such a way as to have nearly the same height as the columnar electrode. A tip end of the columnar electrode is exposed from the surface of the resin layer. An external terminal (or electrode pad) to be connected to each of the columnar electrodes is formed on the resin layer. A solder bump can be provided on this external terminal. Further, a rewiring conductor portion constituted by a conductor pattern is formed on the surface of the wafer, so that the positions of the columnar electrodes differ from those of the electrode pads formed on the wafer.
Moreover, Japanese Unexamined Patent Publication (Kokai) No. 9-260428 discloses that a semiconductor chip is mounted on a mounting substrate by using a metallic wire. An end of the metallic wire is bonded to the electrode pad of the semiconductor chip, while the other end thereof is connected to the mounting substrate by solder. With this constitution, stress generated due to the difference in amount of thermal expansion between the semiconductor chip and the mounting substrate can be absorbed by warpage of the metallic wire.
In the case of using the semiconductor device mounted on the circuit substrate, the external terminal (or solder bump) of the semiconductor device is connected to the electrode pad of the circuit substrate. The semiconductor chip of the semiconductor device faces the circuit substrate thereof across the sealing resin thereof. When the semiconductor device is used, thermal stress is generated in the external terminals and the columnar electrodes owing to the difference in amount of thermal expansion between the semiconductor chip and the substrate of the semiconductor device. Thus, the external terminals and the columnar electrodes become fatigued by repetitive generation of thermal stress.
This thermal stress is directly proportional to the difference in amount of thermal expansion between the semiconductor chip and the circuit substrate of the semiconductor device, and is inversely proportional to the thickness of the sealing resin layer. It is, therefore, preferable for alleviating the stress to increase the thickness of the sealing resin layer. It is, however, necessary, for increasing the thickness of the sealing resin layer, to lengthen the columnar electrodes. Usually, the columnar electrodes are formed by plating. However, there is a limit to a possible increase in the length of the columnar electrodes formed by plating.
Thus, when the columnar electrodes are formed from a (bonding) wire, the columnar electrodes can be lengthened, so that the sealing resin layer can be thickened. However, in the case of using a wire processed by a wire bonder as the columnar electrode, such a wire is too thin to be used as the columnar electrode. Hence, it is desired to make a columnar electrode formed from a wire of sufficient length and strength.
Furthermore, a wire, from which a sufficiently long columnar electrode can be provided, has flexibility. Thus, even when thermal stress is applied on the columnar electrode that is constituted by the wire, the columnar electrode is not destroyed. However, when the sealing resin layer of the semiconductor electrode is hard, large stress is exerted on a joint portion between the columnar electrode, which is constituted by the wire restrained by the sealing resin, and the external terminal fixed to the circuit substrate. It is, therefore, preferable that the sealing resin of the semiconductor device should be as soft as possible.
Further, such a conventional semiconductor device has a drawback in that pressure is applied onto the entire wafer and the wafer is thus damaged when an end portion of the columnar electrode is adjusted by being grounded, and that the flow of resin sometimes causes undesired deformation of the columnar electrode when sealed with the resin.
On the other hand, in recent years, semiconductor devices are required not only to be light and small, but also to operate at a high speed and have an advanced function. In the case that a semiconductor chip is mounted on a device, such as an interposer and a mother board, there has been developed a method of mounting a flip chip device as the semiconductor device, which meets the aforementioned demands, by using solder balls. This conventional method, however, has the following drawbacks. That is, because of a narrow pitch between the electrode pads of the semiconductor chip, the solder balls to be used for connection are specifically designed in such a manner as to have small ball diameters and to show less variation in characteristics thereof and are thus very expensive. Further, because an underfill to be used for sealing the circuit surface is required to have a property by which no voids are generated when filling the narrow gap between the semiconductor chip and the mother board, it is often true that the underfill is specifically designed so as to improve the flowability and adhesionability thereof according to each of the specifications of the semiconductor chip and the mother board. Consequently, the cost of the flip-chip semiconductor device is high.
Additionally, there have been developed a connection method using an adhesive, which contains conductive particles, and another connection method using stud bumps. When using these conventional methods, variation in adhesion is caused owing to the warpage of the semiconductor chip, voids and the leveling accuracy of the terminal thereof. Thus, these conventional methods are low in reliability. There is a fear that the cost of managing such variations will increase.
In the case of the method of mounting the flip chip device, it is possible that metallic wires can be used instead of using solder balls. The use of metallic wires is expedited in the conventional wire bonding system by using an automatic wire bonder. However, in the conventional wire boding system, a tip end of the metallic wire is joined to an end portion of the semiconductor chip. Then, a desired portion of the metallic wire is connected to the electrode of the mother board. Subsequently, a capillary is moved to thereby pull and cut the metallic wire. In this case, the metallic wire is torn off. Thus, the conventional system has a drawback in that the section of the metallic wire is not of a uniform shape, and that the length of the torn metallic wire is not uniform.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor device that has superior durability to thermal stress.
To solve such problems, according to an aspect of the present invention, there is provided a semiconductor device which comprises a semiconductor element having a plurality of electrode pads, a plurality of columnar electrodes connected to the plurality of electrode pads, a resin layer covering the semiconductor element and said columnar electrodes and having a surface, and outer terminals disposed on the surface of the resin layer in such a way as to be electrically conn
Aiba Yoshitaka
Fujimoto Yasunori
Fujisawa Tetsuya
Imamura Kazuyuki
Kasai Junichi
Armstrong Westerman & Hattori, LLP
Tran Mai-Huong
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