Active solid-state devices (e.g. – transistors – solid-state diode – Housing or package – For high frequency device
Reexamination Certificate
2003-03-14
2004-02-24
Clark, Jasmine (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Housing or package
For high frequency device
72, 72, C361S709000
Reexamination Certificate
active
06696755
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device having an improved semiconductor package structure, and particularly to a semiconductor device incorporating therein optical elements such as a photosensitive element or a light emitting element.
2. Description of the Related Art
In recent years, an optical transceiver suitable for use in a data communication system typified such as by Local Area Network (LAN) needs to operate at higher speed and be fabricated at lower cost and in smaller size. Typically, the optical transceiver has provided therein a Laser Diode (LD) and a Photo Diode (PD) in addition to an electrical circuit such as a Large Scale Integrated Circuit (hereinafter, referred to as LSI). Furthermore, in terms of optimal design for optical system, optimal packaging and optimal sealing, an optical element needs to be handled in a manner different from that employed to handle an LSI, etc., causing the cost of an entire package to increase.
In order to lower the cost of a package, approach to packaging optical elements has been made and a packaging substrate referred to as a CAN package or a Si bench has been proposed. The CAN package is constructed such that only optical elements are mounted on a Si substrate (hereinafter, referred to also as optical element mounting substrate), etc., on a transmission-side or components ranging from optical elements to a front-end IC (amplifier) are mounted on a Si substrate, etc., on a reception-side and those elements or components are hermetic sealed, and further, a signal is retrieved via a lead line (Hans L. Althaus et. al. IEEE TRANSACTIONS ON COMPONENTS, AND MANUFACTURING TECHNOLOGY vol. 21, pp. 147-156, May 1998). That is, LD, PD, etc., mounted on a Si substrate or the like are sealed within a housing and an input/output signal to and from LD or PD is transmitted via a lead line extended outside the housing. A Si bench generally has high thermal conductivity and is an assembly substrate comprising a Si substrate advantageous for incorporating thereon optical elements and selected in terms of flatness and workability, optical elements mounted on the Si substrate, and a resin encapsulating the Si substrate together with the optical elements (K. Kurata et al. Proc. Conf. 45
th
ECTC pp. 759-765 1995).
However, the CAN package has the following drawbacks. That is, in the CAN package, a signal is transmitted via a lead line and when a high-frequency signal is transmitted, large parasitic inductance and large parasitic capacitance generated within the CAN package prevent the signal from being transmitted at high speed. Furthermore, it is preferable to dispose a driver LSI (Large Scale IC) in the vicinity of an optical element that outputs and/or receives a weak signal. However, in the case of CAN package, since the optical element such as a PD or an LD is sealed within a housing, reduction of a distance between the optical element and the driver LSI becomes limited. Moreover, since the optical element is sealed within the housing, thermal conductivity of the CAN package unfavorably is lowered.
Furthermore, in the case of Si bench, since optical elements are mounted on a Si substrate, an LSI formed on the Si substrate can also be mounted in the vicinity of the optical elements and further, since the Si substrate has high thermal conductivity, the Si substrate has a high heat removal ability. However, an insulation film formed on the Si substrate is thin since the film is formed by thermally oxidizing the Si substrate and therefore, a problem occurs when a signal is transmitted within the Si bench, in other words, a signal is not transmitted at high speed within the Si bench.
As described above, the conventional technique does not yet provide a semiconductor device that is free from the above-stated problems, i. e., enables a signal to be transmitted at high speed within the device and further allows the optical elements to easily be mounted therein. In more detail, when modulating a signal at high frequency on the order of not less than about 1 GHz, parasitic capacitance due to the assembling probably makes device performance significantly degraded and accordingly, both a package design and an LSI design cannot be made without an analogue design technique for designing an optimal circuit taking into account how to incorporate leads of package, which leads have been assembled within the device in a compact manner, in addition to how to incorporate a mother board within the device and how to eliminate parasitic capacitance generated within the device.
For example, in the case of CAN package, etc., the parasitic inductance of a lead line and the parasitic capacitance of a bonding wire used to make connection of the optical element to the lead line largely affect device performance. Therefore, for example, when a transmission side is designed such that a driver LSI for driving an optical element is mounted on a mother board and a CAN package is connected to the mother board, an entire package should be designed taking into account the influence of the above-described parasitic inductance and parasitic capacitance.
Moreover, when the Si substrate, etc., is employed as a substrate that is used to mount an optical element thereon, the optical element is typically connected by wire bonding to the mother board on which a variety of LSIs for performing various processing are mounted. In this case, the inductance component of the wire acts as a reflection point that significantly echoes an electrical signal when the signal is modulated at high frequency and in addition, the wire needs to be encapsulated with a resin, thereby increasing the assembling cost. Additionally, since the Si substrate generally has interconnect lines formed on a silicon dioxide (SiO
2
) film as an insulation film, which is formed on the surface of the substrate by thermally oxidizing the substrate, the parasitic capacitance of the device consisting of the substrate is large and the device is not suitable for high frequency drive. For this reason, the SiO
2
film has been formed to have a large film thickness. However, forming the SiO
2
film to a large thickness unfavorably lowers the productivity of semiconductor device and its availability.
This increases the need for a highly advanced substrate capable of transmitting a signal at high frequency within the substrate and assembling optical elements in a compact manner. Furthermore, the development of a semiconductor package structure is indispensable for reduction of the cost of an optical transceiver, which structure can be constructed such that microelectronic components are physically assembled in the same manner as that employed in the conventional technique and electrically assembled in a complete fashion as well without taking into account how to incorporate therein optical elements when designing an entire package.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor package structure and having a high heat removal ability without sacrificing its electrical performance at high frequency and further, enabling time efficiency in package design associated with packaging or mounting and reduced packaging cost.
A semiconductor device according to the present invention comprises: an insulating film; first and second conductive layers formed on both surfaces of the insulating film and constituting wiring patterns respectively, the first and second conductive layers being constructed such that a part of each of the wiring patterns formed in the first and second conductive layers is a conductive wiring for a high-speed signal, designed taking into account high frequency characteristic of the conductive wiring based on characteristic impedance of the conductive wiring; an integrated circuit mounted on the first conductive layer; and a conductor connecting the wiring pattern formed in the first conductive layer and the wiring pattern formed in the second conductive layer to one another, in which the insulating film is furthe
Doumae Satoshi
Kami Nobuharu
Kurata Kazuhiko
Sugimoto Takara
Clark Jasmine
Hayes & Soloway P.C.
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