1. Field of the Invention
The preferred embodiment of the present invention relates to a hybrid circuit substrate with embedded optical and electrical interconnects, and, more particularly, to a hybrid circuit substrate, which may achieve increased transmission speed with increased capacity of an information signal under high speed and with increased capacity by enabling transmission of an electrical signals and a photo optical signals. Also, the preferred embodiment of the present invention relates to a method for manufacturing the above hybrid circuit substrate. Further, the preferred embodiment of the present invention relates to a hybrid circuit module with optical and electrical interconnects embedded and a method for manufacturing the above hybrid circuit module.
2. Description of the Related Art
A variety of digital electronic appliances such as portable computers, mobile phones, video apparatuses and audio apparatuses, for instance, are equipped with a multi-chip circuit module with various semiconductor chips such as IC (Integrated Circuit) elements and LSI (Large Scale Integration) elements packaged. In the circuit module, increased functionality and flexibility of combination with downsizing, may be accomplished through increasing interconnect pattern micro-fabrication, IC package downsizing, fast progressing integration scale, increasing pin multiplication, assembly technology improvement and the like. In addition, in the circuit module, performance, functionality, multi-functionality and high speed processing, etc. are also being increased with sharply increasing operation speed of the semiconductor chips with increased capacity and the like.
In the circuit module, relatively short-distance transmission of an information signal between boards or intra-board semiconductor chips and the like takes place typically with an electrical signal transmitted through electrical interconnects. In the circuit module, efforts to further increase transmission performance is being made for high speed transmission of the information signal and increasing density of a signal pattern and the like. However, there is a limit in an approach to increased transmission performance with the electrical interconnects, resulting in a difficulty in achieving the increased transmission performance. The circuit module also needs to take measures against problems such as delayed signal transmission caused by a CR (Capacitance-Resistance) time constant that arises in an interconnect pattern, EMI (Electromagnetic Interference) noise, EMC (Electromagnetic Compatibility), inter-interconnect pattern cross talk and so on.
In the circuit module, use of an optical interconnection technology realized using optical interconnects, interconnections and the like has become popular in order to settle the above transmission problems on the electrical signal with the electrical interconnects. The optical interconnection technology enables transmission of an information signal and the like at high speed between appliances, intra-appliance boards or intra-board semiconductor chips. Particularly, in short-distance transmission such as inter-semiconductor chip transmission of a signal, for instance, the optical interconnection technology ensures configuration of a suitable optical signal transmission system with an optical wave-guide as a transmission line by forming the optical wave-guide on a substrate with the semiconductor chips packaged.
In an optical interconnect circuit module, a circuit substrate thereof is mounted with not only the optical wave-guide, but also a light emitting device that outputs a optical signal into the optical wave-guide through conversion of an electrical signal into the optical signal, and a photo-detecting device that outputs the electrical signal through conversion of the optical signal accepted through the optical wave-guide into the electrical signal, or an IC chip and the like adapted to transfer of the electrical signal between the light emitting device and the photo-detecting device. On one hand, the optical interconnect circuit module is designed to have an electrical interconnect pattern, together with the above optical wave-guide, on the circuit substrate in order to meet low speed control signal transmission and the like, with supply of power to optical elements, so that a hybrid circuit substrate with optical and electrical interconnects embedded is equipped.
The hybrid circuit substrate is configured with the optical wave-guide, as a component of the optical interconnect section, on a main surface of a typical printed circuit board having an appropriate interconnect pattern that configures the electrical interconnect section, for instance. Alternatively, when manufacturing the hybrid circuit substrate at relatively micro scale and high density, a silicon substrate, a quartz substrate or a glass substrate is applied, for instance, to deposit a thin film layer of multi layer interconnection having an interconnect pattern on a main surface of the above substrate, and the optical wave-guide composing the optical interconnect section is formed on the thin film layer of multi layer interconnection.
In the hybrid circuit substrate, the optical wave-guide is formed with a photoconductive polymer compound using a low-temperature process. The hybrid circuit substrate needs to have the optical wave-guide that is free from surface irregularities causing a propagation loss and also meets a highly dimensional accuracy. When the hybrid circuit substrate is designed to have the optical wave-guide directly on the main surface of the silicon substrate and the like having the advantage of providing a small surface roughness enough to ensure satisfactory flatness, it is relatively easy to attain the optical wave-guide having the above characteristics.