Optical Semiconductor Sub-Mount with Through-Board Protective Resistor
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Solution Overview
Problem
Conventional optical semiconductor devices require a sub-mount board with an area for a protective resistor, making it difficult to downsize while ensuring the presence of the resistor.
Innovation Solution
The optical semiconductor device incorporates a protective resistor formed as a resistive material filled in a hole, a resistive paste applied to the side wall, or a metallization layer on the sub-mount board, connecting between a conductive pattern and a GND pattern, allowing for a compact design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective resistor is connected in parallel to the capacitor in a conventional structure, then the capacitor is protected from charging of electric charges, but the sub-mount board area increases making it difficult to downsize
Solution Approach 1:
The protective resistor is configured to extend in the board thickness direction (vertical dimension) rather than being laid out on the board surface (horizontal dimension). This allows the resistor to connect between the first conductive pattern on the front surface and the second GND pattern on the back surface, utilizing the third dimension to reduce the footprint area on the sub-mount board while maintaining the protective function.
Solution Approach 2:
The protective resistor is embedded within the board structure by forming it as a hole filled with resistive material or as a metallization layer integrated into the board's internal layers. This nesting approach allows the resistor to occupy space within the board's thickness rather than requiring additional surface area, effectively hiding the protective component within the existing board volume.
2Area of stationary object
If the sub-mount board area is reduced for downsizing, then the device size is reduced, but the area for providing the protective resistor is insufficient
Solution Approach 1:
The protective resistor function is extracted from the traditional surface-mounted discrete component form and integrated directly into the board structure itself. By forming the resistor as an internal hole fill or metallization layer within the sub-mount board, the design eliminates the need for separate surface area allocation while maintaining the protective function through direct integration into the board's manufacturing process.
Data Source
AI summary
Provided here are: a sub-mount board that is provided with, on its front surface, a GND pattern, a capacitor mounting pattern and a signal line, and is provided with, on its back surface, a GND pattern; a light modulation element that is bonded to the surface of the GND pattern; a matching capacitor whose back surface is bonded to the surface of the capacitor mounting pattern and whose front surface is connected through a wire to a front surface electrode of the light modulation element; a matching resistor that makes a connection between the capacitor mounting pattern and the GND pattern; and a protective resistor that makes a connection between the signal line and the GND pattern across the sub-mount board in a board thickness direction, the signal line being connected through a wire to the front surface electrode of the light modulation element. Accordingly, the sub-mount board is small-sized.