Optical Module Connection Substrate Impedance Control
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Solution Overview
Problem
Existing optical modules face impedance mismatching issues due to wider terminal widths at connection points, which degrade optical waveform quality and hinder miniaturization of flexible printed circuits.
Innovation Solution
The optical module incorporates a connection substrate with a first signal line conductor strip and a ground conductor layer that spread outward on both sides, along with signal and ground pad portions on both surfaces, creating a gap to isolate the signal line pads from the ground conductor, allowing for adjustable pad distances to match impedance effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the terminal widths at connection points are increased to secure bonding strength, then the connection strength is improved, but impedance mismatching occurs and optical waveform quality degrades
Solution Approach 1:
The patent applies local quality by creating different pad configurations at different locations. The first pad (closer to the signal line) has different dimensions than the second pad (farther from the signal line), allowing each location to be optimized for its specific function - the first pad for impedance control and the second pad for bonding strength
2Strength
If the terminal widths at connection points are increased to secure bonding strength, then the connection strength is improved, but the flexible printed circuit cannot be miniaturized
Solution Approach 1:
The patent uses local quality to differentiate pad sizes at specific locations, allowing the FPC to maintain bonding strength where needed while minimizing overall area. The asymmetric pad configuration enables strong connections without requiring uniformly wide terminals throughout the FPC
Solution Approach 2:
The patent resolves the area contradiction by utilizing the vertical dimension (thickness) through multi-layer construction. By stacking conductive layers and dielectric layers vertically, the FPC achieves the necessary connection strength and impedance control without increasing the planar area, thus enabling miniaturization
3Manufacturing precision
If the ground conductor layer is extended further outward to improve impedance control, then impedance characteristics are improved, but the wiring pattern region is reduced making miniaturization difficult
Solution Approach 1:
The patent extends the ground conductor layer in the vertical dimension by incorporating it into multiple stacked layers rather than only expanding it horizontally. This allows improved impedance control through extended ground reference without consuming additional planar wiring pattern area
Solution Approach 2:
The ground conductor is segmented into multiple discrete ground pads distributed at different locations and layers, rather than a single continuous ground plane. This segmentation allows impedance control at critical signal locations while preserving wiring pattern area for miniaturization
Data Source
AI summary
There is provided an optical module including an optical subassembly including an optical element, a printed circuit board, and a connection substrate. The connection substrate includes a first connection portion connected to a first signal line conductor strip disposed on a first surface and a first ground conductor layer disposed on a second surface. The first connection portion includes a first signal line pad portion, a first ground pad portion, both disposed on the first surface, a second signal line pad portion disposed, and a second ground pad portion, both disposed on the second surface. In the connection substrate, a distance between the first signal line pad portion and the first ground pad portion in a first region is narrower than that in a second region farther from an inner end portion on the gap portion side than the first region in plan view.