Optical Module Impedance Control via FPC Wiring
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Solution Overview
Problem
High-speed optical communication modules face significant cost challenges due to the need for specialized processing of stems with trenches to mitigate impedance mismatches, which increases costs and is not feasible for inexpensive module production.
Innovation Solution
An optical module design that eliminates the ground pin and trench, using a substrate with a connecting portion and a matching region on the FPC to reduce impedance mismatches, allowing for a more versatile and cost-effective stem without special processing, and connecting the FPC to the stem via electrodes extending from the ground layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a trench is formed in the stem to reduce impedance mismatches, then high-frequency characteristics are improved, but manufacturing cost increases
Solution Approach 1:
The invention extracts the impedance matching function from the stem structure (trench) and relocates it to the FPC wiring pattern. By removing the need for stem modification and placing the impedance control mechanism in the FPC layer, the solution eliminates expensive stem processing while maintaining high-frequency performance through controlled impedance wiring design.
Solution Approach 2:
The FPC wiring pattern acts as an intermediary between the lead terminal and the optical semiconductor device. Instead of modifying the stem directly, the FPC wiring serves as a mediator that provides impedance control and signal integrity, allowing the stem to remain simple and inexpensive while still achieving the desired high-frequency characteristics.
2Reliability
If a trench is formed in the welded portion of the ground pin, then inductance is reduced, but device complexity increases
Solution Approach 1:
The invention extracts the inductance control function from the stem structure and transfers it to the FPC wiring design. By removing the trench requirement from the stem and implementing equivalent inductance control through FPC trace geometry and grounding patterns, the solution simplifies the stem structure while maintaining proper inductance characteristics for high-speed signaling.
3Reliability
If characteristic impedance mismatches are suppressed at the connecting portion, then signal quality is improved, but manufacturing precision requirements increase
Solution Approach 1:
The FPC wiring pattern is designed to self-adjust and control impedance characteristics through its geometric configuration and layer structure. The wiring design inherently provides impedance control without requiring ultra-precise manufacturing tolerances on the stem or connecting portions, allowing standard manufacturing processes to achieve the necessary signal quality.
Data Source
AI summary
An optical module includes an optical semiconductor device and a stem including a lead terminal configured to perform at least one of transmitting an electric signal to the optical semiconductor device or transmitting an electric signal output from the optical semiconductor device. The optical module also includes a substrate having a ground layer, a first opening through which the lead terminal passes, and a connecting portion configured to electrically connect the stem and the ground layer. The connecting portion is formed on one of an edge portion of the substrate and a surface of the substrate on a side on which the substrate is arranged on the stem.