Optical Module FPC Coverlay Layout for Impedance-Matched Connections
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Solution Overview
Problem
The existing optical modulators with integrated Mach-Zehnder interferometers face issues with increased size due to the need for multiple connectors, leading to impedance mismatch and high-frequency reflections, which narrow the transmission frequency band and cause disconnection problems due to manufacturing errors in the coverlay.
Innovation Solution
The optical module employs a flexible substrate with a signal pad and ground pad, featuring a signal line and ground pattern, along with first and second coverlays that include protrusion parts to reinforce the connection area, ensuring proper soldering and impedance matching by covering the signal line and ground pattern without obstructing the pads, thus reducing the risk of disconnection and maintaining frequency band integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a connector is provided for each electrical signal input to the optical modulator, then the reliability of electrical connection is improved, but the size of the optical modulator increases, thereby increasing the mounting area
Solution Approach 1:
Multiple connectors for different electrical signals are merged into a single integrated connector structure. The FPC substrate integrates multiple wiring patterns (MSLs) for different signals (e.g., I+, I-, Q+, Q-) that all connect to the optical modulator through one physical connector interface, eliminating the need for separate connectors for each signal line.
Solution Approach 2:
The single connector on the FPC serves multiple functions by providing electrical connections for multiple different signals simultaneously. The connector structure is designed to handle multiple signal types (in-phase and quadrature signals) through a unified interface, making the connector multi-functional rather than requiring dedicated connectors for each signal.
2Reliability
If the coverlay size is increased to cover and protect the MSL and prevent disconnection, then the reliability of the wiring pattern is improved, but the coverlay prevents part of the pad from being soldered, causing impedance mismatch
Solution Approach 1:
The coverlay is designed with spatially varying properties: it covers and protects the MSL wiring patterns in critical areas to prevent disconnection, but deliberately leaves the pad regions exposed and uncovered. This local differentiation allows the coverlay to provide protection where needed while maintaining soldering access and impedance control at the connection points.
Solution Approach 2:
The coverlay structure is segmented into different functional zones: covered regions over the MSL paths for protection, and uncovered regions at the pad locations for soldering. This segmentation allows simultaneous achievement of mechanical reinforcement and electrical performance.
Data Source
AI summary
An optical module includes a first component, a second component, and an FPC that electrically connects the first component and the second component. The FPC includes a signal pad, a ground pad, a signal line, a ground pattern, a first coverlay including a first protrusion part, and a second coverlay including a second protrusion part. The first protrusion part covers a region on the FPC where the signal line is disposed, and protrudes at a location where the signal pad is disposed, toward an end part of the FPC on the first component side than the region where the signal line is disposed. The second protrusion part protrudes at a location where the signal pad is disposed, toward an end part of the FPC on the first component side, and covers a region on the ground pattern facing at least the signal pad.