Flexible Printed Wiring Substrate for High-Density Optical Modules
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Solution Overview
Problem
In optical transmission modules, especially in 100 Gb/s ROSA modules, the flexible printed wiring substrates face challenges in connecting a large number of electric signal wires and power supply wires within a narrow space, leading to reliability issues, increased complexity, and potential displacement or deformation of electrodes during the soldering process, which affects high-frequency signal transmission and module yield.
Innovation Solution
A flexible substrate with a branch structure is designed, featuring a first body and a second body joined at the connector region, with the second body forming a band-like shape to surround the first body, allowing for even stress distribution and reduced peel stress during folding and soldering, thereby enhancing reliability and preventing electrode displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of signal wires and power supply wires is increased within a narrow width of 7mm, then the transmission capacity is improved, but the flexibility and reliability of the substrate deteriorate
Solution Approach 1:
The flexible substrate is divided into a first body and a second body that can be folded relative to each other. This segmentation allows the substrate to accommodate a large number of wires (48 wires including signal wires and power supply wires) within the narrow 7mm width by distributing them across two bodies, while maintaining flexibility and reliability through the folded configuration.
2Volume of moving object
If the substrate is folded to achieve compact packaging, then the packaging density is improved, but electrode displacement and deformation occur during soldering
Solution Approach 1:
The substrate is designed with a folded structure where the first body and second body are pre-configured in a specific spatial relationship. The electrodes on both bodies are preliminarily positioned to correspond with each other before soldering, ensuring that even when folded, the electrodes maintain accurate alignment during the soldering process and prevent displacement or deformation.
3Device complexity
If a single flexible substrate is used to connect all wires, then the device complexity is reduced, but the substrate cannot accommodate the required number of wires
Solution Approach 1:
The connection structure is segmented into a first body and a second body of the flexible substrate. The first body contains a first set of electrodes while the second body contains a second set of electrodes, allowing the substrate to connect a large number of wires (48 wires) without increasing overall device complexity. The two bodies work together as an integrated connection system.
Data Source
AI summary
A flexible substrate having a branch structure in the related art has problems in that: adhesive strength after two bodies are folded and fixed at a bonding region decreases due to an unfolding and opening force at a curve portion and ends of the bonded portions are peeled off and generate gaps; and in a soldering process of the two bodies, the electrodes of one body soldered first are displaced due to reheating in soldering the other body secondly and deteriorate in soldered connection. The present invention provides a new flexible substrate having a branch structure, including first and second bodies joined together, and having a structure in which one of the bodies can be folded back in a longitudinal direction of the whole flexible substrate. Tip ends of the two bodies are provided with multiple electrodes, and are connected by soldering to approximately corresponding positions on both surfaces of an end portion of a printed substrate concerned.