Optical Module Flexible PCB Impedance Control via Protruding Lead
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Solution Overview
Problem
Existing optical modules and flexible printed circuit boards face issues with high-speed signal degradation due to impedance mismatch and signal reflection in electrical connections, leading to increased propagation loss.
Innovation Solution
The optical module and flexible printed circuit board design includes a substrate with separate signal and ground wirings, where the signal wiring protrudes from the base layer and is connected directly to the package, eliminating the need for vias and allowing for impedance adjustment over a wide frequency range, thereby reducing signal reflection and propagation loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional via connections are used for electrical connections between flexible printed circuit board and package, then assembly is simplified, but impedance mismatch and signal reflection occur causing high-speed signal degradation
Solution Approach 1:
The patent extracts and eliminates the via structure from the electrical connection path. The lead portion protrudes directly from the base layer without passing through vias, removing the source of impedance mismatch and signal reflection while maintaining electrical connectivity between the flexible printed circuit board and package
Solution Approach 2:
The patent transitions from planar via-based connections to a three-dimensional protruding lead structure. The lead portion extends outward from the base layer surface, creating a direct electrical interface that avoids the impedance discontinuities inherent in via structures while simplifying the connection geometry
2Ease of manufacture
If vias are used for electrical connections, then manufacturing is conventional, but signal reflection and propagation loss increase
Solution Approach 1:
The via structure is completely removed from the connection path. The lead portion is formed as a continuous conductor extending from the base layer, eliminating the multiple interfaces and solder joints that cause signal reflection and energy loss in traditional via-based connections
Solution Approach 2:
The patent changes the geometric parameters of the electrical connection by using a protruding lead structure with optimized dimensions. The lead portion's cross-sectional area and length are controlled to maintain characteristic impedance continuity, reducing signal reflection and propagation loss while remaining compatible with conventional manufacturing processes
3Manufacturing precision
If lead portion protrudes from base layer, then impedance control is improved, but assembly precision requirements increase
Solution Approach 1:
The patent optimizes the geometric parameters of the lead portion (cross-sectional area, length, positioning) to achieve characteristic impedance matching with the transmission line. By carefully controlling these dimensions, the design achieves superior impedance control while the protruding structure actually simplifies assembly through direct visual alignment and reduced positioning tolerance requirements
Data Source
AI summary
An optical module according to one embodiment includes a package including a substrate that includes a first signal wiring, and a first ground wiring formed on a second wiring layer located below a first wiring layer; and a flexible printed circuit board including an upper surface wiring layer, a lower surface wiring layer, and a base layer, and including a second signal wiring formed on the upper surface wiring layer, and a second ground wiring formed on the lower surface wiring layer. The second signal wiring includes a lead portion protruding from the base layer in a first direction. The second ground wiring includes a ground terminal located further inside the flexible printed circuit board in the first direction than the lead portion. The lead portion is connected to the first signal wiring, and the ground terminal is connected to the first ground wiring.