Optical Module FPC Ground Pad Thickness Optimization
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Solution Overview
Problem
Existing high-frequency optical modules experience degradation in high-frequency characteristics due to the use of surface mount technology (SMT) which requires vias and lead pins, making it difficult to support faster optical communication speeds such as 400 to 600 Gbps and beyond.
Innovation Solution
The optical module employs a new package structure using a flexible printed circuit (FPC) to connect the PCB and high-frequency package, with a thinner substrate thickness for ground pads and thicker ground pads on the FPC, which suppresses high-frequency loss and supports faster communication speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If surface mount technology (SMT) with vias and lead pins is used for high-frequency packaging, then ease of manufacture is improved, but high-frequency characteristics are degraded
Solution Approach 1:
The patent removes vias and lead pins from the high-frequency signal path by using a substrate with through-holes that are filled with conductive material only for ground connections, while signal connections are made through surface-mounted pads. This extraction of harmful elements (vias and lead pins from signal path) resolves the contradiction by maintaining ease of manufacture while eliminating high-frequency degradation.
Solution Approach 2:
The patent applies different structural qualities to different regions: the signal transmission areas use surface-mounted pads with direct copper traces, while ground connections use filled through-holes. This local differentiation allows the signal path to avoid high-frequency degradation while maintaining manufacturable ground connections, resolving the contradiction between ease of manufacture and high-frequency characteristics.
2Loss of energy
If substrate thickness at ground pad locations is reduced, then high-frequency loss is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent changes the substrate thickness parameter locally at ground pad locations, making it thinner than at signal pad locations. This parameter change reduces the dielectric loss path for ground signals, improving high-frequency characteristics while the manufacturing precision challenge is managed through the standardized process of forming and filling through-holes.
3Reliability
If FPC ground pad thickness is increased, then high-frequency shielding is improved, but device complexity increases
Solution Approach 1:
The patent applies different thickness qualities to different pad types on the FPC: ground pads are made thicker to provide better shielding and lower impedance for high-frequency ground signals, while signal pads maintain standard thickness. This local quality differentiation improves high-frequency shielding without unnecessarily increasing overall device complexity.
Data Source
AI summary
According to the present disclosure, there is provided an optical module, including: a PCB; a DSP mounted on the PCB; a high-frequency package mounted on the PCB, and including an optical transmission element, an optical modulation element, or an optical reception element; and an FPC that electrically connects a signal pad of the PCB and a signal pad of the high-frequency package, and electrically connects a ground pad of the PCB and a ground pad of the high-frequency package, in which a thickness of a substrate at a location where the ground pads of the PCB and the high-frequency package are disposed is thinner than a thickness of the substrate at a location where each of the signal pads of the PCB and the high-frequency package is disposed, and a thickness of a ground pad of the FPC is thicker than a thickness of a signal pad of the FPC.