RF Connection Line Pad Layout for Impedance-Matched Substrate Joints
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Solution Overview
Problem
In high-speed optical communication systems, the challenge is to maintain matching characteristic impedance at the junction of radio frequency lines on rigid and flexible substrates, particularly at high baud rates like 200 GBd, where inductivity issues lead to signal quality deterioration.
Innovation Solution
A radio frequency connection line design where the first and second radio frequency lines on different substrates are connected with specific pad configurations and through-hole structures to ensure matching impedance, including aligned signal and ground pads, and controlled gaps to minimize inductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal pad on the lower surface of the flexible substrate is pulled out to the radio frequency signal line on the upper surface, then electrical connection is achieved, but characteristic impedance matching becomes difficult
Solution Approach 1:
The patent moves the ground pad from the lower surface to the upper surface of the flexible substrate, changing the spatial dimension of the ground connection. This allows both signal and ground pads to be on the same surface, enabling proper RF signal routing and characteristic impedance matching while maintaining electrical connection reliability
Solution Approach 2:
The patent introduces a ground opening in the ground layer at the connection region of the rigid substrate, creating a localized modification that reduces inductivity specifically at the junction point. This local quality change enables impedance matching without affecting the overall structure
2Adaptability or versatility
If different substrates with different materials and thicknesses are used, then substrate flexibility and rigidity requirements are met, but characteristic impedance matching deteriorates
Solution Approach 1:
The patent applies local quality modification by introducing a ground opening specifically at the connection region on the rigid substrate. This localized change compensates for the impedance discontinuity caused by joining different substrate types, enabling impedance matching while maintaining the flexibility advantages of the multi-substrate structure
Solution Approach 2:
The patent modifies the ground layer structure by creating an opening, which changes the electrical parameters (inductivity, capacitance) at the connection point. This parameter change compensates for the impedance mismatch caused by joining substrates with different materials and thicknesses
3Manufacturing precision
If a ground opening is introduced in the ground layer, then inductivity is reduced and impedance matching is improved, but device complexity increases
Solution Approach 1:
The patent segments the ground layer by introducing a controlled opening at the connection region. This segmentation isolates the inductivity reduction effect to a specific location, achieving impedance matching improvement with minimal additional complexity in the overall device structure
Data Source
Figure 1(a)~1(c)
Figure 2(a)~2(b)
Figure 3(a)~3(c)
AI summary
A radio frequency connection line in an embodiment includes a first main line including a first signal line and a first earthing ground of a first radio frequency line and a second main line including a second signal line and a second earthing ground of a second radio frequency line, the first signal line and the second signal line are connected via joining of a first signal pad and a third signal pad, the first earthing ground and the second earthing ground are connected via joining of a first ground pad and a third ground pad, a gap between the third signal pad and an earthing ground layer is set smaller than a quarter of a guide wavelength, and an interval between the second signal pad and the second ground pad is set narrower than an interval between the second signal line and the second earthing ground.