Flexible PCB Shielding for Optical Transmitter Modules
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Solution Overview
Problem
Optical transmitter modules using flexible printed circuit boards suffer from energy loss and distortion in high-frequency signals due to interactions between signal and other patterns, leading to reduced eye opening and increased manufacturing costs and thickness.
Innovation Solution
The optical transmitter module incorporates a flexible printed circuit board with a signal pattern and ground conductor patterns on both sides, covered by insulating and conductive layers, where the conductive layer has a slit over the signal pattern, maintaining a characteristic impedance of 50 Ω without increasing thickness, and providing effective shielding to reduce electromagnetic noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the entire surfaces of the flexible printed circuit board are covered by conductive layers to improve frequency characteristics, then the shielding effect is enhanced, but the thickness of the flexible printed circuit board becomes not less than 500 μm due to manufacturing limitations, leading to loss of flexibility and increased manufacturing costs
Solution Approach 1:
The conductive layer is segmented into multiple separate ground conductor patterns rather than forming a continuous solid layer. These segmented patterns are positioned on both sides of the signal pattern and connected through via holes, creating a distributed shielding structure that achieves effective EMI protection while maintaining board flexibility and reducing thickness requirements
Solution Approach 2:
The ground conductor patterns are nested within the flexible printed circuit board structure, with patterns on both the front and back sides interconnected through via holes. This nested configuration creates an integrated shielding system that provides effective EMI protection without requiring excessive thickness, as the shielding functionality is embedded within the existing board layers
2Reliability
If the entire surfaces of the flexible printed circuit board are covered by conductive layers to improve frequency characteristics, then the shielding effect is enhanced, but manufacturing costs and manufacturing accuracy of the patterns are adversely affected
Solution Approach 1:
The conductive layer is segmented into multiple separate ground conductor patterns rather than forming a continuous solid layer. These segmented patterns are positioned on both sides of the signal pattern and connected through via holes, creating a distributed shielding structure that achieves effective EMI protection while maintaining board flexibility and reducing thickness requirements
Solution Approach 2:
Instead of providing uniform conductive coverage across the entire flexible printed circuit board, ground conductor patterns are strategically positioned only where needed for shielding - specifically on both sides of the signal pattern and connected through via holes. This localized approach provides effective EMI protection for the critical signal regions while reducing overall material usage and manufacturing complexity
3Reliability
If the flexible printed circuit board uses a thick structure to accommodate solid conductive layers, then the shielding effect is improved, but the flexibility of the board is lost
Solution Approach 1:
The conductive layer is segmented into multiple separate ground conductor patterns rather than forming a continuous solid layer. These segmented patterns are positioned on both sides of the signal pattern and connected through via holes, creating a distributed shielding structure that achieves effective EMI protection while maintaining board flexibility and reducing thickness requirements
Solution Approach 2:
The patent uses thin flexible printed circuit board structures with integrated ground conductor patterns and via hole connections to provide EMI shielding. This approach replaces the need for thick rigid conductive layers with a flexible, multi-layer configuration that maintains the board's flexibility while achieving effective shielding performance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances frequency characteristics by suppressing electromagnetic noise, reducing signal dips, and maintaining flexibility and manufacturing accuracy, achieving improved performance even at high bit rates like 9.95 Gbits/s without significant impedance reduction.
Implementation Method 1
a method of shielding the transmission line by conductors, which is generally used as an anti-EMI measure
Data Source
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Figure 2
Figure 3~4
AI summary
An optical transmitter module is described. The optical transmitter module includes a lead pin for electrically connecting the inside and outside of a housing, and a flexible printed circuit board connected to the lead pin. The flexible printed circuit board has a signal pattern and two ground conductor patterns to be connected to an optical modulation element, a laser terminal pattern to be connected to a semiconductor laser, a Peltier terminal pattern to be connected to a Peltier element, and two covering conductive layers in addition to a layer on which such patterns are formed. The covering conductive layers cover all the patterns except for the signal pattern.