Reinforcing Member for Flexible PCB Ground Effect
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Solution Overview
Problem
The ground effect of flexible printed wiring boards is deteriorated due to the formation of a passive film on reinforcing members, especially those made of stainless steel, caused by aging, thermal treatment, and exposure to high-temperature and high-moisture environments, leading to increased electric resistance.
Innovation Solution
A reinforcing member with a conductive metal base and a surface layer of noble metal or alloy, providing higher conductivity and corrosion resistance than the base, is disposed opposite to a ground wiring pattern, ensuring electrical conduction with both the pattern and an external ground member, thereby maintaining the ground effect and resisting passive film formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a reinforcing member made of stainless steel is used, then the strength and structural integrity are improved, but the electric resistance increases due to passive film formation, deteriorating the ground effect
Solution Approach 1:
The reinforcing member is constructed as a composite structure with a metal base (providing strength) and a surface layer of noble metal or alloy (providing low electric resistance and corrosion resistance). This composite design allows simultaneous achievement of high mechanical strength and excellent electrical conductivity for ground effect maintenance.
Solution Approach 2:
Different regions of the reinforcing member are assigned different materials with different properties: the bulk metal base provides structural strength, while the surface layer specifically provides electrical conductivity and corrosion resistance. This local differentiation of material properties resolves the contradiction between strength and electrical performance.
2Adaptability or versatility
If the reinforcing member is exposed to high-temperature and high-moisture environments, then the operational conditions are expanded, but passive film formation accelerates, increasing electric resistance
Solution Approach 1:
The surface layer of noble metal or alloy provides enhanced corrosion resistance that prevents passive film formation even under high-temperature and high-moisture conditions. This allows the reinforcing member to maintain low electric resistance while operating in harsh environments.
Solution Approach 2:
The surface layer material composition is specifically selected and controlled (noble metal or alloy with controlled composition) to provide stable electrical properties that are insensitive to environmental parameter changes such as temperature and humidity, thereby maintaining ground effect reliability.
3Ease of manufacture
If thermal treatment is applied to the printed wiring board, then the manufacturing process is completed, but the passive film on the reinforcing member deteriorates, increasing electric resistance
Solution Approach 1:
The surface layer of noble metal or alloy is designed to be thermally stable and resistant to passive film formation during thermal treatment processes. This allows the reinforcing member to withstand manufacturing thermal cycles while maintaining low electric resistance and ground effect.
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
The solution effectively maintains the ground effect and contact strength of the printed wiring board over time, even in harsh environments, by reducing the formation of passive films and lowering electric resistance, while offering improved corrosion resistance and conductivity.
Implementation Method 1
one surface in electrical conduction with the predetermined part of the ground wiring pattern via a conductive composition layer and the other surface in electrical conduction with an external ground member at a ground potential
Implementation Method 2
the surface layer having higher conductivity and corrosion resistance than the metal base
Data Source
AI summary
A reinforcing member for a flexible printed wiring board that maintains an electromagnetic wave shielding effect and a ground effect of the printed wiring board over a long period of time. A reinforcing member is disposed opposite a predetermined part of a ground wiring pattern and includes one surface opposing and in electrical conduction with the predetermined part of the ground wiring pattern. The other surface is in electrical conduction with an external ground member which is at a ground potential, the one surface and the other surface opposing each other. The reinforcing member includes a base made of conductive metal and a surface layer formed on a surface of the base to constitute at least a part of the other surface, the surface layer has higher conductivity and corrosion resistance than the base made of metal, and the surface layer is 0.004 to 0.2 μm thick.