Pressing Force Sensor Heat-Resistant Flexible Circuit
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Solution Overview
Problem
Existing pressing force sensors face challenges with heat resistance during the solder reflow process, particularly with electrode films made of polyethylene terephthalate, which cannot withstand temperatures above 260°C, and require high production costs to address this issue through separate flexible printed circuit boards and anisotropic conductive films.
Innovation Solution
A pressing force sensor configuration using a flexible printed circuit board with heat resistance sufficient for solder reflow temperatures, where the sensor elements, lead terminals, and wiring conductors are disposed on the board, allowing for a solder reflow process without additional components or costs, and optionally incorporating a shield electrode for electrostatic protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an electrode film made of polyethylene terephthalate (PET) is used, then the pressing force sensor can be manufactured with simpler materials, but the heat resistance is insufficient to withstand solder reflow temperatures (260°C or higher)
Solution Approach 1:
The patent combines the electrode film and protective film into a single integrated structure. The electrode film is sandwiched between two protective films (first protective film on the outer surface, second protective film on the inner surface), creating a composite structure that maintains electrical functionality while providing heat resistance during solder reflow processes.
Solution Approach 2:
The patent uses a composite structure consisting of multiple material layers: PET electrode film combined with protective films. This composite material approach allows the electrode film to maintain its electrical properties while the protective films provide the necessary thermal resistance for solder reflow temperatures.
2Temperature
If a separate flexible printed circuit board is prepared for connection to external circuit, then the heat resistance issue is resolved, but the production cost increases
Solution Approach 1:
The patent merges the electrode film with protective films to create an integrated component that simultaneously provides electrical connectivity and heat resistance. This eliminates the need for separate flexible printed circuit boards and anisotropic conductive films, thereby reducing production costs while maintaining solder reflow capability.
Solution Approach 2:
The protective films serve multiple functions: they provide heat resistance during solder reflow, protect the electrode film from damage, and enable direct connection to external circuits without requiring additional flexible printed circuit boards. This multi-functionality reduces the overall component count and production cost.
3Reliability
If multiple separate components are used to address heat resistance and connection requirements, then the functional requirements are met, but the device complexity and production cost increase
Solution Approach 1:
The patent combines multiple functional requirements into a single integrated structure: the electrode film provides electrical connectivity, while the protective films provide heat resistance and physical protection. This integration reduces device complexity by eliminating the need for separate flexible printed circuit boards, anisotropic conductive films, and multiple assembly steps.
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
Enables reliable connection to an external circuit without heat resistance issues and reduces production costs by integrating sensor components on the flexible printed circuit board, eliminating the need for separate components and complex assembly processes.
Implementation Method 1
a piezoelectric film or a resistor film
Implementation Method 2
a piezoelectric film or a resistor film
Data Source
AI summary
A pressing force sensor that includes a sensor element configured with a piezoelectric film, a lead terminal for connection to an external circuit, a wiring conductor which connects pressing force detection electrodes and the lead terminal, and a flexible printed circuit board which withstands solder reflow temperatures. The flexible printed circuit board has the pressing force detection electrodes formed on a first principal surface thereof, and is folded via a folding line while the first principal surface faces inward. The sensor element is deflected by a pressing force applied to a second principal surface which faces outward and is in a first area of the flexible printed circuit board which is on one side with respect to the folding line, and a signal corresponding to the pressing force is thus taken out from the pressing force detection electrodes.