Touch Sensor FPC Connection Terminal Corrosion Prevention
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Solution Overview
Problem
The existing FPC-connection structures for touch sensors face reliability issues due to corrosion and mechanical stress when the anisotropic conductive film is thermally hardened, particularly when the insulating film overlaps with the FPC terminals, leading to reduced electrical and mechanical connections.
Innovation Solution
A touch sensor design that includes a flexible circuit board with an insulating film covering part of the connection terminal, except the tip, and an electrically conductive adhesive bonding the tip to the FPC wiring, with a protruding part of the FPC film creating a space that is filled with an anti-rust material to prevent corrosion, maintaining connection reliability even when thermally hardened.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the insulating film overlaps with the FPC terminals to prevent moisture penetration, then corrosion resistance is improved, but connection reliability deteriorates due to heating and pressurization during thermal hardening
Solution Approach 1:
The connection structure is divided into three distinct zones: an exposed portion of the connection terminal not covered by the insulating film, an overlapping portion covered by the insulating film, and a protruding part of the FPC film. This segmentation allows different regions to serve different functions - the exposed portion enables reliable bonding, the overlapping portion provides corrosion protection, and the protruding part creates protective spacing.
Solution Approach 2:
The protruding part of the FPC film acts as an intermediary element that spaces the insulating film away from the exposed portion of the connection terminal. This intermediary structure prevents direct contact between the insulating film and the bonding area, eliminating the harmful heating and pressurization effects during thermal hardening while maintaining the corrosion protection function of the insulating film.
2Strength
If the FPC film overlaps with the connection terminal to provide coverage, then structural integrity is improved, but connection reliability deteriorates due to incomplete ACF coverage and hardening issues
Solution Approach 1:
The FPC film is segmented into a main body portion and a protruding part. The protruding part extends beyond the FPC wiring to create a space that overlaps with the insulating film in plan view. This segmentation allows the FPC film to provide structural coverage while the protruding part creates necessary spacing to prevent connection reliability issues.
Solution Approach 2:
The solution moves from a two-dimensional overlap problem to a three-dimensional spacing solution. By creating a protruding part that extends in the thickness direction, the patent creates a space between the FPC film and the connection terminal, transforming the problem from planar overlap to volumetric spacing, which resolves the ACF coverage and hardening issues.
3Object-affected harmful factors
If the insulating film covers the connection terminal to prevent corrosion, then corrosion resistance is improved, but electrical and mechanical connection reliability deteriorates
Solution Approach 1:
The insulating film is applied selectively to specific regions - it covers the overlapping portion of the connection terminal and the protruding part of the FPC film, but deliberately excludes the exposed portion where the connection terminal bonds to the FPC wiring. This local quality approach ensures corrosion protection is provided where needed while maintaining connection reliability at the bonding interface.
Solution Approach 2:
The insulating film is extracted or removed from the critical bonding area (the exposed portion of the connection terminal). This extraction ensures that the insulating film does not interfere with the electrical and mechanical connection between the FPC wiring and the connection terminal, while still providing corrosion protection in non-critical areas.
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 prevents corrosion of the electrode terminals without compromising the reliability of electrical and mechanical connections, ensuring consistent performance of the touch sensor.
Implementation Method 1
an electrically conductive adhesive that bonds a tipmost part of the connection terminal and the FPC wiring
Implementation Method 2
an anti-rust material that fills the space so as to cover the exposed portion of the connection terminal
Data Source
AI summary
In a flexible printed circuit (FPC) connection structure for a touch sensor, corrosion of an electrode terminal is prevented without reducing connection reliability. In a touch sensor, a tip of a first passivation layer and a tip of an FPC wiring are spaced apart from one another, and consequently an exposed portion, which is adjacent to a tipmost part and is not covered by the first passivation layer, is formed on a connection terminal. An FPC film includes a tip, which further extends from the FPC wiring and extends to a location at which it overlaps, in a plan view, the first passivation layer, and thereby a space is formed between the tip and the exposed portion. The touch sensor further includes an anti-rust material, which fills the space and thereby covers the exposed portion of the connection terminal.