Dual-Layer Adhesive Structure for Fingerprint Sensor Stability
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Solution Overview
Problem
The adhesive layer in electronic devices with fingerprint identification functions is susceptible to deformation and decomposition due to environmental conditions, leading to unintentional detachment of the flexible printed circuit (FPC) from the TFT substrate, affecting the stability of the electronic connection.
Innovation Solution
The use of a dual-layer adhesive structure with a first adhesive portion and a second adhesive portion, where the second adhesive portion is spaced apart from the substrate and has a lower hardness, reduces the impact of deformation forces and maintains the electrical connection between the FPC and the TFT substrate, preventing separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer adhesive structure is used to join the FPC and substrate, then the device structure is simple, but the adhesive layer is susceptible to deformation and decomposition from environmental conditions causing FPC detachment
Solution Approach 1:
The adhesive layer is divided into two distinct portions: a first adhesive portion with first hardness and a second adhesive portion with second hardness. This segmentation allows each portion to perform different functions - the first adhesive portion provides strong bonding to the substrate, while the second adhesive portion provides compliant bonding to the FPC, accommodating thermal expansion and contraction without causing detachment.
Solution Approach 2:
Different regions of the adhesive layer are assigned different hardness properties. The first adhesive portion (near substrate) has higher hardness for structural support, while the second adhesive portion (near FPC) has lower hardness for flexibility. This local quality differentiation resolves the contradiction by optimizing each region for its specific function while maintaining overall connection stability.
2Strength
If the adhesive layer is made harder to maintain structural integrity, then the bonding strength increases, but the adhesive becomes more susceptible to deformation and decomposition from environmental conditions
Solution Approach 1:
The adhesive layer employs spatially varying hardness - the first adhesive portion near the substrate has higher hardness for strong bonding and structural integrity, while the second adhesive portion near the FPC has lower hardness to accommodate environmental deformation. This local quality gradient resolves the contradiction between strength and environmental resistance.
Solution Approach 2:
The adhesive layer functions as a composite structure with two different adhesive materials or formulations having different hardness values. This composite approach allows the system to simultaneously achieve high bonding strength (from the harder first portion) and environmental flexibility (from the softer second portion).
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 the stability of the electronic connection by isolating the FPC from deformation-induced forces, ensuring consistent functionality despite adhesive shrinkage and environmental changes.
Implementation Method 1
the second adhesive portion is spaced apart from the substrate and has a lower hardness, reduces the impact of deformation forces
Data Source
AI summary
An electronic device able to identify fingerprints ultrasonically includes a substrate, a fingerprint identification structure, and an adhesive layer. The fingerprint identification structure includes a thin film transistor (TFT) substrate and a flexible printed circuit (FPC). The FPC includes a first portion and a second portion. The first portion is located on a surface of the TFT substrate facing away from the substrate. The second portion is extended from an end of the first portion to be electrically connected to a surface of the TFT substrate facing the substrate. The second portion is separated from the adhesive layer. A space is defined between the second portion and the substrate. The adhesive layer is susceptible to deformation and decomposition from environmental conditions.