Flexible PCB Fingerprint Sensor Durability
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Solution Overview
Problem
Conventional fingerprint sensing chips face issues with durability due to fragile insulating layers that cannot withstand pressure, force impact, or electrostatic charge damage, as they are often too thin and prone to wear and electrostatic discharge.
Innovation Solution
A fingerprint sensing device featuring a chip substrate with fingerprint sensing cells connected to a flexible printed circuit board, where the flexible board's thicker polyimide material and anti-contamination layer enhance durability and electrostatic discharge resistance, allowing the device to withstand pressure and force while providing a robust contact surface for fingerprint sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin insulating layer is formed on the chip surface to enable fingerprint sensing, then the sensing function is achieved, but the chip cannot withstand pressure, force impact, or electrostatic charge damage
Solution Approach 1:
The patent employs a composite structure consisting of a flexible printed circuit board layer and a protective film layer stacked together. The flexible printed circuit board provides mechanical strength and electrostatic discharge protection, while the protective film maintains the sensing function. This composite material approach resolves the contradiction by combining materials with complementary properties to achieve both durability and pressure resistance.
Solution Approach 2:
The flexible printed circuit board acts as an intermediary layer between the chip substrate and the external environment. It provides a thicker protective barrier that can withstand pressure and electrostatic charges while allowing the thin insulating layer on the chip to maintain its sensing function. This intermediary structure protects the fragile sensing elements without compromising the overall durability.
2Measurement precision
If the insulating layer is made thinner to improve sensing sensitivity, then the fingerprint detection accuracy is enhanced, but the chip becomes more vulnerable to electrostatic discharge and mechanical damage
Solution Approach 1:
The flexible printed circuit board serves as a protective intermediary that shields the thin insulating layer from electrostatic discharge and mechanical damage. It allows the sensing layer to remain thin for high accuracy while providing the necessary protection against harmful factors through its own thicker structure.
Solution Approach 2:
The composite structure combines the thin insulating layer (for sensing accuracy) with the thicker flexible printed circuit board (for protection). This composite approach enables the system to achieve both high measurement precision and resistance to electrostatic discharge by leveraging the complementary properties of different material layers.
3Reliability
If a thick protective layer is added to the chip to improve durability and electrostatic resistance, then the chip can withstand pressure and impact, but the sensing sensitivity may be compromised
Solution Approach 1:
The protective function is segmented into two distinct layers: the flexible printed circuit board provides mechanical strength and electrostatic protection, while the thin insulating layer on the chip substrate maintains sensing sensitivity. This segmentation allows each layer to specialize in its function without compromising the other, resolving the contradiction between durability and sensing precision.
Solution Approach 2:
The patent uses a composite structure where the flexible printed circuit board and protective film work together to provide durability, while the thin insulating layer on the chip maintains sensing sensitivity. The composite material approach ensures that the thick protective elements do not interfere with the thin sensing elements, achieving both wear resistance and sensing precision simultaneously.
4Ease of manufacture
If the insulating layer is formed by film deposition to create a thin protective barrier, then the chip surface is protected from wear, but the layer is too thin to withstand large pressure or impact forces
Solution Approach 1:
The patent merges the thin film deposition layer (which provides basic protection and ease of manufacture) with a thicker flexible printed circuit board layer (which provides impact resistance). This combination allows the system to benefit from both the manufacturability of thin film deposition and the strength of thicker protective structures, resolving the contradiction between ease of manufacture and impact resistance.
Data Source
AI summary
A fingerprint sensing device includes a chip substrate, first connecting pads and a flexible printed circuit board. The substrate has fingerprint sensing cells. The first connecting pads are respectively disposed on the fingerprint sensing cells and exposed from a top surface of the substrate. The printed circuit board is disposed above the substrate and has signal transmission structures exposed from a bottom surface of the printed circuit board. The fingerprint sensing cells are respectively electrically connected to the signal transmission structures, and a top surface of the printed circuit board serves as a contact surface for a finger so that sensed fingerprint signals of the finger are transmitted to the fingerprint sensing cells through the signal transmission structures. The numbers of the first connecting pads, the fingerprint sensing cells and the signal transmission structures are equal to one another. A method of manufacturing the fingerprint sensing device is also disclosed.