Printed Wiring Board Fingerprint Authentication Circuit Design
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Solution Overview
Problem
Existing printed wiring boards for fingerprint authentication face challenges in achieving high accuracy and reliability due to surface unevenness and permittivity differences, which affect the capacitance measurements and noise levels, leading to reduced authentication accuracy and increased measuring time.
Innovation Solution
A printed wiring board design featuring a first and second insulating layer with embedded conductor circuits and a solder resist layer, where the conductor circuits are positioned to oppose each other across the insulating layers, with specific permittivity values and layer thicknesses optimized to enhance flatness and capacitance measurement, reducing noise and improving authentication accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conductor circuits are embedded in insulating layers for fingerprint authentication, then authentication functionality is achieved, but surface unevenness occurs reducing measurement precision
Solution Approach 1:
The patent transitions from a single-layer conductor circuit design to a multi-layer embedded structure. The first conductor circuit is embedded in a first insulating layer, which is then embedded in a second insulating layer containing a second conductor circuit. This multi-layer embedding approach flattens the surface by distributing conductor circuits across multiple depth levels, eliminating surface unevenness and improving capacitance measurement precision for fingerprint authentication.
Solution Approach 2:
The patent introduces insulating layers as intermediary materials between conductor circuits and the fingerprint sensing surface. The first insulating layer embeds the first conductor circuit, and the second insulating layer embeds the second conductor circuit, creating a smooth intermediate surface that eliminates protrusions and凹陷. This intermediary embedding structure ensures uniform capacitance distribution across the fingerprint sensing area, directly improving measurement precision.
2Measurement precision
If multiple insulating layers with different permittivities are used to improve authentication accuracy, then recognition performance improves, but device complexity increases
Solution Approach 1:
The patent optimizes the permittivity parameters of insulating layers to enhance fingerprint authentication accuracy. The first insulating layer has a permittivity of 3.0 to 4.5, while the second insulating layer has a permittivity of 2.0 to 3.5. By carefully selecting and controlling these permittivity parameters, the patent achieves optimal capacitance distribution for fingerprint sensing. This parameter optimization improves recognition accuracy without requiring complex additional structures, as the permittivity values themselves are the key design parameters.
Solution Approach 2:
The patent employs composite insulating layer structures with different material properties. The first insulating layer and second insulating layer are made of different materials with distinct permittivity values, creating a composite multi-layer structure. This composite approach allows each layer to contribute differently to the overall capacitance distribution, enhancing fingerprint recognition accuracy through material property differentiation rather than structural complexity.
3Measurement precision
If conductor circuits are positioned to oppose each other across insulating layers, then capacitance measurement is enhanced, but manufacturing precision requirements increase
Solution Approach 1:
The patent positions conductor circuits in different vertical layers rather than attempting precise lateral alignment in a single plane. The first conductor circuit is embedded in the first insulating layer at one depth level, while the second conductor circuit is embedded in the second insulating layer at a different depth level. This vertical separation in the third dimension reduces the stringency of lateral positioning requirements, as the opposing conductor circuits naturally align through the stacked layer structure during the embedding process, thereby reducing manufacturing precision requirements.
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 design increases the flatness of the solder resist layer, enhances fingerprint authentication accuracy, and reduces measuring time by optimizing permittivity ratios and layer thicknesses, resulting in improved recognition performance and repeat accuracy.
Implementation Method 1
a first conductor circuit 58L for fingerprint authentication that is formed on the first surface Z of the first insulating layer 50; a second conductor circuit 158L for fingerprint authentication that is formed on the third surface F of the second insulating layer 150
Data Source
AI summary
A printed wiring board includes a first insulating layer, a first conductor circuit including fingerprint authentication circuitry and embedded in the first insulating layer such that the first circuit has exposed surface exposed from surface of the first insulating layer, a second insulating layer on which the first insulating layer is formed, a second conductor circuit including fingerprint authentication circuitry and embedded in the second insulating layer such that the second circuit has exposed surface exposed from surface of the second insulating layer and is interposed between the first and second insulating layers, and a solder resist layer formed on the surface of the first insulating layer and covering the first circuit. The first and second circuits are positioned such that the first and second circuits are opposing each other across the first insulating layer and that a finger for fingerprint authentication is placed on the solder resist layer.