Fingerprint Sensor ESD Conductor for Flexible Substrates

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Electrostatic discharge (ESD) poses a significant risk to sensitive circuitry in fingerprint sensing electronics, particularly in flexible sensors with non-conductive substrates like polyimide, where charge buildup can lead to damage when the path of least resistance is found and the charge dissipates to the sensor circuitry.

Innovation Solution

Incorporating an electrostatic discharge (ESD) conductor on the non-conductive surface of fingerprint sensing circuits, positioned between the area where a fingerprint is swiped and the sensor circuit, to safely dissipate accumulated electrostatic charge by providing a path of least resistance to ground, thereby protecting the sensitive components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a non-conductive substrate is used for the fingerprint sensor, then the sensor can be made flexible and allow user touch without direct contact with circuitry, but electrostatic charge accumulates on the surface and can discharge to damage the sensor circuitry

Engineering Contradiction:

Improveflexibility and user touch capabilityVSAvoidelectrostatic discharge damage

Core Design Contradiction:

Adaptability or versatilityVSObject-affected harmful factors

Solution Approach 1:

A conductive layer is introduced as an intermediary between the non-conductive substrate surface and the sensor circuitry. This conductive layer serves as a charge dissipation path, allowing electrostatic charge to be safely discharged without reaching the sensitive circuit components, thus protecting against ESD damage while maintaining the flexible non-conductive substrate structure

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The ESD protection is implemented by adding a dimensional layer (conductive layer) between the substrate surface and the circuitry, creating a new protective dimension that intercepts and redirects electrostatic charge before it can reach vulnerable components

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Ease of operation

If the sensor allows direct user contact with the sensing surface, then fingerprint sensing is convenient and intuitive, but the circuitry is exposed to electrostatic discharge from the user's body

Engineering Contradiction:

Improveuser touch convenienceVSAvoidcircuitry protection from ESD

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The conductive layer acts as a mediator between the user's finger and the sensor circuitry. It allows the user to directly touch the sensing surface for convenient operation while simultaneously providing a safe path for electrostatic charge from the user's body to dissipate without damaging the underlying circuit components

Inventive Principle:

Principle #24Intermediary (Mediator)

3Strength

If the polyimide substrate is used to isolate the user's finger from the circuitry, then mechanical protection is provided, but electrostatic charge can still build up and discharge around the edges to the circuitry

Engineering Contradiction:

Improvemechanical isolationVSAvoidedge discharge damage

Core Design Contradiction:

StrengthVSObject-affected harmful factors

Solution Approach 1:

The conductive layer is selectively positioned at critical locations where electrostatic discharge is most likely to occur, such as around the edges of the polyimide substrate near the circuitry. This localized ESD protection addresses the specific vulnerability at edge regions while maintaining the overall mechanical isolation properties of the polyimide substrate

Inventive Principle:

Principle #3Local quality

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

Effectively prevents damage to sensitive electronic components by ensuring that electrostatic charge is safely discharged from the non-conductive surface, reducing the risk of ESD-induced damage to ICs and other circuitry, while maintaining user convenience by allowing direct finger contact without the need for grounding.

Implementation Method 1

An electrostatic discharge conductor is applied to the non-conductive surface and is located between an area where a fingerprint is swiped and the sensor circuit. The electrostatic discharge conductor discharges the electrostatic charge resulting from a user swiping a fingerprint across the first surface.

Methodology Applied

Scientific EffectElectrostatic discharge: Electrostatic Discharge

Data Source

PatentUS8107212B2Apparatus and method for protecting fingerprint sensing circuitry from electrostatic discharge

Publication Date: 2012.01.31 SYNAPTICS INC

AI summary

A fingerprint sensor in accordance with the invention includes a non-conductive substrate providing a first surface onto which a user can apply a fingerprint to be sensed. A sensor circuit is applied to a second surface of the non-conductive substrate opposite the first surface to sense a fingerprint when juxtaposed proximally thereto. An electrostatic discharge conductor is applied to the non-conductive surface and is located between an area where a fingerprint is swiped and the sensor circuit. The electrostatic discharge conductor discharges electrostatic charge resulting from a user swiping a fingerprint across the first surface.