Solder Joint Touch Sensor Module for Low Resistance

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Solution Overview

Problem

Conventional anisotropic conductive films (ACF) used in touch sensor modules face limitations in reducing contact resistance between touch sensors and flexible printed circuit boards (FPCBs) and enhancing the tensile strength of FPCBs, hindering the development of thinner, lighter, and more reliable display devices.

Innovation Solution

A touch sensor module is designed with a solder joint that includes solder balls and flux, where the pad portions of the touch sensor and terminal portions of the FPCB are electrically connected through metal bonding, optimizing the ratio of solder ball diameter to gap size and flux content to achieve stable electrical properties and increased tensile strength.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional anisotropic conductive film (ACF) is used to connect touch sensor and FPCB, then the connection is simple, but the contact resistance is high and tensile strength is insufficient

Engineering Contradiction:

Improvecontact resistanceVSAvoidconnection structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention changes the connection method from ACF-based mechanical/physical contact to solder joint-based metal bonding, optimizing parameters such as solder ball diameter ratio (1:0.2-0.6), flux content (5-40 wt%), heating temperature (200-400°C), and pressing force (0.1-10 MPa) to achieve low contact resistance and high reliability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention uses composite solder paste material consisting of solder balls (95-99.5 wt%) and flux (5-40 wt%), combining the advantages of metal bonding (low resistance) with flux-assisted bonding (improved wetting and strength) to resolve the contradiction between simple connection and low contact resistance

Inventive Principle:

Principle #40Composite materials

2Strength

If conventional ACF is used for connection, then the manufacturing process is simple, but the tensile strength of FPCB is not enhanced

Engineering Contradiction:

Improvetensile strength of FPCBVSAvoidmanufacturing process

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The invention introduces controlled heating (200-400°C) and pressing (0.1-10 MPa) parameters during solder joint formation, which not only creates electrical connection but also enhances mechanical bonding strength through metal diffusion and intermetallic compound formation, thereby improving tensile strength while maintaining manufacturability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention replaces the purely mechanical/physical contact of ACF with metal bonding through heated and pressed solder joints, where thermal and mechanical energy are converted into strong metallurgical bonds, significantly enhancing FPCB tensile strength

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Area of stationary object

If larger pad portions are used for connection, then electrical connection is more stable, but the bezel region increases and screen size decreases

Engineering Contradiction:

Improvepad portion areaVSAvoidscreen area

Core Design Contradiction:

Area of stationary objectVSArea of moving object

Solution Approach 1:

The invention optimizes solder ball diameter (1:0.2-0.6 ratio to gap size) and flux content (5-40 wt%) to achieve reliable electrical connection with minimal pad area, reducing the need for large pad portions and thereby minimizing bezel region while maintaining connection stability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention applies localized high-density solder balls and optimized flux distribution only at the critical connection points between pad portions and terminal portions, achieving stable electrical connection with concentrated material usage rather than widespread large pads

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

This configuration significantly lowers contact resistance, reduces the area of touch sensor pads, and enhances the reliability of the touch sensor module, enabling a larger screen size with minimized bezel regions and improved tensile strength for flexible displays.

Implementation Method 1

the pad portions and the terminal portions are electrically connected through the solder balls compressed by heating and pressing

Methodology Applied

Scientific EffectMetal bonding: Soldering

Implementation Method 2

the solder joint includes a solder paste including solder balls and a flux

Methodology Applied

Scientific EffectFlux action: Oxidation

Data Source

PatentUS11445615B2Touch sensor module and image display device comprising same

Publication Date: 2022.09.13 DONGWOO FINE CHEM CO LTD

AI summary

The present invention relates to a touch sensor module and an image display device including the same. The touch sensor module includes a touch sensor including pad portions, a flexible printed circuit board (FPCB) including terminal portions, and a solder joint interposed between the touch sensor and the flexible printed circuit board, in which the solder joint includes a solder paste including solder balls and a flux, the pad portions and the terminal portions are electrically connected through the solder balls compressed by heating and pressing, the flux is used in an amount of 5 to 40 wt % based on the total weight of the solder paste, and the ratio of the diameter of the solder balls included in the solder paste to the gap between the pad portions of the touch sensor and the terminal portions of the flexible printed circuit board is 1:0.2-0.6.