Smart Card Hot-Melt Adhesive Sheet for Solder and Bending Reliability

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing smart card technologies using anisotropic conductive films experience reliability issues due to resin expansion during high temperature and humidity tests, leading to loss of electrical conduction.

Innovation Solution

A method involving thermocompression bonding with a conductive particle-containing hot-melt adhesive sheet, using solder particles of a non-eutectic alloy in a binder with crystalline polyamide having a carboxyl group, to improve solder wettability and connection reliability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If an anisotropic conductive film with conductive particles blended in a binder containing a crystalline resin is used, then electrical conduction is achieved, but the conduction is lost due to resin expansion during high temperature and high humidity tests

Engineering Contradiction:

Improveconnection reliabilityVSAvoidresin expansion

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the chemical composition parameters of the binder by introducing a carboxyl group-containing crystalline resin and controlling the molecular weight and crystallinity of the resin. This modifies the resin's expansion characteristics and improves its resistance to environmental factors, thereby maintaining electrical conduction reliability under high temperature and humidity conditions.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite adhesive material combining conductive particles with a specific binder system consisting of a carboxyl group-containing crystalline resin and a monomer. This composite structure leverages the flux effect of the carboxyl group to prevent resin expansion while maintaining electrical conductivity through the conductive particle network.

Inventive Principle:

Principle #40Composite materials

2Reliability

If conductive particles are used for electrical connection, then electrical conduction is achieved, but the connection is sensitive to environmental conditions causing conduction loss

Engineering Contradiction:

Improveelectrical conduction stabilityVSAvoidenvironmental resistance

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The carboxyl group-containing crystalline resin acts as an intermediary material between the conductive particles and the external environment. The carboxyl group provides a flux effect that protects the conductive particle network from environmental degradation, while the crystalline structure maintains stable electrical conduction properties under varying conditions.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Strength

If a binder containing crystalline resin is used, then structural integrity is maintained, but solder wettability may be insufficient without additional flux

Engineering Contradiction:

Improvestructural integrityVSAvoidsolder wettability

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The carboxyl group-containing crystalline resin performs multiple functions simultaneously: it provides structural integrity through its crystalline structure, acts as a flux agent through the carboxyl group to improve solder wettability, and maintains electrical conduction stability. This multi-functionality eliminates the need for separate flux additives while achieving both structural and electrical reliability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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

Enhances solder wettability and achieves excellent connection reliability and bending resistance by utilizing the flux effect of the carboxyl group in the crystalline polyamide, preventing resin swelling and maintaining electrical conductivity.

Implementation Method 1

improve the solder wettability of the non-eutectic alloy by the crystalline polyamide having a carboxyl group

Methodology Applied

Scientific EffectFlux effect: Wetting

Implementation Method 2

thermocompression bonding a card member and an IC chip with a conductive particle-containing hot-melt adhesive sheet interposed therebetween

Methodology Applied

Scientific EffectThermocompression bonding: Heating

Implementation Method 3

solder particles of a non-eutectic alloy

Methodology Applied

Scientific EffectMelting: Melting

Data Source

PatentUS20250250466A1Method for manufacturing smart card, smart card, and conductive particle-containing hot-melt adhesive sheet

Publication Date: 2025.08.07 DEXERIALS CORP

AI summary

A method for manufacturing a smart card capable of achieving excellent connection reliability and bending resistance, a smart card, and a conductive particle-containing hot-melt adhesive sheet. A conductive particle-containing hot-melt adhesive sheet containing solder particles of a non-eutectic alloy in a binder containing a crystalline polyamide having a carboxyl group is interposed between a card member and an IC chip and subjected to thermocompression bonding. The crystalline polyamide having a carboxyl group improves the solder wettability of the non-eutectic alloy, thereby achieving excellent connection reliability. This effect is considered to be a flux effect due to the carboxyl group present in the crystalline polyamide, and as a result, it is possible to prevent the decrease in the elastic modulus of the adhesive layer which would be caused by the addition of a flux compound and to achieve excellent bending resistance.