Smart Card Thermocompression Bonding With Carboxylated Polyamide Sheets
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Solution Overview
Problem
Existing smart card manufacturing methods using anisotropic conductive films and pastes face reliability issues due to loss of electrical conduction under high temperature and humidity conditions, leading to connection failures.
Innovation Solution
A smart card manufacturing 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 a crystalline polyamide having a terminal carboxyl group concentration of 0.5 mgKOH/g or more, to enhance solder wettability and connection reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional anisotropic conductive film or paste is used for mounting IC chip, then electrical connection is established, but connection reliability is lost under high temperature and humidity conditions due to resin expansion
Solution Approach 1:
The invention changes the chemical composition parameters of the binder by specifying a terminal carboxyl group concentration of 0.5 mgKOH/g or more in the crystalline polyamide. This parameter change enables the binder to maintain dimensional stability under high temperature and humidity conditions while preventing resin expansion that would disrupt electrical conduction, thereby resolving the reliability issue without sacrificing compositional stability
Solution Approach 2:
The invention creates a composite adhesive sheet combining crystalline polyamide binder with specific carboxyl group concentration, solder particles of non-eutectic alloy, and conductive particles. This composite structure leverages the dimensional stability of crystalline polyamide, the metallurgical bonding capability of non-eutectic solder, and the conductive properties of conductive particles to simultaneously achieve reliable electrical connection and resistance to environmental degradation
2Reliability
If eutectic alloy solder particles are used, then bonding is achieved, but solder wettability is insufficient and connection reliability is reduced
Solution Approach 1:
The invention changes the alloy composition parameter by specifying non-eutectic alloy solder particles instead of eutectic alloy. This parameter change extends the molten state duration of the solder during thermocompression bonding, allowing more time for the solder to wet the metal surfaces and form reliable metallurgical bonds, thereby improving both wettability and connection reliability
Solution Approach 2:
The invention ensures continuous useful action by maintaining solder particles in a semi-molten state for an extended period during the bonding process. This continuity allows the solder to progressively wet the metal surfaces and form strong metallurgical bonds throughout the bonding cycle, rather than rapidly solidifying as with eutectic alloys, thereby achieving superior connection reliability
3Reliability
If crystalline polyamide with low terminal carboxyl group concentration is used, then binder properties are maintained, but solder wettability and connection reliability are insufficient
Solution Approach 1:
The invention changes the chemical composition parameter by specifying a terminal carboxyl group concentration of 0.5 mgKOH/g or more in the crystalline polyamide binder. This parameter change enhances the chemical reactivity and surface interaction capability of the binder, improving solder wettability and promoting metallurgical bonding between solder particles and metal surfaces, thereby achieving superior connection reliability
Solution Approach 2:
The crystalline polyamide binder with high terminal carboxyl group concentration acts as an intermediary substance that facilitates metallurgical bonding between the non-eutectic alloy solder particles and the metal surfaces. The carboxyl groups in the binder chemically interact with both the solder and metal surfaces, enabling strong adhesion and reliable electrical connection while maintaining the dimensional stability of the adhesive sheet
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 method improves solder wettability, ensuring excellent connection reliability and bending resistance by maintaining the solder particles in a semi-molten state longer, preventing resin swelling and enhancing electrical continuity.
Implementation Method 1
thermocompression bonding a card member and an IC chip with a conductive particle-containing hot-melt adhesive sheet interposed therebetween
Implementation Method 2
improve the solder wettability of the non-eutectic alloy by the crystalline polyamide having a carboxyl group
Implementation Method 3
maintaining the solder particles in a semi-molten state longer
Implementation Method 4
enables electrically-conductive particles to be metallurgically bonded to each other and to metal surfaces contacted by the adhesive material during bonding
Implementation Method 5
when the smart card is put into a reliability test such as a high temperature and high humidity test, the conduction is sometimes lost due to the expansion of the resin
Data Source
Figure 1~2
AI summary
Provided is 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 (10) and an IC chip (20) 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.