Low-Temperature Bonding Material for Remelt-Resistant Joints
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Solution Overview
Problem
Existing bonding materials for printable electronics face challenges with low heat resistance due to remelting at elevated temperatures and the need for long annealing times, which can cause thermal damage to resin substrates.
Innovation Solution
A bonding material comprising a solder alloy with a median diameter of 100 nm to 2000 nm, made from Sn, Bi, In, and other components with a melting point of ≤100°C, combined with Cu nanoparticles of 50 nm to 500 nm diameter, and a flux component. The Cu nanoparticles have a protective film that separates at temperatures above the solder alloy's melting point but below 100°C, ensuring optimal intermetallic compound formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a PET film base material is used to achieve flexibility and low cost, then flexibility and cost-effectiveness are improved, but heat resistance deteriorates because the low glass transition temperature prevents withstanding soldering temperatures
Solution Approach 1:
The patent changes the bonding temperature parameter from conventional high temperatures (200-300°C for silver paste curing or soldering) to a low temperature range (50-100°C) that matches the PET film's heat resistance capabilities. This parameter change enables the use of PET film base materials while maintaining bonding functionality.
Solution Approach 2:
The patent uses a composite bonding material consisting of low melting point alloy particles (Sn-Bi-In system) combined with organic binder. This composite structure enables bonding at low temperatures while forming heat-resistant intermetallic compounds (Cu6Sn5, Cu3Sn, Cu9In7) that provide thermal stability up to 100°C or higher, resolving the contradiction between low-cost PET film usage and heat resistance requirements.
2Strength
If silver paste with thermosetting resin is used for bonding, then bonding strength is improved, but heat resistance deteriorates because remelting occurs at temperatures above the curing temperature
Solution Approach 1:
The patent fundamentally changes the bonding mechanism from thermosetting resin curing at high temperatures to low melting point alloy-based bonding at 50-100°C. This parameter change eliminates the remelting problem while maintaining bonding strength through intermetallic compound formation.
Solution Approach 2:
The patent replaces expensive silver paste with a cost-effective low melting point alloy composition (Sn-Bi-In system) that achieves bonding functionality at lower temperatures. The alloy particles are consumed during bonding to form intermetallic compounds, providing both bonding strength and heat resistance without the remelting issues of conventional silver paste.
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 bonding material achieves high heat resistance by forming intermetallic compounds with high melting points, preventing remelting at temperatures up to 100°C, and allowing bonding at a low temperature for a short time, thus minimizing thermal damage to resin substrates.
Implementation Method 1
a solder alloy having a median diameter D50 of 100 nm to 2000 nm, made from Sn, Bi, In, and other unavoidable components, and having a melting point of less than or equal to 100° C.
Implementation Method 2
the metal nanoparticles include a protective film on a surface of the metal nanoparticles, the protective film separating at a temperature higher than a melting point of the solder alloy and lower than 100° C.
Implementation Method 3
a weight ratio between the solder alloy and the metal nanoparticles is a ratio at which all Sn and In contained in the solder alloy become intermetallic compounds with the metal nanoparticles in an equilibrium state diagram
Data Source
AI summary
A bonding material includes a solder alloy having a median diameter D50 of 100 nm to 2000 nm, made from Sn, Bi, In, and other unavoidable components, and having a melting point of less than or equal to 100° C., metal nanoparticles that are Cu nanoparticles having a median diameter D50 of 50 nm to 500 nm, and a flux, wherein the metal nanoparticles include a protective film on a surface of the metal nanoparticles, the protective film separating at a temperature higher than a melting point of the solder alloy and lower than 100° C., and a weight ratio between the solder alloy and the metal nanoparticles is a ratio at which all Sn and In contained in the solder alloy become intermetallic compounds with the metal nanoparticles in an equilibrium state diagram.