Ag-Sn Intermetallic Composition for High-Temperature Lead-Free Solder
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Solution Overview
Problem
Current lead-free solder technologies fail to meet the high temperature and mechanical stress requirements of advanced electronic chips, such as those using SiC or GaN, as they have melting points below 250°C, and existing synthesis methods for Ag-Sn intermetallic compounds are expensive and yield impure phases with uncontrolled morphology.
Innovation Solution
A polyol process involving successive steps of silver salt reduction, tin introduction, reduction, and heating to produce a high-purity Ag-Sn intermetallic compound with a melting point above 470°C, using specific silver and tin salts, protective agents, and reducing agents, followed by recovery through washing and drying to achieve pure phase Ag-Sn intermetallics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If metallurgical synthesis from bulk materials is used, then Ag-Sn intermetallic compound is obtained, but the method is expensive and produces impure phases with uncontrolled morphology
Solution Approach 1:
The invention changes the chemical parameters of the synthesis process by using aqueous salt solutions instead of bulk materials, controlling pH, temperature, and addition rates to achieve pure phase formation with controlled morphology at lower cost
Solution Approach 2:
The invention introduces intermediary substances including protective agents (surfactants, polymers), reducing agents, and chelating agents that mediate the formation process to control nucleation and growth, ensuring phase purity and desired morphology
2Manufacturing precision
If polyol process is used to obtain Ag-Sn intermetallic particles, then finely divided particles are produced, but pure phases cannot be obtained and tin forms as majority phase with impurities
Solution Approach 1:
The invention changes the chemical environment from polyol to aqueous solution, adjusts pH to basic conditions, and controls temperature and addition rates to reverse the phase formation sequence, making Ag-Sn intermetallic the majority phase instead of tin
Solution Approach 2:
The invention uses protective agents and chelating agents as intermediaries to control the reduction process and prevent tin precipitation, ensuring Ag-Sn intermetallic compound forms as the dominant phase with controlled particle size
3Temperature
If current lead-free solders are used, then melting temperature is between 200°C and 250°C, but they cannot operate at temperatures above 250°C required for SiC or GaN chips
Solution Approach 1:
The invention creates a composite intermetallic compound Ag-Sn with specific stoichiometry (Ag3Sn or AgSn) that combines the properties of silver and tin to achieve a eutectic composition with melting point above 470°C, enabling reliable operation at high temperatures
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 process results in a cost-effective, high-purity Ag-Sn intermetallic compound suitable for lead-free soldering and toner printing, capable of operating above 250°C with controlled particle morphology and high melting point, addressing the limitations of existing methods.
Implementation Method 1
during this step the silver salt is reduced by the polyol solvent
Implementation Method 2
during this stage the tin salt is reduced by the reducing agent
Implementation Method 3
the solution is brought to a temperature T1 greater than or equal to 140°C and less than or equal to 180°C
Data Source
Figure 1
Figure 2~3
Figure 4~5b
AI summary
A method for synthesising an Ag-Sn intermetallic compound comprising the following sequence of steps: - a step of providing a mixture (E1) during which a solution of a mixture of a silver salt and a protective agent in a polyol solvent is produced, - a first heating step (E2) during which the solution is heated to a temperature T1 greater than or equal to 140°C and less than or equal to 180°C for a time t1 greater than or equal to 5 minutes and less than or equal to 1 hour, - a step of introducing a tin salt (E3) during which a tin salt and sodium hydroxide are introduced into the solution, - a second heating step (E4) during which the solution is heated to a temperature T2 greater than or equal to 140°C and less than or equal to 180°C for a time t2 greater than or equal to 5 minutes and less than or equal to 1 hour, - a reduction step (E5) during which a reducing agent is introduced into the solution, - a third heating step (E6) during which the solution is heated to a temperature T3 greater than or equal to 160°C and less than or equal to 240°C for a time t3 greater than or equal to 30 minutes and less than or equal to 24 hours, and - a recovery step (E7) during which the Ag-Sn intermetallic compound obtained is recovered.