Sn-Sb-Ag-Cu Solder Alloy High-Temperature Phase Stability
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Solution Overview
Problem
High-temperature lead-free solder alloys, such as Sn-Sb-Ag-Cu, often form low melting point phases during slow cooling, leading to reduced connection reliability and potential fracture of solder joints in semiconductor devices operating at high temperatures.
Innovation Solution
A Sn-Sb-Ag-Cu solder alloy composition with specific mass percentages of Sb (35-40%), Ag (13-18%), and Cu (6-8%), along with optional Ni (0.01-0.1%), is formulated to prevent the formation of low melting point phases, ensuring a solder joint with a melting start temperature of at least 280°C and comprising exclusively high melting point intermetallic compounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a Sn-Sb based solder alloy is used for high-temperature applications, then the operating temperature range is extended to 250-280°C, but a low melting point phase forms during slow cooling which melts at operating temperature and causes joint fracture
Solution Approach 1:
The invention changes the compositional parameters of the solder alloy by precisely controlling the content ratios of Sn, Sb, Ag, and Cu elements. By adjusting these parameters within specific ranges, the alloy achieves a eutectic temperature of 280°C or higher while preventing the formation of low melting point phases during slow cooling, thus resolving the contradiction between high-temperature operation and joint reliability
Solution Approach 2:
The invention creates a composite intermetallic compound structure consisting of multiple phases (SnSb, Ag3Sn, Cu6Sn5, Cu3Sn) with specific volume ratios. This composite structure ensures that all phases have high melting points and remain solid at operating temperatures, eliminating the harmful low melting point phase while maintaining structural integrity under thermal stress
2Quantity of substance
If conventional Sn-Sb-Ag-Cu solder alloys are used, then the material cost is reduced compared to Au-20Sn, but low melting point phases form during solidification segregation which compromise connection reliability
Solution Approach 1:
The invention optimizes the compositional parameters within the Sn-Sb-Ag-Cu system by specifying precise content ranges for each element and their ratio relationships. This parameter optimization prevents solidification segregation and low melting point phase formation while maintaining cost-effectiveness, achieving both economical and reliable soldering
3Stress or pressure
If slow cooling rate (1°C per second) is used during soldering, then thermal stress on components is reduced, but low melting point phase formation is promoted which leads to joint fracture at operating temperature
Solution Approach 1:
The invention applies preliminary anti-action by designing an alloy composition that preemptively prevents the formation of low melting point phases during the cooling process. The specific compositional ratios and intermetallic compound structure ensure that even under slow cooling conditions, no phase with melting point below operating temperature forms, thus counteracting the harmful effect of slow cooling before it can compromise joint reliability
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 alloy composition ensures excellent connection reliability by suppressing the formation of low melting point phases, maintaining strength and heat resistance even at slow cooling rates, and is suitable for high-temperature semiconductor applications without the need for rapid cooling.
Implementation Method 1
a low melting point phase which starts to melt at 230 - 240° C is formed in a soldered portion (also referred to as a solder joint) due to segregation during solidification (solidification segregation)
Implementation Method 2
the proportion of solid phases at 280° C is 100%
Data Source
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AI summary
A Sn-Sb-Ag-Cu based high-temperature lead-free solder alloy which has excellent connection reliability and which does not form a low melting point phase even when solidified by slow cooling is provided. It has an alloy composition consisting essentially of, in mass percent, Sb: 35 - 40 %, Ag: 13 - 18 %, Cu: 6 - 8 %, and a remainder of Sn.