Solder Alloy Thermal Fatigue Resistance
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Solution Overview
Problem
Conventional solder alloys used in electronic devices for vehicles lack sufficient thermal fatigue resistance and mechanical characteristics at high temperatures, particularly above 150°C, leading to potential cracking and failure under thermal cycling.
Innovation Solution
A solder alloy composition of 0.5 to 1.25 mass% Sb, with In content satisfying specific relationships, 0.5 to 1.2 mass% Cu, 0.1 to 3.0 mass% Bi, and 1.0 to 4.0 mass% Ag, forming an alloy structure with a γ phase and β-Sn phase, where Sb is subjected to solid solution, enhancing thermal fatigue resistance and ductility at temperatures up to 175°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solder alloys are used for bonding electronic components to circuit boards, then the soldering process can be completed, but the solder bonding portion deteriorates mechanically at high temperatures and develops cracks under thermal cycling
Solution Approach 1:
The invention changes the chemical composition parameters of the solder alloy by adding specific amounts of Sb (0.01-5 mass%), Cu (0.01-5 mass%), Ni (0.01-5 mass%), and Co (0.01-5 mass%) to the Sn-Ag-In-Bi base alloy. These parameter changes in composition lead to the formation of new intermetallic compounds (Sb-Sn, Cu-Sn, Ni-Sn, Co-Sn) that improve high-temperature strength and thermal fatigue resistance while maintaining solderability.
Solution Approach 2:
The invention creates a composite microstructure in the solder alloy by forming multiple intermetallic compound phases (Sb-Sn, Cu-Sn, Ni-Sn, Co-Sn) distributed within the Sn-rich matrix. This composite structure combines the ductility of the Sn matrix with the strength and thermal stability of the intermetallic compounds, resulting in improved mechanical characteristics at high temperatures and enhanced crack resistance under thermal cycling.
2Reliability
If the solder alloy contains elements to improve thermal fatigue resistance, then reliability increases, but the complexity of alloy composition control increases
Solution Approach 1:
The invention establishes specific parameter ranges for each alloying element (Sb: 0.01-5 mass%, Cu: 0.01-5 mass%, Ni: 0.01-5 mass%, Co: 0.01-5 mass%) to achieve the desired thermal fatigue resistance. By defining these controlled parameter ranges, the invention balances the need for improved reliability with manageable composition control, avoiding excessive complexity while ensuring consistent performance.
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 solder alloy exhibits improved tensile strength and ductility at high temperatures, preventing self-transformation and maintaining reliability even after 500 temperature cycles, thus providing excellent thermal fatigue resistance and mechanical characteristics at 175°C.
Implementation Method 1
forming an alloy structure with a γ phase and β-Sn phase, where Sb is subjected to solid solution
Data Source
Figure 1~2
Figure 3
AI summary
A solder alloy contains 0.5 mass% or more and 1.25 mass% or less of Sb, In which satisfies 5.5≤[In]≤5.50+1.06[Sb] in a case of 0.5≤[Sb]≤1.0; and 5.5≤[In]≤6.35+0.212[Sb] in a case of 1.0<[Sb]≤1.25 (in the expression, [Sb] indicates the Sb content percentage (mass%) and [In] indicates the In content percentage (mass%)), 0.5 mass% or more and 1.2 mass% or less of Cu, 0.1 mass% or more and 3.0 mass% or less of Bi, and 1.0 mass% or more and 4.0 mass% or less of Ag. The remainder is formed from Sn.