Lead-Free Solder Composition for Thermal Fatigue Resistance
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Solution Overview
Problem
Conventional lead-free solders lack sufficient thermal fatigue resistance for severe temperature environments, such as an automobile engine compartment, leading to connection failures due to cleavage and disconnection in electronic component assemblies.
Innovation Solution
A lead-free solder material comprising 1.0-4.0% Ag, 4.0-6.0% In, 0.1-1.0% Bi, and 1% or less of Cu, Ni, Co, Fe, or Sb, which promotes the formation of a Cu—Sn intermetallic compound, providing a blocking structure that enhances thermal and mechanical stability and prevents cleavage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If In content is increased to improve stress relaxation, then thermal fatigue resistance improves, but formation of continuous solder base phase increases which may promote cleavage
Solution Approach 1:
The patent optimizes the In content parameter within a specific range (4.0-6.0% by weight) to achieve the desired balance. This parameter control ensures sufficient stress relaxation capability while preventing excessive continuous solder base phase formation that would promote cleavage, thereby resolving the contradiction between thermal fatigue resistance and connection strength.
Solution Approach 2:
The patent creates local quality differentiation in the solder joint structure by controlling the distribution and morphology of intermetallic compounds versus solder base phase. The specific composition promotes localized intermetallic compound formation at critical interfaces while maintaining adequate solder base phase for stress relaxation, resolving the contradiction through spatial differentiation of material properties.
2Strength
If Bi content is increased to improve connection strength, then mechanical strength improves, but thermal fatigue resistance deteriorates
Solution Approach 1:
The patent optimizes Bi content within a narrow range (0.1-1.0% by weight) to achieve the balance between connection strength and thermal fatigue resistance. This parameter control prevents excessive Bi from forming continuous brittle phases that would deteriorate thermal fatigue resistance, while still providing sufficient connection strength through controlled Bi distribution.
3Strength
If Ag content is increased to improve connection strength, then mechanical strength improves, but thermal fatigue resistance deteriorates
Solution Approach 1:
The patent optimizes Ag content within a specific range (1.0-4.0% by weight) to balance connection strength and thermal fatigue resistance. This parameter control ensures sufficient Ag-based intermetallic compound formation for strength while preventing excessive Ag content from creating continuous brittle phases that would deteriorate thermal fatigue resistance in severe temperature environments.
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 material achieves high thermal fatigue resistance and reduces connection failures, maintaining product functionality even after 3000 cycles in a heat cycle test between −40° C. and 150° C., by forming a stable intermetallic compound that blocks the interface between the electronic component and substrate.
Implementation Method 1
promotes the formation of a Cu—Sn intermetallic compound
Implementation Method 2
providing stress relaxation and a blocking structure to prevent cleavage
Data Source
AI summary
A solder material includes 1.0-4.0% by weight of Ag, 4.0-6.0% by weight of In, 0.1-1.0% by weight of Bi, 1% by weight or less (excluding 0% by weight) of a sum of one or more elements selected from the group consisting of Cu, Ni, Co, Fe and Sb, and a remainder of Sn. When a copper-containing electrode part of an electronic component is connected to a copper-containing electrode land of a substrate by using this solder material, a part having an excellent stress relaxation property can be formed in the solder-connecting part and a Cu—Sn intermetallic compound can be rapidly grown from the electrode land and the electrode part to form a strong blocking structure.