Sn-Bi Solder Alloy Composition for Low-Melt Joint Reliability
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Solution Overview
Problem
Sn-Bi-based lead-free solder alloys face challenges with brittleness and thermal fatigue, leading to reduced mechanical strength and reliability, especially in electronic components with low heat resistance, where existing solutions do not adequately balance melting point and physical characteristics.
Innovation Solution
A lead-free solder alloy composition with 32-40 mass% Bi, 0.1-1.0 mass% Sb, 0.1-1.0 mass% Cu, and 0.005-0.1 mass% Ni, along with optional elements like Ag, Fe, Co, Ga, Mn, V, Ge, and P, to maintain a low melting point while enhancing physical characteristics and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a large amount of Bi is blended in an Sn-Bi-based solder alloy to lower the melting point, then the melting point is reduced, but the solder alloy becomes brittle and mechanical strength decreases
Solution Approach 1:
The invention optimizes the Bi content parameter within a specific range (32-40 mass%) rather than using a large amount, and introduces additional elements (Sb: 0.1-1.0 mass%, Cu: 0.1-1.0 mass%, Ni: 0.005-0.1 mass%) to modify the alloy's physical characteristics. This parameter optimization resolves the contradiction by finding the optimal balance point where the melting point is sufficiently lowered while mechanical strength is maintained through compositional refinement.
Solution Approach 2:
The invention creates a composite solder alloy system by combining Sn, Bi, Sb, Cu, and Ni elements in specific proportions. This composite material approach allows the alloy to benefit from the low melting point contribution of Bi while the other elements (particularly Sb and Cu) provide strength and ductility, thus resolving the contradiction between low melting point and mechanical strength.
2Temperature
If an Sn-Bi-based solder alloy is used for electronic components with low heat resistance, then the melting point is lowered, but thermal fatigue causes cracks and long-term reliability is low
Solution Approach 1:
The invention optimizes the compositional parameters within specific ranges (Bi: 32-40 mass%, Sb: 0.1-1.0 mass%, Cu: 0.1-1.0 mass%, Ni: 0.005-0.1 mass%) to achieve a balance between low melting point and high reliability. The controlled addition of Sb and Cu improves thermal fatigue resistance, while Ni suppresses detrimental intermetallic compound formation, thereby enhancing long-term reliability without sacrificing the low melting point advantage.
Solution Approach 2:
The invention uses inexpensive elements (Sb, Cu, Ni) instead of expensive In to achieve similar or better performance. These elements provide the necessary thermal fatigue resistance and reliability improvement at lower cost, making the solder alloy economically viable for widespread use in electronic components with low heat resistance.
3Temperature
If In is used to lower the melting point of lead-free solder alloy, then the melting point is reduced, but the cost increases due to expensive In
Solution Approach 1:
The invention replaces expensive In with cheaper alternative elements (Bi, Sb, Cu, Ni) that can achieve similar or better performance. By using Bi in a controlled amount (32-40 mass%) combined with small additions of Sb, Cu, and Ni, the alloy achieves low melting point and improved physical characteristics at a fraction of the cost of In-based alloys, making it economically advantageous.
Solution Approach 2:
The invention changes the compositional parameters from In-based to a Sn-Bi-Sb-Cu-Ni system with optimized ratios. This parameter change maintains the low melting point characteristic while dramatically reducing material cost, as Bi, Sb, Cu, and Ni are significantly cheaper than In, thus resolving the contradiction between melting point reduction and cost.
Data Source
Figure 1A~1C
Figure 2
Figure 3A~3C
AI summary
A lead-free solder alloy contains: 32 mass% or more and 40 mass% or less of Bi; 0.1 mass% or more and 1.0 mass% or less of Sb; 0.1 mass% or more and 1.0 mass% or less of Cu; 0.001 parts by mass or more and 0.1 parts by mass or less of Ni; and a remainder of Sn with unavoidable impurities, or the lead-free solder alloy further contains specific elements in amounts in predetermined ranges. Accordingly, it is possible to form a solder joint part that maintains a low level of the melting point of the Sn-Bi-based solder alloy, has better physical characteristics than those in conventional art, and has higher reliability than those in conventional art.