Solder Alloy Composition for Vibration-Resistant Automotive Joints
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Solution Overview
Problem
Existing solder alloys for in-vehicle electronic circuits lack sufficient impact resistance and vibration resistance, particularly in environments with extreme temperature fluctuations, and their evaluation methods are ambiguous, necessitating a design that enhances both tensile strength and vibration resilience.
Innovation Solution
A solder alloy composition with specific mass percentages of Ag, Cu, Bi, Sb, Ni, and Co is developed, optimizing the Ni and Co content to prevent interface fractures and increasing Bi and Sb content to enhance tensile strength and vibration resistance, while maintaining a balance to prevent crack extension and ensure reliable bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the solder alloy uses traditional composition (Sn-3Ag-0.5Cu), then the manufacturing process is simple and cost is low, but the bonding portion fractures under temperature difference and vibration
Solution Approach 1:
The patent modifies the alloy composition parameters by adding specific elements (Ni: 0.01-0.1 mass%, Co: 0.001-0.1 mass%, Bi: 2.0-5.0 mass%, Sb: 1.0-3.0 mass%) to the traditional Sn-Ag-Cu base composition. These parameter changes transform the alloy's microstructure and mechanical properties, enabling it to resist fracture under temperature cycling and vibration while maintaining manufacturability through conventional soldering processes.
Solution Approach 2:
The patent creates a composite solder alloy system by combining multiple elements (Sn, Ag, Cu, Ni, Co, Bi, Sb) that work synergistically. The Ni and Co form intermetallic compounds that strengthen the bonding interface, while Bi and Sb modify the microstructure to improve ductility and fracture resistance. This composite material approach resolves the contradiction by achieving high reliability through compositional complexity while maintaining process simplicity.
2Strength
If the solder alloy increases tensile strength through composition optimization, then the vibration resistance improves, but the bonding becomes too hard and loses effective soldering properties
Solution Approach 1:
The patent carefully controls the concentration parameters of strengthening elements (Ni: 0.01-0.1 mass%, Co: 0.001-0.1 mass%, Bi: 2.0-5.0 mass%, Sb: 1.0-3.0 mass%) to achieve optimal balance. These parameter ranges provide sufficient tensile strength for vibration resistance while preventing excessive hardening that would compromise wetting and soldering effectiveness. The balanced composition ensures both high strength and manufacturability.
3Reliability
If the solder alloy uses high Bi and Sb content to prevent crack extension, then the vibration resistance improves, but the alloy becomes too hard and loses ductility
Solution Approach 1:
The patent optimizes the parameters of Bi (2.0-5.0 mass%) and Sb (1.0-3.0 mass%) content to achieve the right balance between crack resistance and ductility. This controlled compositional adjustment allows the alloy to resist crack extension under vibration while maintaining sufficient ductility for effective bonding and stress absorption, resolving the contradiction between reliability and compositional stability.
Data Source
AI summary
A solder alloy having an alloy composition consisting of, in mass %, Ag: 1% to 4%, Cu: 0.5% to 0.8%, Bi: more than 4.8% and 5.5% or less. Sb: more than 1.5% and 5.5% or less, Ni: 0.01% or more and less than 0.1%, Co: more than 0.001% and 0.1% or less, the balance being Sn. The alloy composition satisfies the following three relationships: 0.020%≤Ni+Co≤0.105%; 9.1%≤Sb+Bi≤10.4%; and 4.05×10−3≤(Ni+Co)/(Bi+Sb)≤1.00×10−2, where Ni, Co, Bi, and Sb each represent a content (mass %) thereof in the solder alloy.