Sn-Bi Solder Alloy Composition for Heat Cycle and Electromigration Resistance
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Solution Overview
Problem
Conventional solder alloys with low melting points, such as Sn-Bi, face challenges with high ductility leading to mechanical and electrical reliability issues, particularly in high-temperature environments and under increased current densities, where electromigration causes solder joint degradation and rupture.
Innovation Solution
A solder alloy composition with specific adjustments in Bi, Ag, Cu, Ni, and Sb content, forming intermetallic compounds to enhance hardness, heat cycle resistance, and electromigration resistance, while controlling crystal grain size and structure homogeneity to prevent Bi segregation and excessive refinement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If Bi content is increased to achieve low melting point, then melting temperature is reduced, but Bi segregation occurs causing coarse Bi phases that deteriorate mechanical properties
Solution Approach 1:
The patent extracts Bi from the continuous matrix phase and confines it to discrete, fine distributed phases. By limiting Bi to specific content ranges and controlling its phase distribution through the presence of other elements, the patent prevents Bi segregation and coarse phase formation while maintaining the low melting point advantage
Solution Approach 2:
The patent creates local quality differences by distributing Bi heterogeneously in fine phases throughout the Sn matrix rather than uniformly. This local distribution strategy, combined with the presence of intermetallic compounds, prevents coarse Bi phase formation while maintaining overall compositional stability
2Reliability
If ductility is increased to improve drop impact resistance, then deformation tolerance is improved, but the solder joint becomes too soft leading to excessive deformation and reliability degradation
Solution Approach 1:
The patent optimizes the ductility-hadness balance by precisely controlling alloy composition parameters, particularly the content ratios of Bi, Ag, Cu, Ni, and Sb. This parameter optimization ensures the solder alloy has sufficient ductility for impact resistance while maintaining adequate hardness to prevent excessive deformation
Solution Approach 2:
The patent creates a composite microstructure with multiple phases that provide complementary properties. The Sn matrix provides ductility for impact resistance, while the distributed Bi phases and intermetallic compounds (Ag3Sn, Cu6Sn5, Ni3Sn4) provide hardness and structural stability, achieving both drop impact resistance and deformation control
3Productivity
If current density is increased to improve productivity, then manufacturing efficiency is improved, but electromigration increases causing solder joint degradation and rupture
Solution Approach 1:
The patent changes the compositional parameters by adding specific elements (Ag, Cu, Ni, Sb) in controlled amounts that enhance electromigration resistance. These compositional modifications create a more stable microstructure that resists electromigration effects even under high current density conditions, enabling high productivity without sacrificing 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 optimized solder alloy achieves high hardness in high-temperature environments, improved heat cycle resistance, and reduced electromigration, maintaining mechanical and electrical reliability even under harsh conditions.
Implementation Method 1
during solidification of the above-described Sn-Bi solder alloy with a high content of Bi, Bi segregates in Sn and coarse Bi phases precipitate
Implementation Method 2
Bi segregates in Sn and coarse Bi phases precipitate
Implementation Method 3
forming intermetallic compounds to enhance hardness, heat cycle resistance, and electromigration resistance
Data Source
AI summary
Provided are a solder, a solder alloy, a solder ball, a solder paste, and a solder joint, which have a low melting point, high hardness in a high-temperature environment, heat cycle resistance, and electromigration resistance. The solder alloy has an alloy composition that includes, by mass %, Bi: 30 to 60%, Ag: 0.7 to 2.0%, Cu: more than 0% and 1.00% or less, Ni: 0.01 to 1.00%, Sb: 0.2 to 1.5%, with the balance being Sn.