Low-Melting Sn-Bi Solder Alloy with Intermetallic Reinforcement
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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 the melting point of solder alloy is reduced to enable low-temperature soldering, then the soldering temperature is lowered, but the mechanical properties such as hardness and strength deteriorate
Solution Approach 1:
The patent employs composite material design by combining Sn-Bi base alloy with intermetallic compound particles (Ag3Sn, Cu6Sn5, or Ni3Sn4) to create a composite solder alloy structure. The intermetallic compounds act as reinforcement phases that enhance hardness and strength while the Sn-Bi matrix maintains low melting point characteristics, thus resolving the contradiction between low-temperature soldering and mechanical strength
Solution Approach 2:
The patent applies local quality enhancement by distributing intermetallic compound particles specifically within the solder alloy matrix. These particles are localized at strategic positions to provide mechanical reinforcement where needed, while the surrounding matrix retains its low-melting-point properties, achieving both low-temperature soldering and improved mechanical properties
2Power
If the current density in solder joint is increased to meet electronic device requirements, then the electronic device performance is improved, but electromigration causes solder joint degradation and rupture
Solution Approach 1:
The patent introduces intermetallic compound particles as intermediary elements within the solder alloy matrix. These particles act as mediators that hinder the electromigration process by creating physical barriers and altering the diffusion pathways of atoms under high current density, thus protecting the solder joint reliability while allowing high current density operation
Solution Approach 2:
The patent converts the potentially harmful effect of electromigration into a beneficial outcome by using the intermetallic compound particles to redirect and control atom diffusion. The particles create a structured pathway that manages electromigration stress, transforming what would be a degradation mechanism into a controlled process that maintains joint integrity under high current density
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.