Solder Paste Third Metal Powder Unreacted Sn
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Solution Overview
Problem
Existing Pb-free Sn-Cu eutectic solder pastes face issues with unreacted Sn components remaining after reflow treatments, leading to decreased bonding strength when reflow is repeated, due to high melting points of intermetallic compounds formed.
Innovation Solution
Incorporating a third metal powder with a smaller average particle diameter than the base metal, capable of forming compounds with both the first and second metal powders, to accelerate reactions and reduce unreacted components, along with dispersing these powders in a flux or thermosetting resin to enhance bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the content of the Sn component is increased to wet and disperse Cu balls uniformly, then the diffusion of Cu powder in flux is improved, but unreacted Sn remains in the solder after reflow treatment
Solution Approach 1:
The patent changes the particle size parameter of the third metal powder to be smaller than the average particle diameter of the base metal. This parameter change increases the surface area to volume ratio, enhancing reactivity and enabling the third metal powder to form compounds with the plated film and second metal powder more effectively, thereby consuming excess Sn component and preventing unreacted Sn from remaining in the solder.
Solution Approach 2:
The third metal powder acts as an intermediary substance that facilitates the reaction between the plated film and second metal powder. By being present in the solder paste composition, it mediates the formation of intermetallic compounds, ensuring that Sn component reacts completely to form desired compounds rather than remaining as unreacted metal.
2Adaptability or versatility
If reflow treatment is performed multiple times to mount different electronic components, then component mounting flexibility is improved, but unreacted Sn melts again causing decreased bonding strength
Solution Approach 1:
The patent modifies the compositional parameters of the solder paste by adding third metal powder with specific properties (smaller particle diameter than base metal). This compositional change ensures that during repeated reflow treatments, the Sn component reacts completely to form stable intermetallic compounds with melting points above the reflow temperature, preventing remelting and maintaining bonding strength.
Solution Approach 2:
The third metal powder provides beforehand cushioning by pre-establishing a chemical environment that promotes complete reaction of Sn component. This preventive measure ensures that even when subjected to repeated thermal stress from multiple reflow treatments, the solder joint remains stable because the Sn has already been consumed in forming compounds with appropriate thermal stability.
3Temperature
If the melting point of intermetallic compounds is high to ensure thermal stability, then thermal resistance is improved, but unreacted Sn component remains after reflow treatment
Solution Approach 1:
The patent changes the particle size parameter of the third metal powder to be smaller than the base metal particles. This parameter change creates a size gradient that enhances diffusion pathways and reaction kinetics, enabling complete consumption of Sn component even though the resulting intermetallic compounds have high melting points and require extended reaction times or higher temperatures to form.
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 approach effectively suppresses unreacted metal components, maintaining bonding strength even after multiple reflow treatments and improving physical bonding strength by preventing void generation, thus ensuring reliable electronic devices with high productivity.
Implementation Method 1
a third metal powder which has an average particle diameter smaller than the average particle diameter of the first metal material and which can form compounds with the plated film and the second metal powder
Implementation Method 2
the Cu balls 102 is uniformly diffused in the flux 106 to form an intermetallic compound 109 composed of Cu6Sn5
Implementation Method 3
the Cu balls 102 is wetted and dispersed in the molten Sn component
Implementation Method 4
the Sn component (derived from the plated films and the Sn powder) is melted
Implementation Method 5
the Cu balls 102 is uniformly diffused in the flux 106 to form an intermetallic compound 109 composed of Cu6Sn5
Data Source
AI summary
In solder paste of the present invention, a first metal powder, a second metal powder, and a third metal powder are dispersed in a flux or a thermosetting resin. The first metal powder includes a first metal material such as Cu, Ag, Au, or Pd that serves as a base metal. A second metal material such as Sn or In that has a melting point lower than that of the first metal material is coated on the surface of the first metal material. The second metal powder is made of a metal material such as Sn or In that has a melting point lower than that of the first metal material. The third metal powder such as a Cu, Ag, Au or Pd powder has an average particle diameter smaller than that of the first metal material and can form compounds with the second metal material and the second metal powder. Accordingly, the likelihood of unreacted components remaining after a heat treatment can be suppressed, and even when a reflow treatment is repeated a plurality of times, a decrease in the bonding strength of solder bonding can be prevented.