Sn-Bi-In-Pd Solder Alloy for Fine Microstructure and Joint Reliability
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Solution Overview
Problem
Conventional low-melting point solder alloys face challenges in maintaining mechanical properties, impact resistance, and heat-cycle resistance due to the presence of coarse Bi phases, which can lead to fusion failures and reliability issues in miniaturized electronic devices.
Innovation Solution
The addition of a predetermined amount of In and Pd to the Sn-Bi solder alloy refines the alloy organization, enhancing tensile strength, ductility, and impact resistance while maintaining a low melting point, thereby suppressing fusion failures and improving heat-cycle resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If large Bi is contained in Sn-Bi solder alloy to achieve low melting point, then the melting point is lowered, but coarse Bi phase precipitates during solidification which deteriorates mechanical properties
Solution Approach 1:
The invention changes the chemical composition parameters by adding specific amounts of In (0.1-5 wt%) and Cu (0.1-5 wt%) elements to the Sn-Bi solder alloy system. This compositional modification alters the solidification behavior and phase distribution, enabling the formation of fine dispersed Bi phases rather than coarse precipitates, thus simultaneously maintaining low melting point and improving mechanical properties
Solution Approach 2:
The invention creates a composite microstructure by introducing In and Cu elements that form intermetallic compounds (such as Cu6Sn5 and In-Sn phases) within the Sn-Bi matrix. These composite phases act as nucleation sites that refine the Bi phase distribution, transforming the harmful coarse Bi structure into a beneficial fine composite microstructure that enhances both mechanical strength and low-temperature soldering capability
2Strength
If content of Bi is reduced to suppress generation of coarse Bi phase, then mechanical properties improve, but melting point increases and fusion failure may occur
Solution Approach 1:
The invention modifies the alloy composition parameters by adding In and Cu elements that act as melting point depressants. These elements form eutectic systems with Sn and Bi, creating additional low-melting-point phases that compensate for the reduced Bi content, thereby maintaining the overall low melting point while allowing for suppressed coarse Bi phase formation
3Temperature
If reflow temperature is increased to melt solder alloy with high melting point, then solder alloy melts, but warpage occurs in substrates or packages and solder alloy separates from electrode
Solution Approach 1:
The invention changes the thermal parameters of the solder alloy by incorporating In and Cu elements that lower the liquidus temperature. This compositional adjustment reduces the reflow temperature requirement, preventing substrate warpage and electrode separation while ensuring complete melting and wetting of the solder alloy
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 Sn-Bi-In-Pd solder alloy achieves excellent mechanical properties, impact resistance, and heat-cycle resistance by maintaining a fine alloy structure, preventing fusion failures and ensuring reliable performance in electronic devices.
Implementation Method 1
The addition of a predetermined amount of In and Pd to the Sn-Bi solder alloy refines the alloy organization
Implementation Method 2
Bi segregates in Sn during solidification and a coarse Bi phase is precipitated
Implementation Method 3
Bi segregates in Sn during solidification
Data Source
Figure 1(a)~1(c)
AI summary
The present invention provides a solder alloy, a solder paste, a solder ball, a resin flux-cored solder and a solder joint, both of which has the low-melting point to suppress the occurrence of the fusion failure and has excellent mechanical properties, impact resistance and excellent heat-cycle resistance. In order to achieve miniaturization of the alloy organization, the alloy composition is composed of 35 to 68 mass% of Bi, 0.5 to 3.0 mass% of In, 0.01 to 0.10 mass% of Pd, and a balance of Sn. The alloy composition may contain 1.0 to 2.0 mass% of In, contain 0.01 to 0.03 mass% of Pd and contain at least one of Co, Ti, Al and Mn in total amount of 0.1 mass% or less. The solder alloy may be suitably used for a solder paste, a solder ball, a resin flux-cored solder and a solder joint.