Step Soldering Alloy Composition for Multi-Stage Joint Stability
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Solution Overview
Problem
Existing lead-free soldering alloys are not suitable for step-soldering processes that require intermediate to low temperature ranges, as they either melt below the required temperature or lack mechanical reliability, making them unsuitable for multi-stage soldering applications.
Innovation Solution
A method involving a two-stage soldering process using a first solder alloy with a melting point between 160° C. and 210° C., composed of 13-22% In, 0.5-2.8% Ag, 0.5-5.0% Bi, 0.002-0.05% Ni, and balance Sn, and a second solder alloy with a lower melting point for specific temperature ranges, ensuring the alloy's mechanical reliability and preventing re-melting during soldering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a lead-free soldering alloy with low melting point (e.g., Sn-58Bi, Sn-52In) is used to enable low-temperature soldering, then the melting point is reduced, but the alloy may be re-melted during intermediate temperature soldering steps
Solution Approach 1:
The patent applies parameter changes by precisely controlling the composition ratios of In, Ag, Bi, and Ni elements in the solder alloy. By adjusting these parameters within specific ranges, the alloy achieves a melting point suitable for low-temperature soldering while maintaining stability during intermediate temperature steps through optimized compositional parameters
Solution Approach 2:
The patent uses composite materials by creating a multi-element solder alloy system (Sn-In-Ag-Bi-Ni) that combines the benefits of different elements. This composite alloy structure enables the material to exhibit both low melting point characteristics and high stability during multi-stage soldering processes
2Temperature
If a soldering alloy with intermediate melting point (e.g., SAC305) is used for intermediate temperature soldering, then the melting point is suitable for intermediate range, but the thermal load on miniaturized electronic parts increases
Solution Approach 1:
The patent applies parameter changes by formulating a solder alloy with specific compositional parameters (In: 2-10%, Ag: 0.5-3%, Bi: 0.5-5%, Ni: 0.01-1%) that enables low-temperature soldering. This parameter optimization allows soldering at temperatures that reduce thermal load on miniaturized electronic parts while maintaining reliable joint formation
3Device complexity
If existing lead-free soldering alloys are used for step-soldering, then the soldering process can be simplified, but the alloys lack mechanical reliability and may be re-melted during low-temperature steps
Solution Approach 1:
The patent applies parameter changes by optimizing the compositional parameters of the solder alloy to achieve a melting point range (120-140°C) that is suitable for low-temperature soldering steps. This parameter control ensures the alloy maintains its shape and provides mechanical reliability while enabling simplified step-soldering processes
Solution Approach 2:
The patent employs a solder alloy composition that is optimized for single-use in specific temperature ranges. The alloy is designed to be applied and solidify reliably in low-temperature steps without requiring complex multi-stage processes, effectively serving its purpose in a controlled, disposable manner for each soldering operation
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 proposed method ensures the soldering alloy meets the melting point requirements and provides excellent mechanical reliability, preventing re-melting during low-temperature soldering and maintaining stability during intermediate temperature soldering, thus enhancing the reliability of electronic components.
Implementation Method 1
applying a first solder alloy having a melting point in a temperature range from 160 to 210° C. to a jointed portion of a first electronic component and a substrate, and heating them in the temperature range from 160 to 210° C.
Implementation Method 2
applying a second solder alloy having the melting point in a temperature range lower than 160° C. to a joint portion of a second electronic component and the substrate to which the first electronic component is joined, and heating them in the temperature range lower than 160° C.
Implementation Method 3
heating them in the temperature range from 160 to 210° C.; and applying a second solder alloy having the melting point in a temperature range lower than 160° C. to a joint portion of a second electronic component and the substrate
Data Source
AI summary
A method for step-soldering includes applying a first solder alloy having a melting point in a temperature range from 160 to 210° C. to a jointed portion of a first electronic component and a substrate, and heating them in the temperature range from 160 to 210° C., and applying a second solder alloy having the melting point in a temperature range lower than 160° C. to a joint portion of a second electronic component and the substrate, and heating them in the temperature range lower than 160° C. The first solder alloy consists of 13-22 mass % of In, 0.5-2.8 mass % of Ag, 0.5-5.0 mass % of Bi, 0.002-0.05 mass % of Ni and a balance Sn.