Step Solder Alloy Composition to Prevent Re-Melting
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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 temperatures or lack mechanical reliability.
Innovation Solution
A method for step soldering 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, applied in conjunction with a second solder alloy having a melting point lower than 160° C., to accommodate the temperature requirements of step-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 soldering can be performed in low temperature range (120-160°C), but the alloy cannot be used for step-soldering in intermediate temperature range because it would be re-melted
Solution Approach 1:
The patent modifies the chemical composition parameters of the soldering alloy by adding specific elements (Ni: 0.01-1.0 mass%, Sb: 0.01-1.0 mass%, Zn: 0.01-1.0 mass%) to Sn-In-Ag-Bi base alloy, thereby adjusting the melting characteristics to achieve solidus temperature ≥160°C while maintaining low-temperature soldering capability
Solution Approach 2:
The patent creates a composite soldering alloy system combining multiple elements (Sn, In, Ag, Bi, Ni, Sb, Zn) with specific composition ranges, where each element contributes specific properties to achieve the desired melting point characteristics for step-soldering application
2Reliability
If existing lead-free soldering alloys are used for step-soldering in intermediate temperature range, then the process can be simplified, but the alloys either melt below required temperatures or lack mechanical reliability
Solution Approach 1:
The patent optimizes the composition parameters within specific ranges (Sn: balance, In: 1-30 mass%, Ag: 0.1-5 mass%, Bi: 0.1-5 mass%, Ni: 0.01-1.0 mass%, Sb: 0.01-1.0 mass%, Zn: 0.01-1.0 mass%) to achieve both reliable mechanical properties and stable melting point characteristics for step-soldering
Solution Approach 2:
The patent introduces trace amounts of specific elements (Ni, Sb, Zn) at controlled concentrations to locally modify the alloy structure and properties, enhancing mechanical reliability while maintaining the overall low-temperature soldering characteristics
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 that the soldering alloy maintains mechanical reliability and prevents re-melting during the soldering process, thereby effectively supporting step-soldering in intermediate to low temperature ranges.
Implementation Method 1
a first solder alloy having a melting point in a temperature range from 160 to 210° C., and heating them in the temperature range from 160 to 210° C.
Data Source
AI summary
A method for soldering includes applying a first solder alloy having a melting point in a temperature range higher than 210° C. to a jointed portion of a first electronic component and a substrate, and heating them in the temperature range higher than 210° C., and applying a second solder alloy having the melting point in a temperature range from than 160° C. to 210° 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 from 160° C. to 210° C., wherein the second 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.