Low-Temperature Lead-Free Solder Paste for Solder Ball Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Low melting point lead-free solder alloys used in electronic components face issues with solder ball generation due to surface oxide layers, which can lead to decreased insulation resistance and short circuits, and existing solutions using dicarboxylic acids are insufficient in preventing these issues.
Innovation Solution
A solder paste containing a lead-free solder alloy with a solidus temperature of 150° C. or less, utilizing a flux with a combination of dicarboxylic acids having 4 to 6 carbon atoms, imidazole compounds, rosin, a solvent, and a thixotropic agent to stabilize the flux and prevent solder ball formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If low melting point lead-free solder alloys (Sn-Bi or Sn-In) are used, then the melting point is reduced for heat-sensitive components, but solder ball generation increases due to surface oxide layers
Solution Approach 1:
The patent modifies the chemical composition parameters of the flux by incorporating specific activators (carboxylic acids with 1-3 carbon atoms, sulfonic acids, and imidazole compounds) in optimized ratios. This changes the chemical reactivity parameters of the flux to more effectively remove surface oxide layers from low melting point solder alloys, thereby reducing solder ball generation while maintaining the low melting point characteristic
Solution Approach 2:
The patent creates a composite flux system combining multiple types of activators (carboxylic acids, sulfonic acids, and imidazole compounds) with rosin and solvents. This composite formulation synergistically enhances the flux's ability to prevent solder ball formation on low melting point solder alloys without compromising their low temperature melting property
2Temperature
If Sn-In-based solder alloys with high In content (50-52 mass%) are used, then the melting point is significantly lowered to 118° C., but the cost increases due to In being a scarce and expensive material
Solution Approach 1:
The patent changes the alloy composition parameters by reducing the In content from 50-52 mass% to lower levels (e.g., 1-10 mass% In combined with 30-60 mass% Bi). This parameter modification maintains the melting point at 150° C. or less while significantly reducing the quantity of expensive In required, thereby lowering material cost
3Temperature
If Sn-Bi-based solder alloys with high Bi content (32-59 mass%) are used, then the melting point is lowered to 139° C. or less, but the alloy becomes hard and brittle with poor elongation and joint characteristics
Solution Approach 1:
The patent optimizes the Bi content parameter to a specific range (32-59 mass%) and combines it with controlled amounts of In (1-10 mass%) and Sn (balance). This parameter optimization prevents excessive brittleness while maintaining low melting point (150° C. or less) and improving alloy elongation and joint characteristics
Solution Approach 2:
The patent creates a composite solder alloy system combining Sn, Bi, and In in specific ratios. This composite composition balances the properties: Sn provides ductility, Bi lowers melting point, and In enhances wetting and reduces brittleness, achieving both low melting point and good mechanical properties
4Ease of manufacture
If conventional flux formulations are used with low melting point solder alloys, then the solder paste can be applied, but solder ball generation increases due to insufficient oxide removal
Solution Approach 1:
The patent modifies the flux composition parameters by incorporating specific activators (carboxylic acids with 1-3 carbon atoms, sulfonic acids, and imidazole compounds) in optimized ratios. This changes the chemical reactivity parameters to more effectively remove surface oxide layers from low melting point solder alloys, thereby reducing solder ball generation while maintaining ease of solder paste application
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
Effectively prevents solder ball generation during the joining process, enhancing the reliability of solder joints in both standard and heat-sensitive electronic components.
Implementation Method 1
a solder paste containing a lead-free solder alloy having a solidus temperature of 150° C. or less and capable of preventing generation of solder balls at the time of joining
Implementation Method 2
heating in a reflow furnace to melt the solder paste, thus joining the electronic component and the electrode
Data Source
AI summary
The present invention relates to a solder paste containing solder powder and a flux, wherein the solder powder is a lead-free solder alloy having a solidus temperature of 150° C. or less, the flux contains: a rosin; a solvent; a thixotropic agent; and an organic acid and an imidazole as an activator, the organic acid includes one or more kinds of dicarboxylic acids having 4 to 6 carbon atoms, and the imidazole includes one or more kinds among imidazole compounds having 3 to 6 carbon atoms and derivatives thereof.