Flux Composition for Hot-Slump Control in Fine-Pitch Solder Paste
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Solution Overview
Problem
In ultra-high-density assemblies, solder pastes printed with areas narrower than the land area tend to oxidize and fail to spread evenly, leading to soldering failures due to susceptibility to hot slump during reflow processes.
Innovation Solution
A flux formulation containing rosin-based resin, a solvent, a thixotropic agent (hardened castor oil or bisamide-based), and an activator (hydrohalide, halogenated aliphatic compounds, and imidazole compounds) is used, with specific weight percentage ranges to prevent hot slump and ensure even solder spread across the entire land area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the printed area of solder paste is made narrower than the land area to prevent displacement in ultra-high-density assembly, then the risk of position error is reduced, but the solder fails to spread to the entire land due to oxidation susceptibility
Solution Approach 1:
The flux is formulated with specific thixotropic agents and activators that are activated before soldering to create a protective environment and promote solder flow in advance, ensuring complete land coverage even when printed area is reduced
Solution Approach 2:
The flux composition parameters are optimized with specific ranges of thixotropic agents (5-15 wt%) and activators containing halogen (9000-50000 ppm) to control viscosity and chemical activity, enabling solder to spread properly from a reduced printed area
2Object-affected harmful factors
If halogen compound content is reduced to minimize harmful effects, then environmental and health safety is improved, but the ability to prevent hot slump deteriorates
Solution Approach 1:
The flux maintains halogen content within the specific range of 9000-50000 ppm, which is sufficient to prevent hot slump while minimizing harmful effects. This optimized parameter range balances effectiveness with safety
Solution Approach 2:
The flux combines multiple components including thixotropic agents, activators with halogen, and other additives to create a composite formulation that prevents hot slump through synergistic effects while controlling overall halogen content to reduce harm
3Reliability
If thixotropic agent content is increased to prevent hot slump, then hot slump prevention is improved, but the flux becomes too viscous to spread properly
Solution Approach 1:
The thixotropic agent content is precisely controlled within 5-15 wt%, with hardened castor oil at 4-10 wt% and bisamide-based agent at 1-5 wt%. This parameter optimization ensures adequate viscosity for hot slump prevention while maintaining spreadability
Solution Approach 2:
The flux exhibits different viscosity characteristics at different stages: sufficiently viscous during storage and application to prevent hot slump, but becomes more fluid during reflow soldering to enable proper spread. The thixotropic properties provide this localized quality change
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 flux and solder paste combination effectively prevents hot slump and ensures solder spread over the entire land area, even when printed with narrower areas, enhancing the reliability of ultra-high-density assemblies by maintaining the integrity of solder joints.
Implementation Method 1
The flux contains a thixotropic agent. The thixotropic agent contains hardened castor oil and/or bisamide-based thixotropic agent
Implementation Method 2
The flux contains an activator. The activator contains hydrohalide and/or halogenated aliphatic compound and/or imidazole compound... chemically removing metal oxides present on solder and a metal surface of a joint target to be soldered
Implementation Method 3
by soldering using the flux, an intermetallic compound can be formed between the solder and the metal surface of the joint target, so that strong joint can be obtained
Data Source
AI summary
Provided is flux containing rosin-based resin, a solvent, a thixotropic agent and an activator. The thixotropic agent includes any or both of hardened castor oil and bisamide-based thixotropic agent. The contents of the hardened castor oil and the bisamide-based thixotropic agent are respectively within the range of 4 wt. % or more and 10 wt. % or less and the range of 1 wt. % or more and 5 wt. % or less based on the total weight of the flux. The contents of the thixotropic agent are within the range of 5 wt. % or more and 15 wt. % or less based on the total weight of the flux. The activator includes hydrohalide, a halogenated aliphatic compound and an imidazole compound. The contents of the halogen in the flux are within the range of 9000 ppm or more and 50000 ppm or less.