Thermally Decomposable Cyanoacrylate Coating for Solder Paste
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Solution Overview
Problem
Solder pastes have a short and unpredictable shelf life due to oxidation of solder powder, which affects reflow performance and reacts with flux, increasing viscosity and making printing difficult, with existing coatings either inhibiting reflow or being environmentally harmful.
Innovation Solution
A thermally decomposable cyanoacrylate polymer coating with a ceiling temperature below the solder's melting point is applied to the metal particles, acting as a physical barrier against oxidation and providing stability, while being removable during reflow to maintain conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder powder is stored without coating, then it maintains good reflow characteristics, but it oxidizes quickly and reacts with flux, reducing shelf life
Solution Approach 1:
A cyanoacrylate polymer coating is applied as an intermediary layer between the solder powder and the oxidizing environment/flux. This coating acts as a protective barrier that prevents direct contact between the solder powder and harmful substances, thereby extending shelf life without significantly impacting reflow performance.
Solution Approach 2:
A thin polymer coating film is formed on the solder powder surface. This flexible thin film provides protection against oxidation and flux reaction while being thin enough to allow heat transfer during reflow and not create excessive barrier to wetting.
2Reliability
If a large amount of coating material is applied to inhibit oxidation, then shelf life is extended, but reflow characteristics deteriorate due to physical obstructions and poor wetting
Solution Approach 1:
The coating thickness parameter is precisely controlled to be in the range of 0.0001 to 3.0 μm. This parameter optimization ensures sufficient protection against oxidation while maintaining adequate heat transfer and wetting characteristics during reflow. The cyanoacrylate polymer's thermal decomposition temperature is also selected to be below the solder melting point, ensuring the coating breaks down at appropriate temperatures.
3Ease of manufacture
If fluorinated hydrocarbons are used as solvents in coating, then coating performance is improved, but environmental pollution increases
Solution Approach 1:
The patent replaces persistent environmental pollutants (fluorinated hydrocarbons) with more environmentally benign alternatives. The cyanoacrylate polymer coating system uses solvents that are less harmful to the environment, sacrificing some long-term environmental persistence in favor of reduced ecological damage. The coating itself is designed to decompose thermally, creating a temporary protective barrier that degrades into less harmful substances after use.
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 polymer coating significantly extends the shelf life of solder pastes by preventing oxidation and maintaining reflow performance, with cyanoacrylate monomers reverting at processing temperatures, ensuring effective electrical interconnections in semiconductor applications.
Implementation Method 1
the cured product of the reactive monomer has as its chief function the task of physically isolating the metal particles from environmental degradation, such as oxidation and chemical reaction with flux media
Implementation Method 2
the thermally decomposable polymer has a ceiling temperature below a degradation temperature of the thermally decomposable polymer and below a melting point of the metal particle
Implementation Method 3
Cyanoacrylate polymers have a ceiling temperature, above which the polymers revert to the monomers from which they were made
Data Source
AI summary
The present invention relates to polymer coated metal powders, such as metal powders used in the formation of solder alloys and pastes. The metal powders are coated with curable compositions of cyanoacrylates. The present invention relates to polymer coated metal powders, such as metal powders used in the formation of solder alloys and pastes. The metal powders are coated with curable compositions of cyanoacrylates, and once cured the coating on the metal powder is a cyanoacrylate polymer.