Lead-Free Solder Dross Reduction via Phosphorus Oxide Film
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Solution Overview
Problem
Lead-free solders produce excessive dross, impairing welding quality and causing economic losses due to high melting points and oxidation issues, with existing methods either being ineffective, costly, or having short-term benefits.
Innovation Solution
A method involving the use of alloys with phosphorus (P), gallium (Ga), and germanium (Ge) to form a dense oxide film on the surface of lead-free solders, which reduces oxidation and maintains a stable dross reduction effect by continuously monitoring and supplementing P levels in the soldering process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If lead-free solder with high Sn content (>95 wt%) is used, then melting point and operating temperature increase, but dross formation increases significantly
Solution Approach 1:
The patent introduces phosphorus (P) as an intermediary element that forms a protective oxide film (P2O5) on the solder surface. This film acts as a barrier between the molten solder and atmospheric oxygen, preventing direct oxidation of Sn and reducing dross formation. The P element mediates the interaction between solder and oxygen, transforming the harmful oxidation process into a controlled protective mechanism.
Solution Approach 2:
The patent modifies the chemical composition parameters of the solder by adding phosphorus at controlled concentrations (0.003-0.03 wt%). This parameter change alters the oxidation behavior of the solder surface, enabling the formation of a stable protective oxide film that reduces dross formation while maintaining the high Sn content and elevated operating temperature characteristics of lead-free solder.
2Object-affected harmful factors
If oxidation resistant oil is used, then oxidation of Sn is reduced, but the oil deteriorates over time, contaminates circuit boards, creates smoke, and degrades worker atmosphere
Solution Approach 1:
The patent replaces the expensive, long-lasting but polluting oxidation resistant oil with a cheap, short-living protective mechanism. The phosphorus element forms a protective oxide film that is consumed during the soldering process along with the dross, which is then removed. This disposable protective film approach eliminates the need for persistent oil coatings that cause contamination and smoke.
Solution Approach 2:
The patent converts the naturally formed SnO2 oxide film, which normally causes dross formation, into a beneficial protective layer by introducing phosphorus. The phosphorus reacts with oxygen to form P2O5, which is less dense and more protective than SnO2. This transforms the harmful oxidation process into a beneficial protective mechanism that reduces rather than increases dross formation.
3Object-generated harmful factors
If nitrogen protection is implemented, then dross is reduced effectively, but solder balls increase on circuit board surface and equipment investment increases
Solution Approach 1:
The patent enables the soldering system to protect itself from oxidation through the addition of phosphorus to the solder composition. The phosphorus automatically forms a protective oxide film on the solder surface during the soldering process, eliminating the need for external nitrogen protection systems. This self-service approach reduces dross formation without requiring complex gas protection equipment.
4Object-generated harmful factors
If anti-oxidation elements (P, Ga, Ge) are added to the alloy, then dross reduction effect is good initially, but the effect diminishes after a short period
Solution Approach 1:
The patent optimizes the phosphorus concentration parameter to a specific range (0.003-0.03 wt%) that ensures long-term effectiveness. This precise parameter control prevents the rapid depletion of protective elements while maintaining sufficient P content to continuously form protective oxide films. The optimized concentration balances the rate of P consumption through dross formation with the need for sustained protection.
Solution Approach 2:
The patent acknowledges the dynamic nature of the protective mechanism, where phosphorus is continuously consumed through dross formation and must be replenished. The method establishes a dynamic equilibrium by adding P at controlled intervals based on production volume and dross formation rates, ensuring the protective film is continuously regenerated rather than depleting over time.
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
This approach ensures a long-lasting and stable reduction in dross formation, maintaining optimal solder quality and minimizing economic losses across various soldering processes like wave soldering, dip soldering, and hot air leveling.
Implementation Method 1
those elements have much lower Gibbs free energy with O2, they form oxide film earlier than SnO2 film. Furthermore, the oxide film of P, Ga and Ge are dense and firm, so that they cover the surface layer of the liquid solder and block the contact of the solder with O2 in the air
Implementation Method 2
skin effect exists in the distribution of trace elements such as P, Ga, and Ge in liquid solder
Implementation Method 3
due to the skin effect the elements P, Ga, and Ge, they always have a higher concentration in the surface layer of the solder than in the inner layer of the solder, so that they are continuously taken away by the dross in the liquid surface
Data Source
AI summary
A reducing dross method of lead-free solder includes the steps of: producing master alloy of reducing dross which comprises Sn and 0.1 to 0.8 wt % P; analyzing the percentage of P of the lead-free solder to be modified, in order to reach 0.008 to 0.015 wt % P in the lead-free solder, adding the master alloy into the lead-free solder with the percentage of P less than 0.008 wt % or no P; then sampling the lead-free solder at regular intervals to determine the percentage and the percentage loss of P, if the percentage of P being less than a given value from 0.008 to 0.015 wt %, adding the master alloy to keep the percentage of P as 0.008 to 0.015 wt %.