Substitution Electroless Gold Plating Solution for Copper Wiring
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Solution Overview
Problem
Direct electroless gold plating on copper wiring of printed circuit boards often results in localized corrosion, leading to incomplete adhesion and discoloration of the gold plating surface, due to electrochemical reactions caused by non-uniformities in the copper surface, which complicates the achievement of uniform gold plating and reliable solder mounting.
Innovation Solution
A substitution-type electroless gold plating solution is developed, incorporating a purine or pyrimidine-based compound as a localized corrosion inhibitor, a water-soluble gold compound, a complexing agent, and a surface corrosion inhibitor, which prevents localized corrosion and ensures a uniform gold plating film by inhibiting oxidation reactions and improving the stability of the gold plating bath.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If direct electroless gold plating is performed on copper wiring without intermediate nickel plating, then the number of plating steps is reduced and manufacturing complexity is lowered, but localized corrosion occurs on the copper surface leading to non-uniform gold plating
Solution Approach 1:
The patent applies preliminary action by introducing a corrosion inhibitor that forms a protective film on the copper surface before gold plating occurs. This preventive measure addresses the localized corrosion issue that would otherwise compromise plating uniformity, allowing direct plating without intermediate nickel layers while maintaining quality
Solution Approach 2:
The corrosion inhibitor acts as an intermediary substance between the copper substrate and the gold plating solution. It mediates the interaction by forming a protective barrier that prevents harmful electrochemical reactions while allowing the gold plating process to proceed uniformly, thus resolving the contradiction between process simplification and plating quality
2Manufacturing precision
If intermediate nickel plating is applied to prevent localized corrosion, then gold plating uniformity is improved, but the number of plating steps increases and manufacturing complexity rises
Solution Approach 1:
The patent extracts and eliminates the intermediate nickel plating step by introducing a corrosion inhibitor that performs the protective function alone. This removes the unnecessary complexity of multiple plating layers while maintaining the essential function of preventing localized corrosion and ensuring uniform gold plating
Solution Approach 2:
The invention changes the chemical parameters of the plating system by introducing specific corrosion inhibitors (such as benzotriazole or its derivatives) and adjusting solution composition. This parameter change allows the system to achieve both corrosion protection and uniform plating in a single step, eliminating the need for intermediate nickel layers
3Manufacturing precision
If corrosion inhibitors are added to prevent localized corrosion, then gold plating uniformity is improved, but the composition complexity of the plating solution increases
Solution Approach 1:
The corrosion inhibitor serves multiple functions simultaneously: it prevents localized corrosion, maintains copper surface integrity, and facilitates uniform gold plating deposition. This multi-functionality justifies the addition to the solution composition, as one additive achieves multiple critical objectives that would otherwise require separate process steps
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 solution achieves a uniform gold plating without pitting or crevice corrosion, enhancing solder mounting reliability and extending the life of the gold plating bath, thus improving productivity and quality by preventing base metal elution and re-precipitation.
Implementation Method 1
a purine or pyrimidine-based compound having carbonyl oxygen which prevents localized corrosion of a copper surface by inhibiting oxidation reactions
Implementation Method 2
a heteroaryl carboxylic acid which easily forms a complex salt with the substitution reaction product to improve the stability of the gold plating bath
Implementation Method 3
a cyanide compound or a sulfite compound as a gold ion stabilizer
Implementation Method 4
an azole compound as a surface corrosion inhibitor
Implementation Method 5
substitution-type electroless gold plating solution for performing direct gold plating on a copper wiring
Data Source
AI summary
A substitution gold plating solution for performing uniform gold plating directly on copper wiring of a printed circuit board is provided and a gold plating method using the same is provided, the solution comprising a purine-based compound or a pyrimidine-based compound having a carbonyl oxygen used as a localized corrosion inhibitor, a water-soluble gold compound, an aminocarboxylic acid as a complexing agent, a dicarboxylic acid as a conductivity improving agent, an α-hydroxycarboxylic acid and heteroaryl carboxylic acid as a base metal elution and reprecipitation preventing agent, a sulfite compound as a gold ion stabilizer, an axole compound as a surface corrosion inhibitor, other surfactants, crystal regulators, pH adjuster, and buffers. The substitution-type electroless gold plating solution according to the present invention prevents the localized corrosion of the copper surface, which is the base metal, and thus the gold plating film produced is excellent in solder mounting reliability.