Electroless Gold Plating Bath Corrosion Control
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Solution Overview
Problem
Existing electroless gold plating methods, such as ENIG and DIG, face issues with intergranular corrosion on nickel surfaces, leading to a red appearance of the gold coating due to the use of primary amine compounds, which compromises the coating's quality and reliability.
Innovation Solution
An electroless gold plating bath comprising a water-soluble gold compound, a complexing agent, a formaldehyde metabisulfite adduct, and an amine compound with a specific structure, which allows for a stable and uniform gold deposition without intergranular corrosion, using a molar ratio of formaldehyde metabisulfite to amine compound between 1:30 to 3:1, and employing gold cyanide salts, to maintain a stable deposition rate and prevent corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If primary amine compounds (such as triethylenetetramine) are used in electroless gold plating, then gold deposition can be achieved, but intergranular corrosion occurs on the nickel surface causing the coating to turn red
Solution Approach 1:
The patent changes the chemical parameters of the plating bath by replacing primary amine compounds with alternative complexing agents (such as carboxylic acids, hydroxycarboxylic acids, or their salts) and adjusting the pH range to 2-7. This parameter change eliminates the intergranular corrosion issue while maintaining effective gold deposition through different chemical mechanisms that do not attack the nickel substrate.
Solution Approach 2:
The patent introduces alternative complexing agents that are less harmful to the nickel substrate. These substitutes (such as citric acid, gluconic acid, or their salts) serve the function of complexing gold ions without causing the harmful intergranular corrosion effect, effectively replacing the problematic primary amine compounds with safer alternatives.
2Reliability
If immersion gold plating is performed on nickel/immersion gold coating, then copper diffusion is prevented, but nickel oxidation and corrosion spots occur reducing bonding characteristics
Solution Approach 1:
The patent introduces alternative complexing agents as intermediaries that mediate between the gold ions and the nickel substrate. These agents (such as carboxylic acid salts or hydroxycarboxylic acid salts) enable gold deposition while simultaneously protecting the nickel surface from oxidation and corrosion, acting as a protective intermediary layer during the plating process.
Solution Approach 2:
The patent changes the chemical environment parameters by controlling pH in the range of 2-7 and using specific complexing agents, which alters the redox potential and reaction conditions. This parameter change allows gold to deposit on the nickel/gold coating without causing nickel oxidation or corrosion spots, maintaining good bonding characteristics.
3Reliability
If electroless gold plating is used to increase gold thickness for wire bonding, then nickel diffusion is coped with, but corrosion spots occur due to gold oxidizing nickel
Solution Approach 1:
The patent converts the potentially harmful oxidation reaction into a beneficial process by carefully controlling the chemical environment. Instead of allowing uncontrolled nickel oxidation that causes corrosion spots, the patent uses specific complexing agents and pH control to harness the redox reaction for uniform gold deposition while preventing the harmful corrosion effect, essentially converting a harmful side reaction into a controlled deposition mechanism.
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 gold coating with a good appearance and enhanced reliability by suppressing corrosion, maintaining a stable deposition rate, and allowing for thickening of the gold coating without separate procedures, while preventing nickel surface corrosion and ensuring uniform thickness on various metals like copper and palladium.
Implementation Method 1
gold is deposited by utilizing, in a plating bath, a difference in redox potential from an underlying layer such as of nickel
Data Source
AI summary
An electroless gold plating bath includes a water-soluble gold compound, a complexing agent, a formaldehyde metabisulfite adduct, and an amine compound represented by R1—NH—C2H4—NH—R2 or (CH2—NH—C2H4—NH—CH2)n—R4 (wherein R1 to R4 represent —OH, —CH3, —CH2OH, —C2H4OH, —CH2N(CH3)2, —CH2NH(CH2OH), —CH2NH(C2H4OH), —C2H4NH(CH2OH), —C2H4NH(C2H4OH), —CH2N(CH2OH)2, —CH2N(C2H4OH)2, —C2H4N(CH2OH)2 or —C2H4N(C2H4OH)2, and n is an integer of 1 to 4). A gold plated coating of a good appearance can be formed without causing a failure in appearance owing to the progress of intergranular corrosion in a nickel surface.