Electroless Gold Plating Bath Stability and Corrosion Control
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Solution Overview
Problem
Existing electroless gold plating baths face challenges such as nickel corrosion, instability, and high costs, leading to frequent replacements, and struggle to achieve high plating rates and consistent performance in manufacturing electronic components.
Innovation Solution
An electroless gold plating bath comprising gold ions, sulfite ions, iodide ions, and a phosphonate compound, which provides a stable and efficient gold deposition process with a plating rate of 240 nm/h or greater, suitable for nickel and phosphorus nickel surfaces, without the need for toxic chemicals like cyanide and thiourea.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional electroless gold plating baths are used, then gold deposition can be achieved, but the baths lose their properties quickly and require frequent replacements
Solution Approach 1:
The patent changes the chemical parameters of the plating bath by using a cyanide-free composition with specific concentrations of gold ions (0.5-10 g/L), sulfite ions (5-50 g/L), iodide ions (1-20 g/L), and phosphonate compounds (0.1-5 g/L). This parameter optimization enables the bath to maintain stable performance for at least 10 metal turnovers, resolving the contradiction between achieving gold deposition and maintaining long-term bath stability
Solution Approach 2:
The patent introduces phosphonate compounds as intermediary agents that complex with gold ions and control the reduction process. These phosphonate intermediaries prevent premature gold precipitation while enabling controlled deposition, thereby extending the service life of the plating bath while maintaining reliable gold deposition performance
2Manufacturing precision
If prior art plating baths are used, then gold layers can be deposited, but nickel corrosion occurs between gold and copper lines
Solution Approach 1:
The patent converts the potentially harmful interaction between gold plating and nickel layers into a beneficial process by using phosphonate compounds that selectively complex with nickel ions. This prevents nickel dissolution and corrosion while allowing controlled gold deposition, thus eliminating the harmful nickel corrosion effect while maintaining high-quality gold layer formation
Solution Approach 2:
Phosphonate compounds act as intermediary agents that mediate between the gold plating process and the nickel substrate. These intermediaries preferentially bind to nickel ions, preventing their release into the solution and subsequent corrosion, while still allowing gold ions to be reduced and deposited as high-quality layers
3Adaptability or versatility
If electroless plating is used for small electrical components, then deposition without electrical connections is achieved, but plating rates are insufficient for economical manufacturing
Solution Approach 1:
The patent optimizes the chemical parameters including gold ion concentration (0.5-10 g/L), sulfite ion concentration (5-50 g/L) as reducing agent, iodide ion concentration (1-20 g/L) as catalyst, and phosphonate compound concentration (0.1-5 g/L) to achieve plating rates of 100 nm/h or more. This parameter optimization maintains the advantage of electroless plating for small components while significantly improving productivity for economical manufacturing
Solution Approach 2:
The patent uses iodide ions as a catalyst that facilitates the reduction of gold ions through a catalytic cycle, effectively copying and amplifying the deposition reaction. This catalytic mechanism enables high plating rates without requiring electrical connections, making the process both adaptable to small components and productive for industrial manufacturing
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 long-term stability and high plating rates, reducing nickel corrosion and environmental impact, while maintaining the quality and adhesion of gold layers on substrates, suitable for industrial applications in electronics.
Implementation Method 1
Electroless plating generally describes methods without using external current sources for reduction of metal ions. The main components of an autocatalytic metal baths are the metal salt, a reducing agent... sulfite ions... convert the metal ions to its metallic form
Implementation Method 2
c) iodide ions; and d) at least one phosphonate compound... as for example stabilizing agents
Implementation Method 3
Complexing agents (also called chelating agents in the art) are used to chelate the metal being deposited and prevent the metal from being precipitated from solution... at least one phosphonate compound according to formula (1)
Implementation Method 4
there are still many challenges unresolved... insufficient stabilities of the prior art gold plating baths... provide an electroless gold plating bath having a constant plating rate and performance for at least 5 metal turnovers (MTO), preferably for at least 10 metal turnovers
Data Source
AI summary
The present invention concerns an electroless gold plating bath comprisinga) gold ions;b) sulfite ions;c) iodide ions;d) at least one phosphonate compound according to formula (1)whereineach X is independently an alkanediyl group;R1, R2, R3 and each R4 are independently alkanediyl groups;M is independently hydrogen, a metal atom or a cation forming radical;each n is a rational number and selected in accordance with the valency of the respective M; andb is an integer ranging from 1 to 10.The invention further is directed to the use of the bath and a method for depositing a gold layer on a surface of a substrate. The bath is particularly suitable in the manufacture of printed circuit boards, IC substrates, semiconducting devices, interposers made of glass and the like.