Electroless Gold Plating Bath Stabilizer for Cyanide-Free Stability
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Solution Overview
Problem
Existing electroless gold plating methods require strict safety management due to the use of highly toxic cyanide compounds and suffer from bath instability, leading to decomposition during long-term heating.
Innovation Solution
An electroless gold plating bath comprising a water-soluble gold salt, a reducing agent, and a phosphine compound with specific substituents, which acts as a stabilizer to prevent bath decomposition without using cyanide compounds, even under prolonged heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If cyanide compounds are used as stabilizers in electroless gold plating bath, then bath stability is improved, but safety hazards and toxicity increase requiring strict safety management
Solution Approach 1:
The patent removes cyanide compounds from the plating bath composition entirely, extracting the harmful stabilizing function and replacing it with alternative compounds (isothiazolinone and/or carboxylic acid) that provide stability without toxicity. This eliminates the safety hazards associated with cyanide while maintaining bath stability during long-term heating.
Solution Approach 2:
The patent introduces intermediary compounds (isothiazolinone and/or carboxylic acid) that mediate the stabilizing function previously performed by cyanide. These compounds act as alternative mediators between the gold salt and reducing agent, preventing unwanted reactions and maintaining bath stability without the harmful effects of cyanide.
2Reliability
If mixed reaction gold plating method is used to eliminate underlying metal corrosion, then coatability and film thickness are improved, but plating bath decomposition occurs during long-term heating
Solution Approach 1:
The patent changes the chemical parameters of the plating bath by selecting specific compounds (isothiazolinone and/or carboxylic acid) with appropriate concentrations and molecular structures. These parameter changes enable the bath to maintain stability during long-term heating while still allowing the mixed reaction to proceed effectively for corrosion-free gold plating.
Solution Approach 2:
The patent creates a composite plating bath system combining water-soluble gold salt, reducing agent, and the stabilizing compound (isothiazolinone and/or carboxylic acid). This composite formulation achieves both the corrosion protection benefits of mixed reaction plating and the thermal stability needed for long-term heating without decomposition.
3Device complexity
If displacement gold plating method is used, then simple process is achieved, but underlying metal corrosion and diffusion occur reducing wire bonding quality
Solution Approach 1:
The patent introduces an intermediary stabilizing compound that mediates the displacement reaction to prevent harmful side effects. The isothiazolinone and/or carboxylic acid acts as a controlling intermediary that allows gold deposition while preventing underlying metal corrosion and diffusion, thereby maintaining wire bonding quality despite the simplicity of the displacement method.
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 provides excellent plating bath stability and maintains an acceptable deposition rate, preventing corrosion and ensuring reliable solder joint and wire bonding properties without the need for cyanide additives.
Implementation Method 1
a phosphine compound represented by formula (1)... which acts as a stabilizer to prevent bath decomposition
Implementation Method 2
a reducing agent... promote displacement reaction and reduction reaction concurrently
Implementation Method 3
a water-soluble gold salt
Data Source
Figure 1A~1B
AI summary
The present invention provides an electroless gold plating bath having excellent plating bath stability without containing a cyanide compound under long term plating bath heating time. An electroless gold plating bath of the present invention solving above problems includes: a water-soluble gold salt; a reducing agent; and a phosphine compound represented by a following formula (1) wherein R1, R2, and R3 represent identically or differently either a phenyl group, or an alkyl group having 1 to 5 carbons, and at least one of the phenyl group or the alkyl group is substituted by a sulfonate group or its salt, a cyano group, or a carboxy group or its salt.