Cyanide-Free Gold Electroplating Solution for Void-Free Hole Filling
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Solution Overview
Problem
Conventional gold electroplating solutions struggle to achieve void-free filling of drilled holes in high-density semiconductor devices and printed circuit boards due to inadequate current flow, leading to defects like voids and clefts, and the super-conformal filling method is impractical for mass production and results in inferior plating film properties.
Innovation Solution
A cyanide-free gold electroplating solution with a specific composition of gold (I) sulfite complexes, sulfites, sulfates, bismuth, and thallium catalysts, which preferentially deposits bismuth over thallium, creating a compact U-shaped stacked structure inside drilled holes by optimizing the adsorption and desorption reactions of these catalysts, ensuring sufficient filling without defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional gold electroplating solution is used to fill drilled holes, then the plating process is simple, but voids and clefts form due to inadequate current flow in high-aspect-ratio holes
Solution Approach 1:
The patent modifies the electroplating solution composition by adding specific crystal modifiers (bismuth and thallium compounds) and adjusting pH levels to create conditions that promote uniform current distribution and prevent void formation in high-aspect-ratio holes while maintaining process simplicity
Solution Approach 2:
The patent introduces crystal modifiers (bismuth and thallium compounds) as intermediary substances that mediate between the electroplating solution and the hole surface, facilitating uniform gold deposition by modifying the electrodeposition reaction and preventing localized current concentration that causes voids
2Manufacturing precision
If super-conformal filling method is used to achieve complete hole filling, then void-free filling is achieved, but equipment complexity increases and plating film properties deteriorate
Solution Approach 1:
The patent changes the chemical parameters of the electroplating solution (adding crystal modifiers, adjusting pH) to achieve complete hole filling through modified electrodeposition reactions, eliminating the need for complex super-conformal filling equipment and post-processing heat treatment while maintaining superior plating film properties
3Manufacturing precision
If thallium is used as crystal modifier, then hole filling is improved, but toxic thallium accumulates in the gold deposit
Solution Approach 1:
The patent uses a composite crystal modification system combining bismuth and thallium compounds in specific ratios, where bismuth serves as the primary crystal modifier and thallium serves as a secondary modifier that enhances hole filling while minimizing its own accumulation, creating a synergistic effect that reduces overall toxicity compared to thallium-only systems
Solution Approach 2:
The patent optimizes the concentration ratio of bismuth to thallium compounds in the electroplating solution to control the deposition kinetics, ensuring that bismuth is preferentially incorporated into the gold deposit while limiting thallium accumulation to minimal levels, thereby reducing toxicity while maintaining hole filling quality
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 enables complete and defect-free filling of drilled holes with a U-shaped cross-sectional structure, reducing thallium content and improving plating film properties, allowing for stable and uniform deposition even in high-aspect-ratio holes, and is suitable for mass production without the need for complex equipment or post-processing heat treatment.
Implementation Method 1
the direct current emitted from the anode causes the gold ions of the gold sulfite (I) complex in the gold electroplating solution and molecules such as metal salts and sulfite ions to move toward the surface of the cathode consisting of the object to be plated
Implementation Method 2
Au ions are electrolytically deposited flat as Au metal on the circuit surface around the drilled holes
Implementation Method 3
the adsorption and desorption reactions of these catalysts, ensuring sufficient filling without defects
Implementation Method 4
bismuth catalyst (as bismuth element)30-150mg/L, thallium catalyst (as thallium element)5-50mg/L
Data Source
AI summary
A cyanide-free gold electroplating solution for forming gold deposits contains bismuth and compact-packed via-filling deposit with a U-shaped stacked structure in cross section inside drilled holes. A gold electroplating solution includes 15 g/L of gold (I) sodium sulfite (as gold element), 15 g/L of sodium sulfate, 50 g/L of sodium sulfite, 10 mg/L of thallium formate (as thallium element), 50 mg/L of bismuth nitrate (as bismuth element) and 1 g/L of sodium phosphate.