Indium Alloy Diffusion Barrier for Copper-Gold Electroplating
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Solution Overview
Problem
Current electroplating technologies face challenges in preventing copper diffusion into precious metal layers, particularly gold, without using toxic nickel or expensive palladium, and existing cyanide-free solutions fail to maintain a bright and shiny aspect while effectively blocking copper migration.
Innovation Solution
An electroplating method using an indium alloy as a diffusion barrier layer between a copper-based underlayer and a precious metal top layer, with an indium concentration of 0.1 to 20 g/L and a thickness of 10 to 200 nm, which prevents copper migration and maintains the brightness and thickness distribution of the electroplated product.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If nickel or palladium intermediate layers are used to prevent copper diffusion into precious metal layers, then the diffusion barrier function is improved, but the toxicity (nickel) or cost (palladium) worsens
Solution Approach 1:
The patent replaces expensive palladium with a much cheaper indium-based diffusion barrier layer. The indium layer, though thin (10-200 nm), provides effective copper diffusion prevention without the high cost of palladium, embodying the principle of using cheaper materials to achieve the same protective function.
Solution Approach 2:
The patent changes the chemical composition parameter of the diffusion barrier layer from nickel/palladium to indium-based alloys. This parameter change eliminates the toxicity associated with nickel and the high cost of palladium, while maintaining the essential diffusion barrier function through carefully controlled indium concentration (0.1 to 20 g/L) and layer thickness.
2Object-affected harmful factors
If cyanide-free electroplating solutions are used, then the toxicity is reduced, but the ability to prevent copper diffusion and maintain brightness deteriorates
Solution Approach 1:
The indium-based layer acts as an intermediary between the cyanide-free plating solution and the substrate. It provides the necessary diffusion barrier function that was previously achieved by cyanide complexes, mediating between the non-toxic electrolyte and the requirement for copper diffusion prevention while maintaining surface brightness.
Solution Approach 2:
The patent uses composite indium-based alloys (indium with other metals) as the diffusion barrier layer. This composite material approach allows the system to achieve both non-toxicity (replacing cyanide) and effective copper diffusion prevention, with the indium alloy providing multiple functions simultaneously.
3Reliability
If indium alloy concentration is increased to improve diffusion barrier function, then the copper migration prevention is improved, but the thickness control and brightness distribution worsen
Solution Approach 1:
The patent optimizes the indium concentration parameter within a specific range (0.1 to 20 g/L) and controls the layer thickness (10 to 200 nm) to achieve the desired balance. By carefully adjusting these parameters, the system maintains effective copper diffusion prevention while ensuring uniform brightness and precise thickness control across the electroplated surface.
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 indium alloy effectively blocks copper migration into the gold layer, maintaining the aesthetic properties of the electroplated product even after thermal treatment, and is non-toxic, replacing hazardous materials like nickel and cyanide-based systems.
Implementation Method 1
providing a diffusion barrier layer which prevents the interdiffusion between the underlayer and the top layer under a precious metal top layer
Implementation Method 2
electroplating bath for electrochemical deposition of a novel Cu-Sn-Zn-Pd alloy
Data Source
Figure 1~2
Figure 3
Figure 4~4b
AI summary
The present invention relates to electroplated products having a combination of layers used to provide a diffusion barrier layer under a precious metal top layer on a substrate comprising a copper based material and/or a copper based underlayer, such that the layer or combination of layers prevents or retards the migration of copper into the precious metal layer or the opposite. The diffusion barrier layer comprises indium or an indium alloy. Moreover, the present invention refers a method for preparing such an electroplated product.