Indium Alloy Deposition via Two-Step Electrolytic Process
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Solution Overview
Problem
Current indium deposition methods for electronic and semiconductor applications face challenges such as island-like structure formation, inhomogeneity, and inefficiency in producing smooth submicron indium or indium alloy layers, particularly due to issues like hydrogen evolution and the use of toxic additives, which are not suitable for modern miniaturization demands.
Innovation Solution
A process involving a two-step electrolytic deposition method where a first indium or indium alloy layer forms a composed phase layer with the substrate, followed by partial removal and subsequent deposition of a second layer, using a conventional indium plating bath with controlled potentials to achieve smooth and glossy indium or indium alloy layers on metal or metal alloy surfaces like nickel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional electrolytic deposition is used to deposit indium layers, then the deposition process is simple and fast, but the deposited layers exhibit island-like structures and inhomogeneity which are unacceptable for submicron applications
Solution Approach 1:
The deposition process is divided into multiple sequential steps: initial deposition to form a composed phase layer, selective removal of excess material, and subsequent deposition to form the final smooth layer. This segmentation transforms a single complex deposition into manageable stages, each producing a specific intermediate structure that contributes to the final smooth surface.
Solution Approach 2:
The composed phase layer is formed as a preliminary structure before the final indium layer is deposited. This preliminary layer serves as a foundation that prevents island formation in subsequent deposition, enabling smooth final layers to be formed more easily.
2Manufacturing precision
If multi-step processes with intermediate layers are used to prevent island structures, then smooth indium layers can be achieved, but the process becomes laborious and requires multiple plating baths increasing production time and cost
Solution Approach 1:
Multiple deposition and removal steps are merged into a single plating bath system. The bath contains controlled amounts of indium and gallium ions that enable sequential layer formation without requiring physical transfer between different plating stations, thus maintaining multi-step precision while improving production efficiency.
Solution Approach 2:
The single plating bath performs multiple functions: it deposits both the composed phase layer and the final indium layer, and the chemical composition is designed to enable selective removal of excess material. This multi-functionality eliminates the need for separate plating baths for each step.
3Reliability
If strong chelating agents and strongly alkaline or acidic plating baths are used to prevent indium precipitation, then indium deposition can be maintained, but toxic additives like cyanide are required which are highly undesired
Solution Approach 1:
The plating bath uses mild alkaline conditions (pH 9-11) instead of strongly acidic or alkaline environments. Gallium ions are introduced to form stable complexes with indium at these mild pH levels, eliminating the need for toxic cyanide additives while maintaining deposition stability. The parameter change from extreme pH to mild pH combined with gallium complexation resolves both the stability and toxicity issues.
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
This method effectively produces smooth, glossy indium or indium alloy layers with reduced island-like structures, improving the quality and efficiency of indium deposition, suitable for applications in flip chips and solder bumps, while minimizing hydrogen evolution and eliminating the need for toxic additives.
Implementation Method 1
The electrolytic deposition of indium has been established long ago in the art
Implementation Method 2
a composed phase layer is formed of a part of the metal or metal alloy surface and a part of the first indium or indium alloy layer
Data Source
AI summary
The present invention deals with a process for deposition of indium or indium alloys and an article obtained by the process, wherein the process includes the stepsi. providing a substrate having at least one metal or metal alloy surface;ii. depositing a first indium or indium alloy layer on at least one portion of said surface whereby a composed phase layer is formed of a part of the metal or metal alloy surface and a part of the first indium or indium alloy layer;iii. removing partially or wholly the part of the first indium or indium alloy layer which has not been formed into the composed phase layer;iv. depositing a second indium or indium alloy layer on the at least one portion of the surface obtained in step iii.