Film Formation Method for Copper Substrates
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Solution Overview
Problem
Conventional methods fail to provide a uniform catalyst metal on copper surfaces, leading to uneven palladium film formation, copper diffusion, and reduced solder and wire bondability, resulting in unreliable connections in conductor circuits.
Innovation Solution
A film formation method involving substitution reduction plating to form a thin platinum catalyst film, followed by a dense and uniform palladium film, and a gold film, which acts as a diffusion barrier, enhancing bondability and connection reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick nickel film is formed on copper surface, then copper oxidation is prevented and solder bonding is enabled, but the risk of short-circuit between conductor circuits increases and manufacturing precision deteriorates
Solution Approach 1:
The patent divides the protective film into three functional layers: a thin catalyst layer (0.003-0.5 μm) for enabling plating, a palladium layer (0.03-2 μm) for diffusion barrier and bonding, and a gold layer (0.003-0.5 μm) for oxidation prevention. This segmentation allows each layer to be optimized for its specific function, achieving reliable connections without the short-circuit risks of thick nickel films.
Solution Approach 2:
The patent changes the material composition and thickness parameters of the film structure. By using a thin catalyst layer instead of thick nickel, and combining multiple materials (catalyst, palladium, gold) with specific thickness ranges, the film provides both protection and precision, resolving the contradiction between reliability and manufacturing precision.
2Length of stationary object
If a palladium film is formed directly on copper surface, then nickel layer is eliminated reducing thickness, but the palladium film becomes uneven and copper diffusion occurs
Solution Approach 1:
The patent applies preliminary action by forming a thin catalyst layer on the copper surface before depositing the palladium film. This catalyst layer serves as a foundation that enables uniform palladium deposition, preventing the unevenness and copper diffusion that occur when palladium is deposited directly on copper. The preliminary catalyst layer ensures the subsequent palladium film achieves the desired uniformity and thickness control.
3Reliability
If a catalyst metal is provided on copper surface to enable palladium plating, then palladium film formation is stabilized, but the catalyst metal is not uniformly distributed
Solution Approach 1:
The patent optimizes the catalyst layer parameters including thickness (0.003-0.5 μm), composition (containing Pt, Pd, or Ni), and deposition method to achieve both stable palladium plating and uniform distribution. By carefully controlling these parameters, the catalyst layer provides consistent nucleation sites for palladium deposition without creating the non-uniformity problems of conventional catalyst applications.
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 method achieves high connection reliability by preventing copper and palladium diffusion into the gold film, improving solder bondability and wire bondability, and maintaining a stable film structure.
Implementation Method 1
a catalyst film formation step of forming a catalyst film on a surface of a substrate made of copper or a copper alloy by substitution reduction plating
Implementation Method 2
an intermediate film formation step of forming a palladium-plating film on the catalyst film
Implementation Method 3
a surface film formation step of forming a gold plating film on the palladium-plating film
Implementation Method 4
a gold plating film on the palladium-plating film... acts as a diffusion barrier, preventing copper and palladium diffusion into the gold film
Data Source
AI summary
A film formation method comprises a catalyst film formation step of forming a catalyst film on a surface of a substrate by substitution reduction plating, an intermediate film formation step of forming a palladium plating film on the catalyst film, and a surface film formation step of forming a gold plating film on the palladium plating film.