Liquid Discharge Head Diffusion Prevention Layer Material Selection
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Solution Overview
Problem
The existing production methods for liquid discharge heads face issues with excessive etching of the diffusion prevention layer, leading to undercuts and potential contamination due to galvanic corrosion, especially when using TiW as the diffusion prevention layer, which is prone to dissolution in various solutions.
Innovation Solution
Selecting a metal for the diffusion prevention layer that is passivated or insensitive in a wide pH range, such as Pd, Nb, Rh, Ta, or Pt, which are positioned in a passivation area or insensitive area in the potential-pH diagram, to prevent galvanic corrosion and undercuts, and using these metals in conjunction with Au connection terminals to form the diffusion prevention layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If TiW is used as the diffusion prevention layer, then diffusion of Au into Al electrode portion is prevented, but excessive etching occurs leading to undercuts and potential contamination
Solution Approach 1:
The patent changes the material parameter of the diffusion prevention layer from TiW to a metal selected from Pd, Nb, Rh, Ta, or Pt. These alternative metals exhibit different electrochemical properties that prevent galvanic corrosion with Au, thereby eliminating the undercut issue while maintaining diffusion prevention functionality. This material substitution resolves the contradiction by finding a metal that provides both reliable diffusion prevention and resistance to etching-induced shape degradation.
2Reliability
If TiW diffusion prevention layer is used, then electrical connection reliability is improved, but the layer is prone to dissolution in various solutions causing contamination
Solution Approach 1:
The patent substitutes TiW with metals (Pd, Nb, Rh, Ta, or Pt) that have superior chemical stability and resistance to dissolution in various pH environments. These metals maintain their structural integrity and do not dissolve into the liquid discharge head components, thereby preventing contamination while preserving the electrical connection reliability provided by the diffusion prevention layer.
3Ease of manufacture
If metal layer for diffusion prevention is etched using acid solution with connection terminal as mask, then diffusion prevention layer is formed, but galvanic corrosion causes excessive etching
Solution Approach 1:
The patent changes the material composition of the diffusion prevention layer to metals that are electrochemically compatible with Au connection terminals. By selecting metals from Pd, Nb, Rh, Ta, or Pt, the galvanic potential difference between the diffusion prevention layer and the Au terminal is minimized or eliminated, preventing galvanic corrosion during the acid etching process. This allows the etching to proceed uniformly without the harmful undercut effect, maintaining shape accuracy while preserving the ease of manufacturing through standard photolithographic masking techniques.
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
Prevents excessive etching and undercuts of the diffusion prevention layer, ensuring reliable electrical connections and reducing the risk of contamination by maintaining stability across a wide pH range, thereby enhancing the production process and reliability of the liquid discharge heads.
Implementation Method 1
a step of etching the metal layer with an acid solution using the connection terminal as a mask to form the diffusion prevention layer
Implementation Method 2
peeling the pattern with an alkaline solution
Implementation Method 3
a diffusion prevention layer made of TiW is disposed for preventing diffusion of Au constituting the bump into the electrode portion constituted of Al
Data Source
AI summary
When the metal constituting a metal layer becoming a diffusion prevention layer is defined as a first metal and the metal constituting a connection terminal is defined as a second metal, in a potential-pH diagram for the first metal-H2O system, the first metal is present in a passivation area or an insensitive area at a potential of the difference between the standard electrode potentials of the first metal and the second metal in a pH range of 1 to 14.