Iridium Electrode Pad for Liquid Ejection Head Substrates
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Solution Overview
Problem
Current liquid ejection head substrates face challenges in maintaining surface flatness during electrical inspection, leading to probe marks and potential connectivity issues due to the softness of Au and aluminum layers, which can result in irregularities and increased contact resistance, especially with the miniaturization of ejection systems.
Innovation Solution
A liquid ejection head substrate with an electrode pad portion featuring a cavitation-resistant layer made of iridium metal or alloy, which covers the heating element and is formed in the same layer as the electrode pad, providing enhanced chemical resistance and hardness to minimize probe mark formation during electrical inspection and improve connectivity reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a laminated structure of Au layer/TiW layer/aluminum layer is used for the electrode pad portion, then chemical resistance to acids, alkalis, and organic solvents is improved, but the surface flatness deteriorates due to probe mark formation during electrical inspection
Solution Approach 1:
The invention changes the material parameter of the electrode pad portion from soft materials (Au and aluminum) to a hard material (diamond-like carbon). This parameter change in material hardness prevents probe mark formation during electrical inspection while maintaining chemical resistance through the laminated structure of DLC, TiW, and aluminum layers.
Solution Approach 2:
The invention uses a composite material structure where a diamond-like carbon (DLC) layer is formed on the surface of the electrode pad portion. This DLC layer provides both hardness to prevent probe marks and chemical resistance, while the underlying TiW and aluminum layers provide additional chemical resistance and electrical conductivity, creating a multi-functional composite structure.
2Reliability
If a thick Au layer is formed to cover probe marks, then connection reliability is improved, but manufacturing cost increases and surface uniformity deteriorates
Solution Approach 1:
The invention performs preliminary action by forming the hard diamond-like carbon layer on the electrode pad surface before electrical inspection. This preliminary hardening prevents probe mark formation in advance, eliminating the need for subsequent thick Au layer formation to cover defects, thereby reducing manufacturing cost and maintaining surface uniformity.
3Manufacturing precision
If a thick insulating layer is formed to hide probe marks, then surface flatness is improved, but substrate warpage occurs due to applied stress
Solution Approach 1:
The invention performs preliminary hardening of the electrode pad surface by forming the diamond-like carbon layer before electrical inspection. This prevents probe mark formation at the source, eliminating the need for thick insulating layers that would cause substrate stress and warpage, thereby maintaining substrate shape integrity.
4Productivity
If the electrode pad portion is miniaturized to support smaller ejection systems, then productivity is improved, but probe mark formation becomes more severe due to reduced area
Solution Approach 1:
The invention changes the material parameter of the electrode pad surface to diamond-like carbon, which has extremely high hardness. This parameter change enables miniaturization of the electrode pad area while maintaining resistance to probe mark formation, as the hard DLC material prevents indentation even on smaller surfaces during electrical inspection.
Data Source
AI summary
An electrode pad portion of a liquid ejection head substrate includes a layer containing one of an iridium metal and an iridium alloy, and at least a portion of a cavitation resistant layer is provided in the same layer with the same material as the layer containing one of the iridium metal and the iridium alloy.