Tapered Edge Conductive Layer for Liquid Discharge Head Substrate
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Solution Overview
Problem
In liquid discharge head substrates, the surface material contacting ink can dissolve, leading to corrosion of heat generating resistive elements and disconnection issues due to insufficient coatability of protective layers, especially at the edge portions where ink penetration occurs.
Innovation Solution
A liquid discharge head substrate design featuring a conductive layer with a tapered edge portion, formed by isotropic and anisotropic etching of iridium and tantalum films, improves the coatability of the insulating layer, preventing ink penetration and corrosion by creating an acute angle between the side and bottom surfaces of the edge portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective layer is provided on the heat generating resistive element, then corrosion resistance is improved, but coatability at edge portions deteriorates due to vertical side surfaces
Solution Approach 1:
The conductive layer edge portion is designed with a tapered shape instead of a vertical side surface, creating a curved or inclined surface that allows the insulating layer to be uniformly coated. This curvature modification resolves the coatability issue while maintaining corrosion protection.
Solution Approach 2:
The geometry parameter of the conductive layer edge is changed from a vertical profile to a tapered profile with a specific angle range (30°-60°). This parameter change enables the insulating layer to conform to the surface, improving coatability without sacrificing protective function.
2Ease of manufacture
If the conductive layer edge is vertical, then manufacturing simplicity is maintained, but ink penetration occurs leading to disconnection
Solution Approach 1:
The tapered edge shape is designed in advance to prevent ink penetration before it can cause disconnection. By creating an acute angle at the edge, the design proactively blocks the harmful effect of ink infiltration that would otherwise occur with a vertical edge.
3Temperature
If the insulating layer is made thin, then heat conduction is improved, but protective function against ink corrosion deteriorates
Solution Approach 1:
The insulating layer is designed with varying thickness: thinner in the center region to maintain heat conduction and thicker at the edge portions to enhance protective function. This local quality differentiation allows simultaneous optimization of both heat conduction and corrosion protection.
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 tapered edge design enhances the reliability of the liquid discharge head by reducing ink penetration and corrosion, maintaining the integrity of the heat generating resistive elements and improving the substrate's durability during extended ink discharge operations.
Implementation Method 1
etching a part of the second film by isotropical etching in an etching apparatus
Implementation Method 2
after etching the second film, etching a part of the first film by anisotropical etching
Implementation Method 3
ink is heated by a heat generating resistive element to generate bubbles
Data Source
AI summary
One embodiment relates to a liquid discharge head substrate including at least one heat generating resistive element, a first insulating layer covering the heat generating resistive element, a conductive layer disposed on the first insulating layer and overlapping the heat generating resistive element with the first insulating layer interposed therebetween in a plan view with respect to an upper surface of the heat generating resistive element, and a second insulating layer covering an edge of the conductive layer. The edge of the conductive layer has a tapered shape.