Liquid Ejection Head Pad Electrode Hardness for Reliable Mounting
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Solution Overview
Problem
In liquid ejection heads with high-density piezoelectric elements, the narrow pitch between pad electrodes makes it difficult to employ wire bonding for mounting flexible boards, leading to potential shorting and connection failures due to the high voltage required for piezoelectric membrane deformation.
Innovation Solution
The liquid ejection head incorporates pad electrodes with a higher hardness than the wirings, formed from the same material as the first electrodes, to reduce physical damage during electrical inspection and mounting, ensuring reliable connections even at high densities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wire bonding is used for mounting flexible boards on pad electrodes, then electrical connection can be established, but the narrow pitch between pad electrodes (50 μm or smaller) causes difficulty in bonding and increases the possibility of shorting between adjacent pad electrodes
Solution Approach 1:
The patent extracts the bonding process from the mounting method by using NCF/NCP instead of wire bonding or ACF/ACP. This eliminates the need for physical bonding wires or conductive particles, thereby avoiding shorting risks between adjacent pad electrodes at narrow pitches while still establishing reliable electrical connections through the non-conductive film's adhesive properties
Solution Approach 2:
The patent employs NCF/NCP as a disposable mounting method that does not require complex bonding equipment or processes. The non-conductive film serves its purpose of electrical connection and mechanical bonding, then remains as a permanent insulating layer, eliminating the need for subsequent removal or adjustment operations
2Reliability
If ACF/ACP is used for mounting flexible boards, then electrical connection can be established, but the conductive particles in the adhesive cause leak current under the relatively high voltage required for piezoelectric membrane deformation
Solution Approach 1:
The patent removes the conductive particles from the mounting adhesive by using NCF/NCP instead of ACF/ACP. This extraction of conductive elements eliminates the source of leak current while maintaining the adhesive's ability to establish electrical connections through direct contact between the flexible board electrodes and pad electrodes
Solution Approach 2:
The non-conductive film acts as an intermediary mounting material that provides mechanical bonding and electrical connection without introducing conductive particles. It mediates between the flexible board and substrate, enabling voltage application to piezoelectric elements without causing leak current through the mounting adhesive
3Reliability
If soft materials with low electrical resistivity are used for pad electrodes, then electrical conductivity is improved, but the pad electrodes are physically damaged during probing for electrical inspection
Solution Approach 1:
The patent applies different material properties to different regions of the pad electrode structure. The pad electrode itself uses soft, highly conductive materials (gold, aluminum, or copper) for optimal electrical conductivity, while the mounting adhesive uses a harder, non-conductive material (NCF/NCP) that provides mechanical protection during probing operations
Solution Approach 2:
The non-conductive film serves as an intermediary layer that protects the soft pad electrode material during probing. It provides a harder surface that resists physical damage from probe contact while allowing electrical inspection to proceed through the flexible board connection
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 increased hardness of the pad electrodes prevents physical damage during probing, allowing for reliable electrical inspection and mounting of flexible boards, thereby enhancing the electrical reliability of the liquid ejection head.
Implementation Method 1
By being deformed by a piezoelectric element, this vibration plate allows pressure to be applied to the ink in the pressure chamber and an ink droplet to be ejected from the nozzle. The piezoelectric element of such a liquid ejection head includes a piezoelectric membrane, which is a membrane-shaped piezoelectric element
Implementation Method 2
part of a pressure chamber communicating with a nozzle that jets an ink droplet is formed with a vibration plate. By being deformed by a piezoelectric element, this vibration plate allows pressure to be applied to the ink
Data Source
AI summary
A liquid ejection head includes an ejection element substrate having a substrate, a vibration plate provided at the substrate, a piezoelectric element having a first electrode, a piezoelectric layer, and a second electrode in this order on a surface of the vibration plate opposite from the substrate, a first wiring electrically connected to the first electrode, a second wiring electrically connected to the second electrode, and a pad electrode electrically connected to the first wiring and/or the second wiring. The liquid ejection head also includes an electric wiring board electrically connected to the pad electrode with a mounting electrode interposed in between. The pad electrode has higher hardness than the first wiring, and the second wiring and has a pad region bonded to the mounting electrode and a connection region bonded to the wiring electrically connected to the pad electrode.