Liquid Ejection Head Bonding Step for Air Bubble Containment
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Solution Overview
Problem
Air bubbles generated during the bonding process of substrates in liquid ejection heads can reduce bonding strength and cause defects or failures due to impaired electrical insulation and increased voids.
Innovation Solution
A liquid ejection head design that includes a step protruding from at least one face of the bonded substrates, positioned to overlap the connection terminal, and is covered by a sealing resin to trap and minimize air bubbles, thereby preventing their movement into the sealing resin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If substrates are bonded with adhesive to form flow-path-forming substrate, then bonding strength is improved, but air bubbles are generated inside the bonding layer causing reduced bonding strength and electrical insulation problems
Solution Approach 1:
The bonding process is segmented into multiple stages: first bonding the first flow path substrate to the second flow path substrate, then separately bonding the connection terminal to the second flow path substrate. This segmentation allows air bubbles to be excluded from critical areas during each bonding stage, preventing air bubble contamination while maintaining bonding strength.
Solution Approach 2:
The connection terminal is positioned and preliminarily fixed to the second flow path substrate before the final bonding of the flow-path-forming substrate. This preliminary action ensures that the connection terminal is already in place and secured, preventing air bubbles from being trapped between the connection terminal and the substrate during the subsequent bonding process, thereby maintaining both bonding strength and electrical insulation.
2Reliability
If connection terminal is bonded to second flow path substrate, then electrical connection is achieved, but air bubbles cause impaired electrical insulation and short-circuiting
Solution Approach 1:
The bonding operation is segmented into two distinct steps: first bonding the flow-path-forming substrate, then separately bonding the connection terminal. This segmentation ensures that the connection terminal is bonded in a controlled manner without air bubbles being trapped, thereby maintaining electrical insulation reliability and preventing short-circuiting.
Solution Approach 2:
The connection terminal is preliminarily positioned and fixed to the second flow path substrate before the final substrate bonding. This preliminary action ensures that the connection terminal is already secured in the correct position, preventing air bubbles from being trapped between the connection terminal and substrate during subsequent bonding, thus maintaining electrical insulation.
3Strength
If adhesive is applied to bond substrates, then substrate bonding is achieved, but adhesive flow out occurs without proper control
Solution Approach 1:
The connection terminal and its bonding area are given special local consideration through preliminary positioning and separate bonding. This local quality approach ensures that adhesive is precisely controlled at the connection terminal area, preventing adhesive flow out while maintaining strong substrate bonding.
Data Source
AI summary
A liquid ejection head includes: an element substrate including a first flow path substrate having a first face and a second face, a second flow path substrate having a third face and a fourth face and including an energy generating element and a connection terminal, and a bonding layer that bonds the second face and the third face; a wiring substrate having an external terminal; an electrical connection portion that electrically connects the connection terminal to the external terminal; and a sealing resin that covers the electrical connection portion and an end portion of the fourth face of the bonding layer. A step that protrudes from at least one of the second face and the third face is provided between the second face and the third face, and the step is arranged at a position overlapping the connection terminal when viewed in a first direction.