Fluid Ejection Cover-Layer Breaks for Stress and Fluid Ingress
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Solution Overview
Problem
Fluid ejection devices experience mechanical and thermal stresses during manufacturing and use, leading to defects and reduced lifespan due to varying coefficients of thermal expansion and fluid ingress through gaps, which can cause corrosion and electrical failures.
Innovation Solution
Incorporating breaks in the cover layer of fluid ejection devices, filled with materials like polymers and epoxy mold compound, to isolate stress-induced gaps and prevent fluid ingress, thereby protecting sensitive components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous cover layer is used to protect sensitive components, then protection against fluid ingress is improved, but mechanical stress from thermal expansion mismatches causes gaps and defects
Solution Approach 1:
The cover layer is divided into multiple discrete segments rather than forming a continuous layer. These segments are positioned to cover sensitive components like bondpads while leaving gaps between them. The segmentation allows each segment to independently accommodate thermal expansion without causing stress concentration that would create defects, while still providing protection against fluid ingress to critical areas.
2Adaptability or versatility
If different materials with varying CTE are used to construct components, then functional performance is improved, but thermal expansion mismatches cause mechanical stress and defects
Solution Approach 1:
The patent applies different material properties and structural characteristics to different regions of the device. Specifically, the cover layer segments are designed with local adaptations to accommodate thermal expansion in critical areas. The segmentation allows regions with different CTE values to expand and contract independently, reducing mechanical stress at material interfaces while maintaining the functional benefits of using diverse materials.
3Reliability
If wire encapsulation is performed to protect electrical connections, then reliability is improved, but the encapsulation process induces considerable stress on fluid ejection components
Solution Approach 1:
The encapsulation structure is segmented to allow independent movement and stress relief. Rather than a continuous encapsulation layer that would transmit stress uniformly, the segmented design allows different regions to accommodate stress independently, protecting electrical connections while reducing stress transmission to fluid ejection components.
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 solution mitigates mechanical and thermal stresses, reducing defects and extending the lifespan of fluid ejection devices by preventing fluid contact with critical components.
Implementation Method 1
Incorporating breaks in the cover layer of fluid ejection devices, filled with materials like polymers and epoxy mold compound, to isolate stress-induced gaps and prevent fluid ingress, thereby protecting sensitive components.
Data Source
AI summary
In various examples, a fluid ejection device may include a fluid ejection die formed with a first material and that includes a bondpad and a plurality of fluid ejectors, and a cover layer adjacent the fluid ejection die. The cover may be formed with a second material that is different than the first material and may include a first region that overlays the bondpad and a second region that overlays the plurality of fluid ejectors. In various examples, the first and second regions are separated by a break in the cover layer. The break may be filled with a third material that is different than one or both of the first and second material.