Fluid Ejection Cover Layer Breaks for Thermal 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 bondpads, then protection against fluid ingress is improved, but mechanical stress from thermal expansion differences causes gaps and defects
Solution Approach 1:
The cover layer is segmented into discrete regions rather than being continuous. Breaks are introduced at specific locations where stress concentration occurs, allowing the cover layer to accommodate thermal expansion differences while maintaining protection over critical bondpad areas. This segmentation resolves the contradiction by sacrificing continuity to preserve both protection and structural stability.
Solution Approach 2:
The cover layer is designed with non-uniform properties - continuous and protective over bondpad regions, and broken or discontinuous in stress-prone regions. This local differentiation allows the structure to provide protection where needed while accommodating thermal stress where continuous coverage would cause failure.
2Adaptability or versatility
If different materials with varying CTE are used in components, then functional performance is improved, but thermal expansion differences cause mechanical stress and defects
Solution Approach 1:
The cover layer is divided into segments with breaks at strategic locations to interrupt stress transmission paths. This allows different materials with varying CTE to be used in the device while preventing stress accumulation that would otherwise lead to defects.
3Reliability
If wire encapsulation is performed to protect electrical connections, then electrical reliability is improved, but considerable stress is induced on fluid ejection components
Solution Approach 1:
The stress-inducing encapsulation process is separated from the fluid ejection components. Breaks in the cover layer allow stress to be contained in the encapsulation region rather than being transmitted to the fluid ejection components, enabling wire protection without compromising ejection component integrity.
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
Different components of the fluid ejection device may be constructed with different materials that have varying coefficients of thermal expansion ("CTE"). Consequently, each component may exhibit a different physical reaction to the heat.
Implementation Method 2
These breaks between the various regions or portions of the cover layer may mitigate the mechanical stress(es) outlined previously, and thereby may result in an increased fluid ejection device lifespan.
Implementation Method 3
the process of encapsulating wires connecting bondpads of fluid ejection die to other logic components may induce considerable stress to portions of the fluid ejection device. Additionally, during use, the ejection of fluid may impose competing forces on various components of the fluid ejection device, which can lead to further defects and/or shortening of the fluid ejection device's lifespan.
Data Source
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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.