MEMS Inertial Sensor With Patterned Substrate Relief
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Solution Overview
Problem
Inertial sensors, particularly MEMS devices like accelerometers and gyroscopes, face challenges due to thermal expansion coefficient (CTE) mismatches between materials, leading to stress-induced performance issues and alignment problems, which existing solutions like thick compliant die bond layers cannot adequately address without compromising alignment and increasing complexity.
Innovation Solution
A MEMS sensor design featuring a substrate with a patterned relief surface on one side to reduce stress transmission, allowing for a thinner die bond layer and improved alignment, enabling more freedom in die bond material choice and reducing the impact of material property changes over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a thick and compliant die bond layer is used to isolate the MEMS from the package, then stress isolation is improved, but alignment precision deteriorates due to fluidity during curing
Solution Approach 1:
The substrate surface is patterned with relief features (protrusions or recesses) to create localized contact areas between the die bond layer and substrate. This local quality change allows the die bond layer to be thick enough for stress isolation while maintaining precise alignment through defined contact points that prevent excessive fluidity movement during curing.
Solution Approach 2:
The continuous substrate surface is segmented into multiple discrete contact areas through the relief pattern. This segmentation concentrates the bonding interface at specific locations, providing both mechanical support for alignment and stress isolation through the non-contact areas that allow the compliant material to absorb thermal expansion differences.
2Object-affected harmful factors
If a thick die bond layer is used to decouple stress, then stress isolation is improved, but device complexity increases due to alignment difficulty
Solution Approach 1:
By creating localized relief features on the substrate surface, the invention provides defined contact areas that simplify alignment procedures. The relief pattern acts as a mechanical guide that naturally positions the sensor die correctly, reducing the complexity of alignment operations even while maintaining a thick die bond layer for stress decoupling.
3Object-affected harmful factors
If the die bond layer is made compliant to absorb stress, then stress absorption is improved, but reliability deteriorates due to material aging and glass transition
Solution Approach 1:
The relief pattern creates localized contact areas that concentrate the mechanical interface at specific points. This allows the use of compliant die bond materials for stress absorption while the defined contact geometry maintains stable mechanical properties over time by preventing excessive material deformation and reducing the impact of aging effects.
Solution Approach 2:
The relief features are pre-formed on the substrate before die bonding. This preliminary action creates a stable mechanical framework that guides the die bond layer placement and maintains consistent contact pressure, compensating for material property changes due to aging and preventing the compliant material from becoming too rigid or losing adhesion over time.
4Object-affected harmful factors
If an interposer with small contact area is used to reduce stress contact, then stress transmission is reduced, but alignment precision and adhesion deteriorate
Solution Approach 1:
Instead of using a separate interposer component, the invention creates local quality changes directly on the substrate surface through relief features. This integrated approach provides small contact areas for stress reduction while maintaining precise alignment through the geometric definition of the relief pattern, eliminating the need for additional alignment mechanisms.
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 patterned substrate design effectively decouples stress, facilitating thinner packages, improved manufacturing accuracy, and reduced sensitivity to die bond material aging, while maintaining sensor performance and allowing for non-compliant die bond materials.
Implementation Method 1
The patterned substrate design effectively decouples stress, facilitating thinner packages, improved manufacturing accuracy, and reduced sensitivity to die bond material aging
Data Source
AI summary
An micro electro mechanical sensor comprising: a substrate; and a sensor element movably mounted to a first side of said substrate; wherein a second side of said substrate has a pattern formed in relief thereon. The pattern formed in relief on the second side of the substrate provides a reduced surface area for contact with the die bond layer. The reduced surface area reduces the amount of stress that is transmitted from the die bond layer to the substrate (and hence reduces the amount of transmitted stress reaching the MEMS sensor element). Because the substrate relief pattern provides a certain amount of stress decoupling, the die bond layer does not need to decouple the stress to the same extent as in previous designs. Therefore a thinner die bond layer can be used, which in turn allows the whole package to be slightly thinner.