Dual Seal Ring MEMS Package Reduces Window Lid Deflection
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Solution Overview
Problem
Conventional microbolometer packages face limitations in size and thermal sensitivity due to deflection and stress issues caused by pressure differentials, which inhibit the effective isolation of microbolometers from external thermal energy and reduce image quality.
Innovation Solution
A dual seal ring assembly is implemented, comprising an inner seal ring near the MEMS devices and an outer seal ring near the edges of the package, creating a hermetic seal that reduces window lid deflection and stress, allowing for a larger cavity region and thinner window lid, thereby enhancing thermal sensitivity and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the vacuum region size is increased to improve thermal isolation, then thermal sensitivity is improved, but window lid deflection increases causing contact with reference pixels
Solution Approach 1:
The single seal ring is divided into two separate seal rings: an inner seal ring positioned closer to the reference pixels and an outer seal ring positioned closer to the edges of the window lid. This segmentation allows the vacuum region to be larger for improved thermal sensitivity while the inner seal ring provides additional support to prevent window lid deflection from contacting the reference pixels.
2Strength
If the window lid thickness is increased to reduce deflection, then structural strength is improved, but electromagnetic radiation transmission is blocked
Solution Approach 1:
The support function is segmented from the window lid thickness to the seal ring structure. By adding the inner seal ring, the window lid can maintain a thin profile for optimal electromagnetic radiation transmission while the dual seal ring assembly provides the necessary structural support to prevent deflection.
3Ease of manufacture
If the span between solder joints is increased to improve manufacturing, then ease of manufacture is improved, but deflection increases to the fourth power of span
Solution Approach 1:
The seal ring structure is segmented into inner and outer components that can be formed and positioned independently. This allows optimization of the span between solder joints for ease of manufacture while the inner seal ring provides additional support points to control deflection without requiring increased window lid thickness.
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 dual seal ring assembly significantly reduces window lid deflection and stress, enabling a larger pixel array and improved thermal sensitivity, resulting in enhanced image quality and thermal isolation for microbolometer packages.
Implementation Method 1
the requirement of a high vacuum environment that thermally isolates the microbolometers from the external ambient temperatures
Implementation Method 2
the vacuum within the vacuum region 15 creates a pressure differential with respect to the exterior atmospheric pressure
Data Source
Figure 1
Figure 2A~2B
Figure 3A
AI summary
A microelectromechanical systems (MEMS) package includes a substrate extending between a first pair of outer edges to define a length and a second pair of outer edges to define a width. A seal ring assembly is disposed on the substrate and includes at least one seal ring creating a first boundary point adjacent to at least one MEMS device and a second boundary point adjacent at least one of the outer edges. The package further includes a window lid on the seal ring assembly to define a seal gap containing the at least one MEMS device. The seal ring assembly anchors the window lid to the substrate at the second boundary point such that deflection of the window lid into the seal gap is reduced.