MEMS Die Attachment Layer Stress Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Mechanical stress transmitted during the attachment of MEMS die to a mounting surface can adversely affect the performance of MEMS fluid pressure sensors, leading to erroneous readings due to non-transitory stress caused by torque and fluid pressure.
Innovation Solution
A method is developed to determine the maximum acceptable change in pressure due to mounting stress, using a pressure difference transfer function equation to calculate the optimal thickness of the attachment material, which reduces stress transmission by forming a thick, ductile attachment layer between the MEMS die and the mounting surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the MEMS die is soldered directly to the mounting surface, then the attachment strength is sufficient, but mechanical stress is transmitted to the MEMS die causing erroneous readings
Solution Approach 1:
A stress relief layer (epoxy layer) is introduced between the MEMS die and the mounting surface to act as an intermediary that absorbs and distributes mechanical stress, preventing direct transmission of stress to the sensitive MEMS die while maintaining adequate attachment strength
2Measurement precision
If a stress relief layer is added between the MEMS die and mounting surface, then stress transmission is reduced, but the device complexity increases
Solution Approach 1:
The thickness of the stress relief layer is optimized to specific ranges (5-20 micrometers) to achieve the desired stress relief effect while maintaining a simple single-layer structure that does not significantly increase device complexity
3Measurement precision
If the attachment material thickness is increased, then stress transmission is reduced, but the manufacturing precision requirements increase
Solution Approach 1:
The attachment layer thickness is optimized to specific ranges (5-20 micrometers) that provide sufficient stress relief while remaining within achievable manufacturing tolerances for standard PCB fabrication processes
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 method effectively reduces stress transmission to the MEMS die, enhancing its performance by minimizing erroneous readings and ensuring accurate fluid pressure sensing.
Implementation Method 1
provides an attachment layer between the MEMS die and the mounting surface and that reduces the transmission of stress to the MEMS die
Data Source
AI summary
A method of attaching a MEMS die to a base includes selecting an attachment material (x), determining a maximum acceptable change in pressure due to mounting stress (dPtarget) transmitted to a MEMS die, determining a worst-case pressure difference transfer function of the attachment material (x) over a thickness (h) variation of the attachment material (x) using the equation: dPmaxx=h*Bx+Cx, wherein B=pressure variation/thickness (h), and C=pressure variation, substituting dPtarget for dPmaxx in the pressure difference transfer function and solving the equation for h, wherein h=(dPtarget−Cx)/Bx, and attaching the MEMS die to a base using the selected attachment material (x) having at least the calculated thickness (h).