Counterbore Backing Plate for Sensor Stress Isolation
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Solution Overview
Problem
Conventional pressure sensors experience non-zero output signals due to temperature-induced stresses, which are challenging to mitigate without increasing the thickness of the backing plate, given space and cost constraints.
Innovation Solution
The introduction of a counterbore on the backing plate reduces its stiffness, allowing it to absorb package stresses while maintaining a large surface area for bonding, enabling thinner backing plates that effectively isolate stresses without increasing thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the backing plate thickness is increased to minimize package stresses, then stress isolation performance is improved, but device size and manufacturing cost increase
Solution Approach 1:
The backing plate is designed with non-uniform thickness, featuring a thicker peripheral region and a thinner central region. This local quality variation allows the plate to provide enhanced stress isolation at the edges where bonding stresses concentrate, while reducing overall thickness and material usage in the central sensing area.
Solution Approach 2:
The backing plate geometry is segmented into distinct thickness zones - a thicker peripheral portion and a thinner central portion. This segmentation enables different regions to fulfill different functions: the thicker periphery provides structural support and stress isolation, while the thinner center reduces overall device size and allows better access for electrical connections.
2Measurement precision
If the backing plate thickness is increased to reduce Temperature Coefficient of Offset, then TCO is reduced, but assembly process complexity and manufacturing cost increase
Solution Approach 1:
The backing plate thickness parameter is changed from uniform to non-uniform distribution. By optimizing the thickness profile (thicker edges, thinner center), the plate achieves improved TCO performance through better stress isolation while maintaining manufacturability and simplifying the bonding process compared to a uniformly thick plate.
3Reliability
If the backing plate thickness is increased to improve stress isolation, then package stress transmission is reduced, but available space for electrical connections decreases
Solution Approach 1:
The backing plate employs local quality variation with non-uniform thickness distribution. The thinner central region creates additional space for electrical connections and wire bonds, while the thicker peripheral region maintains effective stress isolation. This localized thickness optimization resolves the conflict between stress isolation performance and electrical connection accessibility.
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
This approach significantly reduces the Temperature Coefficient of Offset (TCO) by up to a factor of 4, improving stress isolation and enabling robust electrical connections, even in constrained spaces.
Implementation Method 1
The introduction of a counterbore on the backing plate reduces its stiffness, allowing it to absorb package stresses
Implementation Method 2
the Coefficient of Thermal Expansion (CTE) mismatch between the different materials produce package stresses
Data Source
AI summary
The sensor geometry for improved package stress isolation is disclosed. A counterbore on the backing plate improves stress isolation properties of the sensor. The counterbore thins the wall of the backing plate maintaining the contact area with the package. The depth and diameter of the counterbore can be adjusted to find geometry for allowing the backing plate to absorb more package stresses. Thinning the wall of the backing plate make it less rigid and allows the backing plate to absorb more of the stresses produced at the interface with the package. The counterbore also keeps a large surface area at the bottom of the backing plate creating a strong bond with the package.