Composite Pedestal Small Link Isolates Die-Attach Stress
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Solution Overview
Problem
Conventional dual stack pressure sensors suffer from short and long term drift due to temperature hysteresis and bond relaxation in the RTV adhesive, leading to instability and offset issues, especially in low pressure range sensors with thin diaphragms.
Innovation Solution
A composite pedestal with top and bottom platforms connected by a small link is used to isolate die-attach stresses, reducing the deformation of the pressure sensing diaphragm and minimizing residual null offset output, which includes various geometries such as a flexible membrane, cantilever beam, and dual links to absorb and isolate stress effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If RTV adhesive is used to attach the Pyrex pedestal to the base, then the pedestal can be securely mounted, but temperature hysteresis and bond relaxation cause short and long term drift in sensor offset
Solution Approach 1:
The pedestal is segmented into multiple sections (first pedestal section, second pedestal section, third pedestal section) connected by stress isolation features. This segmentation allows the mounting structure to maintain strength through secure connections while isolating the sensing diaphragm from adhesive-induced stresses, thereby preventing offset drift.
Solution Approach 2:
Stress isolation features (such as compliant layers or geometric transitions) are introduced as intermediary elements between the mounted pedestal and the sensing diaphragm. These intermediaries absorb and isolate the temperature hysteresis and bond relaxation effects from the RTV adhesive, preventing them from transmitting to the sensing elements while maintaining structural integrity.
2Reliability
If slots or channels are etched in the silicon die to isolate stress, then die-attach stress can be reduced, but the geometry requires multiple thin-web channels that are problematical and costly to implement
Solution Approach 1:
The pedestal is divided into multiple sections with stress isolation features positioned between them. This segmentation provides effective stress isolation through simpler geometric transitions rather than requiring multiple complex thin-web channels, reducing manufacturing complexity while maintaining reliability.
Solution Approach 2:
Stress isolation features are strategically positioned at specific locations where stress transmission would otherwise occur (between pedestal sections). This localized approach provides effective stress isolation only where needed, avoiding the complexity of multiple channels throughout the entire pedestal structure.
3Measurement precision
If thin diaphragms are used in low pressure range sensors, then sensing sensitivity is improved, but the sensors become more susceptible to die-attach stress effects
Solution Approach 1:
Stress isolation features act as intermediary elements that protect the thin diaphragm from die-attach stresses. These intermediaries absorb and isolate the temperature hysteresis and bond relaxation effects, preventing them from transmitting to the sensitive thin diaphragm while maintaining the diaphragm's high sensing sensitivity.
Solution Approach 2:
The segmented pedestal structure with stress isolation features creates a protective barrier between the mounting structure and the thin diaphragm. This segmentation isolates the diaphragm from stress sources while allowing it to maintain its thin, sensitive configuration for high measurement precision.
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 significantly improves short and long term stability by reducing die-attach stress on the pressure sensing diaphragm, minimizing temperature hysteresis and bond relaxation effects, and providing a cost-effective manufacturing method for the composite pedestals.
Implementation Method 1
said small link isolating at least some of the stresses, produced by the mounting of the pressure sensing die on the base, from said deflectable pressure sensing diaphragm
Implementation Method 2
sensing elements for detecting the deflection of the diaphragm
Data Source
AI summary
The invention concerns a pressure sensing die to be mounted on a base, comprising:a diaphragm structure with a deflectable pressure sensing diaphragm whose deflection is representative of the pressure and sensing elements for detecting the deflection of the sensing diaphragm;a pedestal supporting the diaphragm structure;wherein the pedestal is a composite pedestal comprising top and bottom platforms connected by at least one small link having a mean cross-section smaller than the cross-section of the top platform, said small link isolating at least some of the stresses, produced by the mounting of the pressure sensing die on the base, from said deflectable pressure sensing diaphragm.