Unconstrained Pressure Sensor Package with Direct Die Mounting
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Solution Overview
Problem
High-accuracy pressure sensors have traditionally been complex and expensive to produce, with conventional methods requiring large packages and isolation layers to mitigate mechanical and thermal stresses, which increases costs and package size.
Innovation Solution
A sensor package design where the pressure sense die is directly mounted to a substrate without intervening isolation layers, using a thick alumina ceramic substrate and compliant adhesives like RTV or silicone, with an ASIC for compensation and direct die-to-die wire bonds to minimize stresses, and compliant metal leads for mounting, allowing for a smaller, cost-effective package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If isolation layers are used between the sense die and package substrate, then mechanical and thermal stresses are mitigated, but package size and manufacturing complexity increase
Solution Approach 1:
The patent removes the isolation layer from the package structure, allowing the sense die to be directly mounted to the package substrate. This extraction of the intermediary component simplifies the package design while maintaining stress mitigation through alternative means such as compliant lead frames and optimized bonding processes
Solution Approach 2:
The sense die is directly bonded to the package substrate without an isolation layer, merging previously separate components into a more integrated structure. This direct mounting reduces the number of interfaces and potential failure points while lowering manufacturing complexity
2Reliability
If isolation layers are used between the sense die and package substrate, then mechanical and thermal stresses are mitigated, but production cost increases
Solution Approach 1:
By removing the isolation layer, the patent eliminates the need to source, handle, and bond this additional component, thereby reducing material costs and assembly steps in the manufacturing process
Solution Approach 2:
The patent employs cost-effective materials and processes for direct mounting, including standard epoxy bonding and conventional lead frame structures, replacing expensive specialty isolation layers with more economical alternatives
3Volume of stationary object
If the sense die is directly mounted to the package substrate, then package size is reduced, but mechanical and thermal stresses increase
Solution Approach 1:
The patent modifies material properties and bonding parameters to enable direct mounting without isolation layers. This includes selecting substrates and adhesives with compatible thermal expansion coefficients and optimizing bond line thickness to accommodate stress variations
Solution Approach 2:
The patent employs compliant lead frames and flexible bonding structures that can absorb and distribute mechanical and thermal stresses, protecting the directly-mounted sense die from stress-related failures
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 results in a stable, high-accuracy sensor with reduced mechanical and thermal stresses, achieving lower production costs while maintaining high precision, suitable for measuring absolute, differential, and gauge pressures.
Implementation Method 1
a pressure sense die directly mounted to a surface of the package substrate with a stress compliant adhesive
Implementation Method 2
for piezo-resistive silicon pressure sense die based sensors
Data Source
AI summary
A pressure detection mechanism having a pressure sense die which may be attached directly to a surface of an alumina-based substrate with an adhesive having an optimum thickness. The adhesive may be stress compliant and may be one or more of silicone, silicone-epoxy, epoxy or any other suitable adhesive material. A compensation and interface application specific integrated circuit may be attached to the surface of the package substrate. The pressure sense die may be electrically connected to the integrated circuit with bond wires. The integrated circuit may be electrically connected to trace conductors on the package substrate with bond wires, and trace conductors may be connected to stress compliant metal conductors or leads for external connection to a mounting surface such as a printed circuit board. Hard plastic, or like material, symmetric covers, with one or more pressure ports or vents, may be attached to both sides of the substrate.