MEMS Pressure Sensor Gel-Free Packaging
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Solution Overview
Problem
Conventional MEMS pressure sensors fail when exposed to corrosive gases and liquids due to gel deterioration and are damaged by high-frequency vibrations during ultrasonic welding, which also dampens their responsiveness.
Innovation Solution
A MEMS pressure sensor design that eliminates gel from the top of the diaphragm, using a silicon cap and device die structure with embedded conductive vias and a piezoresistive bridge circuit, sealed within a recess to protect against harsh media and vibrations, allowing for safe ultrasonic welding without gel-related damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gel is used to protect the MEMS sensing element and lead wires from moisture and mechanical vibration, then the sensing element is protected from environmental damage, but the gel transmits high-frequency vibrations to the diaphragm causing damage and deteriorates in harsh media
Solution Approach 1:
The patent removes the gel entirely from the packaging structure. Instead of using gel to fill the cavity and protect components, the invention uses a hermetic seal created by ultrasonically welding the cover to the housing, eliminating the need for gel and thus avoiding vibration transmission and media deterioration issues
Solution Approach 2:
The patent replaces the mechanical vibration-dampening function of gel with an acoustic isolation approach. The hermetically sealed cavity acts as an acoustic isolation chamber that blocks high-frequency ultrasonic vibrations from reaching the MEMS device, while still providing environmental protection
2Reliability
If gel is used to protect lead wires and bond pads from harsh media, then corrosion is prevented, but the gel deteriorates and fails in corrosive environments
Solution Approach 1:
The patent removes the gel protective layer and replaces it with a hermetic metal seal. The ultrasonically welded cover creates a corrosion-proof barrier that does not deteriorate in harsh media, eliminating the need for gel-based corrosion protection
Solution Approach 2:
The patent uses a composite packaging structure combining metal housing, hermetic seal, and acoustic isolation cavity to provide both corrosion protection and vibration isolation without relying on organic gel materials that deteriorate in corrosive environments
3Reliability
If ultrasonic welding is used to hermetically seal the housing, then a reliable seal is achieved, but high-frequency vibrations damage the MEMS device when transmitted through gel
Solution Approach 1:
The patent converts the harmful ultrasonic vibrations into a beneficial hermetic seal by using the same ultrasonic welding process to create both the seal and the acoustic isolation cavity. The welded structure itself becomes the vibration barrier, turning the source of harm into the solution
Solution Approach 2:
The hermetically sealed cavity acts as an intermediary acoustic isolation chamber between the ultrasonic welding process and the MEMS device. This cavity buffers and isolates the MEMS device from direct vibration transmission while maintaining the hermetic seal
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 effectively protects the sensor from harsh media and prevents diaphragm damage during ultrasonic welding, enhancing the sensor's responsiveness and longevity by eliminating gel-related issues.
Implementation Method 1
Diaphragm deflections caused by pressure applied to the diaphragm change the resistance values of the piezoresistors in the bridge circuit
Implementation Method 2
the cover 3 is ultrasonically welded to the housing 2
Data Source
AI summary
MEMS pressure sensing elements, the fabrication methods of the sensing elements, and the packaging methods using the new sensing elements are introduced to provide a way for a harsh media absolute pressure sensing and eliminating the negative effects caused by the gel used in the prior art. The invention uses vertical conductive vias to electrically connect the enclosed circuit to the outside, and uses a fusion bond method to attach a cap with the embedded conductive vias over a device die having a circuit for example a piezoresistive Wheatstone bridge to sense pressure. New packaging methods comprise a) a two-pocket housing structure and using a surface mounting method to attach a new sensing element into one pocket by a ball grid array (BGA), and b) a single pocket structure and using conventional die attach and wire bonding. Both methods can be used for harsh media pressure sensing but without the negative effects caused by the gel in prior art.