Cavity Pressure Sensor Package Eliminating Metal-Molding Interfaces
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Solution Overview
Problem
Cavity-style pressure sensors in tire pressure monitoring systems are prone to micro gaps between the molding material and metal contacts, leading to air diffusion and bubble formation during rapid decompression events, which can cause errors or device failure.
Innovation Solution
The solution involves forming a cavity over a portion of the control die or substrate, ensuring the only exposed interface with the molding compound is to silicon, thereby eliminating metal-to-molding material interfaces and reducing the occurrence of micro gaps, and using a pressure permeable cap to protect the silicone gel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cavity-style pressure sensors use traditional molding material and metal contacts interfaces, then the device structure is simple and easy to manufacture, but micro gaps form at the interfaces causing air diffusion and bubble formation during rapid decompression
Solution Approach 1:
The patent removes the metal contacts from the molding material interface by routing all electrical connections through the silicon die itself. The cavity style package retains its protective enclosure and pressure sensing functionality, but the problematic metal-to-molding material interfaces are extracted and replaced with silicon-to-molding material interfaces that do not create micro gaps for air diffusion.
Solution Approach 2:
The patent changes the material interface composition at the critical sealing boundary. Instead of having metal contacts embedded in molding material (which creates micro gaps), the interface is changed to silicon die directly bonded to molding material, fundamentally altering the physical and chemical properties of the interface to prevent air diffusion while maintaining structural integrity.
2Speed
If rapid decompression events occur in traditional cavity-style packages, then the device can respond quickly to pressure changes, but air stored in micro gaps escapes forming bubbles that interact with wirebond connections and MEMS structures
Solution Approach 1:
The patent applies preliminary anti-action by preventing the formation of micro gaps before rapid decompression events can occur. By eliminating the metal-to-molding material interfaces where air would be stored, the system preemptively removes the source of the problem, so that when rapid decompression occurs, there is no trapped air to form harmful bubbles that could disrupt wirebond connections or MEMS structures.
3Ease of manufacture
If micro gaps are present at metal contact interfaces, then the package can be manufactured using standard processes, but high-pressure air diffuses through silicone gel and stores in micro gaps causing measurement errors
Solution Approach 1:
The patent extracts the metal contacts from the pressure sensing cavity environment, routing all electrical connections through the silicon die surface or edge. This removes the metal-to-molding material interfaces that create micro gaps, preventing air diffusion pathways while maintaining electrical connectivity and pressure sensing 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
This approach prevents air bubbles from forming in the silicone gel, enhancing the accuracy and reliability of pressure readings and reducing the risk of device failure during decompression events, while also minimizing the size and resource usage of the pressure sensor package.
Implementation Method 1
high-pressure air can diffuse through the silicone gel and be stored in the micro gaps
Implementation Method 2
a pressure permeable cap to protect the silicone gel
Data Source
AI summary
A pressure sensor package is provided that reduces the occurrence of micro gaps between molding material and metal contacts that can store high-pressure air. The present invention provides this capability by reducing or eliminating interfaces between package molding material and metal contacts. In one embodiment, a control die is electrically coupled to a lead frame and then encapsulated in molding material, using a technique that forms a cavity over a portion of the control die. The cavity exposes contacts on the free surface of the control die that can be electrically coupled to a pressure sensor device using, for example, wire bonding techniques. In another embodiment, a region of a substrate can be encapsulated in molding material, using a technique that forms a cavity over a sub-portion of the substrate that includes contacts. A pressure sensor device can be electrically coupled to the exposed contacts.