MEMS Package Moisture Resistance via Segmented Sealant and Barrier Layers
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Solution Overview
Problem
Conventional MEMS package structures are prone to moisture permeation due to cracks in the sealant, especially in high humidity environments, which can lead to device failure.
Innovation Solution
A MEMS package structure with a lid having a recess to reduce the peripheral gap, a sealant with a thickness less than the MEMS device height, a first moisture barrier coated around the chip, lid, and sealant, and additional barriers including a second moisture barrier, molding compound, and moisture absorption element to provide multiple layers of protection against moisture ingress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sealant is used to seal the space between the chip and the cover plate, then the MEMS device is protected from contaminants, but the sealant may crack and moisture may permeate into the space after using a period of time in high humidity environment
Solution Approach 1:
The patent divides the sealing system into multiple independent components: a first sealant layer between the chip and lid, a second sealant layer between the lid and cover plate, and a moisture barrier layer. This segmentation allows each layer to perform specific sealing functions and reduces the risk of complete sealing failure if one layer cracks.
Solution Approach 2:
The patent uses composite sealing structures combining different materials with complementary properties: the first sealant (e.g., epoxy resin) provides strong bonding to the chip, the second sealant (e.g., silicone rubber) provides flexibility and moisture resistance, and the moisture barrier layer provides additional protection. This composite approach leverages the advantages of each material while mitigating their individual weaknesses.
2Volume of moving object
If a large gap exists between the cover plate and the chip, then the MEMS device has space for operation, but moisture can easily permeate into the sealed space through the sealant
Solution Approach 1:
The patent addresses moisture ingress not only in the vertical dimension (through the sealant gap) but also in the horizontal dimension by adding a moisture barrier layer that extends across the entire sealed space. This multi-dimensional approach blocks moisture from reaching the MEMS device through multiple potential pathways.
Solution Approach 2:
The moisture barrier layer acts as an intermediary between the external environment and the MEMS device, providing an additional protective layer that intercepts moisture before it can penetrate through the sealant or reach the device. This intermediary layer is specifically designed to resist moisture while allowing the sealed space to maintain its operational volume.
3Reliability
If the sealant thickness is increased to prevent moisture permeation, then moisture resistance improves, but the peripheral gap between the lid and chip cannot be reduced
Solution Approach 1:
The sealing function is segmented across multiple layers with different thickness requirements: the first sealant layer has thickness t1 determined by the chip-lid gap, the second sealant layer has thickness t2 determined by the lid-cover plate gap, and the moisture barrier layer provides additional protection. This segmentation allows each layer to be optimized for its specific function without compromising the overall sealing effectiveness.
Solution Approach 2:
The patent employs composite sealing layers where the first sealant (e.g., epoxy resin) provides structural bonding, the second sealant (e.g., silicone rubber) provides flexibility and moisture resistance, and the moisture barrier layer provides additional protection. This composite structure achieves superior moisture resistance without requiring excessive thickness, as each material contributes its specific protective properties.
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 structure significantly enhances moisture resistance, preventing contamination and ensuring normal operation of MEMS devices by reducing the peripheral gap and using multiple barriers to block and absorb moisture.
Implementation Method 1
The sealant is disposed between the chip and the lid so as to seal the recess
Implementation Method 2
The first moisture barrier is coated around the chip, the sealant and the lid
Implementation Method 3
a molding compound, disposed in the cavity and sealed around the first moisture barrier
Implementation Method 4
a moisture absorption element, disposed in the cavity
Data Source
AI summary
A MEMS package structure including a chip, a MEMS device, a lid, a sealant and a first moisture barrier is provided. The chip comprises an active surface. The MEMS system device is disposed on the active surface. The lid is covered on the chip and comprising a recess, wherein the MEMS device is in the recess. The sealant is disposed between the chip and the lid so as to seal the recess, wherein a thickness of the sealant is less than a height of the MEMS device. The first moisture barrier is sealed around the chip, the sealant and the lid.