Patterned Adhesive Sheet for Hermetic MEMS Packaging
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Solution Overview
Problem
Microelectromechanical systems (MEMS) devices face contamination and failure due to introduction of contaminants like moisture and oxygen during dicing, and existing bonding materials introduce electrical conductivity or cause contamination, limiting device layout and process capability.
Innovation Solution
A patterned adhesive sheet is used to bond a cover to MEMS devices on a substrate, providing a hermetic seal without additional adhesives, reducing outgassing and damage to MEMS actuators, and enabling efficient packaging and electrical isolation, while allowing for flexible via placement and solder-filled vias for improved thermal and electrical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bonding techniques such as silicon/gold eutectic bond or gold/gold thermal compression bonding are used, then hermetic seal is achieved, but electrical conductivity is introduced and device layout is constrained
Solution Approach 1:
The patent introduces an intermediate adhesive layer between the bonding surfaces that provides electrical isolation while maintaining hermetic sealing. This adhesive mediator allows device layout flexibility without compromising the seal integrity, resolving the contradiction between hermetic seal and layout versatility.
2Ease of manufacture
If glass frit is used as bonding material, then bonding is achieved, but contamination of MEMS devices occurs and process capability is limited
Solution Approach 1:
The patent employs a disposable adhesive sheet that is pre-patterned and single-use, eliminating the need for screen printing processes that cause contamination. This disposable approach maintains ease of manufacture while preventing device contamination through contactless application.
3Strength
If high temperature bonding is used, then strong bond is achieved, but MEMS actuators are damaged
Solution Approach 1:
The patent changes the bonding parameters by using a low-temperature curing adhesive that achieves sufficient bond strength at temperatures safe for MEMS actuators. This parameter modification resolves the contradiction between bond strength and actuator integrity.
4Adaptability or versatility
If additional adhesives are used for bonding, then bonding flexibility is improved, but outgassing potential increases
Solution Approach 1:
The patent merges the bonding function and sealing function into a single adhesive sheet that performs both roles simultaneously. This consolidation reduces the total number of adhesive materials used, thereby reducing outgassing potential while maintaining bonding flexibility.
5Productivity
If dicing is performed without prior sealing, then device separation is achieved, but contamination and device failure occur
Solution Approach 1:
The patent applies preliminary sealing to the entire wafer before the dicing process. This preliminary action protects all devices simultaneously during separation, enabling high productivity while preventing contamination and failure that would otherwise occur during dicing.
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 reduces MEMS production costs, increases yield and reliability, minimizes package size, and enhances thermal and electrical performance by providing a low-profile, hermetic seal that prevents contamination and radio frequency reflections, while allowing for scalable and flexible packaging processes.
Implementation Method 1
bonding it to a substrate with multiple MEMS devices via a patterned adhesive sheet
Data Source
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Figure 7~9
AI summary
Multiple microelectromechanical systems (MEMS) on a substrate (20) are capped with a cover (28) using a layer that may function as a bonding agent, separation layer, and hermetic seal. A substrate (20) has a first side (20A) with multiple MEMS devices. A cover (28) is formed with through-holes (40) for vias (40), and with standoff posts (34) for layer registration and separation. An adhesive sheet (42) is patterned with cutouts (44) for the MEMS devices, vias (40), and standoff posts (34). The adhesive sheet (42) is tacked to the cover (28), then placed on the mems substrate (20) and heated to bond the layers. The via holes (40) may be metalized with leads for circuit board (58) connection. The mems units (22) may be diced from the substrate (20) after sealing, thus protecting them from contaminants.