MEMS Packaging Structure With Silicone Stress Isolation
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Solution Overview
Problem
The challenge is to effectively package microelectromechanical systems (MEMS) devices while minimizing the impact of mechanical and thermal stresses, and ensuring that the packaging does not interfere with the operation of the MEMS.
Innovation Solution
A packaged MEMS device is created using a circuitry chip attached to a substrate with leads, where the MEMS is vertically attached to the chip using a low modulus silicone compound. The MEMS is surrounded by a polyimide ring with a surface that is phobic to silicone compounds, and a dome-shaped glob of cured silicone material covers the MEMS. This configuration uses a polymeric molding compound for encapsulation, which is non-adhering to the silicone glob surface but adheres to all other surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rigid packaging material is used to protect MEMS, then mechanical strength is improved, but stress transmission to MEMS increases
Solution Approach 1:
The patent applies different material properties to different regions: a soft conformal coating (silicone rubber or polyurethane) is applied only to the region surrounding the MEMS device to absorb mechanical stress, while the bulk packaging material can provide overall structural strength. This local differentiation allows the packaging to be strong where needed while protecting the MEMS from stress where critical.
Solution Approach 2:
The patent uses composite packaging structures combining materials with different mechanical properties. The conformal coating layer (softer material with lower modulus of elasticity) is combined with the bulk packaging material (harder material with higher modulus of elasticity) to create a composite structure that provides both mechanical strength and stress protection to the MEMS device.
2Object-affected harmful factors
If a conformal coating is applied to protect MEMS, then stress protection is improved, but adhesion to packaging material becomes problematic
Solution Approach 1:
The patent creates a localized non-adhesive region around the MEMS device by applying a conformal coating with specific surface properties. This coating is non-adhesive only in the region surrounding the MEMS, while other regions of the packaging structure maintain normal adhesion. This selective adhesion property allows stress protection without compromising overall package integrity.
Solution Approach 2:
The patent changes the surface energy parameters of the conformal coating material to create a non-adhesive surface. By selecting materials with low surface energy (such as silicone rubber or polyurethane with appropriate surface treatments), the coating becomes non-wettable by epoxy-based molding compounds, preventing stress transmission while maintaining structural integrity through controlled adhesion in other regions.
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 solution effectively shields the MEMS from mechanical and thermal stresses while maintaining the integrity of the package, ensuring that the MEMS operates undisturbed by external stress. The use of low modulus silicone and polyimide materials allows for stress absorption and distribution, while the non-adhesive properties of the silicone glob prevent stress transmission from the packaging material.
Implementation Method 1
a layer of low modulus silicone compound... stress absorption and distribution... low modulus silicone and polyimide materials allows for stress absorption
Implementation Method 2
a polyimide ring with a surface phobic to silicone compounds... non-adhesive properties of the silicone glob prevent stress transmission
Implementation Method 3
has a surface non-adhesive to epoxy-based molding compounds... non-adhering to the glob surface... non-adhesive properties of the silicone glob prevent stress transmission
Data Source
Figure 1~3
Figure 4~5
AI summary
In described examples, a packaged microelectromechanical system (MEMS) device (100) comprises a circuitry chip (101) attached to a pad (110) of a substrate with leads (111), and a MEMS (150) vertically attached to the chip (101) surface by a layer (140) of low modulus silicone compound. On the chip (101) surface, the MEMS device (100) is surrounded by a polyimide ring (130) with a surface phobic to silicone compounds. A dome-shaped glob (160) of cured low modulus silicone material covers the MEMS (150) and MEMS terminal bonding wire spans (180). The glob (160) is restricted to the chip (101) surface area inside the polyimide ring (130) and has a surface non-adhesive to epoxy -based molding compounds. A package (190) of polymeric molding compound encapsulates a vertical assembly of the glob (160) embedding the MEMS (150), the chip (101), and portions of the substrate; the molding compound is non-adhering to the glob (160) surface yet adhering to all other surfaces.