MEMS Assembly Bond Layer for Stress Reduction
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Solution Overview
Problem
MEMS microphone assemblies face damage and mechanical behavior changes due to stress transmission from hard PCB and solder resist layers during bonding, which affects their sensitivity and reliability.
Innovation Solution
A bond layer with an elastic modulus of less than 500 MPa is applied on the substrate to act as a cushioning layer, reducing stress transfer to MEMS dies and integrated circuits, and allowing direct bonding or adhesive bonding to the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a hard PCB and solder resist layer are used for bonding, then structural strength is improved, but stress is transmitted to MEMS components causing damage or mechanical behavior changes
Solution Approach 1:
A bond layer with intermediate mechanical properties is introduced between the hard PCB/solder resist layer and the MEMS components. This intermediary layer absorbs and distributes bonding stress, preventing direct stress transmission to the acoustic transducer and integrated circuit, thereby resolving the contradiction between structural strength and stress-induced damage
Solution Approach 2:
The patent changes the mechanical parameters (elastic modulus, hardness) of the bonding interface by using a bond layer with softer material properties compared to the hard PCB and solder resist layer. This parameter change allows the bonding structure to maintain strength while reducing stress transmission to sensitive MEMS components
2Strength
If stress is transmitted during bonding, then bonding strength is improved, but MEMS component sensitivity and reliability deteriorate
Solution Approach 1:
The bond layer serves as a mediator that enables strong bonding between the PCB and MEMS components while simultaneously protecting the components from harmful stress. The layer transfers the bonding function away from the hard solder resist layer, allowing bonding strength to be achieved without compromising component reliability
Solution Approach 2:
The bond layer is applied beforehand to cushion and absorb the mechanical stress that will occur during the bonding process. This prior cushioning prevents stress from reaching the MEMS components during bonding, thereby maintaining both bonding strength and component reliability
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 bond layer significantly reduces mechanical damage and increases the yield of MEMS assemblies by providing a mechanical dampening effect during the bonding process, enhancing the reliability and performance of MEMS microphone assemblies.
Implementation Method 1
depositing, on the substrate over the electrically conductive layer, a bonding material having an elastic modulus of less than 500 MPa so as to form a bond layer
Implementation Method 2
The bond layer significantly reduces mechanical damage and increases the yield of MEMS assemblies by providing a mechanical dampening effect during the bonding process
Data Source
AI summary
A method of forming a micro electro mechanical system (MEMS) assembly comprises providing a substrate having an electrically conductive layer disposed thereon. The method also comprises depositing, on the substrate over the electrically conductive layer, a bonding material having an elastic modulus of less than 500 MPa so as to form a bond layer. The bond layer is completely cured, and a MEMS die is attached to the completely cured bond layer.