Flexible Mounting Layer for MEMS Microphone Stress Relief
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Solution Overview
Problem
MEMS microphones face challenges due to mechanical stress from assembly and thermal expansion mismatches, leading to performance impairments and miniaturization limitations in conventional die attach methods, and flip chip assembly introduces rigidity issues prone to static and dynamic stress.
Innovation Solution
An electronic device with a flexible mounting layer and conductive adhesive connections between a carrier board and a MEMS chip, using a laminated multilayer board with structured mounting material to reduce stress and maintain acoustic functionality, while avoiding underfill materials and bond wires.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional die attach with soft and thick bondline is used, then mechanical stress is kept low, but the MEMS internal cavity cannot contribute to acoustic back volume and adds parasitic front volume
Solution Approach 1:
The patent changes the bonding parameters by using a thin bondline (5-20 μm) instead of the conventional thick bondline, and positions the MEMS chip in an inverted orientation. This allows the MEMS internal cavity to contribute to acoustic back volume while maintaining low mechanical stress through the flexible organic substrate.
Solution Approach 2:
The patent inverts the MEMS chip orientation during assembly, mounting the chip such that the microphone capsule faces downward toward the organic substrate. This inversion allows the internal cavity to function as acoustic back volume and enables direct electrical connection through the substrate without requiring wire bonding.
2Reliability
If conventional die attach with wire bonding is used, then electrical connections are established, but lateral space and headroom are required increasing component dimensions
Solution Approach 1:
The patent merges the electrical connection function into the organic substrate itself by integrating conductor tracks and contact pads directly into the substrate structure. This eliminates the need for separate wire bonding operations and reduces the required lateral space and headroom, enabling miniaturization of the component.
3Productivity
If flip chip assembly on solder bumps is used, then acoustic performance is improved, but the sensor chip is rigidly coupled making it prone to stress from assembly, thermal expansion, and external impacts
Solution Approach 1:
The patent changes the mechanical coupling parameter by using a flexible organic substrate with a thin bondline instead of rigid solder bumps. This maintains the close coupling needed for acoustic performance while providing stress relief through the flexibility of the organic material, protecting against stress from assembly, thermal expansion, and external impacts.
4Volume of moving object
If miniaturization is pursued, then component dimensions are reduced, but mechanical stress from assembly and thermal expansion increases
Solution Approach 1:
The patent changes the substrate material parameters by using a flexible organic material instead of rigid ceramic or metal. This allows miniaturization of the component while the flexible substrate absorbs and distributes mechanical stress from assembly and thermal expansion, preventing stress concentration that would occur with rigid materials.
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 reduces mechanical stress, maintains acoustic performance, and miniaturizes the device by using a flexible mounting layer and conductive adhesive connections, enhancing the stability and efficiency of MEMS microphone assembly.
Implementation Method 1
a connection element connecting the chip contact element to the carrier contact element, wherein the connection element is made of a material with a Young's modulus of equal to or less than 300 MPa
Implementation Method 2
a flexible mounting layer and conductive adhesive connections between a carrier board and a MEMS chip
Data Source
AI summary
In an embodiment an electronic device includes a carrier board having an upper surface, an electronic chip mounted on the upper surface of the carrier board, the electronic chip having a mounting side facing the upper surface of the carrier board, a flexible mounting layer arranged between the upper surface of the carrier board and the mounting side of the electronic chip, the flexible mounting layer mounting the electronic chip to the carrier board, wherein the mounting side has at least one first region and a second region, and wherein the electronic chip has at least one chip contact element in the first region and at least one connection element arranged on the at least one first region and connecting the at least one chip contact element to the upper surface of the carrier board, wherein the flexible mounting layer separates the second region from the connection element.