MEMS Microphone Can Sealing With Single-Axis Solder Dispensing
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Solution Overview
Problem
Existing manufacturing processes for MEMS acoustic transducers in microphone assemblies are limited by the size of the silicon die that can be accommodated within a given package due to clearance requirements for solder dispensing, restricting the miniaturization of the microphone assembly.
Innovation Solution
A single-axis solder dispensing process is used to couple a can to a guard ring, reducing the overall size of the microphone assembly by applying solder along only two sides of the guard ring and using epoxy tags for an air-tight seal on the remaining sides, allowing for a larger silicon die without increasing the package size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional multi-axis solder dispensing is used to ensure complete sealing, then reliability is improved, but device complexity and manufacturing time increase
Solution Approach 1:
The soldering process is segmented into two distinct phases: first, a preliminary soldering operation applies solder to establish electrical connections and provide initial sealing; second, a conformal coating layer is applied to provide the final hermetic seal. This segmentation allows each process to be optimized independently, reducing overall complexity while maintaining reliability.
Solution Approach 2:
The solution uses a composite sealing approach combining solder material (for electrical and mechanical connection) with conformal coating material (for hermetic sealing). This composite structure leverages the strengths of both materials: solder provides robust electrical connectivity and structural bonding, while the conformal coating provides complete environmental protection without requiring complex multi-axis dispensing.
2Productivity
If larger silicon die are used to increase functionality, then productivity is improved, but the package size increases
Solution Approach 1:
The conformal coating is applied as a thin film layer in the vertical dimension (z-axis) rather than requiring horizontal expansion. This allows the solder joint to be reinforced with sealing material without increasing the footprint of the package, effectively using the third dimension to solve the sealing problem while maintaining compact form factor.
Solution Approach 2:
The conformal coating provides a thin-film hermetic seal that conforms to the contours of the solder joint and underlying structures. This thin-film approach provides complete sealing without requiring bulky protective structures, enabling larger silicon die to be packaged in compact footprints by adding minimal volume in the form of thin protective layers.
Data Source
AI summary
A microphone assembly includes a substrate defining a port, a MEMS transducer, a guard ring, and a can. The MEMS transducer is coupled to the substrate such that the MEMS transducer is positioned over the port. The guard ring is coupled to the substrate and surrounds the MEMS transducer. The guard ring includes a plurality of edges that further includes a first edge and an opposing second edge. A portion of the first edge and a portion of the second edge have a reduced thickness relative to adjacent ones of the plurality of edges. The can is coupled to the guard ring such that the substrate and the can cooperatively define an interior cavity.