Polished Recesses and Micro-Posts for MEMS Glass Strength
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Solution Overview
Problem
Borosilicate glass used in MEMS pressure sensors is prone to mechanical defects during the wafer sawing process, leading to failure under high pressure, and has weak adhesion with die mounting materials, causing instability and malfunction in harsh environments with thermal shocks and high humidity.
Innovation Solution
The solution involves forming polished recess structures in critical high-stress areas during wafer sawing to prevent defects and creating a micro-roughness structure on the glass surface to enhance adhesion with the mounting material, using an array of micro-posts that allow for gas/vapor venting during die attach, thereby maintaining glass strength and integrity in harsh conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the glass wafers are polished to remove mechanical defects, then the glass strength is improved, but the adhesion with die mounting material deteriorates
Solution Approach 1:
The patent applies different surface treatments to different locations on the glass wafer. The active sensing areas are polished to high smoothness for strength, while the periphery areas (mounting regions) are intentionally left with controlled roughness to enhance adhesion with die mounting material. This local differentiation resolves the contradiction between strength and adhesion.
Solution Approach 2:
The glass wafer surface is segmented into functional zones: polished central regions for pressure sensing that require high strength, and rougher peripheral regions for mounting that require high adhesion. This segmentation allows each zone to have optimized surface properties for its specific function.
2Productivity
If the wafer sawing process is used to singulate individual devices, then productivity is improved, but glass defects are induced leading to reduced strength
Solution Approach 1:
The patent performs preliminary surface treatment and defect prevention measures during the wafer fabrication stage, before the sawing process. By preparing the wafer surfaces in advance with appropriate roughness patterns and protective layers, the subsequent sawing process causes minimal damage to critical areas.
Solution Approach 2:
The patent creates localized surface characteristics in different regions of the wafer. Areas that will be subjected to sawing are prepared with specific surface properties that reduce defect formation, while critical sensing areas are protected or treated differently to maintain strength despite the proximity to sawing zones.
Data Source
AI summary
A sensor device is constructed to maintain a high glass strength to avoid the glass failure at low burst pressure, resulting from the sawing defects located in the critical high stress area of the glass pedestal as one of the materials used for construction of the sensor. This is achieved by forming polished recess structures in the critical high stress areas of the sawing street area. The sensor device is also constructed to have a robust bonding with the die attach material by creating a plurality of micro-posts on the mounting surface of the glass pedestal.