Stress Relief Buffer Layer for Hermetic MEMS Packaging
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Traditional packaging methods for MEMS devices, such as bolometers, face high costs and reliability issues due to thermal stress caused by the difference in thermal expansion coefficients between the solder and the semiconductor wafer, leading to cracks in the overglass and underlying structures.
Innovation Solution
A stress relief buffer layer with a higher ductility and thermal expansion coefficient than the semiconductor wafer but lower than the solder is introduced, extending beyond the edges of the bonding material to alleviate stress and prevent cracking, using materials like titanium to serve as a ductile intermediary between the solder and the brittle overglass.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional Wafer Level Packaging is used with solder bonding, then hermetic sealing is achieved, but high stress buildup occurs due to thermal expansion differences between solder and semiconductor materials
Solution Approach 1:
A stress relief buffer layer is introduced as an intermediary between the solder bonding material and the semiconductor wafer. This buffer layer has a thermal expansion coefficient intermediate between that of the solder and the semiconductor wafer, and higher ductility than the wafer, allowing it to absorb thermal stress and prevent cracking in the hermetic seal while maintaining sealing reliability.
Solution Approach 2:
The patent changes the physical parameters of the packaging structure by introducing a layer with specific material properties: thermal expansion coefficient between solder and semiconductor wafer, and ductility higher than the wafer but lower than solder. This parameter optimization allows the buffer layer to yield under stress rather than transmitting it to the brittle semiconductor wafer, reducing thermal stress buildup while maintaining hermetic sealing.
2Stress or pressure
If a stress relief buffer layer is added between solder and semiconductor wafer, then thermal stress is reduced, but package structure complexity increases
Solution Approach 1:
The bonding interface is segmented into multiple functional layers: the solder bonding material layer, the stress relief buffer layer, and the semiconductor wafer. This segmentation allows each layer to perform its specific function - solder provides bonding, buffer provides stress relief, and wafer provides structural support - thereby reducing thermal stress while maintaining a relatively simple overall package structure through clear functional division.
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 stress relief buffer layer effectively reduces thermal stress on the semiconductor wafer, preventing cracks and enhancing the reliability of the hermetic seal by shifting the stress point from the brittle overglass to a more ductile material, thereby improving the packaging process and reducing the risk of failure.
Implementation Method 1
a first layer of the metal ring includes a stress relief buffer layer disposed on the surface portion of the substrate, the first layer having a higher ductility than that of the surface portion at a predetermined temperature
Implementation Method 2
the stress relief buffer layer having a coefficient of thermal expansion greater than the coefficient of expansion of the surface portion of the substrate and less than the coefficient of expansion of the bonding material
Data Source
AI summary
A sealed package having a device disposed on a wafer structure and a lid structure boned to the device wafer. The device wafer includes: a substrate; a metal ring disposed on a surface portion of substrate around the device and a bonding material disposed on the metal ring. The metal ring extends laterally beyond at least one of an inner and outer edge of the bonding material. A first layer of the metal ring includes a stress relief buffer layer having a higher ductility than that of the surface portion of the substrate and a width greater than the width of the bonding material. The metal ring extends laterally beyond at least one of the inner and outer edges of the bonding material. The stress relief buffer layer has a coefficient of thermal expansion greater than the coefficient of expansion of the surface portion of the substrate and less than the coefficient of expansion of the bonding material.