Wafer-to-Wafer Solder Bond for Thin Hermetic Acoustic Packages
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Solution Overview
Problem
Existing packaging technologies for microelectromechanical systems, such as acoustic wave resonators, face challenges in reducing package size and maintaining a hermetic seal due to process limitations and material interactions, which hinder the integration of additional functionality or reduction in device form factor.
Innovation Solution
A package design utilizing a cap wafer with etched standoffs and transient liquid phase bonding of Sn and Au layers to form a seal ring, reducing standoff height and width, and incorporating a Ti/Cu seed layer for improved bonding, thereby enhancing hermeticity and reducing package thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional packaging technologies are used for acoustic wave resonators, then hermetic seal can be maintained, but package size cannot be reduced
Solution Approach 1:
The patent implements nesting by placing the acoustic wave device inside a cavity formed within the cap wafer itself. The standoffs are integrated as part of the cap wafer structure, and the seal ring is formed within the cavity space, creating a nested configuration where multiple functional elements occupy the same spatial envelope. This nesting approach reduces the overall package volume while maintaining the hermetic seal integrity.
Solution Approach 2:
The patent utilizes three-dimensional cavity formation within the cap wafer to reduce package footprint. By etching the cavity into the cap wafer and forming standoffs with specific height and width dimensions, the design transitions from a two-dimensional planar layout to a three-dimensional structure that optimizes space utilization and reduces overall package size while preserving hermetic sealing.
2Volume of moving object
If standoff height and width are reduced to shrink package size, then hermetic seal reliability deteriorates
Solution Approach 1:
The patent optimizes the standoff dimensions by specifying precise parameter ranges: height between 1μm and 3μm, and width between 10μm and 15μm. These parameter changes are achieved through controlled deposition processes and are designed to provide sufficient mechanical support and hermetic sealing while minimizing the overall package size. The specific parameter optimization resolves the contradiction between small size and seal reliability.
Solution Approach 2:
The patent employs a composite structure consisting of the cap wafer material, standoff material, and seal ring material with different properties. This composite approach allows each material to be optimized for its specific function: structural support, mechanical integrity, and hermetic sealing, thereby achieving reliable sealing with reduced standoff dimensions.
3Adaptability or versatility
If additional functionality is integrated into the package, then device complexity increases
Solution Approach 1:
The cap wafer is designed to perform multiple functions: it provides the hermetic seal, forms the package structure, creates the cavity for the acoustic wave device, and incorporates standoffs for alignment and support. This multi-functionality of the cap wafer reduces the need for additional separate components, thereby integrating additional functionality without proportionally increasing device complexity.
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 new package design achieves a thinner and smaller form factor while maintaining a reliable hermetic seal, enabling more compact electronic devices with integrated acoustic wave filters.
Implementation Method 1
a portion of the layer of the first metal bonded to a portion of the layer of the second metal to define the seal ring
Data Source
AI summary
Aspects and embodiments disclosed herein relate to a package for an acoustic wave device. The package comprises a cap wafer having a cavity defined in a lower surface thereof, outside walls of the cavity defining inner edges of an inner portion of a seal ring formed integral with the cap wafer, a portion of a layer of a first metal disposed on and around the inner portion of the seal ring, and a device wafer including the acoustic wave device and a layer of a second metal, a portion of the layer of the second metal bonded to the portion of the layer of the first metal to define the seal ring, the cavity surrounding the acoustic wave device and hermetically sealed by the cap wafer, device wafer, and seal ring.