Elastic Pillar Decoupling for Thermo-Mechanical Stress in MEMS
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Solution Overview
Problem
Current MEMS devices are sensitive to thermo-mechanical stresses, such as temperature gradients and environmental conditions, which cause deformations and affect the accuracy of measurements due to differences in thermal expansion coefficients between the chip and the package materials.
Innovation Solution
The use of pillars with a low Young's modulus, typically made of dry resist, are strategically placed around the chip to decouple it from the packaging body, allowing deformations to be absorbed by the pillars rather than being transferred to the chip, thereby maintaining the chip's rigidity and reducing sensitivity to mechanical stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the MEMS chip is directly bonded to the package base, then the structural integrity and electrical connection are improved, but the sensitivity to thermo-mechanical stresses and measurement accuracy deteriorate
Solution Approach 1:
The patent introduces an intermediary layer (adhesive layer or compliant mounting structure) between the MEMS chip and package base. This intermediary decouples the chip from thermo-mechanical stresses while maintaining structural support and electrical connections, thereby preserving measurement accuracy without sacrificing structural integrity
Solution Approach 2:
The patent modifies the mechanical properties of the mounting structure by using materials with specific Young's modulus values or creating compliant structures that can deform under stress. This parameter change allows the mounting structure to absorb thermal expansion differences and mechanical stresses, protecting the MEMS chip from stress-induced measurement errors
2Strength
If rigid bonding materials are used between chip and base, then the mechanical strength is improved, but the stress transfer and signal drift increase
Solution Approach 1:
The patent changes the mechanical parameters of the bonding material by using materials with lower Young's modulus (more compliant materials) or by creating a layered bonding structure. This allows the bonding interface to deform under thermal and mechanical stress, preventing stress transfer to the chip while maintaining adequate mechanical strength for structural support
Solution Approach 2:
The patent employs composite bonding structures combining materials with different mechanical properties. For example, a combination of rigid and compliant materials in layers, or materials with matched thermal expansion coefficients, to achieve both mechanical strength and stress isolation, thereby maintaining signal stability
3Adaptability or versatility
If the package materials have different thermal expansion coefficients, then the manufacturing flexibility is improved, but the thermo-mechanical stress and warpage increase
Solution Approach 1:
The patent addresses thermal expansion mismatches by using materials with specifically selected thermal expansion coefficients or by designing compensation structures. The mounting structure is designed to accommodate differential thermal expansion, maintaining package stability despite using diverse materials for manufacturing flexibility
Solution Approach 2:
The patent explicitly accounts for thermal expansion effects by selecting materials with matched or compensating thermal expansion coefficients. The design incorporates thermal expansion compensation mechanisms in the mounting structure, allowing the package to withstand temperature variations without developing excessive stress or warpage that would compromise stability
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 effectively reduces the impact of thermo-mechanical stresses on the MEMS device, maintaining measurement accuracy and stability by creating an uncoupling between the chip and the packaging body, and allowing for large-scale manufacturing with comparable costs to existing encapsulated devices.
Implementation Method 1
The pillar element has a first Young's modulus and the semiconductor material of the first chip has a second Young's modulus. The first Young's modulus is less than the second Young's modulus.
Data Source
AI summary
An encapsulated device of semiconductor material wherein a chip of semiconductor material is fixed to a base element of a packaging body through at least one pillar element having elasticity and deformability greater than the chip, for example a Young's modulus lower than 300 MPa. In one example, four pillar elements are fixed in proximity of the corners of a fixing surface of the chip and operate as uncoupling structure, which prevents transfer of stresses and deformations of the base element to the chip.