Multi-Layer Piezoelectric Substrate Stress Buffering in Packages
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Solution Overview
Problem
Multi-layer piezoelectric substrates in electronic packages face reliability issues due to stresses during the packaging process, leading to cracking of the piezoelectric layer.
Innovation Solution
A polyimide layer is applied over the outer boundary of the piezoelectric layer to act as a buffer between the piezoelectric layer and metal portions, reducing stress and preventing damage, and a thermally conductive structure is attached with a dielectric layer interposed between the piezoelectric layer and the thermally conductive structure to further reduce stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal layers are directly bonded to the piezoelectric layer during packaging, then electrical connection is achieved, but stresses cause cracking of the piezoelectric layer
Solution Approach 1:
A polyimide layer is introduced as an intermediary between the metal layer and the piezoelectric layer. This intermediate layer acts as a stress buffer that absorbs and distributes mechanical stresses during packaging processes, preventing direct stress transmission to the piezoelectric layer and avoiding cracking while maintaining electrical connectivity through the metal layer.
Solution Approach 2:
The packaging process parameters are modified to reduce thermal and mechanical stresses. This includes controlling bonding temperatures and using stress-relief techniques during assembly to minimize the magnitude of stresses applied to the piezoelectric layer, thereby preventing damage while achieving reliable electrical connections.
2Area of stationary object
If metal layer is placed close to piezoelectric layer for compact design, then device size is reduced, but stress concentration increases causing damage
Solution Approach 1:
The polyimide layer serves as a stress-distributing intermediary that allows the metal layer to be positioned closer to the piezoelectric layer for compact design. The intermediate material absorbs stress concentrations that would otherwise occur at sharp interfaces, enabling reduced footprint while maintaining piezoelectric layer integrity.
Solution Approach 2:
The polyimide layer functions as a flexible thin film that can accommodate thermal expansion differences and mechanical deformations between the rigid metal layer and piezoelectric layer. This flexible intermediate structure prevents stress concentration while allowing compact packaging geometry.
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 solution significantly reduces stress on the piezoelectric layer, enhancing the reliability of the electronic packages by preventing deformation and damage, such as cracking, during the packaging process and heat cycle testing.
Implementation Method 1
The outer boundary of the piezoelectric layer is covered with a polyimide layer so that the polyimide layer is interposed between the piezoelectric layer and a metal portion to inhibit stresses from the metal layer damaging the piezoelectric layer
Implementation Method 2
A dielectric layer is disposed over an outer edge portion of the piezoelectric layer and interposed between the piezoelectric layer and the thermally conductive structure to thereby reduce a stress on the piezoelectric layer from the thermally conductive structure
Data Source
AI summary
An electronics package has a multi-layer piezoelectric substrate with a piezoelectric layer over a substrate. The outer boundary of the piezoelectric layer is covered with a polyimide layer so that the polyimide layer is interposed between the piezoelectric layer and a metal portion (e.g., of copper (Cu)) to inhibit (e.g., prevent) stresses from the metal layer damaging the piezoelectric layer..