Multi-Layer Piezoelectric Substrate Packaging With Stress Buffer Layers
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Solution Overview
Problem
Multi-layer piezoelectric substrates in electronic packages face reliability issues due to stresses during the packaging process, which can lead 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. Additionally, a dielectric layer is used between the piezoelectric layer and thermally conductive structures to further mitigate stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal layers are directly bonded to the piezoelectric layer during packaging, then electrical connection and thermal conduction are improved, but stress concentration causes cracking and reliability degradation
Solution Approach 1:
A polyimide layer is introduced as an intermediary between the metal portion and the piezoelectric layer. This intermediate layer buffers the stress transmitted from the metal layer to the piezoelectric layer, preventing stress concentration and cracking while maintaining the electrical and thermal connection functionality.
Solution Approach 2:
The polyimide layer is applied beforehand to the piezoelectric layer before the metal portion is bonded. This pre-applied cushioning layer anticipates and mitigates the stress that will be transmitted during subsequent packaging processes, protecting the piezoelectric layer from damage.
2Ease of manufacture
If the packaging process applies necessary stresses for assembly, then manufacturing is enabled, but the piezoelectric layer cracks due to excessive stress
Solution Approach 1:
The polyimide layer serves as a stress-buffering intermediary that allows the packaging process to proceed with necessary assembly stresses while protecting the piezoelectric layer from exceeding its stress tolerance, thus enabling manufacturing without compromising layer integrity.
3Area of stationary object
If metal portions are placed close to the piezoelectric layer for compact design, then device size is reduced, but stress damage to the piezoelectric layer increases
Solution Approach 1:
The polyimide layer enables compact design by allowing metal portions to be placed close to the piezoelectric layer while still providing stress protection. The intermediate layer buffers any stress transmitted through the close proximity arrangement, maintaining piezoelectric layer strength despite reduced spacing.
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 use of polyimide and dielectric layers significantly reduces stress on the piezoelectric layer, enhancing the reliability of the electronic packages by preventing deformation and cracking, as demonstrated by stress simulations showing a reduction in peak stress by up to 79%.
Implementation Method 1
applying a polyimide layer over an outer boundary of the piezoelectric 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
A method of making an electronics package with a multi-layer piezoelectric substrate includes bonding a piezoelectric layer over a substrate. The method also includes applying a polyimide layer over an outer boundary of the piezoelectric 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.