Variable-Stiffness Module Structure for Conductor Stress Relief
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Solution Overview
Problem
Micro-transfer printed devices on flexible substrates experience mechanical stress due to the mismatch in stiffness between rigid and flexible components, leading to potential conductor failures and deformations.
Innovation Solution
A variable-stiffness module comprising a rigid structure, an intermediate substrate with intermediate stiffness, and a flexible substrate with lower stiffness, where conductors are partially disposed on both substrates, providing a gradual transition in stiffness to reduce mechanical stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a rigid structure is disposed directly on a flexible substrate, then the device can be manufactured with simpler structure, but mechanical stress concentrates at the interface leading to conductor failures and deformations
Solution Approach 1:
An intermediate substrate with intermediate stiffness is introduced between the rigid structure and flexible substrate. This intermediate layer acts as a mechanical mediator that gradually transitions the stiffness difference, preventing stress concentration at the interface while maintaining the overall simple structure of the device.
Solution Approach 2:
The stiffness parameter is gradually changed across multiple layers rather than having an abrupt transition. The intermediate substrate provides a intermediate stiffness value that bridges the gap between rigid and flexible components, reducing mechanical stress and improving conductor reliability without significantly increasing device complexity.
2Reliability
If an intermediate substrate is introduced between rigid and flexible substrates, then mechanical stress is reduced and conductor reliability improves, but device complexity increases
Solution Approach 1:
The intermediate substrate serves as a minimal yet effective mediator that resolves the mechanical incompatibility between rigid and flexible layers. By introducing only one additional layer with intermediate stiffness properties, the solution achieves stress reduction and improved reliability while keeping the increase in device complexity to a minimum.
3Reliability
If conductors extend across the entire path from rigid structure to flexible substrate, then electrical connectivity is maintained, but stress concentration occurs at substrate edges leading to conductor cracks
Solution Approach 1:
The intermediate substrate changes the mechanical parameter profile across the conductor path, creating a gradual stiffness transition that reduces stress concentration. This allows conductors to maintain electrical connectivity across the entire path while experiencing reduced mechanical stress, preventing cracks and maintaining conductor strength.
Data Source
AI summary
A variable-stiffness module includes a rigid structure having a first stiffness, an intermediate substrate having a second stiffness less than the first stiffness, and a flexible substrate having a third stiffness less than the second stiffness. The rigid structure is disposed on the intermediate substrate and the intermediate substrate is disposed on the flexible substrate. A conductor is disposed partially on the intermediate substrate and partially on the flexible substrate and is connected to the rigid structure. The conductor extends from the rigid structure to the intermediate substrate to the flexible substrate. In some embodiments, a variable-stiffness module includes any combination of multiple rigid structures, multiple intermediate substrates, and multiple conductors. The conductor can be an optical conductor or an electrical conductor and can be disposed over the rigid structure or between the rigid structure and the intermediate substrate.