Stress-Engineered Micro-Springs for IC Thermal Expansion
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Solution Overview
Problem
Conventional flip-chip mounting methods for integrated circuits (ICs) face challenges such as stiffness in connections, potential fracture due to thermal expansion mismatch, and damage from etchant chemicals during micro-spring formation on commercially available ICs, which limits the flexibility and ease of assembly in compact multi-chip modules.
Innovation Solution
The development of micro-fabricated, stress-engineered members with etchant-sensitive surface passivation layers, where a stress-engineered film is deposited and patterned on an integrated circuit wafer, and a release layer is undercut to create an out-of-plane structure with a free end biased away from the surface, allowing for flexible connections and protection from etchants.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional flip-chip mounting methods are used, then connections are established between ICs, but the connections become stiff and prone to fracture due to thermal expansion mismatch
Solution Approach 1:
The patent introduces dynamic elastic members (micro-springs) that can deflect and adapt to thermal expansion differences between ICs and the substrate. These members transition from a rigid connection state to a flexible state that absorbs thermal stress, allowing the connection to maintain electrical contact while accommodating dimensional changes during temperature cycling.
Solution Approach 2:
The patent employs thin film elastic members with controlled stress profiles that provide flexibility to the connection. These flexible film structures can bend and deflect to accommodate thermal expansion mismatch, replacing the stiff conventional wire bonds or solder joints with compliant elements that maintain electrical connectivity while absorbing mechanical stress.
2Adaptability or versatility
If micro-springs are formed directly on commercially available ICs, then flexible connections are achieved, but the ICs are damaged by etchant chemicals during the formation process
Solution Approach 1:
The patent segments the fabrication process into distinct stages with protective measures. A release layer is deposited over the IC surface before forming the elastic member, creating a protective barrier that segments the IC from the harmful etchant chemicals used during micro-spring fabrication. This allows the elastic member to be formed with full flexibility while the IC remains protected.
Solution Approach 2:
The release layer serves as an intermediary substance between the IC and the etchant chemicals. This intermediate layer allows the etching process to proceed freely to create the flexible micro-spring structure while preventing direct contact between the etchants and the IC surface, thus protecting the IC from chemical damage while achieving the desired connection flexibility.
3Ease of manufacture
If rigid connections are used in compact multi-chip modules, then assembly is simplified, but mechanical stress causes fracture and reliability decreases
Solution Approach 1:
The patent replaces static rigid connections with dynamic elastic members that can adapt to mechanical stress. These stress-engineered elastic members maintain electrical connectivity while deflecting under mechanical load, providing a simple assembly process similar to rigid connections but with enhanced reliability through their ability to absorb and distribute mechanical stress dynamically.
4Adaptability or versatility
If stress-engineered films are deposited and patterned with undercut release layers, then out-of-plane flexible structures are formed, but the process complexity increases
Solution Approach 1:
The patent applies preliminary action by depositing the stress-engineered film with a built-in intrinsic stress profile before patterning and release layer formation. This pre-established stress profile ensures that when the release layer is undercut, the elastic member automatically deflects into the desired out-of-plane configuration, simplifying the overall process by eliminating the need for complex post-fabrication shaping or assembly steps.
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 approach enables the formation of compact, flexible micro-spring contacts that can be easily assembled and reworked, reducing mechanical stress and preventing damage to ICs during the micro-spring formation process, while maintaining electrical connectivity and adaptability to varying thermal expansion rates.
Implementation Method 1
The intrinsic stress profile in the stress-engineered film biases the released portion away from the surface
Implementation Method 2
The stress-engineered film is patterned and the release layer is undercut etched so that a released portion of the patterned stress-engineered film is released from the surface
Data Source
AI summary
A release layer is formed on a surface of an integrated circuit wafer. The surface is passivated and includes metal contact materials. A stress-engineered film having an intrinsic stress profile is deposited over the release layer. The stress-engineered film is patterned and the release layer is undercut etched so that a released portion of the patterned stress-engineered film is released from the surface while leaving an anchor portion fixed to the surface. The intrinsic stress profile in the stress-engineered film biases the released portion away from the surface. The released portion is placed entirely within an area defined by the metal contact material.