Liquid Metal TIM Thermal Interface Pad for BGA Compatibility
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Solution Overview
Problem
Liquid metal thermal interface materials (TIMs) are not compatible with high volume manufacturing processes due to their inability to wet the surfaces of heat spreaders and dies, requiring manual scrubbing to break an oxide shell for adhesion, which is inefficient and labor-intensive.
Innovation Solution
A thermal interface pad made from materials that preferentially wet liquid metal TIMs is applied to the heat spreader and die using high volume manufacturing compatible processes such as cold-rolling, allowing the liquid metal to remain in the liquid phase during assembly and operation, reducing thermo-mechanical stress and eliminating the need for reflowing or additional metallization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If liquid metal TIM is applied directly to heat spreader and die surfaces, then thermal performance is enhanced, but the material cannot wet the surfaces due to oxide shell formation
Solution Approach 1:
A flux composition is introduced as an intermediary substance between the liquid metal TIM and the heat spreader/die surfaces. The flux contains compounds (such as zinc halides, boron halides, or aluminum halides) that chemically react with and remove the oxide shell from the surfaces, enabling the liquid metal TIM to properly wet and adhere to the surfaces without manual scrubbing
Solution Approach 2:
The chemical composition and properties of the flux are specifically designed to change the surface characteristics of the heat spreader and die. The flux composition parameters (ratio of halide compounds, presence of specific catalysts) are optimized to effectively remove oxides at the operating temperature range while allowing controlled reformation of a thin protective oxide layer that promotes wetting
2Ease of manufacture
If manual scrubbing process is used to break oxide shell, then liquid metal TIM can wet surfaces, but each component requires manual processing reducing productivity
Solution Approach 1:
The manual mechanical scrubbing process is replaced with a chemical system. Instead of physically abrasion to remove the oxide shell, a chemically active flux composition is applied that automatically reacts with and removes oxides from the surfaces. This chemical mechanism can be applied uniformly across multiple components simultaneously through automated dispensing systems, eliminating the need for manual scrubbing while maintaining effective oxide removal and enabling high-volume manufacturing
Solution Approach 2:
The flux composition is designed to automatically perform the oxide removal function when applied to the surfaces. The chemical reactions occur spontaneously at the operating temperature, with the flux self-reacting with the oxide shell without requiring external mechanical intervention. This self-service capability allows automated application systems to simply dispense the flux, and the material does the rest of the work of preparing the surfaces for liquid metal TIM adhesion
3Strength
If indium-based STIM is used, then adhesion is achieved through solder flux and gold metallization, but reflowing at 157°C is required and additional metallization layers are needed
Solution Approach 1:
The complex multi-layer metallization system (gold metallization, solder flux, reflow process) is extracted and replaced with a simplified system. The liquid metal TIM directly contacts and adheres to the heat spreader and die surfaces through the flux-assisted wetting mechanism, eliminating the need for gold metallization layers and the reflow soldering process while maintaining strong adhesion
Solution Approach 2:
The bonding interface becomes a composite system consisting of the liquid metal TIM, the flux composition, and the substrate surfaces. This composite material system provides the adhesion function that previously required separate metallization layers and solder joints, simplifying the overall structure while maintaining or enhancing the bonding strength through the synergistic interaction of the liquid metal and flux components
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 enables the use of liquid metal TIMs in high volume manufacturing without manual processing, maintaining a thin bond-line-thickness and high thermal conductivity while minimizing thermo-mechanical stress on the die, thus enhancing thermal performance and manufacturing efficiency.
Implementation Method 1
the liquid metal TIM wets a thermal interface pad between the die and the IHS
Implementation Method 2
maintaining a thin bond-line-thickness and high thermal conductivity while minimizing thermo-mechanical stress on the die, thus enhancing thermal performance
Data Source
AI summary
Embodiments include an electronic system and methods of forming an electronic system. In an embodiment, the electronic system may include a package substrate and a die coupled to the package substrate. In an embodiment, the electronic system may also include an integrated heat spreader (IHS) that is coupled to the package substrate. In an embodiment the electronic system may further comprise a thermal interface pad between the IHS and the die. In an embodiment the die is thermally coupled to the IHS by a liquid metal thermal interface material (TIM) that contacts the thermal interface pad.