Thermally Reinforced Semiconductor Die Recess for TIM Retention
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Solution Overview
Problem
Semiconductor devices experience significant thermal interface material (TIM) loss due to thermo-mechanical stresses under cyclic loading, leading to reduced thermal performance and potential failure, as the TIM 'pumps out' from the interface between the die and heat spreader.
Innovation Solution
A method involving the formation of a recess in the semiconductor die with a peripheral portion offset from the recess depth, allowing the TIM to be laterally supported and surrounded by the die, reducing its flow away from the interface, and a heat spreader with protrusions to further secure the TIM in place.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a flat semiconductor die interface is used with heat spreader, then the initial thermal contact is good, but the TIM pumps out under cyclic thermal loading leading to degraded thermal performance
Solution Approach 1:
The patent transitions from a two-dimensional flat interface to a three-dimensional recessed interface. The recess in the semiconductor die creates a depth dimension that allows TIM to be contained and laterally supported by the die's peripheral portion, preventing pump-out while maintaining thermal contact.
Solution Approach 2:
The recess structure acts as an intermediary element between the semiconductor die and heat spreader. It provides a geometric feature that mediates the interaction between these components, enabling the TIM to be mechanically retained while maintaining thermal conductivity.
2Temperature
If the TIM layer is made thinner to improve thermal contact, then thermal resistance decreases, but the TIM is more susceptible to pump-out under cyclic loading
Solution Approach 1:
By creating a recess with finite depth, the patent adds a vertical dimension constraint that prevents lateral pump-out of thin TIM layers. The TIM remains thin for low thermal resistance but is contained within the recess boundaries, solving the pump-out issue.
Solution Approach 2:
The recess structure provides preliminary mechanical constraint to the TIM before cyclic thermal loading occurs. The lateral support from the die's peripheral portion counteracts the pump-out force that would otherwise expel the TIM during thermal cycling.
3Reliability
If a recess is formed in the semiconductor die to retain TIM, then TIM pump-out is reduced, but the manufacturing complexity increases
Solution Approach 1:
The recess formation process segments the die manufacturing into distinct stages: standard die fabrication followed by selective recess etching. This allows the majority of the die to be manufactured using conventional processes, with only a localized area requiring additional processing.
Solution Approach 2:
The recess is a localized feature formed only in the specific area where TIM retention is needed, rather than modifying the entire die structure. This minimizes the impact on overall manufacturing complexity while providing the necessary functional improvement.
4Reliability
If the peripheral portion of the back surface is offset from the recess depth, then lateral support for TIM is provided, but the die structure becomes more complex
Solution Approach 1:
The offset peripheral portion creates a stepped three-dimensional structure that provides lateral support for the TIM. This geometric feature uses vertical offset to create a mechanical barrier that prevents TIM pump-out while maintaining structural integrity.
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 configuration enhances thermal performance by maintaining a consistent TIM layer, reducing pump-out and extending the lifespan of semiconductor devices by minimizing TIM loss and heat dissipation issues.
Implementation Method 1
depositing a TIM over the semiconductor die and into the recess... mounting a heat spreader over the semiconductor die and connected to the conductive traces
Implementation Method 2
forming a recess in an interior portion of the semiconductor die that extends from a back surface of the semiconductor die opposite the active surface partially through the semiconductor die such that a peripheral portion of the back surface of the semiconductor die is offset with respect to a depth of the recess... depositing a TIM over the semiconductor die and into the recess such that the TIM in the recess is laterally supported by the peripheral portion of the semiconductor die
Data Source
AI summary
A semiconductor device includes a substrate with conductive traces. A semiconductor die is mounted with an active surface oriented toward the substrate. An underfill material is deposited between the semiconductor die and substrate. A recess is formed in an interior portion of the semiconductor die that extends from a back surface of the semiconductor die opposite the active surface partially through the semiconductor die such that a peripheral portion of the back surface of the semiconductor die is offset with respect to a depth of the recess. A thermal interface material (TIM) is deposited over the semiconductor die and into the recess such that the TIM in the recess is laterally supported by the peripheral portion of the semiconductor die to reduce flow of the TIM away from the semiconductor die. A heat spreader including protrusions is mounted over the semiconductor die and contacts the TIM.