Patterned Package Lid Structure to Inhibit TIM Pump-Out
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Solution Overview
Problem
The thermal interface material (TIM) layer in semiconductor packaging can experience 'pump-out' due to various phenomena such as lateral flow, vertical flow, extrusion, and evaporation, leading to reduced heat transfer efficiency and increased thermal resistance, especially when it has a low melting point and is subjected to temperature increases.
Innovation Solution
A package structure with a patterned bottom surface on the package lid, featuring recessed portions that align with the TIM layer, helps inhibit pump-out by increasing contact area and providing extra spacing, while using a Phase Change Material (PCM) type TIM layer that changes phase to high viscosity semi-liquid around 60°C enhances thermal contact resistance and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a TIM layer with low melting point is used to improve thermal contact, then thermal conductivity is improved, but pump-out risk increases due to evaporation and phase change at elevated temperatures
Solution Approach 1:
The package lid applies preliminary compressive force to the TIM layer through its weight and structural design, creating pre-compression that counteracts the pump-out forces generated during thermal cycling. This preliminary anti-action prevents the TIM layer from flowing laterally or vertically away from the interface, maintaining thermal contact stability even with low melting point materials
Solution Approach 2:
The invention changes the physical state parameters of the TIM layer by controlling temperature and pressure conditions. The package lid maintains the TIM layer in a compressed state below its melting point, preventing phase change and evaporation. By carefully managing thermal and mechanical parameters, the system exploits the high thermal conductivity of low melting point materials while avoiding pump-out through proper parameter control
2Reliability
If the TIM layer is compressed to improve thermal contact, then thermal conductance is improved, but the TIM layer may be extruded from the interface due to mechanical stresses
Solution Approach 1:
The package lid is designed with a distributed weight distribution and structural segmentation that applies compression forces evenly across the TIM layer interface. This prevents localized stress concentrations that would cause extrusion, while maintaining sufficient overall compression for thermal contact. The segmented approach allows controlled compression without excessive mechanical stress
3Reliability
If the contact area between package lid and TIM layer is increased to improve heat dissipation, then thermal conductance is improved, but the package lid structure becomes more complex
Solution Approach 1:
The package lid serves multiple functions simultaneously: it provides structural support, applies compressive force to the TIM layer, dissipates heat, and protects the underlying components. By integrating these functions into a single component rather than adding separate elements, the invention increases contact area for heat dissipation without proportionally increasing structural complexity
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 solution effectively reduces the risk of TIM layer pump-out, maintains thermal contact, and improves heat dissipation by increasing the contact area between the package lid and the TIM layer, thereby enhancing interfacial thermal conductance and preventing electrical failures.
Implementation Method 1
using a Phase Change Material (PCM) type TIM layer that changes phase to high viscosity semi-liquid around 60°C enhances thermal contact resistance and performance
Implementation Method 2
The TIM layer may improve thermal contact by filling the microscopic gaps and irregularities between the surfaces
Implementation Method 3
lateral flow (the TIM layer may flow laterally away from the interface due to shear forces caused by thermal cycling)
Implementation Method 4
vertical flow (the TIM layer may flow vertically away from the interface due to pressure differences caused by thermal cycling)
Implementation Method 5
extrusion (the TIM layer may be extruded from the interface due to mechanical stresses caused by differential thermal expansion between the TIM layer, package module and package lid)
Implementation Method 6
evaporation (the volatile components of the TIM layer may evaporate, causing the TIM layer to shrink and lose its thermal contact with the interface)
Implementation Method 7
improves heat dissipation by increasing the contact area between the package lid and the TIM layer, thereby enhancing interfacial thermal conductance
Data Source
AI summary
A package structure includes a package substrate, a package module on the package substrate, a thermal interface material (TIM) layer on the package module, and a package lid on the TIM layer. The package lid includes a package lid foot portion attached to the package substrate, and a package lid plate portion on the package lid foot portion and including a patterned bottom surface having a plurality of recessed portions, wherein at least a portion of the TIM layer is located in the plurality of recessed portions.