Non-Uniform Thermal Interface Material for 3DIC Heat and Corner Stress
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Solution Overview
Problem
Conventional Thermal Interface Materials (TIMs) in 3DIC packages have low thermal conductivity, leading to high thermal resistance and potential delamination and cracking due to stress concentration at corners, which hampers efficient heat dissipation from device dies to metal lids.
Innovation Solution
A TIM with varying thicknesses, featuring thinner portions over device dies and thicker portions in recesses and corners, designed to reduce thermal resistance and absorb stress, thereby enhancing heat dissipation and mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the TIM is made thin to reduce thermal resistance, then heat dissipation efficiency is improved, but mechanical stability deteriorates due to stress concentration at corners
Solution Approach 1:
The TIM is designed with non-uniform thickness distribution, featuring thinner regions (e.g., 5-15 μm) over the device die area for optimal thermal conduction and thicker regions (e.g., 20-50 μm) at corner and edge areas for stress absorption and mechanical stability. This local variation in thickness allows each region to serve its specific function while resolving the contradiction between thermal performance and mechanical reliability.
2Strength
If the TIM thickness is increased to improve mechanical stability, then stress absorption is enhanced, but thermal resistance increases reducing heat dissipation efficiency
Solution Approach 1:
The TIM exhibits spatially varying thickness where corner and edge regions have greater thickness (20-50 μm) to absorb thermal expansion stress and prevent delamination, while the central region over the device die maintains thinner thickness (5-15 μm) to minimize thermal resistance. This localized thickness optimization allows the TIM to simultaneously achieve both mechanical stability and thermal efficiency.
3Ease of manufacture
If uniform thickness TIM is used, then manufacturing simplicity is maintained, but stress concentration at corners causes delamination and cracking
Solution Approach 1:
The TIM is engineered with position-dependent thickness characteristics, where the material transitions from thinner sections over active device areas to thicker sections at corner and peripheral regions. This non-uniform geometry is achieved through controlled dispensing or molding processes that deposit varying amounts of TIM material, enabling the structure to resist delamination and cracking while maintaining manufacturing feasibility.
Solution Approach 2:
The thicker TIM regions at corners and edges act as pre-positioned stress buffers that absorb thermal expansion forces before they can propagate to cause delamination or cracking. This beforehand cushioning approach proactively mitigates reliability issues by incorporating stress-absorbing features into the TIM design prior to thermal cycling.
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 varying thickness TIM effectively reduces thermal resistance and minimizes delamination and cracking, ensuring efficient heat dissipation and improved mechanical stability in thermal cycles.
Implementation Method 1
The heat generated in the device dies is spread to the metal lid through the thermal interface material
Implementation Method 2
thicker portions in recesses and corners, designed to reduce thermal resistance and absorb stress, thereby enhancing heat dissipation and mechanical stability
Data Source
AI summary
A package includes a package component, a device die over and bonded to the package component, a metal cap having a top portion over the device die, and a thermal interface material between and contacting the device die and the metal cap. The thermal interface material includes a first portion directly over an inner portion of the device die, and a second portion extending directly over a corner region of the device die. The first portion has a first thickness. The second portion has a second thickness greater than the first thickness.