Flexible Copper Pillar Thermal Interface for IC Die Stress
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Solution Overview
Problem
Integrated circuit substrates with lower thermal expansion coefficients than typical heat spreader materials face challenges in thermal dissipation due to coefficient of thermal expansion (CTE) mismatch, leading to mechanical stress and potential packaging failures under temperature changes.
Innovation Solution
A heat dissipation structure featuring pillars with an aspect ratio greater than 1:1, connected to the integrated circuit die via copper nanoparticle layers, which accommodate mechanical strain and facilitate thermal conductivity, allowing for flexible thermal expansion while minimizing die stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional rigid thermal interface structures are used to attach integrated circuit substrates to heat spreaders, then thermal conductivity is improved, but mechanical stress and die failure increase due to CTE mismatch
Solution Approach 1:
The patent employs flexible pillars with aspect ratios greater than 1:1 that can bend and deform to accommodate CTE differences between the IC substrate and heat spreader. These flexible structures maintain thermal contact while absorbing mechanical strain, preventing die stress and failure.
Solution Approach 2:
The thermal interface structure uses composite material systems including copper pillars, copper nanoparticle layers, and copper thermal mount materials. These composite structures provide both high thermal conductivity and mechanical compliance to handle CTE mismatch.
2Reliability
If high aspect ratio pillars are used to accommodate mechanical strain, then die stress is reduced, but thermal conductivity path may be interrupted
Solution Approach 1:
The patent optimizes the aspect ratio parameter of pillars (greater than 1:1, preferably greater than 2:1) to achieve the right balance between mechanical flexibility for strain accommodation and sufficient thermal conduction path. The specific aspect ratio is tuned to allow bending while maintaining thermal contact.
Solution Approach 2:
Copper nanoparticle layers are introduced as intermediary materials between the pillars and connection areas. These nanoparticle layers fill gaps and maintain thermal conductivity even when pillars deform, ensuring continuous thermal paths while accommodating mechanical strain.
3Loss of energy
If copper materials are used for thermal mount and pillars, then thermal conductivity is enhanced, but CTE mismatch with semiconductor die increases
Solution Approach 1:
The copper thermal mount uses flexible pillar structures that can deform to accommodate the CTE mismatch between copper (high CTE) and semiconductor die (low CTE). The flexibility allows the copper material to be used for its superior thermal conductivity without causing excessive stress during thermal cycling.
4Ease of manufacture
If pillars with uniform aspect ratio are used, then manufacturing is simplified, but mechanical strain distribution across the die is non-optimal
Solution Approach 1:
The patent implements non-uniform pillar aspect ratios where pillars at different locations on the thermal mount have different heights. Pillars farther from the center have greater aspect ratios for better strain accommodation, while central pillars have lower aspect ratios. This local optimization improves overall strain distribution while remaining manufacturable.
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 manages mechanical strain and enhances thermal conductivity, reducing the likelihood of packaging failures and improving heat dissipation performance by using copper pillars and nanoparticle layers to match the CTE of the integrated circuit and heat spreader materials.
Implementation Method 1
A thermal conductivity of materials for each of the connection areas, the thermal mount, the pillars and the interface layers is preferably greater than 100 Watts per meter degree Kelvin (W/m·K)
Implementation Method 2
flexure of the pillars accommodates mechanical strain arising from temperature changes and differences in coefficients of thermal expansion for materials of the semiconductor integrated circuit die and the thermal mount
Implementation Method 3
differences in coefficients of thermal expansion for materials of the semiconductor integrated circuit die and the thermal mount
Data Source
AI summary
A heat dissipation structure for a semiconductor integrated circuit die having a plurality of connection areas may include a thermal mount comprising a plurality of pillars each having an aspect ratio preferable greater than 2:1 and each positioned to connect to one of the connection areas on a peripheral portion of the semiconductor integrated circuit die with one of a plurality of interface layers. A thermal conductivity of materials for the connection areas, the thermal mount, the pillars, each of which is preferably copper, and the interface layers, which are preferably copper nanoparticle layers, has a thermal conductivity greater than 100 Watts per meter degree Kelvin (W/m·K). Flexure of the pillars accommodates mechanical strain arising from temperature changes and differences in coefficients of thermal expansion for materials of the semiconductor integrated circuit die and the thermal mount.