Bonded Cold Plate Assembly for Chip Warpage and Heat Flux Control
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Solution Overview
Problem
Chip assemblies face challenges with heat distribution due to coefficient of thermal expansion (CTE) mismatches between components, leading to mechanical failures and warpage, especially in high-power devices like GPUs and ASICs, where traditional heat distribution devices made from single materials fail to effectively manage heat and stress.
Innovation Solution
The use of bonded cold plates with high thermally conductive materials like silver diamond and copper, combined with optimized manufacturing methods and structural modifications such as die thinning and protrusions, to enhance thermal conductivity and control bond line thickness, along with a stiffener to manage warpage and stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a one piece heat distribution device made from a single thermally conductive material is used, then the device structure is simple and manufacturing is easy, but CTE mismatch between the heat distribution device and other components causes stress and warpage during temperature cycling
Solution Approach 1:
The heat distribution device is divided into multiple segments or layers, each made from different materials with varying thermal and mechanical properties. This segmentation allows each layer to be optimized for specific functions (heat conduction, CTE matching, structural support) while reducing overall stress and warpage in the assembly.
Solution Approach 2:
The heat distribution device uses composite materials consisting of multiple layers with different compositions, such as combining high-thermal-conductivity materials with materials having CTE values matched to adjacent components. This composite structure enables simultaneous optimization of thermal performance and mechanical compatibility.
2Power
If high power chips like GPUs and ASICs are used to increase processing capability, then computing performance improves, but heat generation increases requiring more complex cooling solutions
Solution Approach 1:
The heat distribution device incorporates regions with different thermal properties tailored to specific locations. High-thermal-conductivity materials are positioned directly beneath heat-generating chips to efficiently conduct heat away, while other regions use materials optimized for heat spreading or CTE matching, creating a spatially varying thermal architecture.
Solution Approach 2:
The heat distribution device acts as an intermediary thermal management system between the high-power chips and the cooling infrastructure. It includes intermediate structures such as thermal interface materials, heat spreaders, and graduated thermal pathways that facilitate efficient heat transfer from the chip junctions to the external cooling system.
3Reliability
If multiple reflow processes are used to bond components, then assembly reliability improves, but substrate and chip warpage increase due to repeated thermal cycling
Solution Approach 1:
The patent modifies process parameters such as reflow temperature profiles, bonding sequence, and cooling rates to minimize cumulative thermal stress. By carefully controlling these parameters, the assembly achieves reliable bonding while reducing warpage accumulation across multiple reflow cycles.
Solution Approach 2:
The heat distribution device incorporates pre-designed stress-compensating structures and compliant layers that anticipate and cushion against thermal expansion differences during reflow processes. These built-in compensation mechanisms reduce warpage before it becomes a critical issue during subsequent bonding operations.
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 approach improves thermal management by increasing heat flux and reducing warpage, allowing for efficient cooling of high-density electronics while minimizing material costs and manufacturing complexity.
Implementation Method 1
bonded cold plates with high thermally conductive materials like silver diamond and copper
Implementation Method 2
coefficient of thermal expansion (CTE) mismatches between components, leading to mechanical failures and warpage
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A method of manufacturing a chip assembly comprises joining an in-process unit to a printed circuit board; reflowing a bonding material disposed between and electrically connecting the in-process unit with the printed circuit board, the bonding material having a first reflow temperature; and then joining a heat distribution device to the plurality of semiconductor chips using a thermal interface material ("TIM") having a second reflow temperature that is lower than the first reflow temperature. The in-process unit further comprises a substrate having an active surface, a passive surface, and contacts exposed at the active surface; an interposer electrically connected to the substrate; a plurality of semiconductor chips overlying the substrate and electrically connected to the substrate through the interposer, and a stiffener overlying the substrate and having an aperture extending therethrough, the plurality of semiconductor chips being positioned within the aperture.