Chip Assembly Heat Spreader Structure for CTE Mismatch
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Solution Overview
Problem
The coefficient of thermal expansion (CTE) mismatch between heat distribution devices and other components in chip assemblies leads to stress and warpage due to temperature changes during manufacture and use.
Innovation Solution
A microelectronic device assembly is designed with a substrate, microelectronic elements, a stiffener element with a higher CTE, and a heat distribution device with a lower CTE, where the stiffener element extends around the microelectronic elements and the heat distribution device is bonded to the rear surface of the microelectronic elements using a thermal interface material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a one piece heat distribution device comprised of a single thermally conductive material is used to cool microelectronic elements, then heat dissipation is improved, but CTE mismatch between the heat distribution device and other components causes stress and warpage during temperature changes
Solution Approach 1:
The heat distribution device is divided into multiple segments or layers with different materials, each having different CTE values. This segmentation allows the device to accommodate thermal expansion differences between components while maintaining effective heat dissipation pathways through the thermally conductive layers.
Solution Approach 2:
The heat distribution device uses composite materials with different thermal and mechanical properties in different layers. The composite structure combines materials with high thermal conductivity for heat dissipation and materials with appropriate CTE values for each component interface to reduce stress and warpage during temperature cycling.
2Ease of manufacture
If a single material heat distribution device is used, then manufacturing is simplified, but CTE mismatch causes mechanical failure during reflow processes and operation
Solution Approach 1:
The device is segmented into multiple attachable components rather than a single monolithic piece. This allows each segment to be optimized for its specific function (heat conduction, CTE matching, structural support) while maintaining relative manufacturing simplicity through modular assembly processes.
Solution Approach 2:
Intermediate layers or compliant materials are introduced between the heat distribution device and adjacent components. These intermediary layers act as buffers that accommodate CTE mismatches during reflow and operation, preventing mechanical failure while allowing the heat distribution function to proceed.
3Temperature
If heat distribution device directly attaches to substrate and chip, then thermal management is effective, but cycling through reflow processes and operation causes warpage of substrate and chip
Solution Approach 1:
The heat distribution device structure is designed with local variations in material properties and thickness to accommodate different thermal and mechanical requirements at different locations. Areas with higher heat flux have optimized thermal conductivity, while areas with greater CTE mismatch have compliant or buffer layers to prevent warpage.
Solution Approach 2:
Composite material layers are strategically positioned within the heat distribution device structure to provide both effective thermal management pathways and mechanical compliance. The composite structure allows heat to conduct efficiently while accommodating dimensional changes during reflow and operation to prevent substrate and chip warpage.
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 effectively manages thermal expansion, reduces warpage, and enhances thermal conductivity, thereby improving the reliability and performance of chip assemblies.
Implementation Method 1
The coefficient of thermal expansion (CTE) mismatch between the heat distribution device and other components in the chip assembly can stress the assembly when any one of these components expands at a different rate than other components due to temperature changes
Implementation Method 2
heat distribution devices can be utilized within a microelectronic assembly to aid in the reduction of heat generated by microelectronic elements
Data Source
AI summary
According to an aspect of the disclosure, an example microelectronic device assembly includes a substrate, a microelectronic element electrically connected to the substrate, a stiffener element overlying the substrate, and a heat distribution device overlying the rear surface of the microelectronic element. The stiffener element may extend around the microelectronic element. The stiffener element may include a first material that has a first coefficient of thermal expansion (“CTE”). A surface of the stiffener element may face toward the heat distribution device. The heat distribution device may include a second material that has a second CTE. The first material may be different than the second material. The first CTE of the first material of the stiffener element may be greater than the second CTE of the second material of the heat distribution device.