Hybrid Bond Sheet Layout for Uniform Power Module Cooling
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Solution Overview
Problem
Current thermal interface materials in power modules suffer from high thermal mismatch, stress, and warpage due to unbalanced vertical package structures, limiting the homogenization of junction temperature and thus the performance and reliability of power modules.
Innovation Solution
A hybrid bond sheet with a metallic and dielectric pattern is used, which can be permanently laminated between the power module and heatsink, providing local variation in thermal conductivity to compensate for temperature non-uniformity and reduce thermal stress, utilizing standard PCB manufacturing equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If traditional thermal interface materials are used, then thermal conduction is provided, but thermal mismatch and stress cause warpage and accelerate fatigue-based failure
Solution Approach 1:
The patent uses a composite bond sheet comprising a metal layer (e.g., copper) and a polymer layer (e.g., polyimide) bonded together. The metal layer provides high thermal conductivity for efficient heat transfer, while the polymer layer has a coefficient of thermal expansion matched to the ceramic substrate, reducing thermal stress and warpage. This composite structure resolves the contradiction by combining materials with complementary properties to achieve both thermal conduction and reliability.
Solution Approach 2:
The bond sheet is designed with spatially varying thermal conductivity through different metal layer thicknesses or patterns. Areas with higher heat generation have thicker metal layers or higher thermal conductivity materials, while areas with lower heat generation have thinner metal layers. This local optimization enables effective heat dissipation where needed while minimizing thermal stress in other areas, thereby improving both temperature management and reliability.
2Temperature
If thermal interface materials are applied to increase performance, then thermal management improves, but large area interfaces and unbalanced vertical package structures cause high stress and warpage
Solution Approach 1:
The composite bond sheet with matched CTE polymer layer compensates for the unbalanced vertical package structure by providing a thermal expansion buffer that matches the ceramic substrate. This reduces the stress caused by differential thermal expansion between dissimilar materials in the package structure, enabling effective thermal management without excessive stress or warpage.
Solution Approach 2:
The patent changes the material parameters of the bond sheet, specifically selecting a polymer material with a coefficient of thermal expansion that matches the ceramic substrate. This parameter matching reduces thermal stress by eliminating the CTE mismatch that would otherwise cause stress and warpage during thermal cycling, while still providing adequate thermal conduction through the metal layer.
3Ease of operation
If limited routing layers are used for interconnection, then functional constraints are met, but thermal optimization and homogenization of junction temperature cannot be achieved
Solution Approach 1:
Instead of attempting to solve thermal management problems in the limited planar routing layers, the patent moves the thermal optimization to the vertical dimension by using a multi-layer bond sheet structure between the power module and heatsink. The varying thicknesses and material compositions in the vertical direction enable heat spread and temperature homogenization without interfering with the functional routing layers, thus achieving thermal optimization in a different dimension.
Solution Approach 2:
The bond sheet is segmented into multiple layers with different functions: a metal layer for thermal conduction, a polymer layer for stress reduction, and potentially patterned structures for heat spreading. This segmentation allows each layer to optimize its specific function while working together to achieve overall thermal management, enabling temperature homogenization without compromising functional performance.
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 solution effectively reduces thermal mismatch and stress, increases the reliability and performance of power modules by homogenizing junction temperature, and is cost-competitive with existing high-performance conductive TIM solutions.
Implementation Method 1
The metallic surface of the bond sheet is divided into islands by a dielectric grid or mesh pattern... The metallic island areas take the function of main heat conductor
Implementation Method 2
The sheets can be permanently laminated between power module and heatsink/cooler using moderate temperature and pressure (e.g., for a target of 170° C. to 200° C., 1 MPa to 5 MPa)
Data Source
AI summary
A hybrid bond sheet for mounting a semiconductor power module to a heat sink includes a thermally conductive core layer having an upper main face and a lower main face; a first bond layer formed at the upper main face of the core layer for bonding the hybrid bond sheet to a semiconductor power module; and a second bond layer formed at the lower main face of the core layer for bonding the hybrid bond sheet to a heat sink; where the core layer is subdivided into a plurality of core metal sections and core polymer sections which are formed side-by-side between the upper main face and the lower main face, the subdivided core metal sections being configured to enable a uniform heat transfer between the semiconductor power module and the heat sink and to reduce thermal stress at interfaces between the hybrid bond sheet and the heat sink.