Millichannel Substrate for Power Electronics Cooling
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Solution Overview
Problem
High-performance power electronics require effective cooling to prevent overheating, but existing heat sink technologies face challenges with mechanical distortion and residual stress due to thermal expansion differences between metal and ceramic layers, leading to deformation and poor bonding at high temperatures.
Innovation Solution
A method for creating a millichannel substrate by attaching a first layer with millichannels to a second layer, which is then coupled to a base plate, allowing coolant passage and reducing deformation, with the substrate being planar to ensure secure bonding to both the base plate and power electronics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the substrate is made with metal and ceramic layers bonded at high temperature, then thermal conductivity is improved, but mechanical distortion and residual stress occur due to CTE mismatch
Solution Approach 1:
The patent changes the bonding temperature parameter from conventional high temperature (600-1000°C) to low temperature (room temperature to 250°C). This parameter change resolves the contradiction by enabling thermal conductivity through alternative bonding methods that do not require high temperature, thereby avoiding mechanical distortion and residual stress from CTE mismatch between metal and ceramic layers
Solution Approach 2:
The patent applies different bonding approaches to different regions or interfaces of the substrate. Specifically, the millichannels are formed in the metal layer with precise local geometry while the bonding interface between metal and ceramic is treated differently from the bonding interface between metal and base plate, allowing each interface to be optimized for its specific function without compromising the other
2Ease of operation
If millichannels are fabricated in the bottom metal layer, then coolant flow is enabled, but substrate deformation occurs due to stress relief from metal removal
Solution Approach 1:
The millichannels are formed in the metal layer before the bonding process. This preliminary action allows the channels to be precisely defined while the metal layer is still in its original state, preventing subsequent deformation that would occur if channels were formed after bonding and stress relief
Solution Approach 2:
The substrate is segmented into distinct functional layers: the metal layer with millichannels for coolant flow, the ceramic layer for electrical isolation and thermal conduction, and the base plate for structural support. This segmentation allows each layer to be optimized independently, with the metal layer's channel geometry not compromising the overall substrate shape
3Reliability
If the substrate is bonded to the heatsink at high temperature, then thermal contact is improved, but bonding fails due to excessive substrate deformation
Solution Approach 1:
The bonding temperature parameter is changed from high temperature to low temperature (room temperature to 250°C). This resolves the contradiction by achieving adequate thermal contact through alternative bonding methods that do not induce excessive substrate deformation, thereby maintaining substrate planarity and enabling successful bonding to the heatsink
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 method effectively reduces mechanical distortion and enhances thermal conductivity, enabling reliable and efficient cooling of power electronics by minimizing deformation and maintaining a stable bond, even at elevated temperatures.
Implementation Method 1
the base plate is configured to cooperate with the substrate to pass a coolant through the millichannels
Implementation Method 2
The heat sinks operate by transferring the heat away from the power electronics thereby maintaining a lower temperature of the power electronics
Implementation Method 3
the cooling may result in mechanical residual stress at the metal to ceramic interfaces due to the difference in coefficient of thermal expansion (CTE) between the metal and the ceramic layer
Data Source
Figure 1~2
Figure 3~4
Figure 5(a)~5(b)
AI summary
A substrate (12) for power electronics (100) mounted thereon, comprises a middle ceramic layer (120) having a lower surface (124) and an upper surface (123), an upper metal layer (121) attached to the upper surface (124) of the middle ceramic layer (120), and a lower metal layer (122) attached to the lower surface (124) of the middle ceramic layer (120). The lower metal layer (122) has a plurality of millichannels (125, 126) configured to deliver a coolant for cooling the power electronics (100), wherein the millichannels (125, 126) are formed on the lower metal layer (122) prior to attachment to the lower surface (124) of the middle ceramic layer (120). Methods for making a cooling device and an apparatus (10) are also presented.