Brazed Copper Ceramic Thermal Management Assembly
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Solution Overview
Problem
The existing direct bonded copper (DBC) method for microheat exchangers often results in cracking of ceramic materials, formation of microvoids at interfaces, and warping due to differing thermal coefficients of expansion, leading to reduced thermal efficiency and increased chances of delamination.
Innovation Solution
A microheat exchanging assembly is configured with ceramic layers bonded to conductive copper layers using active brazing alloys, which are etched to form electrically isolated conductive pads, providing improved thermal conductivity while minimizing the high-temperature bonding process's adverse effects through the use of brazing and metallized ceramic approaches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high temperature joining process is used to bond copper to ceramic, then bonding strength is improved, but ceramic cracking occurs
Solution Approach 1:
An intermediate layer is introduced between the copper and ceramic layers to act as a buffer during the bonding process. This intermediate layer absorbs thermal stress and prevents direct transmission of high temperature to the ceramic, thereby avoiding ceramic cracking while still achieving strong bonding between copper and ceramic through the mediator.
2Strength
If high temperature joining process is used to bond copper to ceramic, then bonding strength is improved, but microvoids form at interface
Solution Approach 1:
The intermediate layer serves as a mediator that fills and compensates for surface irregularities and microvoids at the copper-ceramic interface. During the bonding process, the intermediate material flows into and seals these voids, creating a dense, void-free interface while maintaining strong bonding strength.
3Strength
If copper and ceramic are bonded at high temperature, then bonding is achieved, but warping occurs due to thermal expansion difference
Solution Approach 1:
The intermediate layer acts as a compliant buffer that accommodates the differential thermal expansion between copper and ceramic during high temperature bonding. This mediator layer absorbs the expansion mismatch stresses, preventing warping of the bonded assembly while still achieving strong bonding between the dissimilar materials.
4Adaptability or versatility
If larger ceramic plate is used for multiple heat generating devices, then device capacity is improved, but microvoid impact increases
Solution Approach 1:
The intermediate layer provides continuous, uniform bonding across the entire large ceramic plate surface, effectively sealing and isolating microvoids throughout the extended area. This mediator ensures consistent thermal performance across the whole plate, allowing the system to support multiple heat generating devices without the microvoids degrading overall thermal efficiency.
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 enhances thermal efficiency by filling microvoids and reducing warping, ensuring a strong, reliable bond between ceramic and copper layers, thereby improving heat transfer and mechanical stability.
Implementation Method 1
A first active brazing alloy is bonded between the first copper layer and the ceramic layer to form a first joining layer, and a second active brazing alloy is bonded between the ceramic layer and the second copper layer to form a second joining layer
Implementation Method 2
A brazing process is performed to bond the ceramic layer to the conductive layer via a joining layer
Implementation Method 3
The top conductive layer and the joining layer are etched to form the electrically isolated conductive pads
Implementation Method 4
Microheat exchangers are made of thermally conductive material and are used to transfer heat from a heat generating device, such as an integrated circuit or a laser diode, to a fluid flowing through fluid pathways within the microheat exchanger
Data Source
AI summary
A ceramic assembly includes one or more electrically and thermally conductive pads to be thermally coupled to a heat generating device, each conductive pad is electrically isolated from each other. The ceramic assembly includes a ceramic layer to provide this electrical isolation. The ceramic layer has high thermal conductivity and high electrical resistivity. A top surface and a bottom surface of the ceramic layer are each bonded to a conductive layer, such as copper, using an intermediate joining material. A brazing process is performed to bond the ceramic layer to the conductive layer via a joining layer. The joining layer is a composite of the joining material, the ceramic layer, and the conductive layer. The top conductive layer and the joining layer are etched to form the electrically isolated conductive pads. The conductive layers are bonded to the ceramic layer using a bare ceramic approach or a metallized ceramic approach.