Multilayer Assembly for Low-Temperature Joining and Warpage Control
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Solution Overview
Problem
Existing insulating circuit boards experience warpage due to thermal expansion differences between heat sinks and ceramic substrates during high-temperature joining, leading to reduced joinability.
Innovation Solution
A multilayer assembly is formed with a ceramic substrate, aluminum plates, intermediate metal layers, and sintered copper layers, using copper, nickel, silver, or gold layers to facilitate joining at lower temperatures, reducing thermal expansion discrepancies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-temperature joining is used to join heat sink to ceramic substrate, then joining strength is improved, but warpage occurs due to thermal expansion difference
Solution Approach 1:
The joining process is divided into two stages: first, the aluminum plate is joined to the ceramic substrate at high temperature (600°C or higher) to ensure strong bonding; second, the heat sink is joined to the aluminum plate at low temperature (room temperature to 200°C) to avoid warpage. This segmentation allows each joining operation to occur under optimal temperature conditions, resolving the contradiction between joining strength and warpage prevention.
Solution Approach 2:
The aluminum plate is pre-joined to the ceramic substrate before the heat sink is attached. This preliminary action creates an intermediate layer that serves as a buffer, absorbing thermal expansion differences and enabling subsequent low-temperature joining of the heat sink without causing warpage to the entire assembly.
2Strength
If high-temperature joining is used to join copper plate to aluminum plate, then joining strength is improved, but warpage occurs due to thermal expansion difference
Solution Approach 1:
The joining temperature parameter is changed from high temperature to low temperature (room temperature to 200°C) for joining the copper plate to the aluminum plate. This parameter change reduces thermal expansion differences between materials, preventing warpage while maintaining adequate joining strength through the use of a copper-based joining material with appropriate mechanical properties.
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 multilayer assembly suppresses warpage and improves joinability by allowing for low-temperature joining, maintaining high thermal conductivity and electrical conductivity.
Implementation Method 1
a first sintered copper layer which is joined to a surface of the first intermediate metal layer opposite to the first aluminum plate
Data Source
AI summary
Joining is made at a low temperature and warpage is suppressed in the formation of a multilayer assembly, such as joining of a heat sink to an insulating circuit board. A multilayer assembly including: a ceramic substrate; a first aluminum plate which is joined to one surface of the ceramic substrate and contains aluminum or an aluminum alloy; a first intermediate metal layer which is joined to a surface of the first aluminum plate opposite to the ceramic substrate and contains any of copper, nickel, silver, or gold; a first sintered copper layer which is joined to a surface of the first intermediate metal layer opposite to the first aluminum plate; and a first metal member which is joined to a surface of the first sintered copper layer opposite to the first intermediate metal layer and contains any of aluminum, an aluminum alloy, copper, or a copper alloy.