Power Module Substrate Bonding for Thermal Stress Reliability
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Solution Overview
Problem
The bonding force between the nickel plating layer on copper heat dissipation substrates and the molding compound in power modules is weak, leading to thermal stress-induced disconnections and cracking due to mismatched thermal expansion coefficients, compromising the structural integrity and insulation of the ceramic substrate.
Innovation Solution
A power module design featuring a second substrate region with a copper, copper alloy, or copper oxide surface exposed to the package body, eliminating intermediate plating layers, and incorporating surface roughening and grooves to enhance bonding strength, thereby maintaining connection under thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a nickel plating layer is applied on the copper heat dissipation substrate to prevent corrosion, then corrosion resistance is improved, but bonding force with the molding compound deteriorates
Solution Approach 1:
The patent applies different surface treatments to different regions of the heat dissipation substrate. The first region (under the ceramic substrate) maintains nickel plating for corrosion protection, while the second region (exposed to molding compound) uses copper or copper oxide with roughened surface for strong bonding. This local differentiation resolves the contradiction between corrosion resistance and bonding strength.
2Adaptability or versatility
If thermal expansion coefficients of different materials are mismatched, then thermal stress occurs during temperature changes, but connection strength between heat dissipation substrate and molding compound deteriorates
Solution Approach 1:
The patent changes the physical parameters of the heat dissipation substrate surface in the second region by removing the nickel plating layer and roughening the copper surface. This parameter change enables the molding compound to directly bond to the copper base material, which has better thermal expansion compatibility, thereby maintaining connection strength under thermal stress.
3Reliability
If thermal stress concentrates on the ceramic wafer due to disconnection, then cracking risk increases, but structural reliability deteriorates
Solution Approach 1:
The patent beforehand cushions the thermal stress by creating a strong bonding interface between the heat dissipation substrate and molding compound in the second region. This strong interface acts as a stress-distributing layer that prevents stress concentration on the ceramic wafer, thereby preventing cracking and improving structural reliability.
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 solution improves structural reliability by maintaining adequate connection strength between the second substrate and the package body, reducing thermal stress-induced cracking risks, and enhancing the overall structural integrity of the power module.
Implementation Method 1
When a temperature of an external environment or inside the power module changes, thermal stress causes a disconnection between the heat dissipation substrate and the molding compound due to a difference between thermal expansion coefficients of different materials
Implementation Method 2
surface roughness of the second region is greater than surface roughness of the first region. The surface roughness of the second region is increased, so that connection strength between the second region and the package body can be further improved
Data Source
AI summary
A power module includes a first substrate, a second substrate, a chip, and a package body. The first substrate includes a first surface and a second surface, and the first surface is configured to mount the chip. The second substrate includes a bearing surface, the bearing surface is configured to bear the first substrate, and the bearing surface is in contact with the second surface. The bearing surface includes a first region and a second region, the first region is opposite to the first substrate, the second region is disposed in a ring shape around the first region, and a surface material of the second region includes copper, a copper alloy, or a copper oxide. The package body is configured to wrap the chip, the first substrate, and at least a part of the second substrate, and the package body is in contact with the second region.