Metal-Ceramic Composite Surface Roughness for Potting Bond Stability
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Solution Overview
Problem
Ceramic circuit carriers in power electronics face challenges with mechanical stresses at the interface between the ceramic substrate and the encapsulant due to thermal expansion coefficient mismatches, leading to potential detachment and humidity ingress, which can damage the power module.
Innovation Solution
A metal-ceramic composite is developed with a silicon nitride ceramic substrate having a metal coating on one side with recesses that expose the ceramic surface, achieving an elongated surface ratio Sdr of at least 7.0% to enhance adhesion with a polymeric potting compound.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the ceramic substrate and encapsulant are bonded together, then mechanical support and protection are provided, but thermal expansion coefficient mismatch causes mechanical stresses leading to detachment
Solution Approach 1:
The patent creates a porous or roughened surface layer on the ceramic substrate through controlled oxidation or chemical treatment. This porous structure increases the surface area and allows the encapsulant to penetrate and mechanically interlock, significantly enhancing bond strength while accommodating thermal expansion stresses.
Solution Approach 2:
The patent forms a composite interface structure consisting of the ceramic substrate, an intermediate oxidized/roughened layer, and the encapsulant. This multi-layer composite structure combines the advantages of each layer: the ceramic provides structural support, the intermediate layer provides adhesion and stress relief, and the encapsulant provides protection and thermal management.
2Strength
If the interface between ceramic substrate and encapsulant is smooth, then manufacturing is easier, but adhesion strength is insufficient under thermal stress
Solution Approach 1:
The patent changes the surface parameters of the ceramic substrate by controlling oxidation time, temperature, and chemical composition to achieve the desired roughness and porosity. By optimizing these parameters, the process becomes repeatable and manufacturable while achieving superior adhesion strength.
Solution Approach 2:
The patent uses strong oxidizing agents or controlled oxidation processes to rapidly create a porous surface layer on the ceramic substrate. This accelerated oxidation method efficiently produces the required surface morphology without excessive complexity, balancing adhesion improvement with manufacturing feasibility.
3Object-affected harmful factors
If voids form at the ceramic-encapsulant interface, then humidity can penetrate and damage the module, but achieving perfect bonding is difficult due to thermal expansion stresses
Solution Approach 1:
The patent creates a controlled porous surface layer that allows the encapsulant to penetrate and form strong mechanical interlocking. This penetration eliminates voids and creates a gradient transition zone that prevents humidity ingress while accommodating thermal expansion stresses.
Solution Approach 2:
The patent anticipates thermal expansion stresses and pre-cushions them by creating a compliant intermediate layer through oxidation. This layer acts as a buffer that absorbs expansion stresses before they can cause detachment or void formation, preventing humidity penetration pathways.
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 improved surface roughness of the ceramic substrate significantly enhances the adhesion strength of the potting compound, reducing the risk of mechanical stress-induced detachment and humidity damage, thereby ensuring the reliability and performance of power electronic modules.
Implementation Method 1
the adhesion strength of the potting compound to the ceramic substrate is improved
Data Source
AI summary
The present invention relates to a metal-ceramic composite comprising a ceramic substrate having a front side and a back side and containing a silicon nitride, a metal coating present on the front side of the ceramic substrate, wherein the metal coating has at least one recess and a surface of the ceramic substrate is exposed through the recess, wherein the surface of the ceramic substrate exposed by the recess has an elongated surface ratio Sdr according to the standard ILNAS-EN ISO 25178-2:2022 of at least 7.0%, wherein Sdr is determined by confocal microscopy.