Direct Bonded Copper Ceramic Substrate Passivation
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Solution Overview
Problem
The existing direct bonded copper ceramic substrates used in high-power IGBT modules face issues with bonding strength, thermal conductivity, and reliability due to reactions between copper oxide and aluminum nitride surfaces, leading to the formation of bubbles that degrade performance.
Innovation Solution
A direct bonded copper ceramic substrate is developed with a nitride ceramic substrate coated with a passivation layer of aluminum or silicon oxide doped with metals like titanium, vanadium, chromium, manganese, iron, cobalt, nickel, or copper, which is applied between the ceramic substrate and copper layers to enhance bonding and reduce bubble formation, thereby improving peel strength and thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If copper oxide is used to bond to aluminum nitride ceramic substrate, then bonding is achieved, but bubbles form at the interface reducing bonding strength and thermal conductivity
Solution Approach 1:
A magnesium oxide layer is introduced as an intermediary between the copper oxide and aluminum nitride ceramic substrate. This intermediate layer prevents direct harmful reactions between copper oxide and aluminum nitride, eliminating bubble formation at the interface while maintaining effective thermal and mechanical coupling. The magnesium oxide acts as a protective mediator that resolves the contradiction between achieving bonding and preventing interface defects.
Solution Approach 2:
The potential harmful reaction between copper oxide and aluminum nitride is converted into a beneficial process by controlling the oxidation sequence. Copper is first oxidized to copper oxide, which would normally be harmful, but then magnesium is oxidized to form magnesium oxide that protects the aluminum nitride from direct contact with copper oxide. The harmful copper oxide reaction is thus transformed into a useful protective mechanism.
2Loss of energy
If aluminum nitride ceramic substrate is used for high thermal conductivity, then thermal performance is improved, but surface treatment is required to prevent bubble formation
Solution Approach 1:
Magnesium oxide layer is formed on the aluminum nitride substrate surface before the copper bonding process. This preliminary action of creating the protective magnesium oxide barrier prevents the need for complex surface treatments later, as it inherently protects the aluminum nitride from harmful reactions with copper oxide while maintaining thermal conductivity.
Solution Approach 2:
The substrate structure is transformed into a composite system with multiple layers: aluminum nitride ceramic substrate, magnesium oxide protective layer, and copper bonding layer. This composite structure combines the high thermal conductivity of aluminum nitride with the protective properties of magnesium oxide, eliminating the need for complex surface treatments while maintaining energy efficiency.
3Strength
If direct bonding of copper to ceramic is performed at high temperature, then bonding strength is achieved, but thermal cycle reliability decreases due to bubble formation
Solution Approach 1:
The magnesium oxide layer serves as a stable intermediary that remains intact during high-temperature bonding and subsequent thermal cycling. It prevents direct contact between copper oxide and aluminum nitride, eliminating bubble formation that would compromise long-term reliability. This mediator enables strong bonding while ensuring durability through thermal cycles.
Solution Approach 2:
The magnesium oxide layer is formed beforehand to cushion and protect the aluminum nitride substrate from harmful reactions during the bonding process and subsequent thermal cycling. This prior protective measure prevents bubble formation that would otherwise develop during thermal expansion and contraction, ensuring long-term 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 significantly enhances the peel strength and thermal conductivity of the copper foil to the ceramic substrate, reducing bubble formation and improving the reliability of the substrate for high-power applications.
Implementation Method 1
the surfaces of the aluminum nitride ceramic substrate need an additional treatment (e.g. oxidation) to form stable inert passivation layers
Implementation Method 2
the copper oxide of the copper foil surface bonds to the ceramic substrate
Implementation Method 3
heated under an inert atmosphere to 1050° C. to 1080° C., so that the copper oxide of the copper foil surface bonds to the ceramic substrate
Data Source
AI summary
A direct bonded copper ceramic substrate is provided, which includes a nitride ceramic substrate, a first passivation layer, and a first copper layer. The first passivation layer includes aluminum oxide or silicon oxide doped with another metal. The other metal is titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, or a combination thereof. The aluminum or silicon and the other metal have a weight ratio of 60:40 to 99.5:0.5. The first passivation layer is disposed between the top surface of the nitride ceramic substrate and the first copper layer.