Metal-Ceramic Substrate Insulation Filling Against Electromigration
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Solution Overview
Problem
Metal-ceramic substrates used in semiconductor power modules face issues with thermal and mechanical stress leading to cracking, and electromigration at high electric field strengths, which can result in short circuits and substrate destruction.
Innovation Solution
A method involving the application of an electrically insulating filler material to trench-shaped intermediate spaces between metallization regions on the ceramic substrate, covering both edges of the metallization, to prevent electromigration and reduce thermal stress, using techniques like DCB or AMB for metallization and incorporating materials like glass or glass-based fillers with adapted thermal expansion coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high temperatures are used for metallization bonding, then strong bonding between metal and ceramic is achieved, but thermal stress causes cracking in the ceramic layer
Solution Approach 1:
A transition layer comprising a ceramic filler material and a glass binder is introduced between the metallization and the ceramic substrate. This intermediary layer has thermal expansion characteristics that bridge the gap between the metal and ceramic, reducing thermal stress during temperature cycles while maintaining bonding strength.
Solution Approach 2:
The transition layer is formed as a composite material combining ceramic filler particles (such as aluminum oxide, aluminum nitride, or silicon nitride) with a glass binder. This composite structure provides both mechanical strength and tailored thermal expansion properties to match the metallization-ceramic interface.
2Reliability
If trench-shaped intermediate spaces are left empty between metallization regions, then electrical insulation is provided, but electromigration occurs at high electric field strengths
Solution Approach 1:
The trench-shaped intermediate spaces are filled with the same ceramic filler material and glass binder composition used in the transition layer. This filler material acts as an intermediary that maintains electrical insulation while providing a pathway that reduces electric field strength, preventing electromigration at the metallization edges.
3Reliability
If the edges of metallization regions are covered by filler material, then electromigration is prevented, but manufacturing complexity increases
Solution Approach 1:
The formation of the transition layer and the filling of trench-shaped intermediate spaces are merged into a single manufacturing step. The same ceramic filler material and glass binder composition is used for both the transition layer and the trench filler, allowing both features to be created simultaneously through one application and firing process.
Solution Approach 2:
The ceramic filler material with glass binder serves multiple functions: it forms the transition layer for stress reduction, fills the trench-shaped intermediate spaces for electromigration prevention, and provides electrical insulation. This multi-functionality eliminates the need for separate materials and processing steps.
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 method significantly reduces or prevents electromigration and thermal stress-related cracking, enhancing the reliability and lifespan of metal-ceramic substrates by providing electrical insulation and protecting against moisture and gas ingress, while allowing for easy production and integration with electronic components.
Implementation Method 1
at least the intermediate space is filled with an electrically insulating filler material
Implementation Method 2
incorporating materials like glass or glass-based fillers with adapted thermal expansion coefficients
Implementation Method 3
The metal part is then placed onto the ceramic substrate and heated together with the ceramic to a temperature above the melting point of the eutectic and below the melting temperature of the metal
Implementation Method 4
Another known method for producing a thick metallization on a ceramic substrate is the so-called active brazing process (AMB: Active Metal Brazing)
Implementation Method 5
Oxidizing of a copper foil, such that an even copper oxide layer is formed
Implementation Method 6
a coat made of a chemical compound of the metal and a reactive gas - in particular, oxygen
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a method for producing a metal-ceramic substrate (1, 11, 12), in which at least one metal layer (3) is attached to at least one surface side of a ceramic layer (2), which metal layer (3) is structured into several metallization regions (5, 6) respectively separated from one another by at least one trench-shaped intermediate space (4) to form conductive paths and/or connective surfaces and/or contact surfaces, wherein at least the intermediate space (4) is filled with an electrically insulating filler material (7). First edges (8) of the metallization regions (5, 6) facing and adjoining the surface side of the ceramic layer (2) in the intermediate space (4), as well as at least one second edge (9) of the metallization regions (5, 6) facing away from the surface side of the ceramic layer (2) in the intermediate space (4), are covered by the filler material (7). Furthermore, the invention relates to an associated metal-ceramic substrate (1, 11, 12).