Copper Paste Adhesion on Aluminum Nitride Substrates
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Solution Overview
Problem
The application of thick-film pastes on aluminum nitride substrates is limited by the lack of compatible compositions that exhibit sufficient adhesion, which is crucial for metal conductors in high-temperature, high-voltage, and high-amperage electronics applications.
Innovation Solution
A copper conductive paste composition comprising 50-90 wt.% copper particles, 0.5-10 wt.% glass frit, 0.1-5% adhesion promoter, and 5-20 wt.% organic vehicle, specifically designed to adhere well to aluminum nitride substrates, with copper particles of varying diameters and specific surface areas, and a glass frit comprising lead-free oxides, is used. The paste is applied in multiple layers and fired in a nitrogen atmosphere to achieve excellent adhesion and conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional thick-film paste compositions are used on aluminum nitride substrates, then the manufacturing process is simple, but the adhesion of metal conductors to the substrate is insufficient
Solution Approach 1:
The patent employs a composite paste composition containing copper particles, glass frit, adhesion promoters (such as titanium oxide, zirconium oxide, or boron resinate), and organic vehicle. This composite formulation specifically addresses the adhesion problem by combining multiple functional materials that work synergistically to bond copper conductors to aluminum nitride substrates, resolving the technical contradiction between achieving strong adhesion and maintaining composition simplicity.
Solution Approach 2:
The patent introduces adhesion promoters (titanium oxide, zirconium oxide, boron resinate) and glass frit as intermediary materials between the copper particles and aluminum nitride substrate. These intermediaries facilitate bonding by creating chemical bridges or physical anchors that enhance adhesion, directly resolving the contradiction between simple manufacturing and sufficient adhesion strength.
2Power
If copper particles with larger diameter are used, then the conductivity and amperage capacity are improved, but the surface area for adhesion is reduced
Solution Approach 1:
The patent uses a composite particle system combining large-diameter copper particles (for conductivity and amperage) with smaller adhesion promoter particles and glass frit (for bonding surface). This composite approach allows the large copper particles to provide power capacity while the accompanying fine particles ensure sufficient adhesion surface area, resolving the contradiction between power and adhesion.
Solution Approach 2:
The patent applies local quality by having different particle sizes perform different functions: large copper particles (4.0-4.9 μm or 3.0-3.9 μm) provide conductivity and power capacity in the bulk, while smaller adhesion promoter particles and glass frit concentrate at the substrate interface to provide adhesion. This spatial differentiation of particle functions resolves the contradiction between power capacity and adhesion surface area.
3Reliability
If the paste is designed for high-temperature applications, then the reliability in high-power electronics is improved, but the adhesion stability during thermal cycling becomes challenging
Solution Approach 1:
The patent optimizes the chemical composition parameters of the paste, specifically selecting glass frit with appropriate softening point and adhesion promoters that form stable compounds at high temperatures. The copper particles are formulated with controlled oxide content to ensure proper reactivity at firing temperature while maintaining stability during thermal cycling, resolving the contradiction between high-temperature reliability and adhesion stability.
Solution Approach 2:
The patent uses a composite formulation where glass frit and adhesion promoters create a thermally stable matrix that binds copper particles to the aluminum nitride substrate. This composite structure maintains adhesion stability during thermal cycling by providing thermal buffer and chemical stability, while enabling high-temperature operation, thus resolving the contradiction between reliability and composition stability.
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 copper conductive paste composition demonstrates excellent adhesion and plateability on aluminum nitride substrates, enabling reliable performance in high-temperature and high-power electronics applications, such as electric vehicles, with the ability to withstand thermal cycling and maintain adhesion after aging.
Implementation Method 1
adhere the conductor via a thin reactive layer (oxide film) formed between the metal and substrate by introducing the metal in atomic form to the surface of the ceramic substrate so that the metal, which is extremely active chemically, bonds with the excess oxygen that exists in the surface of the substrate
Implementation Method 2
the glass frit comprises oxides which are substantially lead-free... the glass frit comprises bismuth, boron and silicon oxides
Implementation Method 3
the metal, which is extremely active chemically, bonds with the excess oxygen that exists in the surface of the substrate
Data Source
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AI summary
An electroconductive paste for use on an aluminum nitride substrate comprising a copper particle, a glass frit, an adhesion promoter which is at least one selected from the group consisting of cuprous oxide, titanium oxide, zirconium oxide, boron resinate, zirconium resinate, amorphous boron, lithium phosphate, bismuth oxide, aluminum oxide, and zinc oxide, and an organic vehicle. The invention also provides a method of forming copper conductor on an aluminum nitride substrate using electroconductive paste compositions described herein, comprising (i) depositing a first layer of base layer electroconductive paste on an aluminunn nitride substrate; (ii) drying the aluminum nitride substrate with the deposited base layer electroconductive paste; (iii) subjecting the deposited base layer electroconductive paste and the aluminum nitride substrate to a temperature of about 900°C to about 1000°C in a nitrogen atmosphere; (iv) depositing a second layer of a top layer electroconductive paste on the substrate; (v) drying the aluminum nitride substrate with the deposited top layer elertroconductive paste; and (vi) subjecting the deposited layers and the aluminum nitride substrate to a temperature of about 900°C to about 1000°C in a nitrogen atmosphere.