Copper Thick Film Paste for Silicon Nitride Circuit Adhesion
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Solution Overview
Problem
There is a lack of suitable metallic conductive thick film pastes for forming circuits on silicon nitride substrates, which are non-reactive and experience extreme temperature variations, requiring improved adhesion and electrical conductivity.
Innovation Solution
Development of lead- and cadmium-free conductive copper thick film pastes containing copper, silver, and titanium metal powders, suitable for silicon nitride, alumina, and aluminum nitride substrates, with specific particle size ranges and firing conditions to ensure good adhesion and low electrical resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thick film pastes are used on silicon nitride substrates, then the substrates experience extreme temperature variations, but the paste adhesion and electrical conductivity are insufficient
Solution Approach 1:
The patent uses a composite paste formulation containing multiple metal powders (silver, copper, nickel) in specific size ranges, combined with glass particles and organic vehicles. This composite structure enables the paste to simultaneously achieve strong adhesion to silicon nitride substrates and maintain electrical conductivity under extreme temperature variations, resolving the contradiction between adhesion and temperature resistance.
Solution Approach 2:
The patent employs a multi-size particle distribution strategy where fine metal powders (0.5-5 μm) provide adhesion and wetting at the substrate interface, while coarser particles (5-20 μm) maintain electrical conductivity and structural integrity. This local differentiation of particle functions within the paste composition enables simultaneous optimization of adhesion and temperature stability.
2Object-affected harmful factors
If lead- and cadmium-free copper thick film paste is developed, then environmental safety is improved, but achieving low electrical resistivity becomes more difficult
Solution Approach 1:
The patent combines multiple conductive metal powders (silver, copper, nickel) in a lead-free formulation. The silver and copper particles provide high electrical conductivity, while nickel adds oxidation resistance. This merging of multiple metal elements achieves low electrical resistivity without relying on lead or cadmium, resolving the contradiction between environmental safety and electrical conductivity.
Solution Approach 2:
The patent optimizes the particle size distribution parameters of the metal powders, using a broad range from 0.5 to 20 μm with specific emphasis on the 0.5-5 μm range for fine conductivity pathways. This parameter optimization enables the lead-free paste to achieve low electrical resistivity by creating efficient conductive networks through controlled particle packing and contact.
3Reliability
If multi-size metal powder mixture is used, then firing process control becomes complex, but sintering density and adhesion are improved
Solution Approach 1:
The patent segments the metal powder into distinct size ranges (0.5-5 μm and 5-20 μm) with different functional roles. The fine particles (0.5-5 μm) fill voids and create adhesion bonds during sintering, while coarser particles (5-20 μm) provide structural framework and conductivity. This segmentation enables improved sintering density and adhesion while the clear size classification simplifies process control compared to uncontrolled multi-size mixtures.
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 pastes provide excellent electrical conductivity, adhesion, and thermal stability, suitable for high-temperature applications, with improved solderability and wire bondability, and are applicable in various electronic devices including IGBTs and automotive components.
Implementation Method 1
The successive layers are dried after printing
Implementation Method 2
fired in a belt furnace to sinter the material
Data Source
Figure 1
Figure 2
AI summary
Conductive thick film compositions compatible to aluminum nitride, alumina and silicon nitride substrates for microelectronic circuit application. The conductive thick film composition includes first copper powder, second copper powder, and glass component. The conductive thick film composition further includes CU2O, Ag, and at least one metal element selected from Ti, V, Zr, Mn, Cr, Co, and Sn. After firing, the conductive thick film composition exhibit improved sheet resistivity, and improved adhesion with underlying substrate.