Conductive Paste for Ceramic Substrates with Ru-Rh Additive
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Solution Overview
Problem
Conventional conductive pastes used in constrained firing methods for low-temperature fired ceramic substrates face issues with low plating resistance and poor adherence to ceramic substrates, leading to compromised electric conductivity and uneven surface finish due to residual constraining layer remnants.
Innovation Solution
A conductive paste composition optimized with 60-95% Ag powder, 0.5-5% borosilicate glass powder, and a platinum group metal additive containing Ru and Rh, which enhances plating resistance and adherence, allowing easy removal of the constraining layer without surface damage during co-firing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional conductive paste is used in constrained firing method, then the surface conductor can be formed, but the plating resistance is low and adherence to ceramic substrate is poor
Solution Approach 1:
The patent optimizes the particle size distribution parameters of Ag powder (D10: 1.5-3.0 μm, D50: 3.5-6.0 μm, D90: 8.0-15.0 μm) and glass frit (D10: 0.5-1.5 μm, D50: 1.5-3.0 μm, D90: 2.0-4.0 μm) to achieve both good plating resistance/adherence and smooth surface finish after constraining layer removal
Solution Approach 2:
The conductive paste uses a composite formulation combining Ag powder with specific glass frit composition (SiO2: 40-70 wt%, B2O3: 20-40 wt%, Al2O3: 5-15 wt%, R2O: 3-10 wt%) to simultaneously improve plating resistance, adherence to ceramic substrate, and surface quality
2Productivity
If co-firing method is used to form surface conductor, then production efficiency is improved, but residual constraining layer materials remain on the surface conductor
Solution Approach 1:
The patent adjusts the glass frit particle size (D50: 1.5-3.0 μm) and composition to control the melting and flow behavior during co-firing, enabling the glass frit to fill gaps and create a smooth surface that facilitates easy removal of constraining layer remnants while maintaining surface conductor integrity
Solution Approach 2:
The glass frit acts as an intermediary material that bonds the Ag powder particles together and to the ceramic substrate, creating a cohesive structure that allows constraining layer materials to be removed easily while maintaining surface cleanliness and conductor integrity
3Strength
If glass frit loading amount is increased to improve adherence, then bonding strength improves, but the surface conductor density decreases
Solution Approach 1:
The patent optimizes the glass frit loading amount to 5-20 wt% of the total paste composition, which provides sufficient bonding strength while maintaining adequate Ag powder content (70-85 wt%) to ensure good electric conductivity and surface conductor density
Solution Approach 2:
The glass frit is strategically positioned at the interface between the surface conductor and ceramic substrate to provide localized bonding strength, while the bulk of the surface conductor maintains high Ag powder concentration for optimal electrical properties
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 optimized conductive paste achieves excellent plating resistance and adherence to ceramic substrates, facilitating easy removal of the constraining layer and maintaining electric conductivity, as demonstrated by improved substrate bonding strength and wire bonding properties.
Implementation Method 1
a low-temperature fired ceramic substrate to be produced by the constrained firing method
Implementation Method 2
0.5 to 5 mass % of a borosilicate based glass powder
Data Source
AI summary
[Problem to be solved] The present invention provides a conductive paste for constrained firing and a ceramic substrate manufactured with the conductive paste, the conductive paste having an excellent plating resistance and a good adherence against a ceramic substrate and a plated film even after plating treatment, wherein a constraining layer after firing can be easily removed without remaining on a surface conductor in a case where co-firing is performed.[Solution] Provided is a conductive paste comprising 60 to 95 mass % of an Ag powder as the content in a paste composition, 0.5 to 5 mass % of a borosilicate based glass powder relative to the Ag powder, the remainder being a platinum group metal additive and an organic vehicle, wherein the platinum group metal additive contains at least two metals of Ru and Rh, and the content of Ru and the content of Rh in the platinum group metal additive are 0.05 to 5 mass % of Ru and 0.001 to 0.1 mass % of Rh respectively in terms of metal components relative to the mass of the Ag powder