Conductive Paste Rheology Control for Multilayer Screen Printing
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Solution Overview
Problem
Conductive pastes with high metal powder content face challenges in continuous screen printing on ceramic green sheets, experiencing issues like bleeding, low spots, and shear droop, which hinder the formation of high-definition conductor patterns with thick film thickness and high aspect ratios, especially in mass production scenarios.
Innovation Solution
A conductive paste composition with 70-95 weight % conductive metal powder, a resin, and a solvent, optimized to achieve a specific phase angle range in dynamic viscoelastic measurements, ensuring stable printing properties and preventing defects such as bleeding and shear droop.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high metal powder content (70-95 wt%) is used in conductive paste, then conductor resistance is reduced and film thickness is increased, but printing defects such as bleeding, low spots, and shear droop occur during continuous screen printing
Solution Approach 1:
The patent applies parameter changes by optimizing the viscosity of the vehicle component within a specific range (10-100 Pa·s at 25°C) and controlling the particle size distribution of metal powder (D50: 1-10 μm, D90: 15-20 μm). These parameter optimizations enable the high metal content paste to maintain stable rheological properties during screen printing, preventing bleeding and shear droop while achieving thick film deposition with high definition patterns.
Solution Approach 2:
The patent uses composite materials by formulating a vehicle consisting of multiple resin components (e.g., nitrocellulose, ethyl cellulose, polyvinyl butyral) combined with specific solvents and dispersants. This composite vehicle system provides balanced flow characteristics and adhesion properties, allowing the high metal powder content paste to maintain printing stability and prevent defects during continuous screen printing operations.
2Manufacturing precision
If thick film thickness and high aspect ratio patterns are formed, then conductor resistance is reduced, but continuous printing accuracy deteriorates due to paste defects
Solution Approach 1:
The patent applies parameter changes by controlling the viscosity of the vehicle within 10-100 Pa·s at 25°C and optimizing metal powder particle size distribution (D50: 1-10 μm, D90: 15-20 μm). These parameters enable the paste to maintain stable flow characteristics during screen printing, allowing continuous printing of high aspect ratio patterns (thickness/width ratio) without bleeding or shear droop defects, thus achieving both thick films and high productivity.
Solution Approach 2:
The patent applies dynamics by formulating the vehicle with resin and solvent components that provide time-dependent rheological behavior. The vehicle maintains higher viscosity at rest to prevent bleeding, but exhibits shear-thinning characteristics during the dynamic screen printing process, allowing smooth paste flow through the screen mesh and squeegee action, thereby enabling continuous high-accuracy printing.
3Stability of the object's composition
If solid content of conductive paste is increased to reduce firing shrinkage, then interlayer separation and cracks are minimized, but printing defects such as bleeding and shear droop increase
Solution Approach 1:
The patent applies parameter changes by optimizing the vehicle viscosity to 10-100 Pa·s at 25°C and controlling metal powder particle size (D50: 1-10 μm, D90: 15-20 μm). These parameters enable the high solid content paste (70-95 wt% metal powder) to maintain stable composition during firing with minimal shrinkage, while simultaneously preventing printing defects like bleeding and shear droop through controlled rheological properties.
Solution Approach 2:
The patent uses composite materials by formulating a vehicle with multiple resin components (nitrocellulose, ethyl cellulose, polyvinyl butyral) and solvents that provide balanced rheological and adhesive properties. This composite vehicle system allows the high solid content paste to maintain pattern definition during screen printing while ensuring firing shrinkage consistency and preventing interlayer separation or cracks.
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
Enables continuous high-accuracy screen printing with reduced defects, allowing for the mass production of multilayer electronic parts with thick film thickness and high aspect ratio patterns, even after 1,000 printing cycles, and ensures excellent via filling properties.
Implementation Method 1
A conductive paste is printed on the green sheet by a screen printing method to form a predetermined conductor pattern
Implementation Method 2
A conductive paste composition with 70-95 weight % conductive metal powder, a resin, and a solvent, optimized to achieve a specific phase angle range in dynamic viscoelastic measurements, ensuring stable printing properties
Implementation Method 3
The cut laminated body is fired
Implementation Method 4
the conductive paste is filled in the via hole... Subsequently, the cut laminated body is fired
Implementation Method 5
as for the conductive pastes, the followings are used; at least conductive powder, a vehicle including a resin and an organic solvent... the amount of the resin and the solvent to be burnt off during firing is decreased
Data Source
AI summary
Disclosed is a conductive paste for a multilayer electronic part to be screen-printed on a ceramic green sheet, comprising 70-95 weight % of conductive metal powder, a resin, and a solvent, wherein a phase angle δ in a dynamic viscoelastic measurement is within a range of from 43° to 72° at a frequency of 0.05 Hz and is within a range of 63° or less at a frequency of 30 Hz.