Pre-oxidized Copper Paste for Blister-Free Conductive Layers
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Solution Overview
Problem
Existing Cu-comprising compositions for forming thick conducting layers face challenges in maintaining good conductivity and adhesion before and after thermal treatment, while also experiencing issues with blister formation and delamination, and often contain harmful materials like Pb, Cd, or Ni.
Innovation Solution
A Cu-comprising composition with specific weight percentages of Cu particles, vehicle, Bi2O3, Cu oxide, and Pd, characterized by certain oxygen content and particle size distribution, is developed, along with a process involving pre-oxidation of Cu particles and mixing with other constituents to create a paste that forms thick conducting layers with improved conductivity and adhesion, and is free from Pb, Cd, or Ni.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick conducting layers are formed with conventional compositions, then conductivity is achieved, but blister formation and delamination increase
Solution Approach 1:
Pre-oxidation of Cu particles is performed before composition formulation. This preliminary treatment creates a surface layer that prevents blister formation during thermal processing while maintaining the conductive network. The oxidized surface acts as a buffer that accommodates thermal stress without forming blisters.
Solution Approach 2:
The natural tendency of Cu to oxidize, which is typically considered harmful to conductivity, is converted into a beneficial effect. The controlled pre-oxidation creates a surface layer that prevents blistering and delamination, while the core metallic Cu maintains conductivity. The harmful oxidation is thus transformed into a protective feature.
2Ease of manufacture
If conventional Cu-comprising compositions are used, then conducting layers can be formed, but harmful materials like Pb, Cd, or Ni are present
Solution Approach 1:
Harmful materials (Pb, Cd, Ni) are completely removed from the composition formulation. The invention achieves this by replacing traditional binder systems and particle treatments that contained these harmful substances with environmentally friendly alternatives, specifically pre-oxidized Cu particles with organic vehicles.
Solution Approach 2:
The chemical composition parameters are changed to eliminate harmful elements. The invention uses only Cu, O, and organic vehicle components, excluding all Pb, Cd, and Ni. This parameter change maintains manufacturability while achieving environmental compliance.
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 solution achieves thick conducting layers with high conductivity and low blister formation, maintaining adhesion before and after thermal treatment, and is cost-effective, using environmentally friendly materials.
Implementation Method 1
heating the Cu particles in an oxidizing atmosphere to a temperature in the range from 100 to 200°C to obtain pre-oxidized Cu particles
Implementation Method 2
heating the Cu particles in an oxidizing atmosphere to a temperature in the range from 100 to 200°C
Implementation Method 3
firing the composite precursor
Implementation Method 4
the composition is applied to a substrate surface in order to obtain a composite precursor; firing the composite precursor
Data Source
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Figure 3a
AI summary
The invention relates generally to a composition comprising as constituents: a. at least about 2 wt.-% of a vehicle; b. at least about 42 wt.-% of Cu particles; each based on the weight of the total composition with the wt.-% of the constituents adding to 100 wt.-%; wherein the composition has color values of L* less than about 63 and a* more than about 13, each according to the L*a*b* color space and a composite made from this composition.