Gold Paste Surface Coverage for Dried State Processability
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Solution Overview
Problem
Conventional gold pastes face challenges in processability during the drying step due to high strength of the dried matter, leading to issues like residual powder on masks or scooping out of powder from pattern holes, despite maintaining low-temperature sinterability and dispersibility.
Innovation Solution
A gold paste with a gold powder of specific purity and particle size, partially covered by chlorine, bromine, iodine, or sulfur elements or functional groups, achieving a coverage ratio of 33% to 100%, ensuring reduced bonding during drying while maintaining low-temperature sinterability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional gold paste is used, then low-temperature sinterability is maintained, but processability in dried state deteriorates due to high strength of dried matter
Solution Approach 1:
A covering agent is introduced as an intermediary substance that adsorbs onto the gold powder surface. This covering agent prevents strong bonding between gold particles during drying, improving processability. The covering agent is subsequently removed during sintering, allowing the gold particles to bond properly and maintain low-temperature sinterability.
Solution Approach 2:
The chemical composition of the gold powder surface is changed by introducing a covering agent. This parameter change modifies the interfacial properties between gold particles and the organic solvent, reducing bonding strength in the dried state. The covering agent concentration and type are optimized to achieve the desired balance between processability and sinterability.
2Manufacturing precision
If gold powder with high purity and fine particle size is used, then low-temperature sinterability is improved, but dried matter strength increases making excessive powder removal difficult
Solution Approach 1:
The covering agent acts as a mediator between the fine gold particles, preventing direct contact and strong bonding during the drying process. This allows the dried matter to have reduced strength for easy removal of excessive powder, while the fine particle size and high purity of gold are preserved for good sinterability.
Solution Approach 2:
The covering agent is applied to the gold powder before forming the paste and applying it to the substrate. This preliminary action of coating the gold particles modifies their surface properties in advance, ensuring that when the paste is dried, the gold particles do not bond strongly, facilitating easy removal of excessive powder before sintering.
3Ease of operation
If covering agent is added to improve processability, then dried matter processability is improved, but composition complexity increases
Solution Approach 1:
The covering agent concentration is optimized to achieve the desired processability with minimal addition. By controlling the concentration parameter, the paste composition remains relatively simple while still achieving the goal of improved dried matter processability. The covering agent is subsequently removed during sintering, so it does not remain in the final product.
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 gold paste achieves improved processability in the dried state without compromising low-temperature sinterability, allowing efficient removal of excess powder and preventing aggregation, with the covering agent being volatilized during sintering.
Implementation Method 1
at least a part of the gold powder is covered with a covering agent containing at least one of: any element of Cl, Br, I, and S, or an ion containing any of these elements, or a functional group containing any of these elements
Implementation Method 2
an organic solvent contained in the gold paste is removed by volatilization in a drying step
Implementation Method 3
the covering agent being volatilized during sintering
Implementation Method 4
can form a dense sintered body by sintering at a low temperature (of 350°C or less)
Data Source
AI summary
The present invention provides a gold paste containing a gold powder and an organic solvent. The gold powder has purity of 99.9% by mass or more, and an average particle size of 0.1 µm or more and 0.4 µm or less. The gold powder is at least partially covered with a covering agent containing at least one of: any element of Cl, Br, I, and S, or an ion containing any of these elements, or a functional group containing any of these elements. The coverage ratio defined as a ratio SC/SAu is 33% or more and 100% or less, wherein Sc is a total cross-sectional area of the element derived from the covering agent calculated based on a concentration of the element in 1 g of the gold paste, and SAu is a specific surface area of the gold powder. The gold powder is excellent in low-temperature sinterability, and a gold paste including the same is good in processability in a dried state after coating.