• Proceedings of the KWS Conference
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• 2009.11a
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• pp.217-220
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• 2009

Conductive adhesives have been investigated for use in microelectronics packaging as a lead-free solder substitute due to their advantages, such as low bonding temperature. However, high resistivity and poor mechanical behavior may be the limiting factors for the development of conductive adhesives. The metal fillers and the polymer resins provide electrical and mechanical interconnections between surface mount device components and a substrate. As metal fillers used in conductive adhesives, silver is the most commonly used due to its high conductivity and the stability. However the cost of conductive adhesives with silver fillers is much higher than usual lead-free solders and silver has poor electro-migration performance. So, copper can be a promising candidate for conductive filler metal due to its low resistivity and low cost, but oxidation causes this metal to lose its conductivity. In this study, electrically conductive adhesives (ECAs) using surface modified copper fillers were developed. Especially, in order to overcome the problem associated with the oxidation of copper, copper particles were coated with silver, and the silver-coated copper was tested as a filler metal. Especially the effect of silver coating on the electrical resistance just after curing and after aging was investigated. As a result, it was found that the electrical resistance of ECA with silver-coated copper filler was clearly lower and more stable than that of ECA with pure copper filler after curing process. And, during high temperature storage test, the degradation rate of electrical resistance for ECA with silver coated copper filler was quite slower than that for ECA with pure copper filler.

• Journal of Ocean Engineering and Technology
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• v.15 no.3
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• pp.49-57
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• 2001

One of the most important considerations to braze Cu-Al dissimilar materials is control of brittle metallic compound which makes it difficult to obtain a sound brazed joint. Nowdays, several attempts were made to control the metallic compound. But effective method for controlling metallic compound was not established. In this point of view, commercially pure aluminum and copper were used as base metal and Al-Si-X and Zn-Al-X alloy systems were developed as filler metal. Brazing was carried out to find optimum conditions for Cu-Al dissimilar joint. The results obtained in this study were summarized as follows: 1) The joint brazed by Al-Si-X filler metal showed good brazeability and mechanical properties. The tensile strength of the joint brazed over solidus temperature was more than 90% of Al base metal. Especially, the joint brazed at liquidus temperature was fractured in the Al base metal. 2) Fluorides fluxes(a mixture of potassium fluoro-aluminates) were used to improve surface cleanliness of base metal and wettability of Al-Si-X filler metal. It was melted at the temperature about 1$0^{\circ}C$ lower than that of the filler metal, and made appropriate brazing environment. Therefore, it could be a proper selection as flux.

• Journal of the Korean Society of Propulsion Engineers
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• v.7 no.4
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• pp.73-79
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• 2003

The tensile strength test and the analysis for the section of brazing were performed in the cases of materials used for combustion chamber of regeneratively cooled liquid rocket engine. BNi-2 and BNi-7 based on nickel were used for brazing as filler metal. The properties of material and filler metal were analyzed by tensile strength test and metal microscope for 12 specimens. The tensile-strength of brazing for chrome-copper alloy and other kinds of alloy was higher than that of chrome-zirconium-copper alloy and other kinds of alloy The tensile strength in the case of BNi-2 as filler metal was higher than that of BNi-7 because the wetting property of BNi-2 was better than that of BNi-7.

• Proceedings of the KWS Conference
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• 1993.10a
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• pp.45-50
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• 1993

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.7
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• pp.112-117
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• 2003

The brazing of copper alloys and duplex stainless steels is an indispensable manufacturing technology for thrust chambers with regenerative cooling. For setting up the optimized brazing conditions, C18200 copper alloy plate with machined cooling channels and S31803 stainless steel plate are brazed with AMS4764 filler metals of which thickness is 50${\mu}m$ and 80${\mu}m$ They are tested by X-ray radiography, strength/leakage and fracture tests, and fracture surface inspection. The results obtained by the suggested conditions are that the specimen brazed with filler metal thickness of 50${\mu}m$ has good strength properties and brazed zone. However, the specimen with filler metal thickness of 80${\mu}m$ has the brazed zone with cooling channel obstruction and enlargement.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.152-154
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• 2005

Austenitic stainless steel has good weldability but is sensitive to hot cracking such as solidification crack and liquation crack. In this study, the specimens of dissimilar metals made between austenitic stainless steel and Al-brass were welded by GTAW process using four different filler metals. Cracks were detected in the heat-affected zone of the stainless steel when welded with CuAl, CuSn and NiCu filler metals, but no cracks were detected a Ni filler metal was used. The cracks propagated along the grain boundary in the heat affected zone near the fusion line to base metal of 316L stainless steel. The cracks were located inside the weld bead with very fine hairline crack. All cracks initiated at the fusion line and moved forward in the base metal. From energy dispersion spectroscopy (EDS), Cu peak was detected only in the crack-opening area.

• Journal of Korea Foundry Society
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• v.23 no.5
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• pp.244-250
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• 2003

The aim of this study is fabricating of composite filler metal (CFM) by a combination of selective laser sintering (SLS) of stainless steel powders (RapidSteel $2.0^{TM}$ and liquid phase infiltration of Ag-28 wt.%Cu alloy. Porous stainless steel body with inter-connected pore channels was fabricated by SLS, binder decomposing and densification processes. By the direct contact infiltration, the narrow inter-particle channels of the porous body were completely filled with the Ag-28 wt.%Cu alloy infiltrant. During infiltration, the dissolved elements of Fe, Ni and Cr from the porous body were solved into copper solid solution phases, which consist of eutectic structure of composite metal matrix. The S10C/CFM/S10C joints, which have narrow clearance gaps between them up to 10 micrometers, were joined successfully by self-feeding of filler metal from the matrix of CFM. The CFM kept its original thickness and microstructure after brazing. The tensile strength of brazed specimen was higher than 30 kgf/$mm^2$ and showed a typical ductile fracture mode in the CFM.

• Korean Chemical Engineering Research
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• v.58 no.1
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• pp.64-68
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• 2020

In this study, metal copper clad laminate can be prepared using epoxy composite filled with thermally conductive fillers. In order to improve the thermal conductivity of epoxy composites, it is important factor to form conductive networks through appropriate packing of conductive fillers in epoxy composite matrix and to decrease the amount of thermally resistant junctions involving a epoxy composite matrix layer between adjacent filler units. This is because epoxy has a thermal conductivity of only 0.2-0.3W, so in order to maintain high thermal conductivity, thermally conductive fillers are connected to each other, so that the gap between particles can be reduced to reduce thermal resistance. The purpose of this study is to find way to achieve highly thermally conductive in the epoxy composite matrix filled with Al₂O₃ and Boron Nitride(BN) filler by filler loading and uniform dispersion. As a results, the use of Al₂O₃/BN hybrid filler in epoxy matrix was found to be effective in increasing thermal conductivity of epoxy composite matrix due to the enhanced connectivity offered by more continuous thermally conductive pathways and uniform dispersion without interfacial voids in epoxy composite matrix. In addition, surface treatmented s-BN improves the filler dispersion and adhesion between the filler and the epoxy matrix, which can significantly decrease the interfacial thermal resistance and increase the thermal conductivity of epoxy composite matrix.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.1083-1091
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• 1988

Vacuum brazing is the most modern brazing process and is at present, far from being completely understood. By brazing under high vacuum, in an atmosphere free of oxidizing gases, a superior product with greater strength, ductility and uniformity can be obtained. In this study, the influence of brazing parameters such as base metal characteristics, joint clearance and brazing time were described in relation to the metallurgical phenomena and shear strength of vacuum-brazed joints between carbon steels and 304 stainless steel (SUS 304) brazed by copper filler metal. In copper brazing of SUS 304 to a medium carbon steel(M.C.S) the columnar Fe-Cr-Ni-Cu-C alloy structure was formed and grew from the M.C.S side and at the same time, the surface of M.C.S. was decarbonized. The driving force for the formation and growth of columnar structure was the difference of carbon content between base metals. As the joint clearance is narrower and brazing time is longer, the formation and growth of columnar phase and decarburization of carbon steels were more noticeable. Because of decarburization of carbon steels, the shear strength of brazed joints were reduced as the formation of columnar structure was increased.

• Journal of the Korean Electrochemical Society
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• v.27 no.1
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• pp.8-14
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• 2024

Austenitic stainless steel 316L has been used a lot of applications because of its high corrosion resistance and formability. In addition, copper brazing is employed to create complex shape of 316L stainless steel for various engineering parts. In such system, copper-based filler metals make galvanic cell at metal/filler metal interface, and it accelerates corrosion of stainless steel. Furthermore, Cu-rich region formed by diffused copper in austenitic stainless steel can promote a pitting corrosion. In this study, we used an ammonia (NH₃) gas to nitride the 316L stainless steel for improving the corrosion resistance. The thickness of the nitride (nitrogen high) layer increased with the treatment temperature, and the surface hardness also increased. The potentiodynamic polarization test showed the improvement of corrosion resistance of 316L stainless steel by enhancing the passivation on nitride layer. However, in case of high temperature nitriding, a chromium nitride was formed and its fraction increased, so that the corrosion resistance was decreased compared to the intact 316L stainless steel.