• Journal of the Microelectronics and Packaging Society
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• v.22 no.4
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• pp.57-63
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• 2015

In order to prepare a low-cost conductive filler material possessing improved anti-oxidation property, Ag-coated Cu flakes were fabricated and the effects of an applying method of ammonium-based pretreatment solution on the Cu flakes were analyzed. The pretreatment solution was used to remove the surface oxide layer on Cu flake. During a single-stage pretreatment process, hole-shaped defects were formed on the flake surface during the pretreatment after 2 min, and the number and size increased in proportion to the pretreatment time. In the case that Ag plating solution was injected in the pretreatment solution after the pretreatment for 2 min, the defects were also formed during Ag plating. In contrast, the defects tremendous decreased in the case that the pretreatment solution was removed after the first pretreatment for 2 min and the Ag plating proceeded after the second pretratment using a low concentration pretreatment solution. As the final result, the 15 wt% Ag-coated Cu flake sample which was fabricated using the single-stage pretreatment oxidized at $166^{\circ}C$, but the sample fabricated by the double-stage pretreatment oxidized at $224^{\circ}C$, indicating definitely improved anti-oxidation property.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.3
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• pp.57-62
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• 2017

In the process for preparing Ag-coated Cu flakes by electroless silver plating using hydroquinone reducing agent, Ag coating qualities were compared by changing various process parameters such as type of pretreatment solution, plating temperature, pH of plating solution, type and injection rate of plating solution, and pulp density. Effective pretreatment solution for removing the oxide layer on a Cu flake was preferentially suggested. The conditions of low plating temperature, pH value of 4.34, slow injection rate of Ag plating solution, elimination of deionized water in the Ag plating solution, and high pulp density significantly suppressed the formation of separated tiny Ag particles, and thus the surface coverage of Ag coating on Cu flakes was enhanced.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.4
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• pp.51-56
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• 2014

After the preparation of low-cost conductive paste containing Ag-coated Cu flakes, thermal conductivity and electrical resistivity of the paste were measured with different curing conditions. Under air-curing conditions, the thermal conductivity of the cured sample increased with an increase of curing time from 30 to 60 min. After identical curing time of 60 min, the sample cured under nitrogen indicated more enhanced thermal conductivity than that cured under air, approaching that of paste containing pure Ag flakes. Under air-curing conditions, meanwhile, the electrical resistivity of the cured sample increased with an increase of curing time from 30 to 60 min. After identical curing time of 60 min, however, the sample cured under nitrogen indicated extremely enhanced electrical resistivity ($7.59{\times}10^{-5}{\Omega}{\cdot}cm$) in comparison with that cured under air.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.2
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• pp.97-104
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• 2016

In the preparation of Ag-coated Cu flakes using L-ascorbic acid as a reductant for the electroless Ag plating, the effects of pretreatment methods and the reductant concentration on the uniformity of Ag coating layer and the anti-oxidation property of Ag-coated Cu flakes during the heating in air were evaluated. It was found that the removal degree of surface oxide layer during the pretreatment has great influence on the uniformity of Ag coating layer and the formation degree of hole defects in the flakes has slight effect on the anti-oxidation property of Ag-coated Cu flakes. It was also verified that the reductant concentration has great influence on the coverage uniformity and thickness of Ag coating, thus it was could be considered a main process parameter. When the reductant concentration was 0.04 M, high-quality Ag-coated Cu flakes was obtained. When the concentration increased to 0.06 M, however, the anti-oxidation property of Ag-coated Cu flakes became remarkably worse owing to remnant of Cu surface non-coated with Ag by the formation of pure Ag fine particles.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.4
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• pp.133-137
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• 2014

As a preceding process for preparing several micrometer sized Ag-coated Cu flakes, ball milling of submicrometer-sized Cu particles synthesized through a wet chemical method was performed in order to convert the particles into flakes. To suppress oxidation and aggregation of the particles during ball milling, ethylene glycol and ethyl acetate were used as a medium and a surface modifying agent, respectively. Results obtained with different rotation speeds of a jar indicated that the rotation speed changes a rotating mode, and strikingly alters the final shapes and shape uniformity of Cu particles after milling. The diameter of zirconia ball was also confirmed. Although there was aggregates in the initial submicrometer-sized Cu particles, therefore, well-dispersed Cu flakes with a size of several micrometers were successfully prepared by ball milling through optimization of rotation speed, amount of ethyl acetate, and diameter of zirconia ball.