Preparation of Multi-Walled Carbon Nano-Tube Composite Copper Plating from Acidic Solution

Abstract

Copper has excellent thermal properties including thermal conductivity; therefore copper has been used as the thermal heat dissipation materials. However, the materials with more excellent thermal properties are needed for the increasing of the packaging density of electronic equipment. The authors have focused on the excellent thermal properties of Multi-Walled Carbon Nano-Tube (MWCNT). MWCNT has excellent thermal properties, mechanical properties and electrical properties, then, it is expected to be applied to various fields such as electronic component, semiconductor, medical, biotechnology and so on. It was considered that the thermal properties of the copper plating could be greatly improved by compositing MWCNT with copper plating. The purpose of this study is to prepare MWCNT composite copper plating with more excellent thermal properties than conventional copper plating. MWCNT composite copper plating was obtained from the copper sulfate bath with suspended MWCNT by general electrolytic method. Various plating conditions had been investigated in order to increase the content of MWCNT in the films such as the concentration of MWCNT and pH of the plating baths, surfactant, current density, film thickness and agitation speed were researched. The content of MWCNT in the films was measured by combusting the samples in oxygen atmosphere and measuring amount of generated gas, CO and CO2, by infrared absorption method. There were optimal conditions for preparing the composite copper plating with higher amount of MWCNT. It should be noted, that the higher amount of MWCNT in the films increased the thermal conductivity of the films, but that the using additives for MWCNT dispersion reduces the thermal conductivity comparing to the copper plating without additives by the thermal conductivity measurement. Then the authors also focused on the hydrothermal treatment to MWCNT in various acidic solutions as a method that used no additives. It was effective for improvement of the amount of MWCNT in the films. The samples containing the largest amount of MWCNT was prepared when using MWCNT treated in mixed acid of sulfuric acid and nitric acid at the ratio of 3 to 1 at 150 °C for 2 hours. The MWCNT content in the copper film was 1.01 mass%, which was maximum value in this study. The sample which was prepared using hydrothermal treated MWCNT, without using addition agent, had slightly higher thermal conductivity than that of the conventional copper plating without additives.