Electrical properties of conductive adhesives as affected by particle compositions, particle shapes, and oxidizing temperatures of copper powders in a polymer matrix

Abstract

The effects of particle compositions, particle shapes, and oxidation temperatures on the electrical properties of conductive adhesives have been investigated. Silver-coated copper powders and uncoated copper powders with spherical and flake-shaped particles are oxidized at temperatures such as 30, 175, 240, 300°C and 350°C for 2 h and dispersed in an epoxy matrix. The results of this study indicate that the electrical properties of the conductive adhesives are strongly affected by the particle compositions and oxidation temperatures and only slightly affected by the particle shapes. Silver-coated copper powders show significantly greater oxidation resistance than uncoated copper powders. To understand how silver-coated copper powders show such oxidation resistance, they are analyzed by the techniques of thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Auger spectroscopy to observe how metal oxides such as AgO, Cu 2 O, and CuO affect the electrical properties of the conductive adhesives.

Improvement of the thermal stability of dendritic silver-coated copper microparticles by surface modification based on molecular self-assembly

“…We also investigated the thermal stability of the electrically conductive films. As established by the TGA of the untreated Ag/Cu powder and previously reported studies [ 17 , 29 ], the oxidation of Ag/Cu powder commences at a temperature of approximately 170–175 °C. Accordingly, the change in the linear resistance of each electrically conductive film over time was monitored in an oven at temperatures of 160 and 180 °C, respectively; the results are plotted in Fig.…”

“…The dendritic Ag/Cu powder particles used in this study have a few micron scale and high density; therefore, the alkanethiols adsorbed to the surface of a treated Ag/Cu powder particle does not significant contribute to its weight. In practice, the TGA of Ag/Cu powders evaluates their degree of oxidation at high temperatures rather than their organic matter content [ 12 , 17 , 29 ]. Accordingly, the degree of oxidation of the Ag/Cu powders was examined by TGA under the same conditions but without nitrogen injection.…”

“…Another study reported that limited oxidation occurs from 175 °C, and between 175 and 260 °C the weight increases by ~ 1 wt%. At temperatures exceeding 260 °C, oxidization occurs more rapidly and a weight increase of ~ 7 wt% is recorded once the temperature reaches 400 °C [ 17 ]. In this study, the weight of the untreated Ag/Cu powder increases very slowly from ~ 170 °C; however, the rate of weight increase accelerates from ~ 260 °C and a weight increase of approximately 7.5 wt% is recorded once the temperature reaches 400 °C.…”

“…The vulnerability of Ag/Cu powders to oxidation depends on their Ag content. For example, the electrical performance of an electrically conductive, epoxy-based adhesive containing 20 vol% Ag/Cu powder with a Ag content of 15 % remains relatively steady for approximately 2 h at 200 °C, however, its resistance increases rapidly above 250 °C [ 17 ]. In contrast, the resistance of an adhesive containing non-coated Cu powder increases significantly at a mere 100 °C.…”

Effects of Trace Elements in Copper Fillers on the Electrical Properties of Conductive Adhesives

“…In order to overcome the problems associated with oxidation of Cu, Ag-coated Cu powder has been used as a metallic filler and the effect of oxidation in conductive adhesives investigated. [24][25][26] From the viewpoint of prevention of surface oxidation, oxidation of Cu and Cu 3 Ge thin films had been reported by Liou et al, 27 who found that the excellent oxidation resistance of Cu 3 Ge was attributed to a protective surface GeO 2 layer, as the formation of GeO 2 on the surface oxide layer protected Cu from oxidation.…”