Solvent-free Cu sintering pastes using acidic activators

Abstract

This study delves into the critical evaluation of solvent-free liquid-type acidic additives for their effectiveness in the copper (Cu) sintering process, a crucial method for achieving robust electrical and thermal connections in semiconductor packaging. Sintering is a process of compacting and forming a solid mass of material by heat and/or pressure without melting to the point of liquefaction. It plays an essential role in the manufacturing of electronic components. It creates highly conductive pathways necessary for the reliable performance of semiconductor devices. However, the presence of an oxide layer on Cu surfaces poses a remarkable challenge by impeding thermal and electrical conductivity, thus necessitating the removal of this layer to enhance the performance of sintered components. The study primarily focused on the application of various liquid-type acidic additives, namely, formic acid (FA), acetic acid (AA), hexanoic acid (HA), lactic acid (LA), hydrochloric acid (HcA), and sulfuric acid (SA) to achieve solvent-free sintering and to ascertain their efficiency in oxide layer removal and their impact on the thermal and electrical properties of the sintered Cu chips. Through a series of analytical methods, including thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and lab shear strength tests, the study revealed significant insights into the thermal stability, oxide layer removal efficiency, and connectivity between Cu particles. Our findings demonstrated that FA and LA additives markedly enhanced the sintering quality by effectively removing the Cu oxide layer, thereby facilitating superior particle connectivity and improving the thermal and electrical conductivities of sintered Cu chips. By contrast, HA, HcA, and SA were less effective, largely because of their inability to remove the oxide layer adequately and their tendency to leave organic residues, resulting in lower mechanical integrity of the sintered Cu chips. The superior performance of FA and LA was attributed to their optimal thermal properties and the high concentration of carboxylic groups capable of efficiently reducing the oxide layer on Cu surfaces. This study contributed to the optimization of the Cu sintering process by identifying effective acidic additives that enhanced the mechanical, thermal, and electrical properties of sintered Cu chips. These findings hold significant promise for advancing semiconductor packaging technologies by providing insights into selecting suitable sintering additives for developing high-performance electronic components.