Study On Anti-oxidant Conductive Silver Electronic Paste System And Its Anti-oxidation Mechanism

Electrically conductive silver paste has been widely used in the field of electronic component manufacturing because of its excellent usability. However, the sivler thick films made from the paste are always oxidated slowly by oxygen and/or sulfur-containning gas(e.g., H2 S and SO2) when they are exposed to the invironments of high temperature, high pressure, and high humidity. This will be shorten its working life and severely limit its application. So it is necessary to modify its properties and to improve its anti-oxidantion capability.In this paper, an anti-oxidation electrically conductive silver paste was prepared, which used micron silver powder as conductive phase. Tin powder and indium powder from five kinds of additives, i.e., acetylacetone indium, tin-lead alloy powder, micron tin oxide powder, tin powder, indium powder, were selected as its beneficial additive ingredients. Scanning electron microscopy, UV-Vis-NIR, spectrophotometry, digital four-probe method, probe contour analysis method were applied to test and analyze the thick film's surface micromorphology, diffuse reflectance, sheet resistance and roughness before and after oxidation, repsectively. It showed that: when the sintering temperature is 750?, the thick film's surface could achieve the optimal photoelectric performances, e.g., high surface density, large diffuse reflectance, surface roughness of 1-2?m, the thickness of 4-8?m, and the sheet resistance of 5-8m?/?. Orthogonal experiment was used to optimize the formula composition, i.e., tin powder 0.1 wt. %, indium powder 1-2 wt. %, Ag powder 75 wt. %, glass powder 2 wt. %, and the rest of organic vehicle. In this condition, thick film samples would still show good photo electrochemical properties after 90-days placement in atmospheric environment at room temperature. In addition, the self-made micropen direct writing equipment was modified and improved to realize the uniform dispensation of the paste on free form surface.Preliminary results showed that the oxidation of the silver thick film started from the defect, such as crystal boundary or holes. During the sintering, the residual stress and interfacial energy between the metallurgical interfaces could be larger than that of other sites, so it was easier to adsorp O2 and S-containing gas in air. Verified the correctness of the oxidation process' mechanism by analysis of the domestic and thick sample's surface oxidation. According to the thermodynamics calculation, tin and indium were easier to be oxidized than silver. Herein, the resulted oxides(such as Sn S) distributed on the surface of the thick film, so as to lose the samples' metallic luster, decrease of its surface diffuse reflectance, increase of surface roughness, and reduction of the electrical conductance. Therefore, the oxidation of silver was slowed down. In other word, the anti-oxidation ability of the silver thick film was improved.