Analysis of SnNi Electroplate by Secondary Ion Mass Spectrometry, Ion Scattering Spectrometry, and Rutherford Backscattering

Abstract

Two batches of SnNi electroplate, expected to be composed of equal atomic amounts of Sn and Ni, have been examined by secondary ion mass spectrometry, ion scattering spectrometry, and Rutherford backscattering. Tin oxides and hydroxides were found in the surface region, which is Sn-rich; no Ni oxides or hydroxides were seen. The Sn/Ni ratio for the two batches was 45/55 and 52/48 a/o. After Ar+-sputter cleaning, films of the type which occur during and immediately after electroplating could not be reproduced in 10 .8 Torr O3. The regenerated films contained substantial amounts of nickel oxides and hydroxides.Electroplated metastable SnNi is of technological interest for a broad range of metallic coating applications. It is suitable as a decorative coating and as a protective corrosion barrier (1). Usage as one of the electroplated components of electrical components has also been proposed (2). Its main attractive feature is that surface films on electroplated SnNi form rapidly in air or most aqueous solutions and exhibit a high degree of passivity to further corrosion (3-5). In order to understand the nature of these films, a detailed analysis is important.With reasonable care during electroplating, the deposit is expected to have equiatomic composition (3), although a broad range of compositions can be plated (6). Current knowledge of the surface film composition has been obtained through Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA), and passivation potential curves. AES studies show the surface to be a tin-rich oxide (7) or a nickel polystannate (8). These two results are not in conflict since AES does not detect hydrogen nor chemical bonding in general. The ESCA study has reached a similar conclusion (9). Passivation-potential techniques indicate that the surface is nickel stannate (3, 4), however, with films that are only tens of angstroms thick (7,9), electrochemical techniques are not sufficient to give an unambiguous analysis. This paper describes the surface analysis of SnNi electroplate by three techniques; Rutherford backscattering (RBS), ion-scattering spectrometry (ISS), and secondary ion mass spectrometry (SIMS). ExperimentalThe SIMS experiments were carried out in a stainless steel ion pumped UHV system. These included molecular composition depth profiles and film regeneration with 02 exposure. A 2 keV focused Ar + ion source with variable current density has been de-

Secondary Ion Mass Spectrometric Analysis of Cobalt‐Hardened Gold Electroplate Surfaces

“…Secondary ion mass spectrometry (SIMS) used in the static mode is ideal for a qualitative chemical surface analysis (11)(12)(13)(14). Static SIMS uses sufficiently low primary ion beam densities (,~1011 ions/sec-cm 2 _--16 nA/cm 2) such that less than 10% of a monolayer of the surface is destroyed through sputtering during an analysis.…”