A Rutherford Scattering Study of Catalyst Systems for Electroless Cu Plating: II . Sensitization and Activation

Abstract

High energy ion backscattering has been used to study the surface chemistry of the sensitization false(SnCl2false) and activation false(PdCl2false) processes used to prepare nonconductive substrates for electroless plating. This method of surface preparation is compared to catalysis using mixed Pd‐Sn colloidal solutions. While the redox reaction between divalent Sn and Pd may occur during the activation of sensitized surfaces, it is suggested that any zero‐valent Pd so produced only becomes catalytically active after a significant (∼100 sec) immersion time in the electroless plating solution.

Reductive spectrophotometry of divalent tin sensitization on soda lime glass

“…For cleaved graphite substrates treated with ∼72 mM SnCl 2 ·2H 2 O for over 120 s, Rutherford backscattering yielded a tin (II) plus tin (IV) concentration of 33.2 nmol/cm 2 [23]. In contrast with reductive spectroscopy employed in the present work, neither ICP-OES nor Rutherford backscattering distinguishes tin (II) from tin (IV).…”

“…This was lower than the values in the current study, which were measured on soda lime glass. As with Rutherford backscattering, X-ray fluorescence successfully quantitated total tin content but did not distinguish tin (II) from tin (IV) [21,23,27]. Mossbauer and radiochemical tracer analysis could distinguish elemental states of tin, but have not been used for rapid, in situ quantitation of tin, as in the present study [24][25][26].…”

“…Froment reported non-linear increases in total tin deposited on silicon nitride (Si 3 N 4 ) substrates from 0 to 600 s [21], and rapid saturation at 600 s. The analyte solution however contained aged palladium, Pd (II), and tin (II) in the ratio of 1:3.1 along with 4.3 M HCl. Meek measured linear increases in total tin (tin (II) + tin (IV)) deposited on cleaved graphite surfaces (1 cm 2 ) from 2 to 300 s when the analyte solution was prepared by adding acid after dissolving tin (II) in H 2 O [23]. Tin deposition increased linearly and saturated ≥100 s when acid was added before dissolving the tin (II).…”

“…But they have not been applied to quantitate the mass of tin (II) deposited on substrates to sensitize EL plating. The effects of tin sensitization, and activation steps on EL plating along with substrate properties have been evaluated by Rutherford backscattering [21][22][23], radiochemical tracer analysis [24,25], Mossbauer spectroscopy [26], X-ray fluorescence spectrometry [27] and X-ray photoelectron spectroscopy (XPS) [28]. Challenges of these methods [13,29] underscore a need for rapid, in situ evaluation of tin (II) deposited during sensitization with respect to operational variables, e.g., sensitization time, analyte concentration, aqueous immersion, and acid content.…”

Tunable surface metal morphologies and electrical properties of monodispersed polystyrene beads coated with metal multilayers via electroless deposition

“…Therefore, a conventional electroless-plating method often involves treating the polymer surface with SnCl 2 to sensitize the surface. In the presence of SnCl 2 , palladium particles are surrounded by an SnCl 2 shell after Pd 2þ is reduced to Pd 0 [16,17]. SnCl 2 is not an active catalyst for electroless plating and the bonding force between SnCl 2 and the polymer surface is weak because it is based on physisorption [17].…”