A Study on Activation and Acceleration by Mixed PdCl2 / SnCl2 Catalysts for Electroless Metal Deposition

Abstract

Five different compositions of mixed acidic PdCl2/SnCl2 catalysts for electroless plating were investigated mainly by electrochemical and x‐ray photoelectron spectroscopy measurements, and also by ultraviolet and visible photospectroscopy, transmission electron microscopy, and Auger electron spectroscopy. It is shown that the potential sweep technique using a catalyzed gold electrode in 1MnormalHCl yields voltammograms which depend upon the catalyst activity, and that this technique is applicable for simple diagnosis of the activity of mixed PdCl2/SnCl2 catalyst systems. It was found by transmission electron microscopy that large colloidal particles are required for high catalytic activities. X‐ray photoelectron spectroscopy showed that these colloidal particles consist of a system in which Pd and Sn atoms have an interaction such as in Pd‐Sn intermediates or alloys. The ratio of Pd/Sn after acceleration is not constant but depends on the catalyst activity. The accelerator ( 1MNH4BF4 or 1:1 normalHCl ) not only removes Sn(IV) ions from the substrate but also causes coagulation of small particles adsorbed on the substrate, and these actions result in a drastic increase in the activity of low activity catalysts.

Microstructure evolution during electroless copper deposition

“…Special attention has been paid to the question of the existence of "hydrogen bubbles" described in previous works [7,12,21]. Small voids trapped in the bulk material can be easily ob^rved through the Fresnel fringe by off-focusing the image.…”

“…The sensitization and activation process by double immersion in SnClj and PdClj solutions has been studied [1][2][3] and one-step activation in PdClj-SnClj colloid solution followed by acceleration (HCl or NH4HF2 and others) was also investigated [4][5][6][7][8]. In contrast to the detailed chemical analyses presented in these researches [1][2][3][4][5][6][7][8], we studied the activation process through microstructure analysis by scanning transmission electron microscopy (STEM). This method provides information on sizes and distributions as well as chemical composition of the catalytic particles.…”

Activity of Small Silver Nanocubes as Activators for Electroless Copper Deposition

“…In the fabrication of printing circuit boards, Cu layers are deposited onto the side walls of holes in the circuit board via Pd-Sn colloidactivated ECD [11]. Pd-Sn colloids, prepared from PdCl 2 and SnCl 2 , are typical commercial catalysts used in ECD [13,[15][16][17][18][19]. However, Ag catalysts have been recently investigated as catalysts for ECD owing to the high cost of Pd.…”

Characterization of PdSn catalysts for electroless metal deposition

“…Electrochemical techniques show promise for this purpose. One simple method of measuring PdSn activity is the monitoring of the mixed potential of an activated surface as electroless plating is initiated [23,24]. The initiation time is shorter for more active catalysts.…”

“…Voltammetry of colloid-covered surfaces has also been used to evaluate the catalysts [23][24][25]. Osaka et al [23] adsorbed the colloid on a Au electrode, then stripped it from the surface with a positive-going potential sweep. The charges under the stripping peaks could be taken as a measure of the surface coverages of Pd and tin.…”