Ag/Sn Nanoparticles Reduced by Tin(II) Pyrophosphate, Tin(II) Oxalate, and Tin(II) Sulfate for Catalyzing Electroless Copper Deposition

Abstract

Different-sized Ag/Sn nanoparticles were prepared using various tin salts, including tin(II) pyrophosphate, tin(II) oxalate, and tin(II) sulfate, and applied as activators for electroless copper deposition. The transmission electron microscopy and X-ray photon electron spectroscopy data showed Ag nanoparticles of 8.2 and 10.2 nm were prepared and coated by SnO x when tin(II) sulfate and tin(II) oxalate were used, respectively. When tin(II) pyrophosphate was employed, 5.8 nm Ag nanoparticles with a thicker shell composed of SnO x and Sn 2 P 2 O 7 were obtained. Furthermore, a comparison of the activities and actual deposition rates of these three Ag/Sn nanoparticles was carried out by monitoring the deposition in situ with a quartz crystal microbalance (QCM) and measuring the surface morphology of the deposited layer with a field-emission scanning electron microscope (FE-SEM). The activities and deposition rates observed by QCM had the order Ag/Sn P2O7 > Ag/Sn SO4 > Ag/Sn C2O4 , which demonstrated that the size of the Ag nanoparticles controls the activity of electroless copper deposition (ECD), even in the presence of a thick Sn shell. However, the FE-SEM images showed that a thick shell influenced the uniformity of deposited Cu film. Therefore, among these three Ag/Sn nanoparticles, the nanoparticles reduced by tin(II) sulfate showed the best performance as an activator for ECD.The activation of a nonconductive substrate is a key issue in determining the characteristics of a deposited layer and the cost of electroless copper deposition (ECD) in industrial processes, including the fabrication of printed circuit boards 1-3 and ink-jet printable circuits. 4-6 Activation, which is a catalytic reaction, is induced by active colloids on the surface of substrates that are dipped into an electroless deposition bath. The active catalyst acts as an electron carrier in the transfer of electrons from the reducer to the metal ions. Accordingly, the activator can be regarded as increasing the deposition rate and improving the performance of advanced circuit processes. In the fabrication of printed circuit boards, Cu layers are deposited onto the side walls of holes in the circuit board via activator-catalyzed ECD. 1-3 The electronic circuits for an advanced process can be directly and rapidly deposited on a flexible polyimide substrate 7 or FR-4 plate 8 where an activator ink was previously coated using an ink-jet printing method.A typical activator is a Pd/Sn colloid solution, 9-13 which is prepared from a mixture of PdCl 2 and SnCl 2 in an acidic aqueous solution. 11,14 In the synthesis of Pd/Sn colloids, metallic Pd 0 can be reduced by Sn 2+ ions, which are simultaneously oxidized to Sn 4+ ions; therefore, catalytic Pd particles are surrounded and stabilized by an excess of Sn 4+ ions in aqueous solution. With the advancements in the synthesis of nanoparticles in the last decade, solutions containing Pd nanoparticles protected by an organic stabilizer can be prepared and used as new activators for ECD to interconnect print...

Sn-Nanorod-Supported Ag Nanoparticles as Efficient Catalysts for Electroless Deposition of Cu Conductive Tracks

“…Activation is an indispensable process for electroless copper deposition, in which the copper ions are reduced by the reducing agent, and the activator (catalyst) acts as the medium transferring electrons from the reducing agent to the copper ions. , The excellent catalytic activity of Pd for the ECD reaction makes the Pd-based activation technology the most common application in the contemporary ECD industry. Nevertheless, it is the high material cost of Pd that makes the idea of exploring the cost-efficient alternatives attractive. , It is well-established that, in addition to Pd, the transition metals including Au, Ag, and Cu also exhibit different degrees of catalytic activity toward the ECD reaction . Interestingly, some investigations indicated that Ag-based catalysts can be prepared similar to the formation of conventional Sn/Pd colloidal catalyst, , and recently, copper patterns fabricated with printing technology and the ECD process that applies Ag as catalyst were also reported. , Consequently, Ag as a promising alternative to Pd in catalyzing the ECD reaction is worthy of attention.…”

“…34,35 It is well-established that, in addition to Pd, the transition metals including Au, Ag, and Cu also exhibit different degrees of catalytic activity toward the ECD reaction. 36 Interestingly, some investigations indicated that Ag-based catalysts can be prepared similar to the formation of conventional Sn/Pd colloidal catalyst, 37,38 and recently, copper patterns fabricated with printing technology and the ECD process that applies Ag as catalyst were also reported. 29,39 Consequently, Ag as a promising alternative to Pd in catalyzing the ECD reaction is worthy of attention.…”