Chiew Ying Heong 1 , A.S.M.A.Haseeb, Goh Yingxin, Lee Seen Fang Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia 1 E-mail: heongyingchiew@hotmail.com Abstract Sn-Bi alloys were electroplated from sulphuric acid based plating baths containing tin sulfate (SnSO 4 ) and bismuth nitrate (Bi(NO 3 ) 3 ). The electrochemical behavior of the plating bath was investigated by electrochemical studies. Potentiodynamic polarization curves of the plating bath revealed the large potential gap between the two elements. The effects of SnSO 4 concentration and current density on the composition and morphology of the Sn-Bi electrodeposition were investigated. The surface morphology and composition of the Sn-Bi electrodeposited were investigated by scanning electron microscopic (SEM) coupled with energy dispersive X-ray (EDS) spectroscopic. The Sn content in the deposits increased with increasing of Sn content in the bath. Bi content was found to decrease with increasing current density because of the more noble deposition potential of Bi. The microstructure and surface morphology of the Sn-Bi electrodeposits become finer and smoother with increasing Sn content in bath but rougher and less compact when current density is increased. Sn-36.47 wt.% Bi alloy was fabricated from this additive free plating bath. Keywords Electroplating, Parameters variation, Sn-Bi alloy, additive free bath. 1. Introduction Solder plays an important role in the electronic industry. It is a fusible alloy that acts as a joint material to interconnect the chip and bonding pad. In early 1950s, Sn-Pb eutectic alloy is widely used as solder material in the electronic packaging due to its outstanding properties. However, the usage of Pb is restricted by many countries due to its detrimental effects on health and the environment [1- 4]. The electronics industry has moved on to lead-free solder and a few alternatives to Sn- Pb solders are developed which are generally Sn-based alloys. Sn-based solder alloys including Sn-Ag, Sn-Bi, Sn-Zn and Sn- Cu have been studied. Among the various alternative solder systems, Sn-Bi alloys are favorable alloy as a solder material for electronics due to their low process temperature, cost savings, high reliability and suppression of PCB distortion [1, 4]. Sn-Bi alloy with eutectic composition (Sn-58 wt.% Bi) is most suitable for soldering at low temperature [2]. There is a huge demand on producing multifunctional electronic products with higher performance. This brings challenges on electronic industries, as nowadays this is a need for a reliable process that can deposit solder film. They are several methods to obtain fine solder bumping which includes vacuum evaporation, stencil printed and electroplating. Among these three methods, electrodeposition is preferred as it can give better reliability of the solder bumping process [5]. The main challenges faced during electrodeposition of eutectic Sn-Bi are the large difference in the standard reduction potential (454 mV) and displacement of Sn by Bi. These issues hindered the composition control of Sn-Bi electrodeposition. Besides, dendrite formation on the surface of electrodeposits is another problem found during Sn-Bi electroplating [4]. Dendrites formation in cathodic metal deposition has to be prevented in order to obtain dense coating. Literatures suggested that the incorporation of additives is needed to overcome the problems faced during Sn-Bi electrodeposition [1, 2, 4]. However, the cost of production and complexity of the process will be increased with the addition of additives. To minimize the production cost and complexity, further studies on the effects of electroplating parameters on the properties of electrodeposits are required in order to obtain the Sn-Bi eutectic alloy. Variation of the metal salt concentration and current density are found to influence the composition and morphology of an alloy deposit [5]. The main objective of this study is to investigate the effects of tin concentration and current density on the composition and the surface morphology of Sn-Bi electrodeposits. 2. Experimental Sn-Bi electrodeposition was carried out at room temperature using dc current in sulphuric acid solutions for 60 minutes with magnetic stirrer. The basic plating bath was composed of 0.30M of tin sulphate, 0.02M of bismuth nitrate and 1.88M of sulphuric acid. 0.3mm thick Cu sheet (3cm x 3cm) were used as cathode while anode is platinised Ti. The distance between the anode and cathode was fixed at 5cm. The Cu sheets were cleansed with detergent, polished with grit paper, and etched with 10% sulphuric acid solution before the deposition process. The variation of bath composition and plating parameters are shown in Table 1. The deposits were rinsed with distilled water and air dried after electroplating. The electrochemical polarization tests were performed on plating solutions with a Potentiostat/Galvanostat (Gamry, model PC14/300). The reference electrode was a Ag/AgCl electrode with saturated KCl while the Pt wire served as counter electrode. Surface morphologies of the deposits are observed by scanning electron microscopy (SEM). The alloy compositions of the deposits are analyzed by energy dispersive X-ray spectroscopy (EDS). Table 1: Plating parameters for electrodeposition of Sn-Bi alloys Parameters Conditions Current Density Agitation Sn concentration 5-25 mA cm -2 80 rpm 0.15 - 0.30M Effects of Sn Concentration and Current Density on Sn-Bi Electrodeposition in Additive Free Plating Bath 978-1-4673-2688-9/12/$31.00 ©2012 IEEE 286 4th Asia Symposium on Quality Electronic Design