Composition Control of Sn–Bi Deposits: Interactive Effects of Citric Acid, Ethylenediaminetetraacetic Acid, and Poly(ethylene glycol)

Abstract

Interactive effects of complex agents, including citric acid ͑CA͒, ethylenediaminetetraacetic acid ͑EDTA͒, and poly͑ethylene glycol͒ ͑PEG͒ on the electroplating behavior of Sn-Bi deposits from a basic bath containing 0.15 M Sn 2+ and 0.05 M Bi 3+ with pH 2, were systematically compared by linear sweep voltammetry ͑LSV͒ analyses. The onset potential of Bi deposition is obviously shifted to a negative value close to that of Sn deposition by the simultaneous addition of the above three compounds into the basic plating solution. Based on the LSV results, the composition of Sn-Bi deposits with Sn varying from 44 to 96 wt % can be controlled by varying the current density of electroplating and the concentration of EDTA from the basic plating bath containing 0.3 M CA and 0.2 M PEG. This plating bath provides a reliable route to obtain Sn-Bi alloys of high Sn content ͑e.g., 80Sn-20Bi and 90Sn-10Bi͒ and the eutectic 42Sn-58Bi deposit. Tin-bismuth deposits plated from the basic bath with different combinations of the above three complex agents were also characterized by scanning electron microscopic and energy-dispersive spectroscopic analyses.Attention has been paid to flip-chip technology for microchip packaging and high level system assembly, owing to several benefits such as excellent electrical performance, small package size ͑as chip size͒, good heat removal, and improved signal integer for high speed or high frequency designs. 1 Based on these advantages, Sn-Pb solder bumps, as the first priority of flip-chip interconnection proposed by IBM, have been widely recognized as the most prominent material for interconnecting and packing electronic components. 2 However, due to environmental consideration and the toxicity of lead in Sn-Pb solders, the European Union declared that the usage of lead component has to be limited in many of the electronic assembly processes on July 1, 2006 3-7 although Sn-Pb solders are the most extensively used solder bumps in electronic packaging. Consequently, developing the substitutes, lead-free solder alloys, for electronic applications becomes an urgent assignment in the electronic assembly industry.There are several types of lead-free solder materials ͑e.g., SnCu, Sn-Ag, Sn-Bi, Sn-Ag-Cu, Sn-Zn, Sn-Zn-Bi, etc.͒ with distinct physicochemical properties for the electronic assembly industry, which have been found to strongly depend on the metal type as well as their composition. 3-13 There is a renewed interest in employing the Sn-Bi system with/without the addition of other elements because of the merits of the eutectic 42Sn-58Bi solder bumps with a low reflowing temperature ͑a eutectic point of 139°C͒, good joint strength, low surface tension, excellent creep resistance, high shear strength, good anticorrosive properties, etc., 3,4,7,14,15 although this system has been used for over 20 years in assembling mainframes. 7 Besides, 80Sn-20Bi and 90Sn-10Bi with their melting points of 185 and 200°C, respectively, were reported to replace the eutectic Sn-Pb solder bumps because of the similar m...

Electrodeposition of Tin-Bismuth Alloys: Additives, Morphologies and Compositions

“…It primarily suppresses Bi deposition and hydrogen evolution. EDTA may also facilitate reduction of Sn 4+ on the surface, similar to the well-known behavior of tartarates [18].…”

“…Tin-bismuth alloys have been electrodeposited from different baths using direct-current and pulsed-current techniques [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. The standard reduction potential of Bi 3+ is 444 mV nobler than that of Sn 2+ .…”

Electroplated and Light-Induced Plated Sn-Bi Alloys for Silicon Photovoltaic Applications

“…10 When the plating bath temperature was maintained at 20 ± 2 • C, eutectic Sn-Bi was electroplated at a current density of 16 ± 1.5 mA/cm 2 . The plated alloy composition estimated using ICPOES and EDS were similar, and did not change with plating duration.…”

New porous bismuth electrode material with high surface area

“…In general, BFEs can be prepared by many methods, such as electrodeposition [19], thermal evaporation [20], molecular beam epitaxy [21], direct current sputtering [22] and radio frequency magnetron sputtering [23]. Among these methods, electrochemical deposition is a simple route to control the surface morphology of the deposits by changing some parameters of the electroplating solutions such as the complexing agents, the composition, the pH, the additives, and the temperature, as well as the deposition conditions e.g., the applied potential and the current density [24,25]. Moreover, it holds other advantages including a mass productivity, a high deposition rate, a cost-effectivity and an industrially well-established technology.…”