Communication—A Cyanide-Free Electrolyte for Hard Gold (Au-Co) Electrodepositing Utilizing DMH as Complexing Agent

Abstract

A novel cyanide-free electrolyte was reported for Au-Co alloy electrodepositing. Firstly, an optimized electrolyte for Au-Co alloy electrodepositing was obtained from orthogonal experiment. By using optimized electrolyte, a desirable hard gold layer was obtained, which has a similar surface morphology, thickness and a comparative hardness to PCB bonding finger hard gold film. Then, XRD analysis revealed electrodeposits from the cyanide-free system performed supersaturated cobalt dissolved into gold crystal lattice and grew preferentially on Au (111). In summary, the electrolyte would have an extensive application in hard gold cyanide-free electroplating.

Cyanide-free electrolyte for Au/Co–Au nano-multilayer electrodeposition utilising 5,5-dimethylhydantoin as a complexing agent

“…On the basis of the above experimental data of adjustable deposits by controlling current density, the deposited alloy components changed quickly, and the Co content was difficult to control. 27,28 Before the electrodeposition experiment, the electrodeposition of the prepared electrolyte was analysed. The cathodic polarisation curve of electrodeposition is shown in Fig.…”

“…Before the preparation and characterisation of Au/Co overlapping coating, orthogonal experiments were carried out on DMH system gold-plated cobalt alloy, as shown in ESI, PART 1. † 27 The optimal combination of factors of the best plating solution and overall performance of the coating was obtained as follows: DMH 18 g L −1 , NaAuCl 4 ·2H 2 O 2 g L −1 , CoSO 4 ·7H 2 O 0.5 g L −1 , C 6 H 8 O 7 ·H 2 O (citric acid) 20 g L −1 , pH 9. To improve coating quality, the total molar amount of gold/cobalt was unchanged, that is, Au + Co = 6.15 × 10 −3 mol L −1 .…”

Novel and Green Chemical Compound of HAu(Cys)2: Toward a Simple and Sustainable Electrolyte Recipe for Cyanide-Free Gold Electrodeposition

“…11 In the cyanide-free Au(I) electrodeposition baths, the representative Au + complexing agents are the sulfite ion (SO 3 2− ) and thiosulfate ion (S 2 O 3 2− ). 19 SO 3 2− and S 2 O 3 2− ions can coordinate with Au + ions forming Au(SO 3 ) 2 3− and Au(S 2 O 3 ) 2 3− ions, respectively, and their corresponding K f values are 10 10 and 10 26 , respectively. 18 However, the main salt of sodium gold sulfite and the complexing agents of SO 3 2− and S 2 O 3 2− ions in the baths are not stable enough due to the disproportionation reaction of the complexed Au + ion in a weaker coordination and the decompositions of SO 3 2− and S 2 O 3 2− ions.…”

“…Although the disproportionation reaction of the Au + ion is somehow suppressed, the decompositions of SO 3 2− and S 2 O 3 2− ions always happen in their baths. 19 Therefore, it is exceedingly significant to develop a novel, green, and stable main salt or complexing agent instead of toxic Au(CN) 2 − ions and unstable Au(SO 3 ) 2 3− or Au(S 2 O 3 )(SO 3 ) 3− ions applying to cyanide-free Au(I) electrodeposition.…”

“…However, the main salt of potassium gold cyanide and the complexing agent of cyanide in the bath are highly toxic . In the cyanide-free Au­(I) electrodeposition baths, the representative Au + complexing agents are the sulfite ion (SO 3 2– ) and thiosulfate ion (S 2 O 3 2– ) . SO 3 2– and S 2 O 3 2– ions can coordinate with Au + ions forming Au­(SO 3 ) 2 3– and Au­(S 2 O 3 ) 2 3– ions, respectively, and their corresponding K f values are 10 10 and 10 26 , respectively .…”