Additives for electroplating of the hottest gold a

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Gold and its alloy electroplating additives

[Abstract] this paper studies a large number of gold plating and its alloy materials at home and abroad, introduces some additives and representative typical formulas and operating conditions, and puts forward the problems that should be paid attention to in the relevant process

[subject words] gold plating alloy additives

1 preface

today, generally talking about gold plating process is not suitable for the development of modern science and technology. Two years ago, I proposed to establish the discipline of surface gilding, and many people responded. In my paper entitled "theoretical research on surface gilding" [1], I introduced the recent achievements of using modern physical and non physical methods to study gold deposition and coating structure, and also predicted the development direction of surface gilding. Over the past two years, gold and its alloy electroplating has made great progress. Taking some time to introduce the latest achievements of its additives may give people a new understanding of the development of surface gilding in the future

2 additives

2.1 sulfur containing complexing agent

cyanide free gold plating and its alloy process have become the most concerned technology in today's electroplating industry. Choosing appropriate additives has become the key to such technology. A European Patent introduces the free sulfur-containing complexing agent [2], which has the obvious characteristics of good dissolution, strong stability, low steam pressure and no odor, and has received extensive attention

it is reported that this sulfur-containing complexing agent of gold is actually mercaptan sulfonic acid, which can also be disulfide sulfonic acid, or aromatic and heterocyclic mercaptan compounds. For example, mercaptan sulfonic acid has the above four characteristics, which may be the result of the substitution of hydrogen in the sulfur hydroxyl group of this compound molecule by metals

Formula 1: [2]

Gold: (in the form of sulfur complex) 0.5 ~ 30g/l

soluble alloying salt 0 ~ 50g/L

sulfur containing complexing agent of gold (free state) 1 ~ 200g/L

conductive salt or buffer 0 ~ 200g/L

wetting agent (appropriate amount)

brightener (appropriate amount)


(1) soluble alloying salt in the formula refers to Ag, Cu, in, and salts such as CD, Zn, Sn, Bi, as or sb

(2) conductive salt or buffer is added in the form of alkaline borate, phosphate, citrate, tartrate or gluconate

2.2 piperazine hexahydrate

also known as piperazine hexahydrate (C4H10N2 · 6H2O), is a white or light yellow crystal in the foreseeable future, soluble in water and acid. In a French patent, a gold-plated tin alloy solution containing a mixture of piperazine and arsenic compounds is introduced. Its function is to act as a brightener. It is reported that this kind of plating solution can obtain a bright gold tin alloy coating containing 92% gold and 9% tin

formula 2: [3]

potassium gold cyanide 20g/L

tin chloride 30g/L

potassium hydroxide 10g/L

d-potassium gluconate 60g/L

citric acid 10g/L

potassium citrate 50g/L

piperazine and arsenic oxide 20mg/L


(1) operating conditions: pH 4, temperature 45 ℃, cathode current density 2a/dm2, and plating speed 1 μ m/min。

(2) potassium d-gluconate is used as complexing agent, and glucuronic acid or glucuronic acid can also be used

2.3 hydrazine sulfate

also known as hydrazine sulfate (nh4n2 · H2SO4), is a white rhombic crystal or powder, which is easily soluble in hot water and slightly soluble in cold water and alcohol. A Japanese patent introduces its new uses. That is, adding hydrazine sulfate additive, potassium pyrophosphate and potassium sulfite to the gold plating solution with potassium gold cyanide as the main salt can obtain the results of wide current density and stable cathode current efficiency. When the concentration of metal impurities such as iron and nickel is high after soaking in the solution for 24 ± 1 hours, the co deposition of gold and such impurities will not occur

formula 3: [4]

main salt (potassium gold cyanide)

conductive salt

grain control agent (not published)

potassium pyrophosphate 30 ~ 100g/l

hydrazine sulfate 0.1 ~ 10g/l

potassium sulfite 0.1 ~ 10g/l


(1) in addition to hydrazine sulfate, hydrazine hydrochloride, L-ascorbic acid and oxalic acid can also be selected

(2) the main salt, conductive salt, grain control agent and operating conditions are not published, and can be selected according to their own process requirements

2.4 dimethylamine borane

in the patent solution of electroless gold plating, some people use boron hydride as reducing agent. A prominent example is the use of dimethylamine borane. This electroless gold plating solution is used in the electronic circuit manufacturing industry, and the line spacing is only 10 μ M graphic printed board. This patent solution is used by some manufacturers

formula 4: [5]

gold (added in the form of gold potassium cyanide) 4G/L

dimethylamine borane 8g/L

thallium (added in the form of thallium formate) 10mg/L

nitrile acetic acid 2G/L

potassium hydroxide 35g/L

potassium cyanide 2G/L

dimethylamine 5g/L

pH 11 ~ 14

temperature 70 ℃

2.5 zirconium nitrate

trace elements indium, zirconium, antimony and other compounds are often added to gold plating and its alloy plating solution, It can also get good results. A British patent describes that adding zirconium nitrate to the gold iron alloy plating solution can obtain a high-k gold coating with strong corrosion resistance. This plating solution is widely used in the production of rings, eyeglass frames and some civil light industries. Its biggest advantage is that it does not contain toxic cadmium, and there is no allergy when the skin contacts the plating solution

formula 5: [6]

potassium gold cyanide 2.5 ~ 3.5g/l

iron nitrate 0.6 ~ 0.8g/l

zirconium nitrate 0.2 ~ 0.5g/l

diammonium hydrogen citrate 75 ~ 125g/L

citric acid 40 ~ 80g/L

3 - (1-pyridine) - 1-propane sulfonate 1 ~ 3G/L

2.6 ammonium sulfate

a Japanese version.The patent introduces the electroless gold plating solution using ammonium sulfate as chelating agent and sodium thiosulfate as reducing agent. When the conductive coating produced by this solution is used for PCB plugs, the stability of the plating solution is also very good, so people pay attention to it. Its pH value is controlled within the range of 5 ~ 9, and potassium gold cyanide is still used as the main salt 7]。

2.7 gold plating solution of Huamei Electroplating Technology Co., Ltd.

it is reported that the company's gold plating solution for printed circuit boards includes autronex r-a-gold 402, 702; Electroless gold plating immersion gold I. The company is used for decorative performance gold plating aurobond TN; Bright gold-plated auroflash 7001, NO2; PTS series water gold plating; Neutral gold plating HM cold No.1

2.8 West Germany high performance neutral gold plating solution gold-3

the gold salt content of this solution is 0.5g/l, which can produce a gold plating layer with uniform color, high hardness and strong corrosion resistance

2.9 gold plating solution of Singapore super international chemical company

the plating solutions launched by the company include: 14k gold alloy solution jsau-14kt; Decorative high alloy liquid jsau-16kt; 18 K gold alloy solution jsau-18kt; High purity electronic industry gold plating solution jsau-8400, 9305; Neutral, 24K decorative liquid gold flash Au-1; Electronic industry gold plating solution jsau CS; JAAu-CI。

3 related issues

3.1 great efforts have been made to develop new additives

the additive research of gold plating solution has always been valued by gold plating workers and relevant experts in various countries. However, by contrast, its achievements and academic papers are much less than those in the fields of copper plating, nickel plating and tin plating. In a sense, it will reach 1.5 million tons in 2020. The significance of the discipline of gold plating engineering is not understood by some people. The research investment in cyanide free gold plating is not enough. The advantages of large and fine gold solution with acid low cyanide plating and then measuring output are still playing a role. Therefore, the author appeals that qualified scholars should turn their attention to the development of new additives and new processes for gold plating, and strive to make a great development in the theory and application of surface gold plating within 10 years

3.2 attach importance to the development of gold imitation rare earth additives

at present, the ready-made rare earth additives added to the gold imitation plating solution are very few in quantity and high in price, which affects the further development of the gold imitation industry. A chemical plant in Jiangsu Province has made a valuable exploration. A rare earth additive called CG type gold imitation plating has made amazing achievements in gold imitation fidelity and anti discoloration ability [7]. However, there are too few reports about such articles. Scientists, senior engineers and electrochemistry workers from some powerful national team research units and colleges and universities should be duty bound to join this team to develop more gold like rare earth additives

3.3 strengthen the research on the aging mechanism of gold plating solution

what is the reason for the aging of gold plating solution? What people usually study most is the metal impurities in the gold plating solution. Admittedly, this is one reason for the aging of the plating solution, but it is by no means the only reason. Even the mechanism of this reason is not clear. A research institute in Guangzhou has made a useful exploration in this regard, and the enlightenment to us is also very good [8]. In particular, their practical experience of "using alkaline cyanide gold plating as the base and acid gold plating as the surface gold" is worth popularizing

the source of metal impurities is not only the workpiece, hanger, operation mode, process specification and other factors, but also the purity of the additive itself. In addition to looking for the aging factors of the plating solution in terms of metal impurities, we should also look for the reasons from the quality of additives, process selection, operation specifications, process environment, equipment quality and other factors. An all-round study of various factors can find effective countermeasures

3.4 the problem of deplating and re plating cannot be ignored

any process has the problem of deplating and re plating, especially the process of gold plating and its alloy. The utilization of waste gold plating is not limited to economic benefits. Some foreign companies pay special attention to the research of gold withdrawal solution, put forward many little-known patented formulas, and put forward unique opinions on the research of the principle of gold withdrawal. Some of us have engaged in such work very early [9]. At present, the removal methods include chemical method, electrochemical method, electropolishing, metallographic micro corrosion, physical method, etc., which have also achieved results to varying degrees. It is hoped that there will be better and more refund methods


1 Wu Shuiqing Theoretical study of surface gilding Surface technology, 1998; 27 (5):1 ~ 5

2 (European patent) EP 9077671999 04 14

3 (French patent) de 44064341995 08 10

4 (Japanese patent) jp96402 4711996 03 13

5 (British patent) GB 23065081999 04 28

6 (Japanese patent) jp953314521999 12 19

7 Yang Shengqi.The Development of rare earth additive imitating gold for electroplating Electroplating and environmental protection, 1999; 19 (1):21 ~ 22

8 Chen Xiangling Xiaoyaokun Discussion on the recycling process of aging gold plating solution Electroplating and environmental protection, 1998; 18 (6):16 ~ 17

9 Gao Qiaoming Removal of gold coating Surface technology 2000; 29(2):42~43

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