化学镀钯拖缸现象的电化学研究

Electrochemical Study on Dummy Plating in Electroless Palladium Plating

目的用电化学的方法探究化学镀钯出现拖缸现象的原因方法通过开路电位方法探测化学镀钯的引发过程,利用线性扫描伏安法测量极化曲线。在测量阳极极化曲线时不加入钯盐;在测量阴极极化曲线时,不加入次亚磷酸钠。分别求得次亚磷酸钠的起始氧化的电位(EO)、钯离子的起始还原电位(ER)随温度变化的关系曲线,以及甘氨酸浓度对EO和ER的影响,并且采用化学镀实验,研究钯层厚度变化与甘氨酸浓度的关系。结果发现第1次使用和多次使用的化学镀钯液对引发钯沉积的快慢存在差异,即存在拖缸现象。在镀钯过程中,温度越高,镀液活性越强,越不容易出现拖缸现象,同时稳定性也会下降。在电化学实验中发现,EO随着温度的升高而负移,ER随着温度的升高而正移,二者的差值|ΔE|总体上随着温度的升高而减小。ΔE可以反映镀液的稳定性和衡量化学镀钯引发的难易程度。ΔE<0意味着镀液稳定,化学镀钯需要在催化剂表面引发。当|ΔE|≤0.73 V时,化学镀钯可以正常引发。当|ΔE|>0.73 V时,引发过程存在拖缸现象。甘氨酸的浓度可以影响ΔE。当甘氨酸的质量浓度接近10 g/L时,拖缸现象不明显,无甘氨酸或者其质量浓度大于20 g/L时,容易出现拖缸现象。结论ΔE的值与化学镀钯液的稳定性和拖缸现象是否发生有关。

The work aims to investigate the causes of dummy plating in palladium plating process by electrochemical methods and explore the electrochemical relationship behind the dummy plating.The initiation process of electroless palladium plating was probed by the electrochemical open-circuit potential,and the linear scanning voltammetry was taken to measure polarization curves.During measurement of anodic polarization curve,palladium salt was not added,while during measurement of cathodic polarization curve,sodium hypophosphite was not added.The onset oxidation potential of sodium hypophosphite(EO)and the onset reduction potential of palladium ion(ER)with temperature,as well as the effect of glycine concentration on EOand ER,were determined respectively by linear scanning voltammetry.In addition,the relationship between the variation of palladium layer thickness and glycine concentration was also investigated by electroless plating experiments.It was found that there was a difference in the rapidity of initiating palladium deposition between the first use and multiple uses of the electroless palladium plating solution,i.e.,there was dummy plating.When the palladium plating solution was used for the first time,there was no palladium initiation for 900 s.When the palladium plating solution was used for the second time,the palladium initiation appeared at 500 s.When the palladium plating solution was used for the third time,the palladium initiation was even advanced to 200 s.In the process of palladium plating,the higher the temperature,the more active the plating solution was,and the less likely it was to show dummy plating,but the stability also decreased.After the onset potentials separately in the experiments of polarization curves measured by linear scanning voltammetry were obtained,the onset oxidation potential of sodium hypophosphite(EO)shifted negatively with increasing temperature and the onset reduction potential of palladium ion(ER)shifted positively with increasing temperature,and the difference between the EOand ER(|ΔE|)decreased with increasing temperature.TheΔE was the electrochemical information of the electroless palladium plating solution,and also revealed the stability of the plating solution and measured the ease of electroless palladium plating,i.e.,the ΔE was associated with the dummy plating.The ΔE<0 indicated that the plating solution was stable and electroless palladium plating needed to be initiated on the surface of the catalyst,while ΔE>0 indicated that the plating solution was unstable and would spontaneously decompose,preventing selective deposition on the surface of the part to be plated.The electroless palladium plating could be initiated normally when|ΔE|≤0.73 V,while the initiation process showed dummy plating when|ΔE|>0.73 V.The concentration of glycine could affectΔE.When the concentration of glycine was close to 10 g/L,the dummy plating was not obvious,but when there was no glycine or its concentration was greater than 20 g/L,the deposition of palladium was not favored and the dummy plating was likely to occur.The value ofΔE is related to the stability of the electroless palladium plating solution and the occurrence of dummy plating.