【作者】 田栋；

【导师】 李宁；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2013， 博士

【摘要】 在电子领域中，精细铜线路表面的化学镀镍通常需要借助钯活化，不但价格昂贵，而且容易造成溢镀，开发在铜表面直接化学沉积镍镀层的方法具有重要意义。基于硫脲与一价铜离子和镍离子形成的络合物稳定常数相差14个数量级，本文选择硫脲为铜的特定配位剂，使铜的稳定电位大幅度负移并低于镍的沉积电位，开发出了铜表面置换镀镍的方法。根据不同条件下制备的置换镀镍层组成和性能的差异，将其用作自催化型化学镀镍的催化层来代替钯活化，或者直接作为铜基体的保护性镀层。利用XPS证明了铜在硫脲溶液中会发生配位溶解生成一价铜离子。通过考察硫脲溶液pH值与铜的配位溶解速率之间的关系，明确了随硫脲溶液pH值的升高，铜表面会逐渐生成一层保护膜，导致硫脲对铜配位溶解能力的降低。依据Nernst方程计算和电化学测试，发现了在高浓度硫脲溶液中铜的稳定电位将低于镍的沉积电位，证明了铜表面置换镀镍的热力学可行性，并利用EDX和XPS验证了置换镀镍层在铜表面的沉积。通过对镀层的成分分析，发现强酸性条件下镍与硫共沉积于镀层之中，但是随着镀液pH值的升高镀层中还会夹杂有硫脲分子。将强酸性条件下制备的置换镀镍层用作自催化型化学镀镍的催化层，探讨了置换镀镍层成分和催化活性之间的关系。通过对镀层的分析和电化学测试，发现了镀层中硫含量随着沉积时间的延长和镀液pH值的升高而上升，导致镀层更容易发生自钝化，从而造成镀层催化活性的降低。当置换镀镍层的沉积时间为10s、置换镀镍溶液的pH=0时，制备的置换镀镍层催化活性最高。根据电化学测试及XPS分析结果，阐释了置换镀镍层必须经过后处理去除吸附的硫脲，才能表现出对化学镀镍的催化活性。从催化活性、所得化学镀镍层的性能以及对化学镀镍溶液寿命的影响等方面对比了基于铜表面置换镀镍的镍活化法和传统的钯活化法，证明了镍活化可以取代钯活化。利用交流伏安法和XPS揭示了镍可以在析氢的电位区间内发生非常规的亚单层氧化，明确了其氧化电位与次亚磷酸根在镍表面氧化电位之间的关系，并根据亚稳态水合氧化物催化模型提出了镍的亚单层氧化催化了次亚磷酸根氧化的假说。将近中性条件下制备的置换镀镍层用作铜的保护性镀层，发现镀层可以为铜基体提供有效的电化学保护。对镀层成分与耐蚀性之间的关系进行了探讨，认为当镀液pH=6.0时，镀层中夹杂的硫脲分子以及氧化亚铜有利于镀层耐蚀性的提高。详细研究了镀液pH值、沉积时间、施镀温度和镀液组成等因素对置换镀镍层耐蚀性能的影响，优化出了最佳的施镀工艺，即：置换镀镍溶液的pH为6.0，沉积时间为4min，施镀温度为60℃，镀液组成为40g/L柠檬酸钠、30~40g/L硫酸镍和150g/L硫脲。更多还原

【Abstract】 In electronic field, Pd-activation is usually required to initiate the electroless Niplating on Cu circuits with fine dimensions. It will increase cost and sometimescause some defects. Therefore, the development of direct electroless Ni plating onCu without Pd-activation is significant. Because the stability constant ofCu（I）-thiourea complex is14orders of magnitude higher than that of Ni（II）-thioureacomplex, thiourea has been chosen as the specific complexing agent for Cu in thispaper. As a result, the steady potential of Cu in thiourea solution would shiftnegatively and be negative enough for the reduction of Ni2+. According to thesefindings, a methodology for replacement Ni plating on Cu surface was developed.The Ni films prepared under different conditions had significant differences incomposition and properties. Therefore, they could be used as the catalytic films forelectroless Ni plating in order to replace Pd-activation and as the protective films forCu substrate, respectively.It was demonstrated by X-ray photoelectron spectroscopy （XPS） that Cu+wasgenerated during the dissolution process of Cu in thiourea solution, and wascoordinated by thiourea via S atom. With the increase of the pH value in thioureasolution, a passive film would be formed on Cu surface, resulting in the inhibition ofactive dissolution of Cu. Based on Nernst equation and electrochemicalmeasurements, it was demonstrated that the steady potential of Cu in highconcentrated thiourea solution would be negative enough for Ni deposition.According to the thermodynamic principle, the deposition of Ni on Cu byreplacement plating could be realized, and the obtained Ni films were illustrated byXPS and energy dispersive X-ray spectrometry （EDX）. It suggested that Ni and Swere co-deposited in strong acidic solution, and thiourea was doped in the Ni filmwith the rise of pH.The Ni films prepared in strong acidic solution were used as the catalytic filmsfor eletroless Ni plating. The significance of film composition for its catalyticactivity was investigated. EDX results revealed that the sulfur content in theprepared Ni films increased with the increase of plating time and pH. Theelectrochemical measurements indicated that the Ni films with higher sulfur contentwere more prone to be passivated, with negative influence on its catalytic activityfor hypophosphite oxidation. Thus, the catalytic activity for electroless Ni platingwould be the highest when the plating time and pH value were10s and0,respectively. It was demonstrated by electrochemical measurement and XPSanalysis, that the post-treatment to eliminate the adsorbed thiourea must be performed in order to trigger the catalytic activity for electroless Ni plating.Importantly, the developed Ni-activation method was systematically compared withthe traditional Pd-activation method in terms of the catalytic activity, the propertiesof resulting Ni-P layers and the influence on the electroless nickel plating bath. Itindicated that the developed Ni-activation method was capable of replacingPd-activation. Moreover, underlying premonolayer oxidation of Ni electrode inhydrogen evolution reaction potential region was revealed by AC voltammetry andXPS. The relationship between its potential range and that of hypophosphiteoxidation on Ni was investigated. Based on the incipient hydrous oxide adatommediator （IHOAM） model, it was proposed that the premonolayer oxidation of Nicatalyzed hypophosphite oxidation.The Ni films prepared in neutral solution were used as protective films for Cusubstrate, which could provide effective electrochemical protection. The influnce offilm composition on corrosion resistance was studied. It was demonstrated thatthiourea and Cu₂O were doped in the Ni film prepared at pH of6.0, which mightplay a promotional role in the improvement of corrosion resistance. The influencesof pH value, plating time, temperature and bath composition on the properties of thedeposited Ni films were investigated in detail to determine the optimized platingconditions. When the pH value was controlled at6.0, the plating time was4minutes,the temperature was maintained at60℃, and the plating bath comprised40g/Lsodium citrate,30⁴0g/L nickel sulfate and150g/L thiourea, the prepared Ni filmsexhibited the best corrosion resistance.更多还原