【作者】 杨斌；

【导师】 杨防祖；

【作者基本信息】 厦门大学 ， 物理化学， 2007， 硕士

【摘要】 自1947年Narcus首次报道了化学镀铜以来,经过半个多世纪的发展,目前化学镀铜已广泛应用于电子、机械、航天等工业领域。传统的化学镀铜工艺多以甲醛为还原剂。由于该工艺存在镀速较低、镀液稳定性差且挥发的甲醛蒸汽对人体及环境有害,因而急需寻找新的还原剂作为甲醛的替代物。以次磷酸钠为还原剂的化学镀铜具有工艺参数范围宽,镀液寿命长,且无有害的甲醛蒸汽,有可能取代甲醛化学镀铜。因此,研究次磷酸钠化学镀铜有理论和实际意义。本文通过大量实验开发出以次磷酸钠为还原剂,柠檬酸钠为络合剂的化学镀铜体系,较好地解决了镀液稳定性和沉积速率等问题,并在此基础上应用电化学方法及扫描电子显微镜(SEM)、能量色散谱(EDS)、X射线衍射(XRD)、X射线光电子能谱(XPS)、四探针电阻仪、电子拉力试验机等现代表征技术对镀层性能、形貌、结构、成分及镀液的阴、阳极极化特性进行了深入研究。应用电化学现场原位红外光谱(FTIR)对再活化剂镍离子在以次磷酸钠为还原剂的化学镀铜中的作用机理进行探讨。本论文的主要研究结果如下:1.化学镀铜镍合金的工艺条件及其作用规律通过大量实验,确定了以次磷酸钠为还原剂的化学镀铜工艺。其适宜的施镀条件为:温度60～70℃;pH值8～9;再活化剂NiSO4·6H2O浓度1～2g/L。温度、pH值及再活化剂镍离子浓度的提高均使化学镀沉积速率增大。获得的镀层为面心立方结构的Cu-Ni合金,无明显晶面择优取向现象。铜和镍的质量百分含量分别为87.70%和12.30%。探索了温度、pH和镍离子对次磷酸钠阳极氧化和铜(镍)离子阴极还原的影响。线性扫描伏安法的实验结果表明,温度的升高同时促进次磷酸钠阳极氧化与铜离子的阴极还原;pH值的增大有利于次磷酸钠的氧化而抑制Cu(II)的还原; Ni2+离子对次磷酸钠的氧化起催化作用;镍离子与铜离子共沉积形成合金。该合金起催化作用,使化学镀反应持续进行;电化学实验进一步证实了本体系中,次磷酸钠的氧化为速度决定步骤。电化学研究实验结果与化学镀铜工艺结果相吻合。2.添加剂在化学镀铜中的作用研究2,2ˊ-联吡啶、苯亚磺酸钠和甲基橙是本化学镀体系有效的添加剂。探索了它们对化学镀铜的沉积速率、表面形貌、结构及镀液阴、阳极极化过程的影响。结果表明:镀液中加入添加剂后,镀液稳定,获得的镀层光亮度提高。2,2ˊ-联吡啶使化学沉积速率降低;而苯亚磺酸钠与甲基橙相似,低浓度范围内使沉积速率上升,而高浓度时又使沉积速率有所下降。极化曲线的研究结果与工艺实验相一致。2,2ˊ-联吡啶对次磷酸钠的氧化起阻化作用,而一定量的苯亚磺酸钠与甲基橙促进次磷酸钠的氧化。铜离子的阴极还原过程较为复杂,2,2ˊ-联吡啶使铜离子的还原电势和峰电势与未加入添加剂时的相比略有负移,但峰电流逐渐增大;苯亚磺酸钠在低浓度范围内促进铜离子的还原,浓度较高时则起抑制作用;甲基橙使铜离子的还原峰电势有所正移,但随着甲基橙浓度的提高,峰电流减小。2,2ˊ-联吡啶影响了晶粒生长,导致镀层颗粒由锥状转变为团粒状,镀层的致密程度有所提高,而苯亚磺酸钠与甲基橙对晶粒的形状影响不大。特别值得注意的是,混合添加剂的作用效果优于单一添加剂。其中以2,2ˊ-联吡啶和苯亚磺酸钠组合的效果最好,获得的镀层表面呈光亮状态。EDS实验结果表明,添加剂的加入使镀层中铜的质量百分含量提高,有助于铜的沉积。XRD结果表明,加入添加剂后,镀层仍为Cu-Ni合金,呈面心立方结构,无明显的晶面择优取向现象,且Cu2O在镀层中的夹杂量很少。3.与甲醛化学镀铜工艺的比较考察并比较了甲醛及次磷酸钠化学镀铜溶液各自的性能,发现它们各有优点。次磷酸钠镀液的稳定性要远高于甲醛镀液,该镀液经过7个循环周期仍然不发生分解,而甲醛镀液仅三个周期后就发生分解;次磷酸钠镀液的沉积速率高于甲醛镀液。以甲醛为还原剂的铜镀层晶粒细小。以次磷酸钠为还原剂的镀层呈团粒状,为铜镍合金。镀层中铜和镍均以单质态形式存在,P的含量极低。镀液中含2,2ˊ-联吡啶的次磷酸钠化学镀铜层中,铜的质量百分含量约为93.90%,镍的质量百分含量约为6.10%。镀层中镍的存在使其电导率、抗拉强度、延伸率等物理性能均不如甲醛化学镀铜层。因此,次磷酸钠化学镀铜工艺更适宜应用于对导电性要求相对较低的行业。4.再活化剂镍离子的作用机理研究深入地探索并阐明了镀液中再活化剂镍离子的作用机理。以次磷酸钠作还原剂的化学镀铜液中,需添加再活化剂Ni2+离子以保证化学镀反应的持续进行。在铜表面,次磷酸盐的氧化能力很弱。实验结果首次证实,再活化剂Ni2+离子的作用是通过沉积在电极表面形成的Cu-Ni合金催化次磷酸钠的氧化,使化学镀铜保持自催化反应特性。纯镍比铜镍合金的催化作用更强。电化学现场原位红外光谱实验中检测到一新的吸收峰,结合文献,推测为中间物HPO2-ads的吸收峰,说明次磷酸钠在氧化过程中存在一前置的电极过程。根据实验事实,建立了以次磷酸钠为还原剂的化学镀铜中,镍离子作用机理及化学镀过程的理论模型。更多还原

【Abstract】 Since its discovery by Narcus in 1947, electroless copper plating has been wildly used in electronics, machinery, aerospace and many other industries. Most of the traditional electroless copper deposition used formaldehyde as reducing agent. Due to this technology had many drawbacks, such as the low deposition rate, bad stability of the solution and the steam of formaldehyde was harmful for human and environment, it was very urgent to look for substitutes for formaldehyde. Electroless copper plating using sodium hypophosphite as reducing agent possessed the advantages of wide operation range, long-life of the electrolyte and without the deleterious steam, and it might replace the formaldehyde copper deposition. Therefore, it is very necessary to do this research. In this dissertation, we explored a new copper deposition system using sodium hypophosphite as reducing agent and sodium citrate as chelating agent, which solve the low deposition rate and the solution stability problems. At the same time, many modern analytical techniques, such as scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), four-probe resistance instrument, electronic pull test-bed, etc, were used to detect the morphology, microstructure, composition and performance of the copper deposit. Electrochemical methods were used to test the anodic and cathodal polarization processes. Finally, we used in-situ FTIR spectroscopy to explore the mechanism of activation nickel ions in electroless copper plating using sodium hypophosphite as reducing agent. Main results of this dissertation were summarized as follow:1. Deposition conditions of electroless Cu-Ni and their influence rulesBase on the experiments, we confirmed the basic technology of electroless copper plating using sodium hypophosphite as reductant, which available temperature was between 60～70℃, the pH value between 8～9, and the NiSO4·6H2O concentration 1～2g/L. The deposition rate will be accelerated with the increasing of temperature, pH value and concentration of nickel ions. The deposit was Cu-Ni alloy with face-center cubic configuration without obvious crystal face preferred orientation, which copper and nickel mass percentage were 87.70% and 12.30%.Influence of temperature, pH value and the concentration of nickel ion on oxidation of sodium hypophosphite and reducing of copper ion were explored by liner sweep voltametry. The results showed that higher bath temperature accelerated both of the electrodic process; while the increasing pH value only promoted the oxidation of sodium hypophosphite but blocked the reducing of copper ion; the nickel ions not only intensively catalyzed the hypophosphite oxidation, but also codeposited with the copper ion to form the Cu-Ni alloy. With regard to its catalytic activity, this alloy enabled the continuation of the electroless copper plating reaction. We made a confirmation that the speed determinate step in this system was the oxidation of sodium hypophosphite. The electrochemical results were consistent with the deposition rate experiments.2. Influence of additives on electroless copper plating2,2ˊ-dipyridine, sodium benzene sulphinate and the methyl orange were effective additives on electroless copper plating using sodium hypophosphite as reducing agent. Their effects on deposition rate, surface morphology, deposit structure, the anodic and cathodal polarization processes of electrolyte were explored. The results showed that electrolyte was stable and the deposit appearance was bright when additives were added to the solution. 2,2ˊ-dipyridine slower the deposition rate; sodium benzene sulphinate and the methyl orange both accelerated the plating rate at a certain concentration while slower the deposition rate at high concentration.Results of liner sweep voltametry indicated that the 2,2ˊ-dipyridine blocked the oxidation of sodium hypophosphite; while a certain amount of sodium benzene sulphinate and the methyl orange promoted the oxidation process. The cathodal process was relatively complex: the present of 2,2ˊ-dipyridine made the reducing peak potential of copper ions moved to negative value compared to no additive in the solution and the current peak increased; sodium benzene sulphinate would promote the reducing of copper ions at low concentration while baffled it at high concentration; the reducing peak potential shifted to a positive value and the peak current reduced when the methyl orange concentration increased. The electrochemical results were inosculated with the experiments of deposition rate. SEM experiment displayed that 2,2ˊ-dipyridine affected the growth of the particulate, and their shape changed from prick to agglomerate, and the surface became denser. Sodium benzene sulphinate and methyl orange had less influence on the deposit morphology. Especially, mixture of two additives had a better effect on the surface morphology compared to single additive. The combination of 2,2ˊ-dipyridine and sodium benzene sulphinate possessed the best effect, and the deposit displayed bright appearance.EDS results showed that additive in the electrolyte redounded to the copper aggradations, and copper percentage in the alloy increased. XRD analysis indicated that the layers were still Cu-Ni alloy with face-center cubic configuration without obvious crystal face preferred orientation, and the concentration of Cu2O was very low.3. Compared with the copper deposit using formaldehyde as reducing agentBased on the contrastive experiments, we found that each technology possessed the advantages and the electrolyte using sodium hypophosphite as reducing agent was much more stable than that using formaldehyde as reducing agent. Electrolyte containing sodium hypophosphite didn’t decompose even after seven metal cycles, while the electrolyte of formaldehyde broke up only after three cycles. Besides, the deposition rate of sodium hypophosphite was higher than formaldehyde’s.SEM results indicated that the deposit particulate was very small and dense when using formaldehyde as reductant, and the deposit of sodium hypophosphite was agglomerate. The XPS result indicated the copper and nickel element existed in the deposit as metal state, and the mass concentration of phosphorus was less than 0.05%. In the solution containing 2,2ˊ-dipyridine the mass percentage of copper was 93.90% in the deposit using sodium hypophosphite as reducing agent, and the rest 6.10% was metal nickel. Because of the existence of nickel metal, the resistance, tensile strength and ductibility of formaldehyde’s deposit were better than that of sodium hypophosphite. Therefore, the deposit using sodium hypophosphite as reductant was more suitable for the industries which needed a relatively lower requirement on conductance.4. Mechanism of nickel ions in electroless cooper platingIt was very necessary to add the re-active agent of nickel ions in order to keep the self-catalysis reaction when using sodium hypophosphite as reducing agent, due to the catalysis of copper was very low to hypophosphite. The nickel ions were reduced to nickel metal to form Cu-Ni alloy so as to catalyze the oxidation of hypophosphite, and the alloy could keep the self-catalysis reaction. The catalysis of pure nickel was stronger than that of Cu-Ni alloy.A new absorb peak was detected in situ FTIR spectroscopy experiment, referred to many reference; we speculated it was the intermediate HPO2-ads. Besides, there was a prepositive electrode reaction in the oxidation process of hypophosphite, which created HPO2-ads and H ads. The mechanism of nickel ions was illuminated and the theoretical model of the electroless copper plating using sodium hypophosphite as reducing agent was established based on the experiments.更多还原