化学镀锡中光亮剂PPS、咪唑和HD在Sn表面的吸附作用实验与模拟研究

目的 研究以丙烷磺酸吡啶嗡盐（PPS）、咪唑、己炔二醇（HD）为代表的三大类光亮剂，在化学镀锡过程中改善镀锡层表观形貌和影响镀速的作用机理。方法 采用电化学阴极极化法，研究化学镀锡过程中光亮剂分子对镀锡液在沉锡过程中对沉锡峰电位变化的影响，运用Forcite模块中的 COMPASS力场进行分子动力学计算，研究光亮剂分子在 Sn层表面吸附过程的能量变化。结果 阴极极化结果表明，光亮剂的加入会使沉锡峰电位负移，该过电位导致晶核水平增长速度大于垂直生长速度，从而起到整平作用，并在一定程度上抑制晶须的形成。分子动力学计算结果显示，PPS、咪唑、HD均有自发吸附到Sn层表面的趋势，且在Sn(111)面的吸附能分别为?445.338、?9.84、?22.651 kcal/mol，表明三种光亮剂分子均易吸附在Sn层表面（吸附能数据越低，越容易吸附在锡层表面），从而在一定程度上抑制锡层的增长。结论 光亮剂与Sn作用的吸附能，与其在化学镀过程中对Sn层表观形貌的改善和镀速减少有正相关作用。该研究为化学镀锡过程中光亮剂的选择提供了理论基础。

Adsorb-Ability Experimental and Simulation Study of PPS, Imidazole and HD on the Sn Surface in Electroless Tin Plating

The work aims to study the effect mechanism of improving tin coating apparent morphology and influencing deposition rate by adding propane sulfonic acid pyridine salt (PPS), imidazole, 3-hexyne-2,5-diol(HD) as representatives of three types of brighteners during the process of electroless tin. The effect of brighteners on the peak potential change of tin deposition in tin plating bath was studied by electrochemical cathode polarization method. The molecular mechanics calculation method was carried out by COMPASS force field in Forcite model to explore the adsorption process of brighteners on the surface of Sn layer and. From the results of cathodic polarization, the addition of brightener could make the peak potential of tin deposition negatively shift. The over-potential caused the horizontal growth rate of nuclei to be greater than that of the vertical growth rate, thus leveling the Sn layer and inhibiting the formation of whiskers to a certain extent. Molecular dynamics calculation results demonstrated that PPS, imidazole and HD had a tendency to be spontaneously adsorbed to the surface of the Sn layer and the adsorption energy of PPS, imidazole and HD in the Sn(111) surface were ?445.338 kcal/mol, ?9.84 kcal/mol and ?22.651 kcal/mol, respectively. The molecules of three brighteners were more likely to be adsorbed on the surface of the Sn layer, thereby inhibiting the growth of the Sn layer to some extent. The adsorption energy of brightener on Sn surface has a positive correlation with the improvement of Sn''s apparent morphology and reduction of plating rate during electroless plating and provides some theoretical basis for the selection of brightener.