Meanwhile, fundamental principles about electroless tin plating by reducing agent and disproportionation reaction were explained . function of every component in the bath was explained that complexing agent can effectively change the potential of copper and tin, and accelerate the beginning of replacement reaction favorably; reducing agent can increase the rate of chemical reaction and has the effect of promoting reaction dynamics too; antioxidant can effectively prevent sn2 + in the bath from being oxidated; additive agent a can improve the stability of the bath; additive agent b has such effects as refining and brightening for the tin deposits, and it enlarges the range of brightening section; additive agent c used as leveling agent can not only make the depostis level off, but also improve the dispersive ability of the bath; surface-active agent can solve bubble problem which gathered on the surface of the deposits, and improve the surface quality of the deposits and the bath stability 阐述了镀液中各组分的作用：络合剂能有效地改变铜、锡的电位，促使初期的置换反应顺利进行；还原剂能加快化学反应速度，对反应动力学有积极的促进作用；抗氧化剂能有效地防止镀液中sn~(2+)的氧化；添加剂a能提高镀液的稳定性，添加剂b对镀层能有细化和光亮作用，扩大了镀层光亮区的范围；添加剂c作为平滑剂，不仅能增强镀层表面的平整性，而且能提高镀液的分散能力；表面活性剂较好地解决了化学镀过程中汽泡在镀件表面聚集的问题，提高了镀层的表面质量和镀液的稳定性。
