[目的]研究化学镀镍钯金(ENEPIG)制程中Cu/Ni界面空洞的形成机理，以及钯活化对薄镍钯金板焊接性能的影响。[方法]对比了氯化钯与硫酸钯两种活化体系在不同钯离子浓度和活化时间下对Cu/Ni界面空洞的影响；采用透射电子显微镜(TEM)分析Cu/Ni界面空洞的微观结构与元素分布；通过三维X射线显微镜、扫描电子显微镜(SEM)及能谱仪(EDS)对焊接后样品的截面形貌与元素组成进行表征，结合焊接过程气泡产生机理，探讨界面空洞与焊接空洞的关联。[结果]两种活化体系下，界面空洞的数量和尺寸均随钯离子浓度和活化时间的增加而增大，但氯化钯体系较硫酸钯体系产生更多、更大的Cu/Ni界面空洞，空洞长径可超过1μm。TEM分析表明，氯化钯体系产生的空洞内存在约20 nm厚的局部化学镀镍层，导致空洞封堵并残留水汽。焊接后，氯化钯体系板件焊点内部出现明显焊接空洞，主要分布于金属间化合物(IMC)层上方，而IMC层下方存在大量Cu/Ni界面空洞。硫酸钯体系板件未见明显焊接空洞。[结论]氯化钯体系因钯活性高、氯离子具渗透性，易在钯活化阶段形成更严重的Cu/Ni界面空洞，空洞内残留的水汽在焊接过程中汽化膨胀，是导致薄镍ENEPIG板件形成焊接空洞的关键因素。选用硫酸钯活化体系可有效降低界面空洞程度，提升焊接可靠性。本研究为有机封装基板薄镍钯金制程中活化体系的选择与工艺优化提供了理论依据。

[Objective] To study the formation mechanism of Cu/Ni interfacial voids during electroless nickel/palladium/gold plating(ENEPIG) process and the effect of palladium activation on solderability of thin-nickel ENEPIG boards. [Method] The effects of two activation systems, i.e. palladium chloride and palladium sulfate, on Cu/Ni interfacial voids were compared under different palladium ion concentrations and activation time. Transmission electron microscopy(TEM) was employed to analyze the microstructure and elemental distribution of Cu/Ni interfacial voids. The crosssectional morphology and elemental composition of soldered samples were characterized using three-dimensional X-ray microscopy, scanning electron microscopy(SEM), and energy-dispersive spectroscopy(EDS). The relationship between interfacial voids and soldering voids was explored in combination with the mechanism of gas evolution during soldering. [Result] For both activation systems, the number and size of interfacial voids increased with the increasing palladium ion concentration and activation time. However, the palladium chloride system produced more and larger Cu/Ni interfacial voids than the palladium sulfate system, with void lengths exceeding 1 μm. TEM analysis revealed that voids generated by the palladium chloride system has a localized electroless nickel layer approximately 20 nm thick, leading to void sealing and residual moisture. After soldering, obvious soldering voids were observed inside the solder joints of boards treated with the palladium chloride system, primarily located above the intermetallic compound(IMC) layer, while a large number of Cu/Ni interfacial voids existed beneath the IMC layer. No significant soldering voids were found in boards treated with the palladium sulfate system. [Conclusion] Owing to the high activity of palladium and the permeability of chloride ions, the palladium chloride system is prone to forming severe Cu/Ni interfacial voids during the activation stage. Residual moisture trapped in these voids expands rapidly during soldering, which is a key factor leading to soldering voids in thin-nickel ENEPIG boards. The use of a palladium sulfate activation system can effectively reduce the extent of interfacial voids and improve soldering reliability. This study provides a theoretical basis for the selection and process optimization of activation systems in thin-nickel ENEPIG manufacturing for organic packaging substrates.