盐雾对喷锡和化金印制电路板腐蚀行为的影响

采用交流阻抗谱研究热风整平无铅喷锡处理印制电路板（PCB-HASL）和无电镀镍金电路板（PCB-ENIG）在盐雾环境下的电化学腐蚀行为,并结合体式学显微镜、扫描电镜、X射线能谱等手段分析两种不同表面处理工艺电路板的腐蚀产物形貌、组成和镀层失效机制.结果表明：盐雾环境下,PCB-HASL和PCB-ENIG均发生严重腐蚀;镀Sn层开始发生局部腐蚀,随后几乎整个表面都发生腐蚀,出现类似均匀腐蚀的现象,镀金板主要发生微孔腐蚀.在PCB-HASL腐蚀过程中,Cl^-的侵蚀作用促进Sn层的腐蚀,后来由于逐渐形成大量的覆盖在镀层表面的腐蚀产物,使得腐蚀速率降低;而在PCB-ENIG腐蚀过程中,微孔处形成含Cl^-电解质薄液层,Ni与Au构成腐蚀电偶,从而加速Ni的腐蚀,最终使Cu基底裸露,造成电路板失效.

Effect of salt spray environment on the corrosion behavior of PCB-HASL and PCB-ENIG

The corrosion behavior of hot air solder level printed circuit boards(PCB-HASL) and electroless nickel immersion gold printed circuit boards(PCB-ENIG) in salt spray test was studied by electrochemical impedance spectroscopy. The corrosion product morphology,composition and coating failure mechanism were observed by stereo microscopy,scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results show that PCB-HASL and PCB-ENIG suffer severe corrosion in high salt spray environment. Localized corrosion occurs first in the Sn plating layer,and then almost entire surface corrosion occurs,similar to uniform corrosion. PCB-ENIG mainly generates microporous corrosion. In the PCB-HASL corrosion process,Cl- promotes the corrosion of the Sn layer,then a large amount of corrosion product gradually forms and covers the Sn surface,it makes the corrosion rate reduce.In the PCB-ENIG corrosion process,a thin liquid layer containing Cl- electrolyte forms in micropores,and galvanic coupling between gold and nickel constitutes,which accelerates Ni corrosion. The Cu base directly exposes in the adverse environment after Ni suffers serious corrosion,finally leading to electronic component failure.