霉菌对化学浸银处理印制电路板腐蚀行为影响

 采用扫描Kelvin探针测试技术研究了化学浸银处理(ImAg)印制电路板(PCB)在霉菌作用下的腐蚀行为,同时通过体视学显微镜、扫描电镜结合能谱分析对PCB的腐蚀和霉菌生长情况进行了观察和分析。电镜和能谱结果表明,在湿热环境下,霉菌可以在浸银处理PCB表面附着并生长繁殖,黑曲霉菌表现出更高活性,具有优先生长特性。霉菌的生长代谢作用促进浸银处理PCB的局部(微孔)腐蚀,出现漏铜现象。结合扫描Kelvin探针结果分析表明,随着时间延长,PCB表面电位整体升高,菌落区域金属作为阳极优先发生腐蚀,腐蚀产物面积逐渐扩大。虽然腐蚀反应中生成了少量带毒性的Ag⁺,对孢子的生长代谢有一定的抑制作用,但是这并没有阻止PCB-ImAg霉菌腐蚀的发生。浸银处理工艺不能完全抑制PCB表面霉菌的生长,不能完全满足PCB防霉菌的要求。

Effect of Mold on Corrosion Behavior of Immersion Silver Finished Printed Circuit Board

The corrosion behavior of Immersion Silver (ImAg) finished Printed Circuit Board (PCB) in mold environment was studied using Scanning Kelvin Probe (SKP) technology. The mold growth behavior was observed by using stereo microscope and SEM, and the corrosion product was analyzed by EDS. Based on the results of SEM and EDS, mold could grow on the surface of PCB-ImAg specimens under hygrothermal condition, Aspergillus niger shows higher activity and has a priority growth characteristics. The activity of mold is a promoter in the localized (pore) corrosion process and the leakage of copper of PCB-ImAg covered by mold. SKP results show that the PCB surface potential as a whole increases with time. And the colony region of PCB occurs preferentially corrosion as the anode; then the corrosion product area enlarges gradually. Although the corrosion reaction generates small amounts of toxic Ag⁺, which inhibits the growth and metabolism of the spores, this do not prevent the corrosion of PCB-ImAg caused by mold from occurrence. ImAg finished technology is unable to completely inhibit the growth of mold on PCB surface, which could not fully meet the requirement of PCB anti-mildew.