镀层工艺和尘土介电特性对电化学迁移的影响

发布时间：2018-04-21 02:00

本文选题：电化学迁移 + 电镀银　；参考：《北京邮电大学》2015年硕士论文

【摘要】：大规模集成电路的发展,使得电子元件日益趋于小型化和高密度。PCB导线间、焊点间以及PCB连接器之间的间距越发变小,这就使其间发生电化学迁移的概率大大增加,由此带来的电路板短路等问题逐渐引发人们的关注。在电子元器件内部,PCB和与之相配合的连接器往往采用不同的镀层工艺,因而发生电化学迁移的失效机理和寿命不尽相同。此外,在实际工作环境中,尘土会改变诱发电化学迁移的主要因素,也会造成电化学迁移失效机理和寿命的变化。本课题主要从镀层工艺及尘土介电特性两方面对电化学迁移的影响进行研究。一方面,通过水滴实验、迁移产物成分测试和极化测试实验,研究化学镀银与电镀银工艺的不同迁移机理及镀银层厚度、中间镀镍层对电化学迁移失效寿命的影响程度和作用机理。另一方面,通过有限元仿真分析,研究尘土的介电常数及带电性对均匀电场的影响,并进一步通过加速实验研究其对电化学迁移的影响。研究表明,电镀银层微孔率高、而化学镀银层侧面的底层金属材料易暴露。在镀层缺陷处会首先发生原电池腐蚀而使迁移物质变成底层金属铜,镀层缺陷越多,则迁移金属中银的含量越少,失效时间越长。当银镀层厚度增加时,迁移金属中银的含量会增加,使得失效寿命也减小。有中间镍层时,在镀层缺陷处发生原电池腐蚀使得迁移物质变成镍和铜,也延缓了电化学迁移失效。通过有限元静电场分析得出,尘土介电常数和带电荷量对均匀电场分布产生影响,使得在尘土上、下端出现两个强电场区,而尘土内部场强最小。介电常数的影响远高于带电量。最后通过加速电化学迁移实验证明了在有尘土污染的情况下,晶枝总是沿着电势变化梯度最大的方向生长,生长路径表现出不同程度的弯曲,从而延长了电化学迁移的路径和失效时间。
[Abstract]:With the development of large scale integrated circuits, electronic components tend to be miniaturized, and the distance between solder joints and PCB connectors becomes smaller and smaller, which increases the probability of electrochemical migration. As a result, the circuit board short-circuit and other problems gradually aroused the attention of people. Different coating processes are often used in PCB and connectors in electronic components, so the failure mechanism and lifetime of electrochemical migration are different. In addition, in the actual working environment, the dust will change the main factors that induce the electrochemical migration, and will also cause the change of the failure mechanism and lifetime of the electrochemical migration. In this paper, the effects of coating technology and dielectric properties of dust on electrochemical migration were studied. On the one hand, the different migration mechanism and thickness of electroless silver plating and silver plating were studied by water drop test, migration product composition test and polarization test. The effect of intermediate nickel coating on the failure life of electrochemical migration and its mechanism. On the other hand, the influence of the dielectric constant and charge of dust on the uniform electric field is studied by finite element simulation analysis, and the effect on the electrochemical transport is further studied by accelerated experiments. The results show that the micropore ratio of silver plating layer is high, but the bottom metal material on the side of electroless silver plating layer is easy to be exposed. The corrosion of the primary cell will first occur at the defects of the coating and the migrating material will become the metal copper. The more defects in the coating, the less the silver content in the migrated metal and the longer the failure time. When the thickness of silver coating increases, the content of silver in the migrated metal increases and the failure life decreases. When there is an intermediate nickel layer, the primary cell corrosion occurs at the defect of the coating, which results in the change of the migrating material into nickel and copper, which also delays the electrochemical migration failure. Through the finite element electrostatic field analysis, it is found that the dielectric constant and charge amount of dust have an effect on the uniform electric field distribution, which makes two strong electric fields appear on the dust and the lower end of the dust, while the internal field intensity of the dust is the smallest. The effect of dielectric constant is much higher than that of band. Finally, the accelerated electrochemical migration experiments show that in the presence of dust pollution, the dendrites always grow in the direction of the maximum potential gradient, and the growth path shows varying degrees of bending. Thus, the electrochemical migration path and failure time are prolonged.
【学位授予单位】：北京邮电大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN47

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