本文選題：電化學遷移 + 電鍍銀�。� 參考：《北京郵電大學》2015年碩士論文

【摘要】：大規(guī)模集成電路的發(fā)展,使得電子元件日益趨于小型化和高密度。PCB導線間、焊點間以及PCB連接器之間的間距越發(fā)變小,這就使其間發(fā)生電化學遷移的概率大大增加,由此帶來的電路板短路等問題逐漸引發(fā)人們的關(guān)注。在電子元器件內(nèi)部,PCB和與之相配合的連接器往往采用不同的鍍層工藝,因而發(fā)生電化學遷移的失效機理和壽命不盡相同。此外,在實際工作環(huán)境中,塵土會改變誘發(fā)電化學遷移的主要因素,也會造成電化學遷移失效機理和壽命的變化。 本課題主要從鍍層工藝及塵土介電特性兩方面對電化學遷移的影響進行研究。一方面,通過水滴實驗、遷移產(chǎn)物成分測試和極化測試實驗,研究化學鍍銀與電鍍銀工藝的不同遷移機理及鍍銀層厚度、中間鍍鎳層對電化學遷移失效壽命的影響程度和作用機理。另一方面,通過有限元仿真分析,研究塵土的介電常數(shù)及帶電性對均勻電場的影響,并進一步通過加速實驗研究其對電化學遷移的影響。 研究表明,電鍍銀層微孔率高、而化學鍍銀層側(cè)面的底層金屬材料易暴露。在鍍層缺陷處會首先發(fā)生原電池腐蝕而使遷移物質(zhì)變成底層金屬銅,鍍層缺陷越多,則遷移金屬中銀的含量越少,失效時間越長。當銀鍍層厚度增加時,遷移金屬中銀的含量會增加,使得失效壽命也減小。有中間鎳層時,在鍍層缺陷處發(fā)生原電池腐蝕使得遷移物質(zhì)變成鎳和銅,也延緩了電化學遷移失效。 通過有限元靜電場分析得出,塵土介電常數(shù)和帶電荷量對均勻電場分布產(chǎn)生影響,使得在塵土上、下端出現(xiàn)兩個強電場區(qū),而塵土內(nèi)部場強最小。介電常數(shù)的影響遠高于帶電量。最后通過加速電化學遷移實驗證明了在有塵土污染的情況下,晶枝總是沿著電勢變化梯度最大的方向生長,生長路徑表現(xiàn)出不同程度的彎曲,從而延長了電化學遷移的路徑和失效時間。
[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.
【學位授予單位】：北京郵電大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TN47

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