現今電子產品以不斷追求輕、薄、短、小、高功能為目標，隨著三維度積體電路封裝與覆晶技術的發展, 電子元件與接點尺寸不斷地縮小，通過電子接點的電流密度相對地增加，使得電流效應對銲料的影響更加顯著。在本研究中我們選擇了錫鉛與鉍鎳兩種合金銲料系統，去探討文獻中發現的錫鉛合金在電流作用下的錫相於富鉛相過飽和現象與鉍鎳系統三明治反應偶界面反應的非極性效應(non-polarity effect)。本研究以理論計算的方法使用第一原理量子力學計算輔助CALPHAD熱力學模擬，探討電流作用下錫鉛與鉍鎳兩種二元系統的相平衡變行為。在錫鉛系統中，本研究發現電流密度須大於臨界值約3x104 A/cm2，相平衡才會有明顯的改變，而此改變使得在電流作用下的錫相在富鉛相之平衡溶解度增加及鉛相在富錫相之平衡溶解度減少，此模擬結果吻合並解釋了文獻中發現的錫相於富鉛相過飽和現象。在鉍鎳系統中，文獻中觀察到鎳鉍界面反應的生成相為NiBi3，在電流效應下鉍鎳系統的相平衡改變，造成主要擴散物質鉍元素在此界面反應中的化學勢能差在NiBi3相中變大，也就是說鉍元素擴散的驅動力增加了，而此驅動力增加造成NiBi3相生成的速率增加，這個與電流方向無關的改變或許就是造成文獻中所提出的鉍鎳系統三明治反應偶界面反應實驗中所觀察到的非極性效應現象發生的原因之一。此研究能夠開啟學術界新的研究方法去探討並深入了解更多無鉛銲料系統在電流作用下之界面反應與相平衡之改變。

The effects of electric currents on metallic materials, such as the Joule heating and electromigration, crucially affect the reliability of electronic products. With the developments of the advanced packaging methods, e.g. the 3D IC and flip-chip packaging, the current densities applied in modern devices are continuously increased. Thus, the impacts of these electric current-induced effects are more and more pronounced and crucial to the reliability of electronic products. In the study, we choose two systems, Pb-Sn binary alloys and Bi-Ni binary couples, synthesize what is the mechanism of the Sn supersaturation in Pb-rich matrix of Pb-Sn binary system and the non-polarity effect of sandwich reaction couples of Bi-Ni binary system under current stressing. the phase stability of Pb-Sn and Bi-Ni alloys under current stressing are theoretically investigated by using the ab initio-aided CALPHAD approach. For Pb-Sn binary system, we found that the phase equilibria of the Pb-Sn alloys would be changed by electric current stressing, when the current density is higher than the critical value around 3 x104 A/cm2. As the result, for a Pb-Sn alloy, which is composed of the Pb-rich FCC and the Sn-rich BCT phases, under current stressing with a sufficient high current density, the solubility of Sn in the FCC phase would increase, while that of Pb in the BCT phase would decrease. These would lead to the supersaturation of Sn in the FCC phase and precipitation of the FCC phase from the BCT phase under current stressing. For Bi-Ni binary system, we found that the phase stabilities of the Bi-Ni phases would be changed by electric currents. As the only intermetallic compound formed at the Ni/Bi couples is the NiBi3 phase, the meta-stabilities between Ni, NiBi3, and Bi phases were calculated. The chemical potential gradient of the dominant diffusion specie, Bi, in the NiBi3 reaction layer, i.e. the driving force for the NiBi3 layer growth, was increased under current stressing. Therefore, the “non-polarity effect” is likely caused by the larger chemical potential gradients under current stressing, which is independent of the direction of electron flows. We hope that this study opens a door to the fundamental understanding on the electric current effect upon interfacial reactions and the phase stability change, which may lead to further researches on Pb-free solder joints with electric currents applied.

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