電遷移對銅原子在熔融Sn3.5Ag無鉛銲料中擴散行爲之影響

The Effect of Applied Electron Current on the Cu Diffusion in Molten Sn3.5Ag Solder

10.6409/JMSE.200612.0206

張建偉(C.W. Chang)；黃建融(J.R. Huang)；高振宏(C.R. Kao)

電遷移 ； Sn3.5Ag ； Lead-free solder ； electromigration ； Sn3.5Ag ； lead-free solder

材料科學與工程

38卷4期（2006 / 12 / 01）

206 - 212

繁體中文

在以往銲錫的電遷移研究中，探討對象都是固態銲錫，而液態銲錫是未被探討的。本實驗利用了微量毛細管設計了一個Cu/Sn/Cu結構，同時探討電遷移對液態無鉛銲錫Sn-3.5Ag中Cu溶解現象的影響。我們利用維氏硬度計在Cu導線上打入marker以計算Cu導線溶解量，此marker與Cu導線頂端距離300 μm。在實驗中發現，試片於240°C下，施予電流密度6.3×10^3 A/平方公分，會造成陰極端Cu導線相當嚴重的Cu溶解現象，通電時間達3 hr約有125 μm Cu導線溶解，並於陽極端生成大量IMC；而在未通電的情況下，試片於255°C反應3 hr, Cu導線溶解約8.5 μm；這表示電子流、熱效應對於Cu溶解現象有著交互的影響，本實驗對此現象作深入的探討，此現象有助於flip-chip銲點分析，進而對其毀壞機制的探討。這告訴我們，flip-chip銲點的毀壞，很有可能因電遷移造成銲點局部溶解，進而導致嚴重的Cu溶解現象，最後整個銲點失效。

The high local temperature in flip-chip solder joints of microprocessors has raised concerns that the solder, a low melting temperature alloy, might locally liquefy and consequently cause failure of the microprocessors. This article reports a highly interesting electromigration behavior when the solder is in the molten state. A 6.3×10^3 A/cm^2 electron current was applied to molten Sn3.5Ag solder at 255°C through two Cu electrodes. The high current density caused the rapid dissolution of the Cu cathode. The dissolved Cu atoms were driven by electrons to the anode side and precipitated out as a thick and sometimes continuous layer of Cu6Sn5. The applied current caused the dissolution rate of the Cu cathode to increase by one order of magnitude. An equation for the minimum chemical potential gradient that is needed to balance the electromigration flux is derived.