微量添加鈦、錳、鋅元素對SnAg銲點之效應-晶粒細化與界面反應

Abstract

SnAg、SnAgCu銲料目前廣為封裝界所採用，然而，其抗電遷移能力之不足仍尚待改進。由於格隙型擴散原子(銅或鎳)沿Sn晶格中的c軸方向擴散速率較高，因此銲點通電時若是Sn晶格之c軸方向與電子流方向平行時，會導致位於陰極端的Cu或Ni加速擴散，造成介金屬(IMCs)與金屬墊層快速消耗之電遷移失效更容易發生。且目前文獻中觀察到富錫銲點常被數個Sn的大晶粒或甚至是單一巨大的Sn晶粒所佔滿，在單一銲點錫之晶格取向數目不足下，由Sn晶粒取向不良所導致之位於陰極端的Cu或Ni金屬墊層與IMCs加速擴散消耗之電遷移破壞發生之機率相當高。因此本研究希望將利用微量添加元素(Mn, Ti, Zn)以細緻化富錫銲料的顯微組織，使單一銲點具有較多錫之晶格取向性，如此便有機會提升銲點抗電遷移之能力。 另一方面，SnAg、SnAgCu富錫銲料仍具有改進空間。在使用銅基板之系統中，熱儲存時效固態反應時，Cu3Sn的成長常伴隨著Kirkendall voids的生成，造成銲點可靠度之問題。故本研究亦針對微量添加後對銲點界面反應以及介金屬生長之影響與效應做一系列之探討，希望能找出有利於增進銲點界面強度之微量添加元素。 Sn2.4Ag-X (X=none, 0.2Ti, 0.2Mn, 0.4Zn, 0.2Ti0.4Zn) 銲料為本實驗所採用，實驗係利用迴銲製程將銲料與Cu基板接合後，在150℃下進行熱儲存。試片之橫截面以具Cross-Polarizers 之光學顯微鏡、Electron Backscatter Diffraction (EBSD)、掃描式電子顯微鏡 (SEM)、能量散佈光譜儀 (EDS)、場發式掃描式電子顯微鏡 (FE-SEM)、場發射式電子微探儀 (FE-EPMA)，進行仔細之研究與觀察。不同微量添加元素對銲球晶粒微觀組織與銲點界面反應之效應與影響將會進行系統性的深入探討。

SnAg and SnAgCu alloys are widely used in electronic packaging industry. Recently, Sn’s anisotropic properties have been widely reported. Several researchers reported that the interstitial diffusions of Cu and Ni along c-axis of Sn grains are much faster than along a-axis. Electromigration degradation via IMCs dissolutions and metallization layer consumption will be strongly facilitated if electron flow parallels to c-axis of Sn grain. One of the main objectives of this research is to refine the microstructure of solder joints by minor Ti, Mn, Zn additions. With finer Sn grains and random grain orientations, the electromigration-resistance might be enhanced. Interfacial integrity of SnAg and SnAgCu tin rich solder joints still needs to be improved, too. Growth of Cu3Sn has been linked with Kirkendall voids formation, which is one of the main reasons causing deterioration of tin rich solder joints with Cu substrate. Therefore, the other objective of this research is to improve the interfacial integrity by minor Ti, Mn, Zn additions. Interfacial reactions are studied in order to clarify the effects of different minor addition elements on growths of intermetallic compounds. Sn2.4Ag-X (X=none, 0.2Ti, 0.2Mn, 0.4Zn, 0.2Ti0.4Zn) solder balls were bonded with Cu pads by reflow process, and then thermal aged at 150℃. Cross-sections of samples were meticulously observed by Optical Microscopy with Cross-Polarizers, Electron Backscatter Diffraction (EBSD), Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS), Field Emission Scanning Electron Microscope (FE-SEM), Field Emission Electron Probe Micro Analyzer (FE-EPMA). The effects of different minor elements will be discussed.