近年來隨著CPU速度和功能的迅速增加，為了容納更高密度的I/O（Input/Output）數目在晶片上，每個銲料凸塊所承受的電流密度因此快速增加。截至2011年為止，每個銲料凸點的規模已經縮小至接近1~5微米的規模，而且逐年縮小的速度越來越快，因此在每個銲料凸塊上的電流密度將大幅增加，甚至超過10^6 × A/cm2以上。隨之而來產生熱和電遷移（EM）的效應，將對銲點的可靠度造成嚴峻考驗，因此如何選擇適當的表面覆晶金屬墊層是未來應用無鉛焊料的可靠度最主要的關注課題。
本篇論文中，我們藉由實驗結果嘗試找出鎳及鎳合金在銲點凸塊中的界面反應動力學機制。經由實驗的過程與反應動力學機制的推導，可以定義出鎳基金屬銲料凸塊中介金屬化合物成長的動力控制理論。在第三章中，我們成功的藉由液相電化學磊晶(LPEE)的方式製備出具優選方向的銅-錫合金化合物(Cu6Sn5)，經由實驗觀察並計算出鎳金屬原子在不同溫度下於銅錫合金化合物中的擴散係數，由擴散係數結果進一步計算，獲得不同鎳含量下的擴散活化能是隨著銅錫合金化合物的鎳含量增加而減少。經由進一步探討擴散係數與擴散活化能的變化與鎳含量的關係，我們發現兩者隨著銅錫合金化合物中鎳含量增加而減少的原因，主要與合金化合物的結晶相結構發生轉變的動力學機制有關。在第四章裡，我們探討了使用Fe-42Ni合金的LED導線架在浸潤(dipping)錫鉛(SnPb)銲料製程中發生的銲料脫銲(dewetting)機制，藉由脫銲機制理論推導出利用錫鉛銲料中加入微量的鎳以減緩金屬墊層與錫鉛銲料的界面反應，並探討延緩介金屬層成長過程的機制。
最後，在第五章裡我們依據前面各章節討論的機制，歸納出鎳基合金墊層在銲點凸塊中控制介金屬層生成的動力學成長機制，此研究結果可提供有效解決覆晶技術中焊點可靠度的課題參考。As the speed and functionality of CPUs rapidly increases in the past decades, a high density of flip-chip I/O (input/output) counts is required. By 2011, the size of flip-chip solder bumps had been approaching 1~5 µm and is expected to shrink faster than ever before, hence the current density in the flip-chip solder bumps will dramatically increase to over 10^6 A/cm2. Thermal and electron-migration (EM) effects bring the proper selection of the surface finishes for the soldering pads as one of the major concerns related to Pb-free solder joint reliability.
In this thesis, we try to find out the interfacial reaction mechanism of Ni and Ni alloys in the solder joints by experiments. From the experimental results we are able to reveal the reaction kinetics that controls the intermetallics growth in the Ni-based solder bump pads. In Chapter 3, we describe the fabrication of preferred- orientation Cu6Sn5 crystals prepared by liquid phase electroepitaxy (LPEE). Also, we observed that the Ni interdiffusion coefficients in the Cu6Sn5 crystals at different annealing temperatures, and then yield the activation energy for Ni diffusion in the Cu6Sn5 crystals at different Ni content. It is found that as Ni diffuses into the ternary (Cu,Ni)6Sn5 compound phase, the activation energy of the Ni interdiffusion decreases with increasing Ni content because of the transformation of compound phase induced by Ni diffusion. The Ni interdiffusion mechanism and activation energy in binary Cu6Sn5 compound layer are accordingly dependent on the transformation of crystal structure in the host compounds. In Chapter 4, we discussed the mechanism of dewetting on Ag/Cu coated light emitting diode lead frames (LED LFs) (Fe-42Ni alloy) with SnPb immersion process. Then we discuss the mechanism that retards dewetting by Ni additives in the SnPb solder to slow down the soldering reaction and ease the ripening process.
Finally in Chapter 5, based on the experimental results, we summarize the controlled reaction kinetics of the intermetallics on the Ni-based solder bump pads and propose a valuable reference to solve the reliability problems of the solder joints in flip-chip technology.Abstract in Chinese….....................................i Abstract.................................................iii List of Figures..................................................vii List of Tables....................................................xi
Chapter 1 Introduction...............................................1
1-1 UBM with Ni layer in flip-chip solder joints .........1
1-2 Electromigration in flip-chip solder joint ...........7
1-3 Effect of Ni introduced into solder bump .…………….10
Chapter 2 Motivation ...............................................19
Chapter 3 Ni interdiffusion in Cu6Sn5....................23
3-1 Experimental ........................................23
3-2 Ni interdiffusion coefficient and activation energy in Cu6Sn5....................................................27
3-2-1 Ni interdiffusion coefficient.....................29
3-2-2 Kinetics of Ni interdiffusion.....................37
3-3 Summary .............................................43
Chapter 4 Dewetting Retardation on Ag/Cu Coated
Light Emitting Diode Lead Frames
during the Solder Immersion Process............44
4-1 Introduction ........................................44
4-2 Experimental ........................................47
4-3 SnPb solder immersion of Ag/Cu coating...............49
4-3-1 Spalling of intermetallic compounds...............49
4-3-2 Mechanisms for dewetting retardation..............57
4-4 Summary..............................................61
Chapter 5 Conclusion.....................................62
References ...............................................64
Vita and Publication List.................................6
