未來⾃動駕駛技術可以藉由先進駕駛輔助系統（ADAS）與遠端輔助中⼼（RAC）的協作來實現。相較3C 產品，⾞⽤晶⽚的可靠度要求將變得更嚴格，以確保乘客的⽣命安全，因之，封裝中銲點的機械和熱循環可靠度將在⾞⽤電⼦中扮演關鍵⾓⾊。此外，對於遠端輔助中⼼內的伺服器，具有⾼輸⼊/輸出(I/O)密度和⼩封裝尺⼨的三維封裝(3D-IC)將是⾼效能晶⽚的不⼆選擇。本研究將以鎳作為核⼼技術出發，對銲點的微觀結構，晶體學性質和可靠度進⾏改質。
⾸先，本研究利⽤架構改質的⽅式解決三維封裝中的問題。藉由具備兩種不同銲料複合焊點，三維封裝中熱預算、翹曲和堆疊晶⽚過重的疑慮皆可以被改善。透過結合錫-銀-銅與錫-鉍銲料，成功於185℃的迴銲溫度，將銲點接合於銅基版上。鑑於錫-銀-銅銲球有較⾼的熔點，加熱時銲球局部將不會參與反應並維持固態，此固態區域能防⽌三維結構坍塌並進⼀步避免相鄰銲點間的橋接問題。
接著，為了提升⾞⽤晶⽚中銲點之機械可靠度，本研究將對銲料合⾦進⾏改質，以提升銲點的銲球剪切強度。結果顯⽰，透過選⽤0.1 %鎳(重量百分濃度)摻雜的錫-銀-銅銲球與鎳基板的材料系統，能有效細化銲點中的錫晶粒。由於晶相結構呈現隨機晶向，故此結構是由⼤量成核點所形成的細晶結構，⽽⾮樹枝狀結構。同時，鎳細化錫晶粒的機制也會⼀併探討。再者，相較於未摻雜的銲點，銲球推⼒測試也顯⽰鎳摻雜的銲點有更⾼的球剪切強度。
最後，研究⽬標為探討晶粒結構與熱循環試驗下銲點失效模式之間的關係。藉由改質無鍍鎳鈀浸⾦(ENEPIG)球下⾦屬(UBM)，具有超薄鎳鍍層之ENEPIG 能有效粗化Cu/Sn-Ag-Cu/ENEPIG 銲點中的錫晶粒。當ENEPIG 中鎳鍍層為0.26 微⽶時，破壞會沿著錫晶界發⽣。⽽若將鎳鍍層縮減⾄0.13 微⽶，由於銲點中的錫晶粒較⼤，將會在銲料中形成滑移帶。
總結來說，鎳展現出調變錫銲點中晶粒結構的能⼒。針對三維封裝與銲點可靠度所⾯臨之重要議題，本研究也透過三種改質⽅法提出了可能的解決⽅案，期望本研究之結果有助於⾃動駕駛技術之發展。

The autonomous technology can be achieved by the collaboration of Advanced Driver Assistance System (ADAS) on vehicle and Remote Assistance Center (RAC). Since the demands of reliability for automotive ICs are much higher for safe assurance, mechanical and thermal cycling reliabilities of solder joints are crucial for automotive electronics. By contrast, 3D-IC with high Input/Output (I/O) density and small package size is an appropriate choice for high-performance chips for servers of RAC. In this study, Ni is the core technology used to modify the microstructure, crystallographic properties and reliability of solder joint.
Firstly, architecture modification was employed to solve issues in 3D-IC packaging. The hybrid solder joint comprises of two different solders, which show potential to overcome the thermal budget, warpage and overweight concerns in 3D-IC packages. Via using Sn-Ag-Cu and Sn-Bi solder, the joint can be fabricated on Cu pad by reflowing at a peak temperature 185℃. Due to relatively high melting point of Sn-Ag-Cu solder ball, a portion of solder ball retained solid. The solid portions could prevent the chip from collapsing and further inhibit the bridging between adjacent solder joints under reflowing.
To improve the mechanical reliability of solder joints for automotive IC, solder alloy modification was then adopted to enhance the ball shear strength. The results show that reflowing 0.1 wt.% (weight%) Ni doped Sn-3.0Ag-0.5Cu solder alloy on Ni-based pad could completely refine the Sn grains of solder joint. The fine Sn grains in random orientation implied that it was not dendrite structure but truly fine grain structure resulting from sufficient Sn nucleation sites in solder. The refinement mechanism was addressed and discussed in detail. Furthermore, Ni-doped solder joint show higher ball shear strength as compared to those of bare solder joints.
Lastly, the purpose of final goal is to investigate the correlation between the grain structure of assembled joints and the failure mode under thermal cycling test. Through UBM modification on Electroless Ni Electroless Pd Immersion Au (ENEPIG), the Sn grain of Cu/Sn-Ag-Cu/ENEPIG joint can be effectively coarsened by using ENEPIG UBM with ultrathin Ni deposit. For ENEPIG with 0.26 μm Ni, the degradation occurred along Sn grain boundaries. As Ni of ENEPIG was reduced to 0.13 μm, slip band formed in the solder because of relatively large grain.
In summary, Ni exhibits the capability to alter Sn grain structure in Sn-based solder joint. The results of this work through three modification approach demonstrate the promising solution for critical issues of 3D-IC package and solder joint reliabilities, which is believed to be beneficial for developing autonomous technology.

Chapter II Literature Review .................................................. 9
2.1 Microelectronic Packaging ........................................................ 9
2.2 Package Technology ................................................................. 11
2.2.1 Flip-Chip Technology .............................................................................. 11
2.2.2 Three-Dimensional Integrated Circuit (3D-IC) Technology .................. 13
2.3 Solder Bump ............................................................................. 15
2.3.1 Sn-Pb Solder ............................................................................................ 16
2.3.2 Pb-Free Solder ......................................................................................... 17
2.4 Under Bump Metallurgy (UBM) ............................................. 18
2.4.1 Cu-Based UBM ........................................................................................ 19
2.4.2 Ni-Based UBM ......................................................................................... 20
2.5 Metallurgical Reaction in Pb-free Solder Joint ...................... 22
2.5.1 Metallurgical Reactions between Pb-free Solder and Cu-based UBM .. 22
2.5.2 Metallurgical Reactions between Pb-free Solder and Ni-based UBM ... 23
2.6 Crystallographic Structure of β-Sn in Pb-Free Solder Joints 23
2.6.1 Role of Sn grain structure in solder joints .............................................. 23
2.6.2 Correlation between Sn grain structure and mechanical strength in
solder joints .............................................................................................. 25
2.6.3 Correlation between Sn grain structure and thermal cycling (TC)
strength in solder joints ........................................................................... 25
2.6.4 Correlation between Sn grain structure and Electromigration (EM)
strength in solder joints ........................................................................... 27
2.7 Promising way to adjust grain structure and to improve joint
reliability by Ni-doped solder alloy & ultrathin-ENEPIG UBM ... 28
2.7.1 Fourth element addition to solder joints material system to refine β-Sn
.................................................................................................................. 28
2.7.2 Potential of Novel Ni-doped Sn-Ag-Cu solder alloy ............................... 29
2.7.3 Potential of ultrathin-ENEPIG UBM...................................................... 29
2.8 Thesis Overview ...................................................................... 30
2.8.1 Reducing thermal budget of bonding in 3D-IC via employing collapsefree
hybrid solder ..................................................................................... 30
2.8.2 Influence of doping minor Ni into Sn-based solder alloy on Sn grain
structure and orientation in solder joints ............................................... 31
2.8.3 Microstructure and mechanism of Sn grain refinement in Ni-doped
solder joints .............................................................................................. 32
2.8.4 Improving ball shear strength of Sn-Ag-Cu solder joints by using Nidoped
solder and Ni-based UBM ............................................................ 32
2.8.5 Investigating the effects of grain structure on thermal shock behavior
in Cu/Sn-Ag-Cu/ENEPIG joint assembly by modifying thickness of Ni
deposit in ENEPIG .................................................................................. 33
Chapter III Experimental Procedure ................................. 52
3.1 Solder Joint Fabrication ......................................................... 52
3.1.1 Sn-Ag-Cu Solder Joints with Cu-based or Ni-based UBM .................... 52
3.1.2 Sn-Ag-Cu/Cu and Sn-Ag-Cu/Ni Solder Joints with Minor Ni Doping .. 53
3.1.3 Sn-Ag-Cu/Sn-Bi/Cu Hybrid Solder Joints .............................................. 54
3.1.4 Conventional-ENEPIG/Sn-Ag-Cu/Cu and ultrathin-ENEPIG/Sn-Ag-
Cu/Cu joints assembly ............................................................................. 54
3.2 Sample Preparation for Characterization .............................. 55
3.3 Characterization and Analysis ............................................... 56
3.3.1 Microstructure Observation .................................................................... 56
3.3.2 Composition Analysis .............................................................................. 57
3.3.3 Grain Structure Evaluation ..................................................................... 57
3.4 Reliability Tests ....................................................................... 58
3.4.1 Ball Shear Testing .................................................................................... 58
3.4.2 Thermal Shock Testing ............................................................................ 59
Chapter IV Results and Discussion .................................... 66
4.1 Reducing thermal budget of bonding in 3D package via
employing collapse-free hybrid solder ............................................ 66
4.1.1 Microstructure of hybrid solder joints ................................................... 66
4.1.2 Interfacial IMC at SB/Cu interface ......................................................... 67
4.1.3 Micro-Ag3Sn particles in SAC/SB/Cu hybrid solder joint ..................... 67
4.1.4 Micro-Ag3Sn particles in SACN/SB/Cu hybrid solder joint .................. 69
4.2 Influence of doping minor Ni into Sn-based solder alloy on Sn
grain structure and orientation in solder joints ............................. 76
4.2.1 Characterization of β-Sn grains and orientation .................................... 76
4.2.2 Grain boundaries character maps of β-Sn .............................................. 78
4.2.3 The distribution of grain boundaries angle ............................................ 80
4.3 Microstructure and mechanism of Sn grain refinement in Nidoped
solder joints ........................................................................... 85
4.3.1 Microstructure of solder matrix of Ni-doped solder/OSP Cu joints ...... 85
4.3.2 Mechanism of grain refinement in Ni-doped solder/OSP Cu joints ...... 86
4.3.3 Microstructure of solder matrix of Ni-doped solder/NiAu joints .......... 88
4.3.4 Mechanism of grain refinement of Ni-doped solder/NiAu joints ........... 89
4.4 Improving ball shear strength of Sn-Ag-Cu solder joints by
using Ni-doped solder and Ni-based UBM ..................................... 98
4.4.1 Ball shear strength of Sn-Ag-Cu solder joints with and without Nidoping
....................................................................................................... 98
4.4.2 Fracture surface of Sn-Ag-Cu solder joints with and without Ni-doping
after ball shear testing ............................................................................. 98
4.4.3 Analyzing the flat and dimpled region of fracture surface after ball
shear testing ............................................................................................. 99
4.4.4 Cross-sectional view of Sn-Ag-Cu solder joints with and without Nidoping
after ball shear testing ............................................................... 100
4.4.5 Elemental analysis on cross-sectional view of Sn-Ag-Cu solder joints
with and without Ni-doping after ball shear testing ............................. 102
4.5 Investigating the effects of grain structure on thermal shock
behavior in Cu/Sn-Ag-Cu/ENEPIG joint assembly by modifying
thickness of Ni deposit in ENEPIG ............................................... 108
4.5.1 Microstructure and grain structure of as-fabricated solder joints ...... 108
4.5.2 Interfacial IMC in as-fabricated solder joints ...................................... 110
4.5.3 Degradation of solder joints after thermal shock test .......................... 111
4.5.4 Interfacial IMC in solder joints after thermal shock test ..................... 112
4.5.5 Variation of interfacial IMC thickness ................................................. 115
4.5.6 Consumption of Ni deposit in UBM ...................................................... 116
4.5.7 Evolution of interfacial IMC formation and growth ............................ 117
Chapter V Conclusions....................................................... 129
References ............................................................................. 133
Paper Publication .................................................................. 148
International Conference Publication .................................. 150

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