為了增加銲接點強度，本研究嘗試改變迴銲的條件且利用高速撞擊測試(high-speed impact test)去評估銲接點的可靠度。在迴銲後期固化的過程中，對銲接點進行不同溫度和不同時間長度的熱處理，探討在Sn-Ag-Cu/Cu與Sn-Ag-Cu/Ni銲接點內的微結構、錫(β相)的結晶和銲料硬度的變化。
在固化過程中，對Sn-Ag-Cu/Cu 銲接點施以180度或210度的熱處理，以了解不同熱處理溫度的影響。在熱處理後，靠近界面的局部析出物，從點狀分佈轉變成網狀分佈。此外，透過電子背向散射儀(EBSD)的分析可察知析出物的分佈與錫的結晶息息相關。熱處理後，由於銲料內銅元素的再分佈，讓銲料內錫的結晶結構從多個且交織狀成長成少許大顆的錫晶粒。值得注意的是，以210度熱處理會加速上述微結構的改變，並提升銲接點的強度。
為了探討熱處理對不同的凸塊底層金屬的影響，Sn-Ag-Cu/Cu 與Sn-Ag-Cu/Ni銲接點在固化過程中經過210度的50秒或100秒的熱處理。在對照組以快速冷卻的Sn-Ag-Cu/Cu銲料中，其析出物以網狀分佈且佔據大部份的銲球體積，然而在Sn-Ag-Cu/Ni 銲料中析出物係以點狀結構佔據大部份的體積。隨著熱處理時間增加，析出物逐漸成長，界面的介金屬化合物稍微的增厚，而銲料變的較軟。Sn-Ag-Cu/Cu和Sn-Ag-Cu/Ni在熱處理50秒後，銲接點強度皆有所提升且延展性斷裂的比例也增加。然而，當熱處理達100秒後，在Sn-Ag-Cu/Ni銲接點的界面上，因相對硬脆的介金屬化合物(Cu,Ni)6Sn5增厚，導致銲接點強度下降。Sn-Ag-Cu/Cu和Sn-Ag-Cu/Ni在銲接點強度表現的差異性與銲料的微結構及銲料硬度有關。

This study aims to improve the impact performance via modified reflow conditions. A high speed shear tester was used to evaluate the impact reliability of solder joints. During solidification step of reflow process, the solder joints were annealed under various annealing temperature and heating time. The microstructure, β-Sn structure, micro-hardness of Sn-3.0Ag-0.5Cu/Cu (wt. %, SAC/Cu) and Sn-3.0Ag-0.5Cu/Ni (wt. %, SAC/Ni) solder joints were investigated.
To evaluate the effect of annealing temperature on impact performance, the SAC/Cu solder joints were annealed at 180 oC and 210 oC, respectively, during the solidification step. In the annealed solder, the precipitations in the limited region near the joint interface varied from the dot type toward the network type. Additionally, electron backscatter diffraction (EBSD) analysis indicated that the β-Sn grain structure depended on the distribution of precipitations. The β-Sn grain structure was altered from interlaced grains to larger grains due to the redistribution of Cu in the solder. Noteworthily, the annealing at higher temperature (210 oC) can accelerated the variation of above-mentioned microstructure, leading to enhancement of the impact reliability.
The effect of annealing process on various UBMs was investigated. The SAC/Cu and SAC/Ni solder joints were annealed to 210 oC for 50 s and 100 s, respectively. In the rapid-cooled solder joints, the network type precipitations were distributed in all the solder volume of SAC/Cu joint, while the dot type precipitations in the SAC/Ni joint. With increasing annealing time, these precipitations grew larger, the interfacial intermetallic compounds (IMCs) became slightly thicker, and the hardness of solder alloys gradually decreased. After annealing for 50 s, the impact toughness of both SAC/Cu and SAC/Ni solder joints was enhanced, and the fraction of ductile fracture in these solder joints increased. However, the growth of (Cu,Ni)6Sn5 at the SAC/Ni interface degraded the impact toughness as SAC/Ni was annealed for 100 s. The difference of impact toughness in SAC/Cu and SAC/Ni was correlated to the variation of microstructure and hardness in solder joints.

Contents
Contents……………………………………………………….. I
List of Tables…………………………………………………... IV
Figures Caption……………………………………………….. V
Abstract…………………………………………....................... IX
Chapter I Introduction………………………………………..1
1.1 Background…………………………………………….1
1.2 Motivations and Goals in This Study…………………..2
Chapter II Literature Review……….………………………..6
2.1 Electronic Package……………………………………..6
2.2 Solder Bump…………………………………………..8
2.2.1 Sn-Pb Solder………………………………..9
2.2.2 Pb-free Solder…………………………………….10
2.2.3 Sn-Ag-Cu Solder with 4th Minor Addition………11
2.3 Under Bump Metallization……………………………..12
2.3.1 Cu-Based UBM…………………………………..12
2.3.2 Ni-Based UBM…………………………………..13
2.3.2.1 Electroplated Ni………………………….13
2.3.2.2 Electroless Ni-P (EN)……………………14
2.3.2.3 Sputtered Ni(V)………………………….15
2.3.3 Surface Finish…………………………………….16
2.3.3.1 Organic Solderability Preservative
Surface Finish………16
2.4Interfacial Reactions in Solder Joints…………………...16
2.4.1 Interfacial Reactions between Solders and Cu-Based UBM…………………….....................17
2.4.2 Interfacial Reactions between Solders and Ni-Based UBM and Ni UBM…………………...18
2.5 Reliability Test in Solder Joint…………………………19
2.6 Orientation of β-Sn in Solder Joint……………………..21
2.7 Nanoindentation characterization………………………24
Chapter III Experimental Procedures………………………36
3.1 Reflow Profile Design and Sample Fabrication of SAC/Cu Solder joints……………………………36
3.2 Reflow Profile Design and Sample Fabrication of SAC/Cu and SAC/Ni Solder joints……………...37
3.3 Analysis Methods………………………………………37
3.3.1 Microstructure Evolution…………………………38
3.3.2 Composition Analysis…………………………….39
3.3.3 Hardness Variation………………………………..39
3.3.4 Sn structure evaluation…………………………...40
3.3.5 High speed shear testing………………………….40
Chapter IV Results and Discussion…………………………..
4.1 Microstructural and the impact toughness variation of Sn-Ag-Cu/Cu solder joints via various annealing temperature………………………………………48
4.1.1 High speed shear testing for SAC/Cu solder joints……………………………………………..48
4.1.2 Microstructural and β-Sn grain variation in the solder matrix of SAC/Cu………………………..49
4.1.3 Interfacial reactions at the SAC/Cu and SAC/Ni interface………………………………………….51
4.1.4 Mechanism and temperature effect on impact toughness improvement in annealed solder joints……………………………………………..51
4.2. Microstructure evolution and impact toughness in the Sn-Au-Cu/Ni and Sn-Ag-Cu/Cu solder joints via modified reflow conditions…………………………….60
4.2.1 Microstructural variation in the solder matrix of SAC/Cu and SAC/Ni…………………………….60
4.2.2 β-Sn grain structure in the SAC/Cu and SAC/Ni solder joints……………………………………..62
4.2.3 Hardness of the solder alloy near the SAC/Cu and SAC/Ni interfaces……………………………….64
4.2.4 Interfacial reactions at the SAC/Cu and SAC/Ni interface………………………………………….66
4.2.5 High speed shear testing for SAC/Cu and SAC/Ni solder joints……………………………………..67
4.2.6 Mechanism for the improvement of impact toughness in annealed solder joints……………...69
Chapter V Conclusions………………………………………..87
References………………………………………………….......89 

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