Contents Table List IV Figure Captions V Abstract 1 Chapter I Introduction 4 Chapter II Literature Review 8 2.1 Electronic Package 8 2.1.1 Electronic Packaging Technology 8 2.1.2 Solder Materials 14 2.1.3 Composite Solders 17 2.2 Mechanical alloying 24 2.2.1 Introduction 24 2.2.2 Milling Mechanism 25 2.2.3 SnAgCu System 26 2.3 Joint Properties 35 2.3.1 Melting Temperature 35 2.3.2 Interfacial Reaction 35 2.3.3 Wettability 42 Chapter III Experimental Procedures 51 3.1 Fabrication of Lead Free Solder Pastes 51 3.1.1 Mechanical Alloying 51 3.1.2 Solder Pastes 52 3.2 Characterization of Powders 52 3.2.1 X-ray Diffraction 52 3.2.2 Differential Scanning Calorimetry (DSC) 52 3.2.3 Scanning Electron Microscope (SEM) 53 3.2.4 Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) 53 3.2.5 Wettabilty Test 53 3.3 Reflow Process 58 3.4 Microstructural Characterization of Solder Joints 58 Chapter IV Results and Discussion 63 4.1 The Influence of Ni Concentration and Ni3Sn4 Nanoparticles on Morphology of Sn-Ag-Ni Solders by Mechanical Alloying 63 4.1.1 Characteristics of MA powders and milling mechanisms 63 4.1.2 The influence of Ni concentration on morphology of SnAgNi solder 73 4.1.3 Effect of Ni3Sn4 doping on morphology of SnAgNi solders 78 4.1.4 Wetting properties of SnAgNi solders on different types of UBM 92 4.2 Interfacial reactions and compound formation of Sn-Ag-Ni solder and Sn-Ag solder doped with Ni3Sn4 nano particles produced by mechanical alloying on Cu substrate 95 4.2.1 The morphologies of Sn3.5AgxNi solder/electroplate Cu after 3 times reflow at 240oC 95 4.2.2 Effect of nano-sized Ni3Sn4 particles in SnAgNi solders on the characteristics of solder/electroplate Cu after 3 times reflow at 240oC 100 Chapter V Conclusions 106 References 108 Table list Table 2.1 Melting points of Pb-free solder compositions 20 Table 2.2 Activation energies for intermetallic formation for eutectic solder and composite solders 22 Table 2.3 Sessile drop parameters for surface tension calculation 46 Table 2.4 Contact angles of Sn-3.5Ag and Sn-3.5Ag-4Bi solder pastes on EN/Cu/Si at different temperature 47 Table 2.5 Contact angles of SnAgCu solder joints on electroless Ni-P at 240°C 51 Table 4.1 The onset temperature of Sn-3.5Ag-xNi powders measured by differential scanning calorimetry tester 77 Table 4.2 The average particle size of 94.5Sn-3.5Ag-2.0Ni MA powders milled after 10 hrs with different ratio of Ni to Ni3Sn4 powders 83 Table 4.3 ICP-AES results of Sn-3.5Ag-xNi solder powders milled after 30 hrs by MA process 91 Table 4.4 Contact angles of various MA solders and commercial solders on Cu/Si and electroplated Ni at 240°C 94 Table 4.5 The Ni content in (Cu, Ni)6Sn5 phase and solder matrix for pure Ni-doped and Ni3Sn4-doped solder joints after 3 times reflow at 240oC 103 Figure caption Fig. 2.1 Cross-section of a pin through hole connection of a microelectronics component on a printed wring board 10 Fig. 2.2 Cross-section of a surface mount connection of a microelectronics component with leads on a printed wring board 11 Fig. 2.3 Cross-section of a board grid array (BGA) microelectronics component 12 Fig. 2.4 Cross-section of a flip chip connection 13 Fig. 2.5 Thickness of the intermetallic layers at the solder/Cu substrate interface after annealing at 140˚C for 16 days 21 Fig. 2.6 Cross-sectional image of Sn3Ag0.5Cu solder/electroless Ni-P UBM interface after annealing at 240°C for 15 minutes (a) composite solder, (b) commercial solder, (c) MA solder. Figs. (d)~(f) were the enlarged view of Figs. (a)~(c). 23 Fig. 2.7 Narrow particle size distribution caused by tendency of small particles was welded together and larger particles fractured under steady-state conditions 28 Fig. 2.8 Schematic drawing of MA of ductile/brittle system 29 Fig. 2.9 SEI micrographs of various Sn-3.5Ag-xCu MA powders milled for 70hrs (a) Sn3.5Ag0.2Cu, (b) Sn3.5Ag0.7Cu, (c) Sn3.5Ag1Cu 30 Fig. 2.10 X-ray diffraction peaks of Sn-3.5Ag-xCu powders milled for 10hrs 31 Fig. 2.11 SEI micrograph of the Cu6Sn5 nano powder 32 Fig. 2.12 SEI of the Sn3.5Ag0.2Cu MA powders produced by milling Sn, Ag, and Cu6Sn5 nano powders together for 70 hrs 33 Fig. 2.13 DSC profiles of Sn-3.5Ag-0.2Cu MA powders milled for 70hrs (a) doped with Cu6Sn5 nano powder (b) without doping 34 Fig. 2.14 The electron micrographs for samples with different Ni additions reacted at 240oC for 2 min. The Cu6Sn5 phase is clearly visible for all four cases. For the Ni-doped solders, there is a small amount of Ni in the Cu6Sn5 phase according to the electron microprobe analysis 38 Fig. 2.15 Evolution of the microstructure for the reaction between Sn3.5Ag0.5Ni and Cu at 150oC 39 Fig. 2.16 (a) The zoom-in view for the two-region Ni-bearing Cu6Sn5 formed in the reaction between Sn3.5Ag1.0Ni and Cu. (b) Top-view morphology showing the outer region of the compound. The (Cu1-x,Nix)6Sn5 particles in the outer region have faceted surfaces. (c) Top-view morphology showing the outer region of the compound. (Cu1-y,Niy)6Sn5 particles in the outer region have rounded surfaces 40 Fig. 2.17 The total amounts of IMC formed at the interface at 240oC for different solders plotted against the square root of the reaction time 41 Fig. 2.18 The contact angle of a sessile drop/substrate 44 Fig. 2.19 Sessile drop profile 45 Fig. 3.1 (a)Fritsch Pulverisette ball mill. (b)illustration of the ball motion inside the ball mill 55 Fig. 3.2 The schematic diagram of the measurement system for the contact angle of melt solder pastes on substrates 56 Fig. 3.3 The schematic diagram of the environment chamber for measuring contact angles of the melt solder pastes on substrates 57 Fig. 3.4 The schematic diagram of the reflow oven for proofreading real temperature on Cu substrate 60 Fig. 3.5 The reflow profile in 5 zone oven 61 Fig. 3.6 The flow chart of overall experimental procedure 62 Fig. 4.1 SEI micrographs of 94.5Sn-3.5Ag-2.0Ni MA powders after various milling time(a) 10 hrs (b) 20 hrs (c) 30 hrs (d) 50hrs 65 Fig. 4.2 SEI micrographs of detailed microstructure of the 94.5Sn-3.5Ag-2.0Ni MA powders milled after various time (a) 10 hrs (b) 20 hrs 66 Fig. 4.3 SEI micrographs of 94.5Sn-3.5Ag-2.0Ni MA powders after 30 hrs milling, (a) cold welded region (A), and (b) an enlarged view inside the circle in (a), exhibiting the composite lamellar structure 67 Fig. 4.4 (a) SEI micrographs of 94.5Sn-3.5Ag-2.0Ni MA powders milled for 50 hrs, (b) An enlarged view in (a), showing that fakes started to aggregate and stacked to lump 70 Fig. 4.5 X-ray diffraction peaks of 94.5Sn-3.5Ag-2.0Ni powders (a) as-prepared, and milled for (b) 10 (c) 20 (d) 30 (e) 50 hours 71 Fig. 4.6 The particle size of 94.5Sn-3.5Ag-2.0Ni MA powders milled for various time 72 Fig. 4.7 The particle size of Sn-3.5Ag-xNi MA powders with various Ni content milled for 30 hrs 75 Fig. 4.8 X-ray diffraction peaks of Sn-3.5Ag-xNi powders milled after 30 hrs for various Ni contents, (a) x= 0.1, (b) x= 0.5, (c) x= 1.0 , (d) x= 1.5 , (e) x= 2.0 wt.% 76 Fig. 4.9 SEI micrograph of the Ni3Sn4 nano powders 81 Fig. 4.10 X-ray diffraction peaks of the Ni3Sn4 nano powders produced by chemical method. 82 Fig. 4.11 The particle size of 94.5Sn-3.5Ag-2.0Ni MA powders milled for 10 hours with various Ni3Sn4 contents 84 Fig. 4.12 SEI micrographs of 96.4Sn-3.5Ag-0.1Ni MA powders produced by milling for 30 hrs with (a) Sn, Ag, Ni and (b) Sn, Ag, Ni3Sn4 nanopowders 85 Fig. 4.13 SEI micrographs of 96.4Sn-3.5Ag-0.5Ni MA powders produced by milling for 30 hrs with (a) Sn, Ag, Ni and (b) Sn, Ag, Ni3Sn4 nanopowders 86 Fig. 4.14 SEI micrographs of 96.4Sn-3.5Ag-1.0Ni MA powders produced by milling for 30 hrs with (a) Sn, Ag, Ni and (b) Sn, Ag, Ni3Sn4 nanopowders 87 Fig. 4.15 DSC profiles of Sn-3.5Ag-xNi MA powders milled for 30 hrs with various Ni contents (a) x = 0.1, (b) x = 0.5, and (c) x = 1.0 wt.% 90 Fig. 4.16 The cross-sectional images of Sn-3.5Ag-xNi solder/ electroplated Cu interfaces after reflow at 240oC for 3 times, x= (a) 0.1 , (b) 1.0 , (c) 1.5 (d) 2.0 wt.% 97 Fig. 4.17 The enlarged view of cross-sectional images of Sn-3.5Ag-xNi solder/ electroplated Cu interfaces after reflow at 240oC for 3 times, x= (a) 0.1 , (b) 1.0 , (c) 1.5 (d) 2.0 wt.%. 98 Fig. 4.18 The amounts of Ni dissolved in Cu6Sn5 layer at solders/electroplated Cu interface after 3 times reflow at 240 oC 99 Fig. 4.19 Cross-sectional images of 95.5Sn-3.5Ag-1.0Ni solder/Cu interface after 3 times reflow at 240oC, (a) pure Ni-doped solder (b) Ni3Sn4-doped solder, indicating round and pebble-shape Cu6Sn5 particles, with some stacked at the interface, while some stripped to the solder side 104 Fig. 4.20 The average thickness of (Cu,Ni)6Sn5 layer of Sn-3.5Ag-xNi solders 105