List of Abbreviations ......................................... vii
List of Symbols ................................................. x
1 Introduction ................................................. 1
1.1 3D integration in electronics packaging ................. 1
1.2 Comparison of interconnect technologies ................. 3
1.3 State of technology in international research
institutes .............................................. 6
1.4 Aims of the thesis ...................................... 9
1.5 Structure of the thesis ................................. 9
2 Fundamentals of solid-liquid interdiffusion bonding ......... 11
2.1 Comparison of the terminology for SLID bonding
process ................................................ 11
2.2 Description of the SLID bonding process ................ 11
2.3 Intermetallic compounds in Cu/Sn/Ag SLID system ........ 12
2.4 Diffusion mechanisms in Cu/Sn SLID system .............. 14
2.5 Material data for Cu/Sn/Ag SLID system ................. 16
2.5.1 Phase diagrams .................................. 16
2.5.2 Physical and mechanical properties .............. 18
2.5.3 Diffusion parameters ............................ 19
2.5.4 Volume shrinkage during the phase
transformations ................................. 20
2.5.5 Crystal structures of IMCs ...................... 21
2.6 Classification of voids in SLID interconnects .......... 21
2.6.1 Degradation/corrosion pores ..................... 21
2.6.2 Kirkendall voids ................................ 25
2.6.3 Shrinkage voids ................................. 25
2.6.4 Processing voids ................................ 25
3 Materials and methods ....................................... 26
3.1 Description of the test vehicles ....................... 26
3.1.1 Design of the test vehicle A with Cu/SnAg
bumps ........................................... 27
3.1.2 Design of the test vehicle В with Cu/Sn bumps ... 29
3.1.3 Surface morphology of the test vehicles A and
В ............................................... 30
3.2 Comparison of the SLID bonding equipment ............... 31
3.2.1 Fineplacer lambda (Finetech) .................... 31
3.2.2 FC150 flip-chip bonder (Smart Equipment
Technology) ..................................... 32
3.3 Methods for quality and microstructure
characterization of SLID interconnects ................. 33
3.3.1 Shear tests ..................................... 33
3.3.2 Metallographic preparation ...................... 33
3.3.3 Optical and scanning electron microscopy ........ 35
3.3.4 Electron Backscatter Diffraction ................ 36
4 Influence of bonding pressure on quality of Cu/SnAg SLID
interconnects ............................................... 42
4.1 Experimental procedure ................................. 43
4.1.1 Characterization of bump height and bump
roughness ....................................... 43
4.1.2 Optimized bonding process ....................... 44
4.1.3 Shear tests ..................................... 45
4.1.4 Calculation of the quality parameters from
cross-sections .................................. 45
4.2 Results ............................................... 47
4.2.1 Microstructure characterization of the Cu/SnAg
SLID interconnects .............................. 47
4.2.2 Influence of the bonding pressure on tilt and
on standoff height variation in SLID
interconnects ................................... 48
4.2.3 Influence of the bonding pressure on
interlayer thickness and on processing voids
in SLID samples ................................. 49
4.2.4 Influence of the bonding pressure on Cu3Sn
thickness in SLID interconnects ................. 52
4.2.5 Characterization of shear strength and
fracture surfaces of the SLID inter-connects .... 52
4 3 Discussion ............................................. 54
4.3.1 Critical tilt angle for the bonding yield ....... 54
4.3.2 Reasons for the standoff height variation ....... 55
4.3.3 Comparison of the shear strength of the SLID
interconnects with literature references ........ 56
4.4 Summary and Outlook ................................... 57
5 Degradation behavior of Cu/Sn SLID interconnects ............ 59
5.1 Influencing parameters on degradation: temperature,
time, atmosphere and flux agent ........................ 59
5.2 Experimental procedure ................................. 60
5.2.1 Investigated flux agents ........................ 60
5.2.2 Optimized bonding process ....................... 61
5.2.3 Thermal storage procedure for interconnects ..... 62
5.2.4 Thermal storage procedure for dies with Cu/Sn
microbumps ...................................... 62
5.3 Results ................................................ 63
5.3.1 Influence of the bonding time/temperature on
fluxed samples .................................. 63
5.3.2 Influence of the bonding time/temperature on
underfilled samples ............................. 63
5.3.3 Influence of the storage time/temperature on
fluxed samples .................................. 67
5.3.4 Influence of the storage time/temperature on
underfilled samples ............................. 70
5.3.5 Influence of the flux agent and of the
atmosphere on Cu/Sn bumps of single dies ........ 70
5.3.6 Composition analysis of the pore regions in
SLID interconnects .............................. 75
5.4 Discussion ............................................. 76
5.4.1 Proposed mechanism for the pore formation in
the Cu6Sn5 IMC .................................. 76
5.4.2 Comparison of the results with literature ....... 78
5.4.3 Classification of the corrosion type ............ 78
5.5 Summary and Outlook .................................... 80
6 Microstructure investigation of Cu/Sn and Cu/SnAg SLID
interconnects ............................................... 82
6.1 Experimental procedure ................................. 82
6.2 Results ................................................ 84
6.2.1 Growth kinetics of the Cu3Sn IMC ................ 84
6.2.2 Calculation of the diffusion parameters for
the growth of Cu3Sn at the Cu/Cu6Sn5 interface .. 85
6.2.3 Grain growth of the Cu, Sn IMC .................. 87
6.2.4 Orientation analysis of Cu and Cu6Sn5 in
Cu/SnAg SLID interconnects ...................... 90
6.2.5 Orientation analysis of Cu, Cu6Sn5 and Cu3Sn
in Cu/Sn SLID interconnects ..................... 94
6.3 Discussion ............................................. 99
6.3.1 Comparison of diffusion parameters for the
Cu3Sn IMC with literature references ............ 99
6.3.2 Proposed mechanism for the grain growth of the
Cu3Sn IMC in SLID inter-connects ............... 100
6.3.3 Factors influencing the texture development
in Cu6Sn5 and Cu3Sn IMCs ....................... 102
6.4 Summary and Outlook ................................... 105
7 Summary and Outlook ........................................ 107
Bibliography .................................................. 109
List of Figures ............................................... 120
List of Tables ................................................ 124
A Additional figures ......................................... 126
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