氏名　趙　杰
学位の種類　博士（工学）
学位記番号　博甲第225号
学位授与の日付　平成13年3月26日
学位論文題目　Fatigue Crack Growth Behavior of Solder Materials （はんだの疲労き裂伝ぱ特性に関する研究）
論文審査委員
　主査　教授　武藤　睦治
　副査　教授　田中　紘一
　副査　教授　古口　日出男
　副査　助教授　許　金泉
　副査　青山学院大学　教授　小川　武史

• 論文目次
• 論文要旨

［平成12（2000）年度博士論文題名一覧］ ［博士論文題名一覧］に戻る．

Chapter One　Introduction　p.1
1.1 Microstructural characteristics of Sn-Pb and Sn-Ag solder systems　p.1
1.1.1 Microstructural characteristics of Sn-Pb solder　p.3
1.1.2 Microstructural characteristics of Sn-Ag solder　p.5
1.2 Mechanical behavior of Sn-Pb and Sn-Ag solder systems　p.7
1.2.1 Static mechanical behavior　p.7
1.2.2 Cyclic mechanical behavior　p.11
1.3 Microstructure instability of solers　p.15
1.4 Scope of this work　p.17

Chapter Two　Fatigue Crack Growth Behavior in Lead-based 95Pb-5Sn Solder　p.20
2.1 Introduction　p.20
2.2 Experimental procedures　p.21
2.2.1 Material and specimen　p.21
2.2.2 Experimental methods　p.22
2.3 Experimental Results and Discussions　p.25
2.3.1 Crack closure　p.25
2.3.2 Fatigue crack growth curves　p.27
2.3.3 Crack path observations　p.31
2.3.4 Fractographic observations　p.32
2.3.5 Microtructural instability during tests　p.36
2.3.6 Mechanisms of fatigue crack growth in 95Pb-5Sn solder　p.36
2.4 Conclusions　p.38

Chapter Three　Fatigue Crack Growth Behavior in Eutectic 63Sn-37Pb Solder　p.39
3.1 Introduction　p.39
3.2 Experimental procedures　p.40
3.3 Experimental Results　p.42
3.3.1 Microstructure of the eutectic Sn-Pb solder　p.42
3.3.2 Fatigue crack growth behavior of the 63Sn-37Pb solder　p.42
3.3.3 Crack path observations　p.45
3.3.4 Fractographic observations　p.48
3.4 Discussion　p.51
3.4.1 cyclic dependent fatigue crack growth behavior in 63Sn-37Pb solde　p.51
3.4.2 Time dependent fatigue crack growth behavior　p.52
3.4,3 Microstructural instability in 63Sn-37Pb solder　p.54
3.4.4 Mechanisms of fatigue crack growth in the as-cast 63Sn-37Pb solder　p.60
3.5 Conclusions　p.61

Chapter Four　Fatigue Crack Growth Behavior in 96.5Sn-3.5Ag Lead-free Solder　p.62
4.1 Introduction　p.62
4.2 Experimental procedures　p.63
4.3 Experimental Results　p.65
4.3.1 Microstructure of 96.5Sn-3.5Ag solder　p.65
4.3.2 Fatigue crack growth resistance　p.65
4.3.3 Fatigue crack path　p.68
4.3.4 Fractographic observations　p.70
4.4 Discussions　p.72
4.4.1 Effect of Ag3Sn intermetallics　p.72
4.4.2 Formation of small grains in Sn matrix　p.72
4.4.3 Fatigue crack growth process in 96.5Sn-3.5Ag solder　p.75
4.5 Conclusions　p.75

Chapter Five　Fatigue Crack Growth Behavior in Sn-Ag-Cu and Sn-Ag-Cu-Bi Lead-free Solders　p.76
5.1 Introduction　p.76
5.2 Experimental procedures　p.77
5.3 Experimental Results and Discussions　p.79
5.3.1 Microstructural analyses and tensile properties of the solders　p.79
5.3.2 Fatigue crack growth curves　p.82
5.3.3 Time-dependent behavior　p.87
5.3.4 Effect of Bi constituent　p.87
5.3.5 Fractographic observations　p.92
5.3.6 Fatigue crack path　p.96
5.4 Conclusions　p.97

Chapter Six　Comparison of Fatigue Crack Growth Behavior between Lead-rich and Lead-free Solders　p.98
6.1 Melting temperature and range　p.98
6.2 Tensile properties　p.100
6.3 Fatigue crack growth behavior　p.102
6.3.1 Cyclic dependent fatigue crack growth behavior　p.102
6.3.2 Threshold values　p.105
6.3.3 Time dependent fatigue crack growth behavior　p.107
6.3.4 Fracture manners　p.110
6.3.5 Microstructural instability　p.110
6.4 Prospect　p.112

Chapter Seven Summary　p.114

References　p.116

Acknowledgment

　Research efforts on soldering technology have been devoted due to the increasing requirement of joint reliability in electronic packaging, and the demand of Pb-free solders from the viewpoint of environmental pollution. Among the extensive efforts on mechanical behavior investigation, only limited works have been reported on the fatigue crack growth behavior of solder materials. Fatigue is a process of crack initiation and propagation. A steady crack growth stage takes a large part of the failure life in solders under low cycle fatigue tests, and crack propagation is a dominant process in determining the fatigue life. From this point of view, further understanding of fatigue crack growth behavior of solder materials is strongly required. Therefore, the objective of the current work is to investigate basic characteristics and mechanisms of fatigue crack growth of solders.
　The fatigue crack growth tests have been performed on a wide range of solders: from conventional lead-rich solders to newly developed lead-free solders. The tests were carried out using CT type specimens at various stress ratios ranged from 0.1 to 0.7 and frequencies ranged from 0.01Hz to 10Hz at constant temperature of 20℃ and humidity of 55%. Creep crack growth tests were also performed for comparison. Fracture surfaces, side surfaces and longitudinal cross-sections of the specimens were observed using a scanning electron microscopy （SEM） to analyze crack growth processes.
　Based on the experimental results, it was found that cyclic dependent behavior was dominant for the tests at low stress ratios and high frequencies, where the cracks predominantly propagated in transgranular manner. With an increase of stress ratio and decrease of frequency, time dependent FCG behavior became dominant, where a crack propagated dominantly in intergranular manner.
　Significant crack closure has not been observed in all the solders except for the SnAgCuBi1 solder, Kcl-value of which was about 0.86MPa m1/2. The fatigue crack growth rates were correlated as a function of ΔJ under the cyclic dependent testing conditions. The Sn-Pb solders exhibited higher fatigue crack growth rates than the Sn-based lead-free solders in da/dN-ΔJ relationship. When correlating the fatigue crack growth rates using normalized effective stress intensity factor range ΔKeff/E, all the date fall in a narrow band regardless of materials and testing conditions. The expression between da/dN and ΔKeff/E was given as: da/dN=6.83x10-12（ΔKeff/E）4.05.
　For the experiments under time dependent testing conditions, the crack growth rates could be arranged as a function of C* and the results were in accord with the creep crack growth data. The expression between da/dt and C* was given as: da/dt=8.34x10-8C*1.08. The Sn-based lead-free solders with Bi content exhibited higher resistance in the time dependent regime even when the melting temperature was reduced with Bi addition.
　The grain size change and the formation of small grains were observed in the Sn-Pb and Sn-Ag solders after the fatigue crack growth tests because of the high homologous temperature of the solders at room temperature. The grain size change in Pb-rich phase of the 9Pb-5Sn solder resulted from recrystallization, while the formation of small grains in Sn-rich phase of the eutectic 63Sn-37Pb and Sn-3.5Ag solders attribute to polygonization of Sn-rich phase.
　Based on the experimental results, it is found that the current Sn-based lead-free solders have superior fatigue crack growth property to the Sn-Pb lead-base solders at both cyclic and time dependent testing condition. Therefore, from the viewpoint of fatigue, the Sn-based lead-free solders can be used for electronic packaging instead of conventional Sn-Pb lead-base solders.