氏名　Chaosuan Kanchanomai
学位の種類　博士（工学）
学位記番号　博甲第256号
学位授与の日付　平成14年8月31日
学位論文題目　Study on Low Cycle Fatigue Behavior and Mechanisms of Lead-Free Solders　（無鉛はんだ材の低サイクル疲労特性に関する研究）
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　井原　郁夫
　副査　株式会社　東芝　研究開発センター　研究主幹　川上　崇
　副査　Nanyang Technological University Associate Professor　John H. L. Pang

• 論文目次
• 論文要旨

［平成14（2002）年度博士論文題名一覧］ ［博士論文題名一覧］に戻る．

Chapter 1:Introduction　p.1
1.1 General considerations　p.2
1.2 Performance characteristics of solders　p.4
1.3 Electrical properties　p.10
1.4 Mechanical properties　p.11
1.5 Reliability　p.15
1.6 Conclusion　p.19
1.7 Scope of the present work　p.20
1.8 References　p.22

Chapter 2: Materials and Experimental Procedures　p.25
2.1 Introduction　p.26
2.2 Materials　p.27
2.3 Experimental procedures　p.33
2.4 Calculation method for fracture parameters　p.41
2.5 Test program　p.44
2.6 References　p.45

Chapter 3: Low Cycle Fatigue Behavior and Mechanisms of Solders at Room Temperature　p.47
3.1 Introduction　p.48
3.2 Sn-Ag eutectic solder （96.5Sn-3.5Ag）　p.49
3.3 Sn-Pb eutectic solder （63Sn-37Pb）　p.62
3.4 Discussion　p.75
3.5 References　p.77

Chapter 4: Frequency Effects on Low Cycle Fatigue Behavior And Mechanisms of solders　p.80
4.1 Introduction　p.81
4.2 Sn-Ag eutectic solder （96.5Sn-3.5Ag）　p.82
4.3 Sn-Pb eutectic solder （63Sn-37Pb）　p.100
4.4 Discussion　p.110
4.5 References　p.112

Chapter 5: Temperature Effects on Low Cycle Fatigue Behavior And Mechanisms of Solders　p.115
5.1 Introduction　p.116
5.2 Sn-Ag eutectic solder （96.5Sn-3.5Ag）　p.117
5.3 Sn-Pb eutectic solder （63Sn-37Pb）　p.128
5.4 Discussion　p.135
5.5 References　p.137

Chapter 6: Hold Time Effects on Low Cycle Fatigue Behavior And Mechanisms of Solders　p.139
6.1 Introduction　p.140
6.2 Stress relaxation　p.140
6.3 Low cycle fatigue with tensile hold　p.141
6.4 Conclusion　p.146
6.5 References　p.146

Chapter 7: Alloying Effects on Low Cycle Fatigue Behavior And Mechanisms of Solders　p.148
7.1 Introduction　p.149
7.2 Low Cycle fatigue behavior　p.150
7.3 Crack initiation mechanism　p.155
7.4 Crack propagation mechanism　p.157
7.5 Conclusion　p.159
7.6 References　p.160

Chapter 8: General Conclusions and Future Prospects　p.161
8.1 General conclusion　p.162
8.2 Future Prospects　p.167

　Lead-free solder 96.5Sn-3.5Ag （Sn-Ag eutectic alloy） is one of the candidates for surface mount technology （SMT） due to the environmental and health concerns about lead-contained in conventional solder materials. Therefore, understanding of fatigue behavior and mechanisms of deformation and fracture of Sn-Ag eutectic solder is important for developing the reliable SMT electronic packaging. However, a little is known about the low cycle fatigue （LCF） behavior and mechanisms of crack initiation and growth in lead-free solders. In the present study, the effects of frequency, temperature, tensile-hold time and alloying addition on LCF behavior and mechanisms of Sn-Ag eutectic solder have been investigated and compared with those of Sn-Pb eutectic solder （63Sn-37Pb）.
　Chapter 1 Introduction: Many works have been recently published detailing the processing, mechanical properties and reliability of Pb-containing and Pb-free solders. Therefore, the review these results and the scope of the present works have been stated.
　Chapter 2 Materials and Experimental Procedures: In order to avoid this unexpected damage due to the localized deformation and a resultant stress concentration induced at the contact point between the extensometer probe and the specimen surface, a non-contact strain controlled fatigue test system using the digital image measurement system as a part of strain feedback system was developed and used throughout the present study. The detail of this technique as well as microstructure, specimen preparation and experimental procedure were discussed in detail.
　Chapter 3 Low Cycle Fatigue Behavior and Mechanisms of Solders at Room Temperature : A comprehensive study of fatigue behavior as well as crack initiation and propagation mechanisms at constant strain rate and temperature of both Pb-free solder （96.5Pb-3.5Ag） and Pb-containing solder （63Sn-37Pb） was presented and discussed. Low cycle fatigue behavior of both solders followed the Coffin-Manson relationship. Sn-Ag eutectic solder had better LCF resistance than 63Sn-37Pb. Cavities could be observed for both solders, around Pb-rich phases on the colony boundaries for Sn-Pb eutectic solder, and around Ag3Sn particles especially along the boundary of Sn dendrites for Sn-Ag eutectic solder. Subgrains due to dislocation rearrangement （polygonization） formed in Sn-rich phases for both solders. Stage II crack propagated in intergranular manner along colony boundaries for Sn-Pb eutectic solder, while mixed manner, i.e. transgranularly through the Sn-Ag eutectic phases, and intergranularly along Sn-dendrite boundaries and/or subgrain boundaries, was the case for Sn-Ag eutectic solder.
　Chapter 4 Frequency Effects on Low Cycle Fatigue Behavior and Machanisms of Solders : Due to high homologous condition, time-dependent mechanisms are possible to occur and significantly increase with reducing frequency and increasing temperature.A study of the effects of frequency on LCF behavior as well as crack initiation and propagation mechanisms at constant temperature of 20 ℃ were presented and discussed. For both solders, the number of cycles to failure decreased with decreasing frequencies. The relationships between time to failure and strain rate of Sn-Ag eutectic and Sn-Ag eutectic solders for different total strain ranges and frequencies could be fitted by a single line and a double-linear line, respectively. The C*-parameter can successfully characterize LCF crack growth rate of both solders.
　Chapter 5 Temperature Effects on Low Cycle Fatigue Behavior and Mechanisms of Solders : The effects of temperature on LCF behavior as well as crack initiation and propagation mechanisms at constant frequency of 0.1 Hz were presented. Time-dependent deformation mechanisms was influenced by temperature, i.e. stress range reduces with increasing temperature. The activation energy, estimated from the relationships between stress range at first cycle and inverse temperature, for 96.5Sn-3.5Ag and 63Sn-37Pb were in the range 62-72 kJ/mol and 37-47 kJ/mol, respectively. Both activation energies correspond to those of creep tests, which dominated by pipe-fiffusion-controlled dislocation climb mechanism. The fatigue life of both solder also reduced with increasing temperature. The relationship between da/dt- C*plot of both solders located together in a narrow band with an exponent of 1.
　Chapter 6 Hold Time Effects on Low Cycle Fatigue Behavior : For high homologous temperature application, understanding of the creep and stress relaxation behavior is of extreme importance to the designers of electronic assemblies. For creep-fatigue interaction, tensile hold time during high temperature fatigue is very damaging in many materials. In the present Chapter, stress relaxation and isothermal LCF tests with tensile hold time in both Pb-free solder （96.5Sn-3.5Ag） and Pb-contained solder （67Sn-37Pb） were carried out and discussed. It was found that most of the stress rapidly relax in less than 100 s and then become stable for both solders. The percentage of stress reduction is higher for case of 96.5Sn-3.5Ag. The number of cycles to failure dramatically decreased with increasing tensile hold times for both solders. The decreasing rate is most rapid for short hold times, i.e. approximately 50 s, and then becomes slower and stable. This correlates well the fact that about half of the stress in these solders has relaxed before 100 s.
　Chapter 7 Alloying Effects on Low Cycle Fatigue Behavior and Mechanisms of Solders : Mechanical properties of the Sn-Ag eutectic solder compare favorably with those of the Sn-Pb eutectic solder, with the solder ability and melting temperature are less favorable than those of Sn-Pb eutectic solder. In order to improve these properties, some additional elements, e.g. Cu, Bi, Zn, In, have been added to Sn-Ag eutectic solder. The melting temperature, i.e. liquidus and solidus temperatures, of Sn-Ag eutectic could be decreased by adding Bi or Zn. However, low melting temperature solder would mean higher homologus temperature of service, which enhances the occurrence of more thermally activated processes such as creep and grain growth. The effects of alloying on low cycle fatigue behavior as well as crack initiation and propagation mechanisms of Sn-Ag eutectic solder at constant temperature of 20℃ and frequency of 0.1 Hz was presented. The addition of Cu does not significantly affect the fatigue life of eutectic Sn-Ag solder. However, the fatigue life significantly reduced with amount of addition Bi. The LCF behavior of all solders followed the Coffin-Manson equation. For constant frequency and temperature condition, the fatigue life of the solders studies is dominated by the fracture ductility, and can be described by the ductility modified Coffin-Manson's relationship.
　Chapter 8 General Conclusions and Future Prospects : The general conclusions and future prospects have been given.