Abstract The effect of joint strength of PbSn and AuSn solder on temperature cycling tests in laser packages has been studied experimentally and numerically. It was found that the solder joint strength increased as temperature cycle number increased, and then became steady after 400 cycles. This is may be due to the redistribution of the residual stresses within the solder during temperature cycling test, and hence reducing the residual stresses and increasing the solder joint as the temperature cycle increased. Numerical calculations were in good agreement with the experimental measurement that the solder joint strength increased as the temperature cycle increased. In this work, we also study the intermetallic compound (IMC) growth of PbSn and AuSn solders under cycling test and aging test. The thickness of IMC growth do not significantly increase under cycling test, because the cycling test temperature was from ¡V40 to 85ºC. However, under the high temperature aging of 200ºC for 25 days, the IMC thickness was increased to 4.71£gm.

The effect of joint strength of PbSn and AuSn solder in aging test for laser module packaging has been studied experimentally. The thermal conditions were aged at 150 ¢J for 1,4,9,16,25 and 36 days. It was found that the joint strength decreased as aging test time increased. The joint strength of PbSn solder with the gold coating on SUS304 substrate of 2 µm and 10 µm decreased about 17% and 28% after aging test, respectively. The joint strength of PbSn solder with the gold coating on SUS304 substrate of 2 µm and 10 µm decreased about 16% and 9% after aging test, respectively. we also presented the microstructure of the intermetallic compound ¡]IMC ¡^growth under aging test. Results showed that the thickness of the IMC increased after aging test. The growth thickness of the IMC from 1 to 36 days for the PbSn and AuSn solder were measured to be 5.26 to 34.37 and 0.48 to 1.64 µm, respectively. The joint strength decreased under aging test may be due to the crack and void defects increased within the solder. The crack and void defects in solder were observed by metallographic photos.

Abstract The influence of thermal aging on joint strength and fracture surface of PbSn and AuSn solders in laser module packages has been studied experimentally and numerically. Al2O3-Solder-Substrate assembled samples were aged at 150oC for one, four, nine, sixteen, twenty-five, thirty-six, and forty-nine days. It was found that the joint strength decreased as the aging time increased. This joint strength decrease is due to the increase of void and crack formations in solder joints. There is a correlation between the intermetallic compound (IMC) growth and the joint strength for PbSn and AuSn solders under aging test. The fracture surface of PbSn specimen is gradually changed from the ductile dominated morphology of as-soldered status to the brittle dominated morphology. The section view indicates Kirkendall voids appeared around the interface of bulk solder and IMC layers after 49 days of aging. However, AuSn specimen still shows a ductile dominated morphology and no Kirkendall voids observed even after 49 days of aging. Through 49 days of aging, the shear force drops of 2£gm Au-coated PbSn and AuSn specimens are 9.48kg and 7.65kg, respectively; the shear force drops of 10£gm Au-coated PbSn and AuSn specimens are 9.42kg and 5.88kg,respectively. A finite-element method (FEM) analysis was performed on the calculation of joint strength variation of PbSn and AuSn solders in thermal aging tests. Simulation results were in good agreement with the experimental measurements that the solder joint strength decreased as the aging time increased. Another study is based on the well-known result of thermal induced fiber alignment shifts of fiber-solder-ferrule (FSF) joints in laser diode package. It indicates fiber alignment shift under temperature cycling tests can be reduced significantly if the fiber can be located closer to the center of the ferrule. An approach to make an FSF with the minimum eccentric offset is studied, an in-house design machine set is used for this purpose, which includes a hot plate, a fiber fix stage, an image capture camera, and a PC with offset analysis program. A preliminary target is set to achieve a maximum 20£gm offset FSF. It was believed that a less than 0.5£gm fiber shift could be measured after 500 temperature cycles. After the practical experiment trial, FSF with around 10 and 12£gm offset is available. However, the continuous improvement is necessary for process stability.

The microstructure of £b'-Cu6Sn5 during in the early stage of growth was studied. Sn was electroplated onto thin Cu foil at room temperature and the specimen was annealed at 150 ºC for 30 s. The Cu and Sn on the £b'-Cu6Sn5 surfaces were removed electrolytically and the specimens were analyzed with scanning and transmission electron microscopes. The £b'-Cu6Sn5 grains on the Cu side were as small as 5 nm but grew rapidly to 0.3 to 0.5 £gm on the Sn side. The orientation relationships between £b'-Cu6Sn5 and Cu were studied by a thin film technique. Cu was evaporated onto the NaCl (001) and (111) surfaces to form epitaxial Cu thin films and Sn was then evaporated onto the Cu films to form £b'-Cu6Sn5. Two types of orientation relationships were found, i.e., (1) [204]£b'//[001]Cu (zone axis), (40-2)£b'//(110)Cu, and (020)£b'//(1-10)Cu, and (2) [204]£b'//[111]Cu (zone axis), (40-2)£b'// Cu, and (020)£b'//(-1-12)Cu. The interfaces were analyzed. (Chapter 1) A very thin £b-Cu6Sn5 layer was formed by dipping thin Cu foil into molten Sn at 240 ºC for 1 second and quenching in ice water. The Sn and Cu on the £b-Cu6Sn5 surface were removed electrolytically to study the surface morphologies. The £b-Cu6Sn5 grains on the Sn side had a worm-type shape, about 0.3-0.5 £gm wide and up to 2 £gm long, but those on the Cu side were very small, about 5 nm in size. The nucleation and growth of the £b-Cu6Sn5 grains were discussed. The orientation relationships between £b-Cu6Sn5 and Cu were determined by transmission electron microscopy. The (11-20) plane of £b-Cu6Sn5 was found to be the interface with both the Cu (001) and (-111) surfaces, and a common orientation relationship of (0001)£b//(110)Cu was observed. The match of atoms between £b-Cu6Sn5 and Cu on the above interfaces were analyzed. (Chapter 2) A thin film technique was developed to study the orientation relationship and interface between £`-Cu3Sn and Cu by transmission electron microscopy. Epitaxial Cu thin films were grown on the NaCl (001) and (111) surfaces and Sn was evaporated to form £`-Cu3Sn directly without breaking the vacuum. The orientation relationship Z=[001]£`//[111]Cu, (100) £` //(-110)Cu, and (010)£` //(-1-12)Cu was found on the Cu (111) surface, but none on the Cu (001) surface. The interface was analyzed. (Chapter 3) The formation of the Fe-Al inhibition layer in hot-dip galvanizing is a confusing issue for a long time. This work presents a characterization result on the inhibition layer formed on a TiNb-stabilized interstitial-free steel after a short time galvanizing. The Fe-Al and steel interface was free from oxide, so that the Fe-Al intermetallic compound could directly nucleate on ferrite grains. TEM electron diffraction showed that only Fe2Al5 was formed and it had a well-defined orientation relationship of [110]FA// [111]Fe, (001)FA//(0-11)Fe and (1-10)FA//(2-1-1)Fe with Fe substrate where FA stands for Fe2Al5. The interfaces between Fe2Al5 and Fe are discussed. The Fe2Al5 grains nucleated epitaxially on Fe substrate had very small grain size, 20 nm or less, and several variants were intimately mixed. The grains grew rapidly to hundreds of nanometers toward the Zn side. (Chapter 4) The orientation relationships and interfaces of £_-AuSn with the Au (001), (110) and (111) surfaces were studied with transmission electron microscopy. Au was evaporated onto the NaCl (001), (011) and (111) surfaces to form epitaxial Au thin films and Sn was evaporated onto the Au film to form £_-AuSn. Two types of orientation relationships were found: (1) (11-20)£_//(001)Au, (0001)£_//(110)Au, and (1-100)£_//(-110)Au, which was found on the (11-20)£_/(001)Au and the(1-100)£_/(-110)Au interfaces; and (2) (11-20)£_//(-111)Au, (0001)£_//(110)Au, and (1-100)£_//(-11-2)Au, which was found on the (11-20)£_/(-111)Au interface. The interfaces were analyzed by the structures of the surfaces and the orientation relationships. The nucleation of £_-AuSn on these interfaces was also discussed. (Chapter 5)

Prior work in this system has indicated that, under favourable conditions, the formation of a martensitic transformation product on cooling may be preceded by a second-order cubic-rhombohedral transformation. In the present investigation, thin film electron microscopy and diffraction have been employed to study the pre-transformation phenomena in the temperature range 20-300°C. The results are interpreted in terms of localized thermal diffuse scattering, resulting from incipient mechanical instability. A model for the cubic-rhombohedral transformation of the rhombohedral phase suggest a moderate degree of co-operation between adjacent domains. Additional data is provided in the form of volumetric and x-ray intensity measurements. / Thesis / Master of Engineering (ME)

Survey work has resolved certain reported anomalies in this system. In particular, TiNi was found to undergo two displacive phase transformations at temperatures near room temperature. Below 50°C the pseudo body-centered cubic compound undergoes a gradual distortion in an unusual second order phase transformation producing the "transition phase”, the existence of which is terminated by a typical martensitic burst transfor­mation at 20°C which produces the "martensitic phase". The crystal structures of the parent phase and transformation products, and the trans­formation characteristics have been studied with X-ray and electron diffrac­tion, electron microscopy, electrical resistance and density measurements. / Thesis / Master of Science (MS)

The orientation relationship and interfaces of Au5Sn with the Au (001), (110) and (111) surfaces have been studied with transmission electron microscopy. Au was evaporated onto the NaCl (001), (110) and (111) surfaces to form epitaxial Au thin films and Sn was evaporated onto the Au film and heat treated to form Au5Sn. Two types of orientation relationships were found: (1) (2-1-10)Au5Sn/(001)Au¡A(0006)Au5Sn //(-220)Au and (03-30)Au5Sn//(220)Au, which was found on the (2-1-10)Au5Sn/(001)Au interface; and (2) (2-1-10)Au5Sn/(-111)Au¡A(0006)Au5Sn //(-22-4)Au and (03-30)Au5Sn//(220)Au, which was found on the (2-1-10)Au5Sn/(-111)Au interface.The structures of the interfaces were analyzed. The free energy formation of AuSn is much larger than that of Au5Sn.Analysis of above results show that the differences of the interfacial energies between AuSn/Au and Au5Sn/Au may not be a significant. Therefore probably has a lower activation energy of AuSn nucleation and in the first plane to form at the AuSn interface.

None

The purpose of thesis is to study the transient analysis of structural responses of solder joints under high-Speed impact. By using the experimental and simulation analysis. The experimental work can be divided into six parts, such as different impact speeds, different solder¡¦s components, different pad finishing, different UBM and Runner, and different thickness of PBO. From experiments, the variations of solder joint strength and mechanical properties were received and discussed and the failure mode. The empirical results show that maximum impact force on solder joints decreases as the impact speed increasing. The solder joint strength becomes stronger with the solder adopting elements of Ni and Co. The strength of solder ball was reduced significantly after a reflow. The intermetallic compound strength reduces with solder ball adopting high content of Ag. In impact test, the resistance of UBM of TiAl is better than that of TiAlTi. The runner adopted with the element Pd can improve the IMC reliablility to reduce Mode I failure. However, the PBO thickness has little influence on IMC strength. From the numerical results, in the consideration of strain rate on solder joint the mechanical properties of solder joint could be effectively investigated. According to the different IMC strength there will produce three failure modes of solder ball and the impact force becomes higher as the IMC strength setting higher. If the lower yield stress is considered in lower IMC strength, the impact force is not the highest of all, but the time duration is the highest of all.

The interfacial reactions of Sn-Zn and Sn-Zn-Al solder balls with Au/Ni surface finish under aging at 150¢J were investigated. With microstructure evolution, quantitative analysis, elemental distribution by X-ray color mapping from an electron probe microanalyzer (EPMA), the reaction procedure of phase transformation was proposed. During the reflow, Au dissolved into the solder balls and reacted with Zn to form £^-Au3Zn7. As aging time increased, £^-Au3Zn7 transformed to £^3-AuZn4. Finally, Zn precipitated near the Au-Zn intermetallic compound. On the other hand, Zn reacted with the Ni layer and formed Ni5Zn21. But the Al-Au-Zn IMC formed at the interface of Sn-Zn-Al solder balls, the reaction of Ni with Zn was inhibited. Even though the aging time increased to 50 days, no Ni5Zn21 was observed. The Joule effect was more apparent than the electromigration in the biased solder balls. First of all, the new phase (Au, Ni)Zn4 was proposed in the biased condition and in 175¢Jaging. Secondly, the thickness of the Ni5Zn21 IMC were the same between the anode and the cathode. Finally, We directly measure the temperature of the biased solder balls which was up to 173¢J.