Effect of a Trace of Bi and Ni on the Microstructure and Wetting Properties of Sn-Zn-Cu Lead-Free Solder

The microstructure and melting behavior of Sn-9Zn-2Cu （SZC） lead-free solder with 3 wt pct Bi and various amount of Ni additions were studied. The wetting properties and the interracial reaction of Sn-Zn-Cu with Cu substrate were also examined. The results indicated that the addition of 3 wt pct Bi could decrease the melting point of the solder and Ni would refine the microstructure and the rod-shape Cu5Zn8 phase changed into square-shape （Cu, Ni）5Zn8 phase. The addition of Bi, Ni greatly improved the wettability of SZC solder. In addition, the interracial phase of the solders/Cu joint was typical planar Cu5Zn8 in SZC-3Bi-INi alloy.     

Solder Size Effect on Early Stage Interfacial Intermetallic Compound Evolution in Wetting Reaction of Sn3.0Ag0.5Cu/ENEPIG Joints

Solder size effect on early stage interfacial intermetallic compound(IMC) evolution in wetting reaction between Sne3.0Age0.5Cu solder balls and electroless nickel electroless palladium immersion gold(ENEPIG) pads at 250 C was investigated. The interfacial IMCs transformed from initial needle- and rodtype(Cu,Ni)6Sn5to dodecahedron-type(Cu,Ni)6Sn5and then to needle-type(Ni,Cu)3Sn4at the early interfacial reaction stage. Moreover, these IMC transformations occurred earlier in the smaller solder joints, where the decreasing rate of Cu concentration was faster due to the Cu consumption by the formation of interfacial(Cu,Ni)6Sn5. On thermodynamics, the decrease of Cu concentration in liquid solder changed the phase equilibrium at the interface and thus resulted in the evolution of interfacial IMCs; on kinetics, larger solder joints had sufficient Cu flux toward the interface to feed the(Cu,Ni)6Sn5growth in contrast to smaller solder joints, thus resulted in the delayed IMC transformation and the formation of larger dodecahedron-type(Cu,Ni)6Sn5grains. In smaller solders, no spalling but the consumption of(Cu,Ni)6Sn5grains by the formation of(Ni,Cu)3Sn4grains occurred where smaller discrete(Cu,Ni)6Sn5grains formed at the interface.     

Bond Strength of the Sn-Ti-Ⅹ Ternary Active Solders on Sialon Ceramic

The bond strength of the Sn based ternary active solders,Sn-5Ti with various contents of Ag,Cu,In,Ni or AI on sialon ceramic was investigated by the ceramic/ceramic joint joining.The bond strengthof Sn-STi (about 80 MPa) may increase to 90-100 MPa by small addition of Ag or Cu (about5-10%).A little Ni (about 1-3%) in the solder is slightly beneficial,but too more Ni (more than 5%)is harmful.Small addition of In is trivial,but too more In is detrimental.On the other hand,small addi-tion of AI in the active solder decreases greatly the bond strength of the solder,therefore it is veryharmful.In discussion,three suggestions for selection of the third element to increase the bondstrength of the soft solders on ceramic,i.e.with a high surface energy,benefiting to wetting on ce-ramic and strengthening the soft solder itself,have been made.     

Microstructure and Property of AlN Joint Brazed with Au–Pd–Co–Ni–V Brazing Filler

An Au–Pd–Co–Ni–V brazing alloy was designed for Al N ceramic joining. Its wettability on Al N was studied with the sessile drop method. The results showed that the contact angle was decreased gradually with increasing temperature and the prolonging of holding time. Sound Al N/Al N joints were achieved with the brazing alloy at 1170 °C for 10 min. The microstructure of the Al N/Al N joints was examined by scanning electron microscopy(SEM). It was found that element V played the active role in the interfacial reaction between the ceramic and the brazing alloy. V reacted with N decomposed from Al N, resulted in the formation of V–N compound. Based on the energy-dispersive spectroscopy(EDS)and X-ray diffraction(XRD) analysis results, the V–N reaction product was verified as V2 N. The overall reaction during the brazing process can be described by the following equation: 2V + AlN + 2Pd = V2 N + Pd2 Al.The Al N/Al N joints brazed with the Au–Pd–Co–Ni–V brazing alloy exhibited three-point bend strength of 162.7 MPa at room temperature, and under the bend test the fracture of the joint occurred at the Al N ceramic substrate.     

Wetting Behaviors and Interfacial Reaction between Sn-10Sb-5Cu High Temperature Lead-free Solder and Cu Substrate

Sn-10Sb-5Cu lead-free solder was fabricated for high temperature application in electronic package. Wetting behaviors and interfacial reaction between such a high temperature lead-free solder and Cu substrate were investigated and compared with those of 95Pb-Sn solder. The results showed that the wetting properties of Sn-10Sb-5Cu solder are superior to those of 95Pb-Sn solder in maximum wetting force, wetting time and wetting angle in the temperature range of 340-400 ℃. However, the surface of the Sn-10Sb-5...     

Effect of TiN diffusion barrier on elements interdiffusion behavior of Ni/GH3535 system in LiF-NaF-KF molten salt at 700℃

A TiN interlayer with high electrical conductivity was prepared between the GH3535 alloy and the Ni coating as a diffusion barrier to elements interdiffusion with the goal of increasing the corrosion resistance of GH3535 alloy in molten FLiNaK salt at 700℃. Results indicated that Ni coating could be directly electroplated on the TiN coated GH3535 alloy without extra conductive transition layer. TiN layer showed excellent thermal and chemical stabilities at elevated temperature in this molten salt system, without phase decomposition. The Ni/TiN composite coating was stable enough to resist corrosion in LiF-NaF-KF molten salt at 700℃. Elements interdiffusion between the substrate and Ni coating could be effectively inhibited and the corrosion resistance of the alloy was greatly enhanced. Besides, the TiN interlayer remained continuous and well adhered to the Ni coating as well as the substrate after corrosion test.     

Brazing of WC–8Co cemented carbide to steel using Cu–Ni–Al alloys as filler metal: Microstructures and joint mechanical behavior

Three novel Cu–Ni–Al brazing filler alloys with Cu/Ni weight ratio of 4:1 and 2.5–10 wt% Al were developed and characterized, and the wetting of three Cu–Ni–Al alloys on WC–8 Co cemented carbide were investigated at 1190–1210?C by the sessile drop technique. Vacuum brazing of the WC–8 Co cemented carbide to SAE1045 steel using the three Cu–Ni–Al alloys as filler metal was further carried out based on the wetting test results. The interfacial interactions and joint mechanical behaviors involving microhardness, shear strength and fracture were analyzed and discussed. The experimental results show that all the three wetting systems present excellent wettability with final contact angles of less than 5?and fast spreading. An obvious degeneration layer with continuous thin strip forms in the cemented carbide adjacent to the Cu–Ni–Al/WC–8 Co interface. The variation of microhardness in the joint cross-section is closely related to the interactions(such as diffusion and solid solution) of WC–8 Co/Cu–Ni–Al/steel system. Compared with the other two brazed joints, the WC–8 Co/Cu–19 Ni–5 Al/steel brazed joint presents more reliable interlayer microstructure and mechanical property while brazing at the corresponding wetting temperatures for 5 min, and its average shear strength is over 200 MPa after further optimizing the brazing temperature and holding time. The joint shear fracture path passes along the degeneration layer, Cu–Ni–Al/WC–8 Co interface and brazing interlayer, showing a mixed ductile-brittle fracture.     

Microstructures and Mechanical Properties of Vacuum Brazed Ti_3Al/TiAl Joints Using Two Ti-based Filler Metals

Vacuum brazing of Ti3Al-based alloy to Ti Al was firstly carried out by Ti—15Cu—15Ni(wt%) filler metal.A continuous Ti3 Al band, Ti2 Ni and Ti2Cu/Cu3 Ti phases formed and the joint showed a shear strength of53.8–112.4 MPa at room temperature. For the improvement of the joint strength, a new Ti—Zr—Cu—Ni—Fe filler alloy was designed, and its wettability on Ti3 Al and Ti Al substrate was studied with the sessile drop method. After holding for 20 min at 1010 °C the Ti—Zr—Cu—Ni—Fe filler showed a low contact angle of20° and 21° on (Ti)_3Al and Ti Al substrate, respectively. The joint brazed with this novel filler mainly consisted of Ti-rich area, (Ti)_3Al reaction layer and residual filler metal. With the increase of the brazing temperature, the amount of residual filler metal decreased and the (Ti)_3 Al reaction layer thickened. The (Ti)_3Al/Ti Al joint brazed with Ti—Zr—Cu—Ni—Fe filler exhibited a lower hardness than that brazed with Ti—Cu—Ni filler. The corresponding joints brazed at 950 °C for 5 min presented the shear strength of257.6 ± 33.6 MPa at room temperature and 304.8 ± 9.9 MPa at 600 °C.     

Effect of Brazing Conditions on Microstructure and Mechanical Properties of Al2O3/Ti--6Al-4V Alloy Joints Reinforced by TiB Whiskers

Al2O3 and Ti-6Al-4V alloy were brazed with Ag-Cu-Ti ＋B fillers in different brazing conditions. Effects of brazing temperature, holding time and additive Ti content on joints microstructure and shear strength were investigated by scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, transmission electron microscopy and shear testing. Results indicate that TiCu and Ti（Cu,Al） decrease, but Ti2Cu and -Ti2（Cu,Al） increase in brazing seam with increasing brazing temperature, holding time and additive Ti content. Area consisting of Ti3（Cu,Al）30 and TiO near Al2O3 becomes gradually discontinuous from continuity when brazing temperature rises or holding time extends. As Ti additive content increases, TiO is absent near Al2O3, area consisting of only Ti3（Cu,Al）30 thickens. TiB whiskers are in situ synthesized by Ti and B atoms during brazing process. The brazing temperature, holding time and additive Ti content on joints microstructure influence the joints shear strength directly. The shear strength of joints, obtained at 850 ℃ holding for 10 min, reaches the maximum of 78 MPa. According to the experimental results, phase diagram and thermodynamics calculation, the interface evolution mechanism of the Al2O3/Ti-6Al-4V alloy joint was analyzed.     

Influence of Thermal Cycling on the Microstructure and Shear Strength of Sn3.5Ag0.75Cu and Sn63Pb37 Solder Joints on Au/Ni Metallization

The influence of thermal cycling on the microstructure and joint strength of Sn3.5Ag0.75Cu （SAC） and Sn63Pb37 （SnPb） solder joints was investigated. SAC and SnPb solder balls were soldered on 0.1 and 0.9 μm Au finished metallization, respectively. After 1000 thermal cycles between -40℃ and 125℃, a very thin intermetallic compound （IMC） layer containing Au, Sn, Ni, and Cu formed at the interface between SAC solder joints and underneath metallization with 0.1 μm Au finish, and （Au, Ni, Cu）Sn4 and a very thin AuSn-Ni-Cu IMC layer formed between SAC solder joints and underneath metallization with 0.9 μm Au finish. For SnPb solder joints with 0.1 μm Au finish, a thin （Ni, Cu, Au）3Sn4 IMC layer and a Pb-rich layer formed below and above the （Au, Ni）Sn4 IMC, respectively. Cu diffused through Ni layer and was involved into the IMC formation process. Similar interfacial microstructure was also found for SnPb solder joints with 0.9μm Au finish. The results of shear test show that the shear strength of SAC solder joints is consistently higher than that of SnPb eutectic solder joints during thermal cycling.     

Effects of Cr,Ni and Cu on the Corrosion Behavior of Low Carbon Microalloying Steel in a Cl~- Containing Environment

The effects of Cr, Ni and Cu on the corrosion behavior of low carbon microalloying steel in a Cl containing environment were investigated. The results revealed that the corrosion process could be divided into the initia stage in which the corrosion rate increased with accumulation of corrosion products and the later stage in which homogeneous and compact inner rust layers started to protect steel substrate out of corrosion mediums. The results of X-ray diffraction (XRD) indicated that the rust layers of the three-group steels (Cr Cr-Ni and Cr-Ni-Cu steels) were composed of α-FeOOH,β-FeOOH,γ-FeOOH, Fe3O4 and large amounts o amorphous compounds. The content of amorphous compounds of CreNieCu steel was about 2%-3% more than that of CreNi steel. The results of electron probe microanalysis (EPMA) showed that Cr concentrated mainly in the inner region of the rust of Cr-Ni-Cu steel, inner/outer interface especially, whereas Ni was uniformly distributed all over the rust and Cu was noticed rarely after 73 wet/dry cycles. The addition of C and Ni was beneficial to the formation of dense and compact inner rust layer, which was the most importan reason for the improvement of corrosion resistance of experimental steel.     

Crystallization of Al-based Amorphous Alloys in Good Conductivity Solution

The corrosion-induced crystallization of Al94 exNixGd6（x=6 and 10, in at.%） metallic glasses as well as phase separation, oxidation and cracking in good conductivity solution has been investigated by various techniques.The transmission electronic microscopy（TEM） result reveals that crystalline intermetallics and oxides present on the electrochemically thinned hole edge, and the phase separation occurs in the matrix of the as-spun ribbons with the circumferential speed Rcof 29.3 m/s. In addition, the bending and cracking of the samples occur after corrosion. The influence of Ni content on the phase separation, bending and cracking can be explained by the fact that the percolation of the backbone clusters in the amorphous alloy melts and glasses is enhanced by increasing the composition of Ni.     

Influence of Al Content on the Atmospheric Corrosion Behaviour of Magnesium-Aluminum Alloys

The influence of Al content on the Mg-Al alloys corrosion performance during sodium chloride induced at- mospheric corrosion has been studied. It was found that the corrosion rate of three Mg-Al alloys was accelerated with increasing Al content. The poor corrosion resistance was attributed to the galvanic coupling between the β phase and eutectic phase or α phase and the formation of porous corrosion products.     

Effect of Cobalt Doping on the Microstructure and Tensile Properties of Lead Free Solder Joint Subjected to Electromigration

Rapid Cu diffusion is one of the main causes of electromigration(EM) failure in lead-free solder joints.In this study, an effort has been made to investigate the detrimental effects of EM on microstructure and mechanical performance of solder joint by introducing Co nanoparticles(NP) doped flux at the interface between SAC305 solder and copper substrate. EM tests were conducted on un-doped SAC305 and Co-doped SAC305 solder joints for different time intervals, with the maximum duration of 1128 h. A DC current was applied to the both types of solder joints to achieve a current density of 1 × 10~4A/cm~2. EM tests were performed in an oil bath maintained at a constant temperature of 80 °C. It is found that Codoped flux significantly reduced the formation of cracks and voids at the cathode interface. Co atoms entered into the lattice of Cu_6Sn_5 leading to the formation of(Cu, Co)_6Sn_5. This thermodynamically stabilized the interfacial intermetallic(IMC) layers both at the anode and cathode sides and suppressed the change in their thickness. The average anodic growth rate of(Cu, Co)_6Sn_5 interfacial IMC in the doped sample was about one order of magnitude lower compared with that of Cu_6Sn_5 in the un-doped samples.Co-NP also improved the tensile strength considerably before and after EM. The report suggests that the reliability of solder joint during EM can be improved by using Co-NP doped flux.     

Failure Modes of Lead Free Solder Bumps Formed by Induction Spontaneous Heating Reflow

The shear failure modes and respective failure mechanism of Sn3.5Ag and Sn3.0Ag0.5Cu lead-free solder bumping on Au/Ni/Cu metallization formed by induction spontaneous heating reflow process have been investigated through the shear test after aging at 120℃ for 0, 1, 4, 9 and 16 d. Different typical shear failure behaviors have been found in the loading curves （shear force vs displacement）. From the results of interracial morphology analysis of the fracture surfaces and cross-sections, two main typical failure modes have been identified. The probabilities of the failure modes occurrence are inconsistent when the joints were aged for different times. The evolution of the brittle NiaSn4 and Cu-Ni-Au-Sn layers and the grains coarsening of the solder bulk are the basic reasons for the change of shear failure modes.     

Interfacial Electronic Structure of Thin Cu Films Grown on Ar^＋—ion Sputter—cleaned α—Al2O3 Substrates

The bonding and electronic structure of Cu/(0001)Al2O3 and Cu/(1120)Al2O3 interfaces has been studied experimentally using spatially-resolved transmission electron energy loss spectroscopy.The specimen were prepared by depositing Cu on single-crystal α-Al2O3 substrates,which have been Ar^ -ion sputter-cleaned prior to the growth of Cu.For both orientations of theα-Al2O3 substrate,atomically abrupt interfaces formed as determined by high-resolution transmission electron microscopy.The investigations of the interfacial Cu-L2,3,Al-L2,3 and O-K energy loss near-edge structures,which are proportional to the site-and angular-momentum-projected unoccupied density of states above the Fermi level,indicate the existence of metallic Cu-Al bonds at the Cu/Al2O3 interface independent of the substrate orientation.     

Effect of Fe Content on the Interfacial Reliability of SnAgCu/Fe-Ni Solder Joints

Fe-Ni films with compositions of Fe-75Ni, Fe-50Ni, and Fe-30Ni were used as under bump metallization （UBM） to evaluate the interracial reliability of SnAgCu/Fe-Ni solder joints through ball shear test, high temperature storage, and temperature cycling. The shear strengths for Fe-75Ni, Fe-5ONi, and Fe-3ONi solder joints after reflow were 42.57, 53.94 and 53.98 MPa, respectively, which were all satisfied the requirement of industrialization （〉34.3 MPa）. High temperature storage was conducted at 150, 175 and 200 ℃. It was found that higher Fe content in Fe-Ni layer had the ability to inhibit the mutual diffusion at interface region below 150 ℃, and the growth speed of intermetallic compound （IMC） decreased with increasing Fe concentration. When stored at 200 ℃, the IMC thickness reached a limit for all three films after 4 days, and some cracks occurred at the interface between IMC and Fe-Ni layer. The activation energies for the growth of FeSn2 on Fe-30Ni, Fe-5ONi, and Fe-75Ni films were calculated as 246, 185, and 81 kJ/mol, respectively. Temperature cycling tests revealed that SnAgCu/Fe-5ONi solder joint had the lowest failure rate （less than 10%）, and had the best interfacial reliability among three compositions.     

Molecular Dynamics Study on Interfacial Energy and Atomic Structure of Ag/Ni and Cu/Ni Heterophase System

The results of molecular dynamics calculations on the interfacial energies and atomic structures of Ag/Ni and Cu/Ni interfaces are presented. Calculation on Ag/Ni interfaces with low-index planes shows that those containing the (111) plane have the lowest energies, which is in agreement with the experiments. Comparing surface energy with interfacial energy, it is found the order of the interfacial energies of Ag/Ni and Cu/Ni containing the planes fall in the same order as solid-vapor surface energies of Ag, Cu and Ni. In this MD simulation, the relaxed atomic structure and dislocation network of (110)Ag||(110)Ni interface are coincident to HREM observations.     

Glass-forming Ability and Corrosion Resistance of Zr—Cu—Al—Co Bulk Metallic Glass

Investigations were carried out to examine the effects of Co addition on the glass-forming ability(GFA)and corrosion resistance of Zr_(46)Cu_(46)(Al)_8 bulk metallic glass in chloride-containing solution. It is found that the GFA of(Zr_(46)Cu_(46)(Al)_8 )100-x Co x(x = 0, 1, 2, and 4 at.%) alloys reduces with the increase in Co content and correlates well with the parameters, such as the supercooled liquid region width ΔT x, the reduced glass transition temperature T rg and γ. The corrosion resistance is however found to be enhanced with the increase in Co concentration. The addition of Co causes the enrichment of Zr and Al, but depletes Cu in the surface films, which effectively enhances the corrosion potential and lowers the corrosion current densit     

Effects of Current Stressing on Shear Properties of Sn-3.8Ag-0.7Cu Solder Joints

Effects of electromigration on microstructure, shear strength, and fracture behavior of solder joints were investigated by single-ball shear samples of eutectic Sn-3.8Ag-0.7Cu (SAC) joined by Cu plates at two sides. The electromigration tests were conducted at a current density of about 1.1×103 A/cm2 and a working temperature of about 83℃. The results showed that the shear strength and flow stress decreased greatly after current stressing. Such a decrease was associated with no significant loss of the fract...