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In this paper, the oxidation thermodynamics and oxidation kinetics of Au-20Sn solder at various temperatures were analyzed. The results indicated that the critical oxygen partial pressure to form SnO and SnO2 in Au-20Sn solder could be 1 × 10−44 Pascal (Pa) and 1 × 10−91 Pa at the temperature of 298 K, respectively. The oxidation kinetics analysis results indicated that the oxide on the surface of Au-20Sn solder consists mainly SnO2, while the major constituent of internal oxide is SnO. The reliability test results under salt spray environment have showed that the hermeticity of the package device gradually decreased with the increasing oxygen content in Au-20Sn solder. Meanwhile, the measured leakage rate of the packaging device could be lowered than 5 × 10−9 Pa·m–3·s–1 when the oxygen content in Au-20Sn solder is less than 28 ppm after high temperature aging.

Ag-based brazing filler metals are preferred in many industries, but the high price of Ag restricts their wider application. Therefore, developing novel low-Ag brazing filler metals has aroused extensive interest. In this study, the effects of the In and Ga elements on the melting behavior and spreading property of Ag10CuZnSn filler metal and the microstructure and strength of the brazed joints were investigated. The results show that both In and Ga can significantly decrease the solidus and liquidus temperatures of the filler metal. The In element can dissolve into the liquid filler metal and the Ga element can decrease the surface tension of the melted filler metal, which, in turn, improves the spreading area. The In element prefers to dissolve into the Ag-rich phase, and the Ga element prefers to dissolve into the Cu-rich phase; both improve the strength of the filler metal through solid-solution strengthening. The shear strength of the 304 stainless-steel brazed joint reached a peak value of 396 MPa when the Ag10CuZnSn-1.5In-2Ga (wt%) filler metal was used. However, the excessive addition of In and Ga forms brittle intermetallic compounds (IMCs) in the brazing seam, which decreases the strength of the brazed joint.

With the rapid iteration of microsystem integrated technology, the miniaturization of electronic devices requires packaging materials with higher reliability. In this work, the microstructure evolution and mechanical properties of novel epoxy composite SAC305 solder joints were studied after isothermal aging to evaluate the enhanced effect of epoxy addition. The thickness variation and morphological evolution of the interfacial layer were analyzed. The results showed that, as the aging time was prolonged, the Cu6Sn5 interfacial layer remarkably coarsened and Cu3Sn compounds formed between the Cu6Sn5 layer and Cu pad due to the continuous atomic diffusion. Compared with the monolithic joint, the epoxy composite SAC305 joints had a lower overall IMC growth rate during aging, closely related to the initial morphologies of the interfacial layers. The shear test results showed an apparent decrease in the shear forces of all the solder joints as the aging time increased. Nevertheless, because of the extra mechanical support provided by the epoxy layer, the epoxy composite joints demonstrated notably enhanced mechanical properties. After 1000 h aging treatment, the shear force of SAC305 joints containing 8 wt.% epoxy was 26.28 N, showing a 24.08% increase over the monolithic joint. Cu-Sn IMCs were detected on the shear fracture of the monolithic joint after 1000 h aging, indicating the fracture occurred near the interface and displayed a ductile/brittle mixed fracture. Concerning the epoxy composite joints, cracks were still initiated and extended within the solder bulk, demonstrating a noticeable enhancement in ductility due to the addition of epoxy.

In this study, trace amounts of In and Ce elements were composite added into a Ag10CuZnSn low-silver brazing filler metal, and the effects of the composite alloying on the solidus and liquidus temperatures, the spreading performance, the microstructure of the filler metal, and the mechanical properties of the joints prepared with these filler metals were studied. The results reveal that the In element can significantly decrease the solidus and the liquidus temperatures of the Ag10CuZnSn alloy, while the Ce element has little effect on the melting temperature. Trace amounts of In and Ce elements can obviously increase the spreading areas of the filler metals on the pure Cu and 304 stainless steel base metals. The In and Ce elements can refine the microstructure of the filler metals. When the contents of In and Ce are 1.5 wt% and 0.15 wt%, respectively, the microstructure refinement effect is the most obvious, and the shear strength of the 304 stainless steel brazed joint also achieves a maximum value of 375 MPa. Excessive addition of In and Ce can form brittle intermetallic compounds in the filler metal, decreasing the brazed joints' shear strength.

The oscillating phenomenon of the weld pool has a direct physical correspondence with its penetration state, which has broad application prospects in the monitoring of weld penetration states. This article studied the characteristics of the oscillating phenomenon of the weld pool in short-circuiting gas metal arc welding (S-GMAW) with different penetration states based on a welding high-speed photography system. The results show that the form of the liquid bridge electric explosion impact on the weld pool is “surface impact” in S-GMAW. The oscillation frequency of the weld pool decreases as the size of the weld pool increases. Compared with the partially penetrated weld pool, the boundary conditions of the fully penetrated weld pool had different boundary conditions, resulting in higher oscillation amplitude and lower oscillation frequency. In S-GMAW, no difference in welding voltage signal, caused by the difference in amplitude of the weld pool oscillation with different penetration states, was observed.

As a novel high-temperature solder with suitable eutectic temperature and excellent solderability, Au–30Ga eutectic alloy shows high application potential as a packaging material for high-power devices. In this work, the evolution of microstructure, shear strength and fracture mechanism of Au–30Ga/Ni solder joint during soldering and aging was studied. It was found that with the increase of soldering time, Ga was seriously consumed to form Ga–Ni interfacial intermetallic compounds (IMCs), resulting in the formation of Ga-poor region near the interface layer. Au7Ga3 phase would be first formed at the valley area of Ga3Ni2 IMC layer. The dominant IMCs growth mechanism eventually transformed from grain-boundary diffusion to volume diffusion after soldering for 0.49 min. The diffusion coefficients are 1.64 × 10−14 and 3.77 × 10−19 m2/s at 500 °C (soldering) and 300 °C (solid-state aging), respectively. With the coarsening of IMC layers, the fracture mechanism of joint changed from solder control mode to solder/IMC mixed control mode. When the thickness is 4.36 μm, the joint strength reaches the maximum value of 77.7 MPa. Furthermore, a reliability evaluation equation of Au–30Ga/Ni solder joint was established to optimize soldering process and solder composition.

With the rapid development of microelectronics packaging technology, the demand for high-performance packaging materials has further increased. This paper developed novel epoxy-containing Sn-3.0Ag-0.5Cu (SAC305-ER) composite solder pastes, and the effects of epoxy resin on their spreading performance, microstructure, and shear behaviour were analysed. The research results showed that with the addition of epoxy resin, SAC305 solder pastes exhibited exceptional spreadability on Cu substrates, which could be attributed to the reduction in the viscosity and the surface tension of the composite solder pastes. With the addition of epoxy resin, the solder matrix microstructure and interfacial morphology of SAC305-ER composite solder joints remained unchanged. However, continuous resin protective layers were observed on the surface of SAC305-ER composite solder joints after the reflow process. The shear properties of the composite solder joints were enhanced by the extra mechanical bonding effect provided by resin layers. When the epoxy resin content was 8 wt%, the shear forces of SAC305-ER composite solder joints reached the maximum value. Fracture analysis indicated that cracked epoxy resin was observed on the surface of SAC305-ER composite solder joints, indicating that the epoxy resin also underwent obvious deformation in the shear test.

With the continuous miniaturization and increase in functionality of the electronic devices used in the aerospace and national defense industries, the requirements for reliability of the solder joints in these devices keep increasing. In this study, a SnPbSb solder with excellent wettability was used as the research object, and the effects of high-temperature aging at 150 °C on the microstructure and mechanical properties of SnPbSb/Cu solder joints were investigated according to the relevant industry standards. It was found that high-temperature aging does not change the eutectic structure of the SnPbSb solder, but it does significantly coarsen the Sn-rich phase and the Pb-rich phase in the solder. In addition, the interfacial intermetallic compound (IMC) layer in the SnPbSb/Cu solder joint changes from a Cu6Sn5 single layer to a Cu6Sn5/Cu3Sn double layer after the aging, and the thickness of the IMC layer increases greatly. High-temperature aging significantly deteriorates the mechanical properties of the solder joints. After aging at 150 °C for 1000 h, the shear strength of the SnPbSb/Cu solder joints decreased by 45.39%, while the ductile fracture mode did not change.

The influence of Ga content on the melting temperature, wettability, microstructure, and mechanical properties of low-silver 12AgCuZnSn-2In-0.15Pr cadmium-free filler metal was investigated systematically by means of differential thermal analysis, X-ray diffractometer, scanning electron microscopy, energy-dispersive spectrometer, etc. The results showed that the addition of the Ga element reduced the solidus and liquidus temperatures of the novel low-silver filler metals, and effectively increased the spreading area of the filler metal on the copper and 304 stainless steel substrates. Furthermore, an appropriate amount of Ga element significantly optimized the interface morphology and improved the mechanical properties of the brazed joints. When the Ga content was 1wt.%, the shear strength of the brazed joints reached a peak value of 448 MPa, and the corresponding fracture morphology showed typical ductile characteristics with obvious dimples.

The Sn–Bi solder paste is commonly used in electronic assembly and packaging, but its brittleness causes poor reliability in shock environments. In this study, the mechanical reliability of Sn–Bi solder paste and Sn–Bi composite solder paste with thermosetting epoxy (TSEP Sn–Bi) was investigated with the board level drop test. The crack characterizations of solder joints were evaluated using a stereomicroscope after the dye and pull test. The microstructure characterization and failure types of solder joints were analyzed by a scanning electron microscope (SEM), and an energy dispersive spectrometer (EDS) was employed to investigate the initial phase identification and elemental analysis. Compared with Sn–Bi solder paste, the results show that the TSEP Sn–Bi solder pastes reduced the proportion of the complete failure and partial failure of the solder joints during the drop test. The microstructure observation of the crack path showed that the Sn–Bi/TSEP Sn–Bi solder joints were reinforced through the cured epoxy resin. The number of drops of the Sn–Bi/TSEP Sn–Bi-x (x = 3, 5, 7) solder joints had 1.55, 2.57, and over 3.00 times that of Sn–Bi/Sn–Bi solder joints after the board level drop test.

The flame brazing of H62 brass using a novel, low-silver Cu-P brazing filler metal was investigated in this study. The effect of the addition of a trace amount of Sn on the microstructure and properties of Cu-7P-1Ag filler metals was analyzed by means of X-ray diffractometer, scanning electron microscopy and energy dispersive spectrometer. The addition of trace Sn led to a decrease in the solidus and liquidus temperatures of Cu-7P-1Ag filler metals. Meanwhile, the spreading performance of the filler metals on a H62 brass substrate was improved. The microstructure of the low-silver, Cu-P brazing filler metal was mainly composed of α-Ag solid solution, α-Cu solid solution and Cu3P; an increase of Sn content led to the transformation of the microstructure of the joints from a block to a lamellar structure. When the Sn content was 0.5 wt. %, the shear strength of the joint at room temperature reached 348 MPa, and the fracture morphologies changed from a cleavage to a quasi-cleavage structure.

The continuous improvement of electronic device performances and the advancement of packaging technology have brought greater challenges to the reliability of solder joints in integrated circuits (ICs). In view of the increase of chip integration and the reduction of micro-bump size in 3D ICs, the high current density and excessive Joule heat will result in serious reliability issues of electromigration (EM) and thermomigration (TM) respectively, which evidently shorten the lifetime of solder joints. This article reviewed the influence of EM, TM and their coupling effect on microstructure evolution and properties of different joints soldered with pure Sn, SnAgCu, SnBi and SnZn solder. What's more, the increase of EM and TM resistances of micro-joints by microalloying, particle reinforcement and substrate improvement was explored. Finally, the shortcomings of current studies and the future research directions were summarized to further improve the EM and TM reliability of micro-joints, which promotes the application of lead-free solders in 3D ICs package.

With the development of electronical technology and the construction of the fifth-generation cellular networks, electronic devices with higher integrated level and power are widely applied. Hence, greater demands are being placed on electronic packaging materials. High-Pb solder alloys were widely used for low- and medium-temperature soldering for the past decades but have been prohibited due to toxicity. Au-based solder alloys with proper melting and mechanical properties show great potential to replace high-Pb solder alloys and are being emphasized recently. But in comparison with Pb-containing solder alloys, the investigation on novel Au-based solder alloys is quite insufficient, and their performance and reliability are still unclear. In this paper, the recent research studies on Au-based solder alloys with low temperature and medium temperature were reviewed and their microstructure, mechanical performance, and reliability were introduced and analyzed. Moreover, the novel processing technologies of Au-based solder alloys were discussed and compared.

Diamond tools were prepared by sintering Fe-Cu-Sn-Zn-Ni pre-alloyed powders and diamonds. The effects of Ni contents in pre-alloyed powders on microstructure evolution of Fe-based matrix, the properties of Fe-based matrix and the service life of diamond tools were investigated. The results showed that adding 3~15 wt.% Ni into the Fe-Cu-Sn-Zn pre-alloyed powders refined the microstructure of the Fe-based matrix and improved its density and hardness gradually. The addition of Ni reduced the loss of low melting liquid phase at a low sintered temperature, thus resulting in a decrease of the pores, an increase of the density and hardness of Fe-based matrix. When the Ni content is less than 9 wt.%, the bending strength of Fe-based matrix and diamond tools, together with the holding force of Fe-based matrix to diamonds increases sharply. They reached up to the optimal value with the Ni content of 9 wt.%. At this sintering powder ratio, the sufficient Fe-Cu-Sn-Zn-Ni liquid phase had a good wettability on the surface of diamonds, thus the optimal performance of sintered matrix and diamond tools was obtained. The service life of diamond tools was prolonged greatly owing to the excellent bonding capacity between matrix and diamonds. Once the Ni content exceeded 9 wt.%, the corresponding value decreased gradually. The fracture morphologies of the matrix changed from the brittle fracture into brittle-ductile fracture, then ductile fracture (with the Ni content of 9 wt.%), brittle-ductile mixed fracture and brittle fracture.

Ag-based and Cu-based brazing filler metals, which are the most widely used brazing materials in industrial manufacturing, have excellent gap-filling properties and can braze almost all the metallic materials and their alloys, except for the low-melting-point metals such as Al and Mg. Therefore, Ag-based and Cu-based brazing filler metals have attracted great attention. In this review, three series of typical Ag-based filler metals: the Ag-Cu, Ag-Cu-Zn, and Ag-Cu-Zn-Sn alloys; and three series of Cu-based filler metals: the crystalline and amorphous Cu-P filler metals, as well as the Cu-Zn filler metals, were chosen as the representatives. The latest research progress on Sn-containing Ag-based and Cu-based brazing filler metals is summarized, and the influences of Sn on the melting characteristics, wettability, microstructure, and mechanical properties of the selected filler metals are analyzed. Based on these, the problems and corresponding solutions in the investigation and application of the Sn-containing Ag-based and Cu-based filler metals are put forward, and the research and development trends of these filler metals are proposed.

The novel low-silver 12AgCuZnSn filler metals containing In and Pr were used for flame brazing of copper and 304 stainless steel in this study. The effects of In and Pr content on the melting temperature, wettability, mechanical properties and microstructure of 12AgCuZnSn filler metal were analyzed. The results indicate that the solidus and liquidus temperatures of filler metals decrease with the addition of In. Trace amounts of Pr have little impact on the melting temperature of the low-silver filler metals. In addition, the spreading area of filler metals on copper and 304 stainless steel is improved. The highest shear strength of brazed joint is 427 MPa when the content of In and Pr are 2 wt.% and 0.15 wt.%, respectively. Moreover, it is observed that the trace amount of Pr significantly refines the microstructure of brazed joint matrix. A bright Pr3Cu4Sn4 phase is found in filler metal and brazing seam when the contents of In and Pr are 5 wt.% and 0.5 wt.%, respectively.

Brazing was one of the earliest material-joining methods to be invented and widely used by humans. In the past 30 years, the technology and materials employed for brazing have developed rapidly and continuously. With the rise of the international new industrial revolution, the manufacturing industry is moving towards diversification, and brazing filler metals are also evolving in the direction of eco-friendliness, compounding and diversification. In the “carbon neutral” environment of 2021, green composite brazing materials will become mainstream. In this paper, the classification and characteristics of flux-containing brazing materials are summarized, and the preparation technology, composition design and typical application of composite brazing materials such as flux-cored brazing filler metal, flux-coated brazing filler metal and powder metallurgy brazing filler metal are analyzed. The article highlights the problems encountered in the research and development of composite brazing materials and proposes future development directions, such as with low-silver and cadmium-free brazing filler metals, the creation of new powder brazing filler metal-forming technology and improvements to the quality of brazing filler metals by shape control and performance optimization, to accelerate the process of brazing automation.

In this study, a Sn–Bi composite solder paste with thermosetting epoxy (TSEP Sn–Bi) was prepared by mixing Sn–Bi solder powder, flux, and epoxy system. The melting characteristics of the Sn–Bi solder alloy and the curing reaction of the epoxy system were measured by differential scanning calorimeter (DSC). A reflow profile was optimized based on the Sn–Bi reflow profile, and the Organic Solderability Preservative (OSP) Cu pad mounted 0603 chip resistor was chosen to reflow soldering and to prepare samples of the corresponding joint. The high temperature and humidity reliability of the solder joints at 85 °C/85% RH (Relative Humidity) for 1000 h and the thermal cycle reliability of the solder joints from −40 °C to 125 °C for 1000 cycles were investigated. Compared to the Sn–Bi solder joint, the TSEP Sn–Bi solder joints had increased reliability. The microstructure observation shows that the epoxy resin curing process did not affect the transformation of the microstructure. The shear force of the TSEP Sn–Bi solder joints after 1000 cycles of thermal cycling test was 1.23–1.35 times higher than the Sn–Bi solder joint and after 1000 h of temperature and humidity tests was 1.14–1.27 times higher than the Sn–Bi solder joint. The fracture analysis indicated that the cured cover layer could still have a mechanical reinforcement to the TSEP Sn–Bi solder joints after these reliability tests.

The Au-20Sn solder is widely used in the packaging of high-end electronic products, and the requirement on the reliability of the solder joints is more and more strict with a continuous increase in the performance of the package products. As the oxygen content in the Au-Sn solder is a key factor dominating the quality of fluxless packaging, in this study, the wettability and spreading performance of the Au-20Sn solder with different oxygen contents and the interfacial microstructure, mechanical properties, gas tightness and ratio of soldering area of the Au-Sn/Cu solder joints prepared using these solders were comprehensively investigated to clarify the effects of trace oxygen content. The results reveal that the wetting and spreading performances of the solder decrease sharply with increasing oxygen conte[nt. When the oxygen content increased from 18 to 77 ppm, the spreading area of the solder on the Cu substrate decreased from 92.8 to 49.2 mm2, reducing by 47%. Meanwhile, pores and microcracks appear in the solder joint with relatively high oxygen content, making the shear strength decrease from 56.6 to 31.7 MPa. The oxygen also greatly affects the gas tightness and ratio of soldering area. For the optical window packaged using Au-Sn solder containing 40 ppm of oxygen, the leakage rate was higher than 5 × 10−11 mbar·m−3·s−1 and cannot fulfill the requirements. With increasing oxygen content in the Au-Sn solder, the cleanliness of the chip packaged with these solders deteriorated, and the solder surface was obviously oxidized. When the oxygen content was 18 ppm, the ratio of soldering area was 92%, but decreased sharply to 53% when the oxygen content increased to 77 ppm. It is demonstrated that an oxygen content lower than 27 ppm is required for the Au-20Sn solder used in fluxless packaging.

The effect of different In contents on the melting characteristics, mechanical properties, and microstructure of 12Ag–Cu–Zn–Sn filler metal was investigated in this paper, and flame brazing of 304 stainless steel and copper plates was done using the 12Ag–Cu–Zn–Sn–xIn filler metal. The results indicate that adding appropriate amount of In can evidently decrease the solidus and liquidus temperatures and improve the wettability of the low silver based filler metals. In addition, the shear strength of 304 stainless steel and copper plates joint brazed by 12Ag–Cu–Zn–Sn–1In are satisfactory due to the solution strength effect, and scanning electron microscopy examination of the braze-zone revealed that more relatively sound joints were obtained when brazing was done with 12Ag–Cu–Zn–Sn–xIn filler metal than with Indium free one; its performance is comparable to that of the joint brazed with the 20Ag–Cu–Zn–Sn filler metal, having a remarkable silver-saving effect.

This work focused on the influence of hydrogen content on the microstructure and mechanical properties of ER5183 Al-Mg-Mn alloy wires for aluminum alloy welding. The hydrogen content of the ER5183 wires was measured, the macroscopic and microscopic morphologies of fractures were observed as well as the microstructure of the wires, and the tensile strength of the wires was also tested and investigated. The experimental results demonstrated three typical irregular macroscopic fractures of the wires appeared during the drawing process when the hydrogen content exceeded 0.23 μg/g. In the meantime, the aggregated pores were observed in the microstructure of the ϕ5.2 mm wire with the hydrogen content of 0.38 μg/g. Such defects may become the origin of cracks in subsequent processing and tensile tests. Moreover, higher hydrogen content in the ϕ5.2 mm welding wire will bring obvious changes in the fracture surface, which are internal cracks and micropores replacing the original uniform and compact dimples. With the higher hydrogen content, the tensile strength and plastic strain rate of ϕ1.2 mm wires would decrease. At the same time, unstable crack propagation would occur during the process of plastic deformation, leading to fracture. Considering the mechanical properties and microstructure, the hydrogen content of the ER5183 wires should be controlled below 0.23 μg/g.

In order to meet the service requirements of electronic devices working at 300 °C in the fields of energy resource prospecting and space exploration, Cr element was added to modify AuGa solder to improve its high-temperature performance. The results showed that the addition of 0.3 wt.% Cr element reduced the loss of Ga element in the smelting and casting process, and effectively improved the problem of the inhomogeneous microstructure of the solder matrix. On the basis of maintaining the good wettability of the solder, the addition of trace chromium effectively restrains the excessive flux of the solder, and the presence of chromium improves the oxidation resistance of the solder. Furthermore, Cr element optimized the interface morphology and improved the mechanical properties of the solder joint. The shear strength of the AuGa-0.3Cr/Ni joint was 87.2 MPa, which was 13.1% higher than that of the joint without Cr element. After 240 h of aging, the shear strength of the AuGa-0.3Cr joint was still the peak value at 84.1 MPa, which was 16.3% higher than that of the AuGa joint.

Extreme temperature change has generally been the great challenge to spacecraft electronic components, particularly in long, periodic, deep-space exploration missions. Hence, researchers have paid more attention to the reliability of component packaging materials. In this study, the microstructure evolution on the interface of Cu/Ni/Au/Au-12Ge/Au/Ni/Cu joints, as well as the effects of extreme thermal shock on mechanical properties and the fracture mode in the course of extreme thermal changes between −196 and 150 °C, have been investigated. Results revealed that the interface layers comprised of two thin layers of NiGe and Ni5Ge3 compounds after Au-12Ge solder alloy was soldered on the Au/Ni/Cu substrate. After extreme thermal shock tests, the microstructure morphology converted from scallop type to planar one due to the translation from NiGe to Ni5Ge3. Meanwhile, the thickness of interface layer hardly changed. The shear strength of the joints after 300 cycles of extreme thermal shock was 35.1 MPa, which decreased by 19.61%. The fracture location changed from the solder to solder/NiGe interface, and then to the interface of NiGe/Ni5Ge3 IMC layer. Moreover, the fracture type of the joints gradually transformed from ductile fracture mode to brittle mode during thermal shock test. Simultaneously, the formation and extension of defects, such as micro-voids and micro-cracks, were found during the process of thermal shock due to the different thermal expansion coefficient among the solder, interface layer and substrate.

In this study, brazing AA6061 to Q235 steel using flame brazing was performed with 70.9 wt.% CsF-0.5 wt.% RbF-28.6 wt.% AlF3 fluxes doped with GaF3, ZnF2, Zn(BF4)2 and Ga2O3 nanoparticles, matched with a Zn-15Al filler metal, and the spreadability of the filler metal and the mechanical properties of brazed joints were investigated at the same time. The results showed suitable amounts of GaF3, ZnF2, Zn(BF4)2 and Ga2O3 doped into the base flux could strengthen the filler metal in wetting and spreading on the surface of aluminum alloy and steel to different degrees. The suitable ranges of GaF3, ZnF2, Zn(BF4)2 and Ga2O3, respectively, were 0.0075–0.01 wt.%, 0.0075–0.01 wt.%, 0.0075–0.01 wt.% and 0.009–0.01 wt.%, and the maximum spreading area was obtained via doping with GaF3. The shear strength of brazed joints reached the peak at 126 MPa when 0.075 wt.% GaF3 was added. Comparative tests proved that the activity of the CsF-RbF-AlF3 flux doped with GaF3 was the best. The reason was that the CsF-RbF-AlF3-GaF3 flux was competent in removing oxides of the base metal and decreasing the interfacial tension, in virtue of the activity of Ga3+ as well as F−.

The influence of heat and droplet transfer into weld pool dynamic behavior and weld metal microstructure in double-pulsed gas metal arc welding (DP-GMAW) was investigated by the self-designed high-speed welding photography system. The heat input, the arc pressure, the droplet momentum and impingement pressure were measured and calculated. It was found that the arc pressure is far less than the droplet impingement pressure. The heat input and droplet impingement pressure per unit time acting on weld pool were proportional to the current pulse frequency, which fluctuated with thermal pulse. The size and oscillation amplitude of the weld pool had noticeable periodic changes synchronized with the process of heat input and droplet impingement. Compared to the microstructure of pulsed gas metal arc welding (P-GMAW) weld metal, that of DP-GMAW weld metal was significantly refined. High oscillation amplitude assisted the enhancement of weld pool convection, which leads to more constitutional supercooling. The heat input and shear force during the peak of thermal pulse causing dendrite fragmentation which provided sufficient crystal nucleus for the growth of equiaxed grains and the possibility of grain refinement. The effects of current parameters on welding behavior and weld metal grain size are investigated for further understanding of DP-GMAW.

The effect of trace amounts of GaF3 and Ga2O3 nanoparticles on the wettability and spreadability of CsF-AlF3 flux matched Zn-15Al filler metal were comparatively studied on 6061 aluminum alloy and Q235 low-carbon steel. The experimental results indicate that appropriate amounts of GaF3 and Ga2O3 added into the flux could significantly promote the Zn-15Al filler metal to wet and spread on the surface of 6061 aluminum alloy and Q235 low-carbon steel. The optimum ranges for GaF3 and Ga2O3 were 0.0075–0.01wt.% and 0.009–0.01 wt.%, respectively. Comparative analysis showed that the activity of CsF-AlF3 flux bearing GaF3 was higher than that bearing Ga2O3. The reason for this is that the former flux has a stronger ability to remove oxides of the base metal and reduce the interfacial tension of the molten filler metal and the base metal.

Droplet transfer plays a crucial role in welding stability and quality of pulsed gas metal arc weld (GMAW), referring to the process of heat and mass transition. In this work, the appearance, microstructure, microhardness, tensile properties, and impact toughness with three typical modes of droplet transfer in pulsed GMAW (ODMP: one drop per multiple pulses; ODPP: one drop per pulse; MDPP: multiple drops per pulse) were studied and compared. The results showed that the better welding appearance, the deeper penetration, and the less fume covered on the steel plate could be found during the ODPP welding process. At the same wire feeding speed and arc length, the average current was similar in ODPP and MDPP conditions. However, the average current in the ODMP condition was about 15 A larger than the other two, contributing to the higher heat input. Compared with MDPP and ODMP, the longest elongation and impact energy of the welded joint were found in the ODPP condition. Furthermore, the decrease of elongation and impact toughness in the ODMP condition might result from the higher heat input and the coarsen microstructure, like the proeutectoid ferrite and ferrite side plate.

The characteristics of weld bead formation and droplet transfer in pulsed gas metal arc weld (GMAW) with different arc lengths were studied by changing the base current time in this work. The results showed that it was easier to cause short circuits and spatters with a short arc. However, the deviation between the deepest point of penetration and the center of bead will be aggravated with the increase of arc length. In addition, more than 90% “one drop per pulse” (ODPP) transfer mode can be obtained when the pulse parameters were selected properly. However, the short arc trended to rise the proportion of “multiple drops per pulse” (MDPP), and the long arc trended towards increasing the proportion of “one drop per multiple pulses” (ODMP). Additionally, with the growth of the arc in the projected transfer zone, the penetration tended to become shallower because of the increase of arc heat dissipation, the fall of arc energy density, and droplet impact force. Overall, the strategy of choosing suitable arc length of pulsed GMAW was summarized: in order to obtain high-quality bead formation and weld joints, a shorter arc in the projected transfer zone was recommended.

The internal relations among the oscillation characteristics of the weld pool, the voltage signal curve and the penetration status of the weld joint in pulsed gas metal arc welding were investigated by using high-speed camera and image analysis system to extract characteristics of weld pool oscillation. The results show that the amplitude of weld pool oscillation decreased with decreasing weld penetration. An abrupt change occurred in the frequency components and amplitude of weld pool oscillation, accompanying the transition from partial to full penetration. The voltage signal curve lost the oscillation frequency characteristic of the pool, due to the curvature of the weld pool surface. While similar to the oscillation amplitude, the fluctuation of the voltage signal caused by the weld pool oscillation reflected the penetration of the weld pool. The abrupt transition in the fluctuation amplitude of the voltage signal in the base duration from partial penetration to full penetration may be used to sense the penetration of the weld pool in real time.

In this study, a Ga2O3 nano-particle was added into CsF-RbF-AlF3 flux to develop a highly active flux for brazing aluminum alloy to steel, and the spreadability and wettability of Zn-Al filler metal that matched the CsF-RbF-AlF3 flux-doped Ga2O3 nano-particle on the steel were investigated. The results showed that the spreadability and wettability of the CsF-RbF-AlF3 flux-doped Ga2O3 nano-particle could be remarkably improved when matching Zn-Al filler metals on both aluminum and low-carbon steel, for which the optimal content is in the range of 0.001−0.003 wt.% of Ga2O3. An investigation and analysis on the mechanism of reactions among CsF-RbF-AlF3-doped Ga2O3 nano-particle flux and filler metal or base metals showed that the Ga2O3 nano-particle is selectively absorbed by the interface of molten Zn-2Al filler metal and base metal, which released the surface-active element Ga to enrich the molten Zn-2Al filler metal and decreased the interfacial tension, so as to promote the enlargement of its spreading area during the brazing process. It was concluded that adding a trace amount of Ga2O3 nano-particle into CsF-RbF-AlF3 flux is a meaningful way to improve the activity of flux for brazing aluminum to steel compared with adding ZnCl2, which poses the risk of corrosion on aluminum.

The evolution of interfacial morphology and shear strengths of the joints soldered with Sn-0.3Ag-0.7Cu (SAC0307) and SAC0307-0.05Pr aged at 150 °C for different times (h; up to 840 h) were investigated. The experiments showed the electronic joint soldered with SAC0307-0.05Pr has a much higher shear strength than that soldered with SAC0307 after each period of the aging process. This contributes to the doping of Pr atoms, “vitamins in alloys”, which tend to be adsorbed on the grain surface of interfacial Cu6Sn5 IMCs, inhibiting the growth of IMCs. Theoretical analysis indicates that doping 0.05 wt.% Pr can evidently lower the growth constant of Cu6Sn5 (DCu6), while the growth constant of Cu3Sn (DCu3) decreased slightly. In addition, the electronic joint soldered with SAC0307-0.05Pr still has better ductility than that soldered with SAC0307, even after a 840-h aging process.

With the development of microelectronic packaging and increasingly specific service environment of solder joints, much stricter requirements have been placed on the properties of lead-free solders. On account of small size effect and high surface energy, nanoparticles have been widely used to improve the microstructure and properties of lead-free solders. Therefore, the composite solders bearing nanoparticles have recently attracted wide attention. This article reviewed the recent research on SnAgCu, SnBi, and SnZn composite solder alloys and introduced the effect of nanoparticles on their microstructure, mechanical properties, wettability, and reliability. The mechanism of nanoparticles strengthening was analyzed and summarized. In addition, the shortcomings and future development trends of nanoparticle-reinforced lead-free solders were discussed, which is expected to provide some theoretical reference for the application of these composite solder in 3D IC package.

Sn-58Bi solder has been widely used for microelectronics packaging due to its low melting point temperature, good wetting performance, good mechanical properties, and low cost. Compared with Sn-Bi solder alloy and Sn-Pb solder alloy, the strength and plasticity of Sn-Bi solder are not enough, due to the higher brittleness of bismuth, which thus limits the application of Sn-Bi solder. In order to improve the properties of Sn-Bi solder, a novel solder paste strengthened with resin was developed by mixing epoxy resin (ER) with Sn-58Bi solder, which enhanced the joint strength at a low cost. Aimed at the electronic industry, in this study, the spreadability of the novel solder paste was investigated, and the mechanical properties and microstructure of solder joints after reflow soldering were tested and analyzed. The results showed that when the content of epoxy resin was in the optimum range, the shear strength was significantly higher, reaching nearly twice that of Sn-58Bi solder alone.

Cosmic radiation has always been the most obvious barrier to planetary travels, especially in long-duration deep space exploration missions. Therefore, the reliability of satellite materials and the requirements of satellite miniaturization have received considerable attention. In this paper, the effect of γ-ray irradiation on the reliability of Sn50Pb49Sb1/Cu solder joints was investigated. It was found that the influence of γ-ray irradiation on the thickness and morphology of the intermetallic compound layer in Sn50Pb49Sb1/Cu was not obvious. However, the formation and growth of micro-voids and micro-cracks was observed in Pb-based solid solutions. Due to the Compton effect, the γ-ray photon could knock the electron out of its orbit, which created the energetic electron. The accumulation of dislocated atoms and lattice vacancies generated by energetic electrons could be the main factor that caused the formation of micro-voids and micro-cracks. The pull force of Sn50Pb49Sb1/Cu solder joints was reduced by 22% after being irradiated at the dose rate of 0.25 Gy(Si)/s for 960 h. Fractographic analysis showed that after irradiation, the fracture type of solder joints was still ductile but the ductility of the solder joints decreased with slightly inconspicuous dimples.

Various heat input conditions and post-weld heat treatments were adopted to investigate the microstructure evolution and mechanical properties of tungsten inert gas (TIG) welded joints of AA6082-T6 with porosity defects. The results show that the fracture location is uncertain when an as-welded joint has porosities in the weld zone (WZ), and overaging in the heat-affected zone (HAZ) at the same time. When the fracture of the as-welded joint occurs in the HAZ, the total heat input has a linear relation with the tensile strength of the joint. An excess heat input induces the overgrowth of Mg2Si precipitates in HAZ and the coarsening of α-Al grains in WZ, resulting in a decrease in the microhardness of the corresponding areas. After artificial aging treatment, the tensile strength of the welded joint is increased by approximately 9–13% as compared to that of as-welded joint, and fracture also occurs in HAZ. In contrast, for solution treated and artificial aging treated joint, fracture occurs suddenly at the rising phase of the tensile curve due to porosity defects throughout the weld metal. Furthermore, the eutectic Si particles of WZ coarsen and spheroidize after solution treatment and artificial aging treatment, due to the diffusion of Si to the surface of the original Si phases when soaking at high temperature.

This work offers an analysis of the wire feedability-related properties of Al-5Mg solid wire electrodes bearing Zr. Effects of Zr content on microstructures and mechanical properties of the Al-5Mg alloys were studied. Experimental results have demonstrated that α-Al dendrites of the as-cast Al-5Mg alloy are refined, and the tensile strength, microhardness and roughness of the 1.2 mm wire electrode are improved with an appropriate addition of Zr. In addition, the tensile strength and elongation of the welded joints welded using Al-5Mg wire electrodes bearing Zr reach the maximum value when 0.12% Zr is added into the wire alloy. However, when excess Zr is added, α-Al phases of the wire alloy and welded joint are coarsened, and the mechanical properties are deteriorated. Moreover, the structure and principle of a novel apparatus, which can enhance the feedability of the wire electrode, are introduced and the apparatus can achieve the rough and fine adjustments of cast and helix of the wire electrode.