Preventing formation of intermetallic compounds in ultrasonic-assisted Sn soldering of Mg/Al alloys through pre-plating a Ni coating layer on the Mg substrate

Magnesium and aluminum alloys are widely used in various industries because of their excellent properties,and their reliable connection may increase application of materials.Intermetallic compounds(IMCs)affect the joint performance of Mg/Al.In this study,AZ31 Mg alloy with/without a nickel(Ni)coating layer and 6061 Al alloy were joined by ultrasonic-assisted soldering with Sn-3.0Ag-0.5Cu(SAC)filler.The effects of the Ni coating layer on the microstructure and mechanical properties of Mg/Al joints were systematically investigated.The Ni coating layer had a significant effect on formation of the Mg_(2)Sn IMC and the mechanical properties of Mg/Al joints.The blocky Mg_(2)Sn IMC formed in the Mg/SAC/Al joints without a Ni coating layer.The content of the Mg_(2)Sn IMC increased with increasing soldering temperature,but the joint strength decreased.The joint without a Ni coating layer fractured at the blocky Mg_(2)Sn IMC in the solder,and the maximum shear strength was 32.2 MPa.By pre-plating Ni on the Mg substrate,formation of the blocky Mg_(2)Sn IMC was inhibited in the soldering temperature range 240–280℃and the joint strength increased.However,when the soldering temperature increased to 310℃,the blocky Mg_(2)Sn IMC precipitated again in the solder.Transmission electron microscopy showed that some nano-sized Mg_(2)Sn IMC and the(Cu,Ni)_(6)Sn_(5)phase formed in the Mg(Ni)/SAC/Al joint soldered at 280℃,indicating that the Ni coating layer could no longer prevent diffusion of Mg into the solder when the soldering temperature was higher than 280℃.The maximum shear strength of the Mg(Ni)/SAC/Al joint was 58.2 MPa for a soldering temperature of 280℃,which was 80.7%higher than that of the Mg/SAC/Al joint,and the joint was broken at the Mg(Ni)/SAC interface.Pre-plating Ni is a feasible way to inhibit formation of IMCs when joining dissimilar metals.

A review of soldering by localized heating

In recent years,the rapid development of the new energy industry has driven continuous upgrading of high-density and high-power devices.In the packaging and assembly process,the problem of differentiation of the thermal needs of different modules has become increasingly prominent,especially for small-size solder joints with high heat dissipation in high-power devices.Localized soldering is con-sidered a suitable choice to selectively heat the desired target while not affecting other heat-sensitive chips.This paper reviews several local-ized soldering processes,focusing on the size of solder joints,soldering materials,and current state of the technique.Each localized solder-ing process was discovered to have unique characteristics.The requirements for small-size solder joints are met by laser soldering,microres-istance soldering,and self-propagating soldering;however,laser soldering has difficulty meeting the requirements for large heat dissipation,microresistance soldering requires the application of pressure to joints,and self-propagating soldering requires ignition materials.However,for small-size solder junctions,selective wave soldering,microwave soldering,and ultrasonic soldering are not appropriate.Because the magnetic field can be focused on a tiny area and the output energy of induction heating is large,induction soldering can be employed as a significant trend in future research.

Diode Laser Soldering Technology of Fine Pitch QFP Devices

The laser provides a controllable means of supplying localized energy for solder joint formation and is a valuable tool in electronics manufacture.Diode laser soldering for fine pitch QFP devices were carried out with Sn-Ag-Cu lead-free solder and Sn-Pb solder respectively,and the mechanical properties of micro-joints of the QFP devices were tested and studied by STR-1000 micro-joints tester.The results indicate that sound QFP micro-joints without bridging or solder ball are gained by means of diode laser soldering method with appropriate laser processing parameters,and the pitch of the QFP devices is as fine as to 0.4mm.Tensile strength of QFP micro-joints increases gradually with the increase of laser output power,the maximum tensile strength presents when the laser output power increase to a certain value.The results also indicate that the mechanical properties of QFP micro-joints soldered by diode laser soldering system are better than those of QFP micro-joints soldered by IR reflow soldering method.The experimental results may provide a theory guide for investigation of diode laser soldering.

Microstructure evolution and mechanical properties of the Sip/Zn- Al composite joints by ultrasonic-assisted soldering in air

Hypereutectic Al -27Si alloys were joined without flux by ultrasonic-assisted soldering at 420 ℃ in air using Zn -5Al the filler alloys, and Si particulate-reinforced Zn - Al based composites filler joints were obtained. The ultrasonic vibration introduced into soldering could influence the migration of Si particles and the microstructure of solidified Zn - Al based alloys. Both the distribution of Si particles and microstructure of the solidified Zn - Al based alloys affected the shear strength of joints. The shear strength increased with the ultrasonic vibration time. The highest average shear strength of joints reached to -68.5 MPa. Transcrystalline rupture mode was observed on the fracture surface.

Mechanism of die soldering during aluminum die casting

Soldering is a unique casting defect associated with die casting or metal mold casting of aluminum alloys. It occurs when molten aluminum sticks or solders the surface of the die steel and remains there after the ejection of the casting, causing a surface defect and dimensional inaccuracy of the castings and increased machine downtime. Soldering occurs easily when a bare die steel mold is used for die casting of aluminum alloys. When molten aluminum comes in contact with the die steel at a temperature higher than a critical temperature, the iron and aluminum atoms diffuse into each other, forming a series of intermetallic phases and a liquid aluminum-rich fcc phase. This liquid phase exists between intermetallic phases. On cooling, the liquid fcc phase solidifi es on the intermetallic phases and grows into the casting, resulting in soldering. The critical temperature is the eutectic temperature near the aluminum corner of the phase diagram. If the die is protected using a nonreactive ceramic coating, soldering starts at locations where local coating failure occurs. Molten aluminum comes into contact with die steel through the coating failure locations and eats into the steel matrix, forming small pits. As these small pits grow, the coating is gradually removed and soldering becomes more severe. Details of die soldering step on a bare steel die and on a coated die material are discussed.

Low temperature soldering alloy using Sn63 Pb37 implantation of silica ceramics and copper solder assisted by ion and deposition

Copper ion implantation and deposition technique was applied as a pretreatment method for low temperature joining of silica ceramic （ SiO2 ） and copper alloy. The effect of copper ion implantation and deposition parameters on the microstructures and mechanical behavior of the soldering joints was investigated by scanning electron microscope （SEM） , X- ray diffraction （ XRD ） and shearing test. The copper implantation depth was about 90 nm with peak concentration of 70% for the SiO2 sample implanted for 90 rain. If copper film was deposited for 4 rain using magnetron sputtering, copper layer with thickness of 150 nm and peak concentration of 80% was obtained. After pretreatment of ion implantation and deposition, SiO2 and copper were joined successfully at low temperature directly using SnPb solder. The SnPb solder filling ratio along joining seams was up to 100% without defects with smooth soldering toes. With the increase of implantation dose, the shear strength of the Si02/Cu joints increases accordingly. After a special pretreatment on SiO2 （ Cu implantation for 30min, following Cu deposition for 4 rain, then Cu implantation for 60 rain and finally Cu deposition for 120 min） , a maximum soldering strength of 22 MPa was achieved, and the soldering joints fractured at the SiO2 base material.

Test research and mechanism analysis of vacuum fluxless laser soldering for SMD

Fluxless soldering can solve a series of problems caused by side-effects afflux essentially. Feasibility research on vacuum fluxless laser soldering and mechanism analysis on fluxless action of vacuum were carried out. Fluxless soldering succeeded in spreading and wetting on Cu pad with laser heating source in vacuum surroundings. What' s more, this fluxless technology was applied in surface mounting of chip resistance successfully.

Study on laser and hot air reflow soldering of PBGA solder ball

Laser and hot air reflow soldering of PBGA solder ball was investigated. Experimental results showed that surface quality and shear strength of solder bump reflowed by laser was superior than the solder bump by hot air, and the microstructure within the solder bump reflowed by laser was much finer. Analysis on interfacial reaction showed that eutectic solder reacted with Au/Ni/Cu pad shortly after the solder was melted. Interface of solder bump reflowed by laser consists of a continuous AuSn 4 layer and remnant Au element. Needle like AuSn 4 grew sidewise from interface, and then spread out to the entire interface region. A thin layer of Ni 3Sn 4 intermetallic compound was found at the interface of solder bump reflowed by hot air, and AuSn 4 particles distributed within the whole solder bump randomly. The combination effect of the continuous AuSn 4 layer and finer eutectic microstructure contributes to the higher shear strength of solder bump reflowed by laser.

THERMAL PROCESS OF VACUUM FLUXLESS LASER SOLDERING AND ANALYSIS ON SOLDER SPREADING AND WETTING

In order to study the mechanism of vacuum fluxless soldering on the conditions of laser heating, the method of measuring temperature by the thermocouple is used to analyze the spreading and wetting process of both fluxless Sn-Pb solder in the vacuum surroundings and flux Sn-Pb solder on Cu pad. Solder spreading and wetting affected by the soldering thermal process is also discussed according to the thermodynamics principle. Results show that vacuum fluxless soldering demands higher temperature, and the fall of the solder surface tension is the important factor achieving fluxless laser soldering.

High-Frequency Heating for Soldering in Electronics

Processes of high-frequency (HF) heating are examined and its parameters for the soldering of electronic modules are optimized. The advantages of HF heating are the following: selectivity by skin-effect;high density of energy;process- ing in any environment, including vacuum or inert gas;high ecological cleanliness, improvement solder flowing by electrodynamics forces increase the quality of soldering connections. Investigation of HF electromagnetic heating has allowed to optimize heating speed in local zones of soldering connections formation and to improve their quality due to joint action of superficial effects and electromagnetic forces.

Fully Connected Convolutional Neural Network in PCB Soldering Point Inspection

In Electronics Manufacturing Services (EMS) industry, Printed Circuit Board (PCB) inspection is tricky and hard, especially for soldering point inspection due to the extremely tiny size and inconsistent appearance for uneven heating in reflow soldering process. Conventional computer vision technique based on OpenCV or Halcon usually cause false positive call for originally good soldering point on PCB because OpenCV or Halcon use the pre-defined threshold in color proportion for deciding whether the specific soldering point is OK or NG (not good). However, soldering point forms are various after heating in reflow soldering process. This paper puts forward a VGG structure deep convolutional neural network, which is named SolderNet for processing soldering point after reflow heating process to effectively inspect soldering point status, reduce omission rate and error rate, and increase first pass rate. SolderNet consists of 11 hidden convolution layers and 3 densely connected layers. Accuracy reports are divided into OK point recognition and NG point recognition. For OK soldering point recognition, 92% is achieved. For NG soldering point recognition, 99% is achieved. The dataset is collected from KAGA Co. Ltd Plant in Suzhou. First pass rate at KAGA plant is increased from 25% to 80% in general.

FORMATION AND CHANGE OF AuSn_4 COMPOUNDS AT INTERFACE BETWEEN PBGA SOLDER BALL AND Au/Ni/Cu METALLIZATION DURING LASER AND INFRA-RED REFLOW SOLDERING

Interactions between 63Sn37Pb solder and PBGA metallization (Au/Ni/Cu) duringlaser and infrared reflow soldering were studied. During laser reflow soldering process,a thin layer of AuSn_4 was observed at the interface of the solder bumps, its morphologywas strongly dependent on the laser reflow power and heating time. The solder bumpsformed by the first laser reflow was reflowed again to form the solder joints. TheAuSn_4 compounds formed in the first laser reflow process dissolved into the bulk solderafter the secondary infrared reflow process. The needle-like AuSn_4 changed into rod-like, and distributed inside the solder near the solder/pad interface.

Mg_(2)Sn-induced whisker growth on the surfaces of Mg/Sn/Mg ultrasonic-assisted soldering joints

In this paper,the phenomena of Mg_(2)Sn-induced Sn whisker growth were explored on the surfaces of Mg/Sn/Mg ultrasonic-assisted soldering joints after aging treatment.The in-situ observation and thermal analysis confirmed that the formation and the corrosion of Mg_(2)Sn nanoparticles were the dominant reason of Sn whisker growth.The Mg_(2)Sn accumulation at the grain boundaries would pin the dislocation slip and affect the continuity of whisker growth,and the boundary angle would thus play a decisive role in the growth shape of Sn whiskers due to the pining effect of Mg_(2)Sn.This study might be conducive to elucidating the growth behavior of Sn whiskers and provide the exploration strategy to further improve the bonding strength of Mg/Sn/Mg ultrasonic-assisted soldering joints.

Significant Inhibition of IMCs Growth between an Electroless Ni-W-P Metallization and SAC305 Solder During Soldering and Aging

The formation and growth behavior of intermetallic compound(IMC) layers after introducing an electroless Ni-W-P metallization into the Sn-3.0Ag-0.5Cu(SAC305) solder joint during soldering and aging were investigated. The soldering was performed at 250 ℃ for 10 min, followed by air cooling and aging treatment at 150 ℃ up to 15 days. The results show that the scallop-like Cu_6Sn_5 IMC layer and planar-like Cu_3Sn formed between solder and Cu substrate during soldering and aging. The Ni_3P and(Ni,Cu)_3Sn_4 compounds were formed between electroless Ni-W-P layer and solder, and Cu substrate was not damaged and kept a smooth interface. When the isothermal aging treatment was applied, the total thickness of IMCs which formed at the SAC305/Cu and SAC305/Ni-W-P/Cu interface increased with increasing aging time. Kirkendall voids emerged at the Cu_3Sn and the Ni_3P layers, but the voids emerged at the Ni_3P layer in the form of crack. The amount of Kirkendall voids increased and the crack elongated with increasing aging time. The Cu_6Sn_5 and(Ni,Cu)_3Sn_4grains grew by merging adjacent grains. In the process of growth, the growing interfacial compounds filled the free space, and new columnar dendrite grain of(Ni,Cu)_3Sn_4 constantly generated during aging treatment. After 15 days aging, the Ni-W-P barrier layer was still remained, which indicated that the Ni-W-P layer can be a good barrier layer between the solder alloys and Cu substrate.

Effect of Bismuth Addition on Structure and Mechanical Properties of Tin-9Zinc Soldering Alloy

Sn-Zn based solder is a possible replacement of Pb solder because of its better mechanical properties. The alloys need to be studied and explored to get a usable solder alloy having better properties. In this work eutectic Sn-9Zn and three Tin-Zinc-Bismuth ternary alloys were prepared and investigated their microhardness and mechanical properties. Microhardness, tensile strength and elastic modulus increase with Bi addition while ductility decreases with Bi addition.

Wetting Behavior and Interfacial Reactions in (Sn-9Zn)-2Cu/Ni Joints during Soldering and Isothermal Aging

The wetting property of （Sn-9Zn）-2Cu （wt pct） on Ni substrate and the evolution of interracial microstructure in （Sn-9Zn）-2Cu/Ni joints during soldering as well as isothermal aging were studied. The wetting ability of eutectic Sn-gZn solder on Ni substrate was markedly improved by adding 2 wt pct Cu into this solder alloy. Plate-like Cu5Zn8 intermetallic compounds （IMCs） were detected in （Sn-9Zn）-2Cu solder matrix. A continuous NisZn21 IMC layer was formed at （Sn-9Zn）-2Cu/Ni interface after soldering. This IMC layer kept its type and integrality even after aging at 170℃ for up to 1000 h. At the early aging stage （before 500 h）, the IMC layer grew fast and its thickness followed a linear relationship with the square root of aging time. Thereafter, however, the thickness increased very slowly with longer aging time. When the joints were aged for 1000 h, a new IMC phase, （Cu,Ni）5Zn8, was found in the matrix near the interface. The formation of （Cu,Ni）5Zns phase can be attributed to the diffusion of Ni atoms into the solder matrix from the substrate.

Thermal and Electrical Properties of Sn-Zn-Bi Ternary Soldering Alloys

Sn-Zn based solder is a possible replacement of Pb solder because of its better mechanical properties. The alloys need to be studied and explored to get a usable solder alloy having better properties. In this work, eutectic Sn-9Zn and three Tin-Zinc-Bismuth ternary alloys were prepared and investigated their thermal and electrical properties. Thermo-mechanical Analysis and Differential Thermal Analysis were used to investigate thermal properties. Microstructural study is carried out with Scanning Electron Microscope. The alloys have single melting point. The co-efficient of thermal expansion and co-efficient of thermal contraction varies with alloy composition and temperature range. Electrical conductivity changes with Bi addition.

Soldering of Zr-based bulk metallic glass and copper by Au-12Ge eutectic alloy

Zr-based bulk metallic glass and copper with different surface roughness were soldered using low temperature eutectic Au-12 Ge(wt%) solder on a thermomechanical simulator. The cross-sectional microstructures of the brazed joints were analyzed by scanning electron microscopy(SEM) and transmission electron microscope(TEM) in detail, and the compositional distribution along the interface was analyzed by energy-dispersive spectrometer(EDS). Results show that the surface roughness of base metals plays an important role in the quality of the brazed joint because the surface roughness can enlarge the effective contact area, which can improve the brazing surface quality between two materials. A moderate roughness of treated Zr-based metallic glass of 18 μm is shown to be the best for the soldering, while the surface roughness has a weak effect on the soldering behavior of Au-12 Ge solder on copper. After soldering, long-range diffusion of atoms occurs between the base metal and solder, and five distinct regions are formed at the joint region.

Rapid Ultrasonic-Assisted Soldering of AZ31B Mg Alloy/6061 Al Alloy with Low-Melting-Point Sn–xZn Solders Without Flux in Air

A novel ultrasonic-assisted low-temperature soldering was developed to join AZ31B Mg alloy and 6061 Al alloy with a series of Sn–x Zn solders. The average maximum shear strength of the joints reaches up to 87.5 MPa at soldering temperature of 300 °C under ultrasonic assistance for only 5 s using Sn–20 Zn solder. The fracture path propagates completely in the soldering seam. The results indicate that the microjet generated by ultrasonic pressure in liquid solder could strike and splinter the Mg_2Sn intermetallic compounds into small pieces, which contributes to the enhancement of the joint strength. In addition, the primary Al(Zn) solid solution phase formed during cooling stage could also strengthen the joint due to the prevention of microcracks propagation.

Microstructure and properties of AgCu/2 wt%Ag-added Sn-Pb solder/CuBe joints fabricated by vapor phase soldering

The purpose of this paper is to investigate the effect of 2 wt%Ag addition in Sn-Pb eutectic solder on microstructure and mechanical properties of AgCu/solder/CuBe joint fabricated by vapor phase soldering.63Sn37Pb and 62Sn36Pb2Ag solder pastes were used to join Cu(1.7 wt%-2.5 wt%)Be and Ag(2 wt%-5 wt%)Cu alloys.Two fracture modes are observed in 62Sn36Pb2Ag and 63Sn37Pb joints after lateral shear tests at room temperature or 120℃,and shear forces of 62Sn36Pb2Ag joints are far higher than those of 63Sn37Pb joints.No obvious difference is observed in morphology and thickness of intermetallic compounds(IMCs)at interfaces of the 63Sn37Pb and 62Sn36Pb2Ag joints.Within the two kinds of joints,for-mation of big blocky or plate-like Ag_(3)Sn is restrained.However,many Ag_(3)Sn IMCs particles(1-3 μm in width)in isolated and dispersed distribution are observed within 62Sn36Pb2Ag joints.The Ag3Sn particles are responsible for the better mechanical properties of 62Sn36Pb2 Ag joints than those of 63Sn37Pb joints.The results present in this paper may provide a guide for restraining formation of big blocky or plate-like Ag_(3) Sn in joints with Ag pads or thick Ag surface finish on pads by utilizing vapor phase soldering process,and improving mechanical properties of Cu/SnPb/Ag joints by adding Ag in SnPb eutectic solder.