Characterization of 17-4PH stainless steel powders produced by supersonic gas atomization

17-4PH stainless steel powders were prepared using a supersonic nozzle in a close-coupled gas atomization system. The characteristics of powder particles were carried out by means of a laser particle size analyzer, scanning electron microscopy （SEM）, and the X-ray diffraction （XRD） technique. The results show that the mass median particle diameter is about 19.15 prn. Three main types of surface microstructures are observed in the powders： well-developed dendrite, cellular, and cellular dendrite structure. The XRD measurements show that, as the particle size decreases, the amount of fcc phase gradually decreases and that of bcc phase increases. The cooling rate is inversely related to the particle size, i.e., it decreases with an increase in particle size.

The effects of pressure, temperature, and depth/diameter ratio on the microvia filling performance of Ag-coated Cu micro-nanoparticles for advanced electronic packaging

Conductive fillers made from metal nanoparticles offer many advan-tages for the fabrication of a variety of electronic devices,but when they have a porous structure,their poor conductivity limits their adoption in many applications.In this study,an Ag-coated Cu micro-nanoparticle paste is used to achieve compact filling of blind vias on flexible copper clad polyimide laminates through a multistep filling and sintering tech-nique.The filled blind vias achieve a resistivity as low as 6.2μΩ·cm,which is comparable that of electroplated blind vias.Higher sintering pressure and temperature promote the filling performance,while the conductivity deteriorates at a via depth/diameter ratio greater than 1:1.Finite element simulations reveal a stress inhomogeneity in vias with large depth/diameter ratios,which is the key to understanding the evolution of the conductive properties of a paste-filled via.This study provides an effective method for high-performance microvia filling as well as insights into the mechanism that influences its performance.

Influence of Mn on wettability and microstructure of low-silver lead-free solders

The influence of Mn on wettability and microstructure of low-silver solders was investigated. Mn degrades the wettability of low-silver solders, while the wettability of the Mn doping solders does not change with Mn content in a linear way. As a result of Mn doping, the cellular/dendritic β-Sn and the eutectic phase are refined. It indicates that Mn promotes the spontaneous and heterogeneous nucleation process of the solder alloys. The growth of intermetallic compound on the joint inter＇ace during soldering is also restrained. Aging experiment shows that Mn suppresses the growth of Cu3Sn and Cu6Sn5 layers at the joint interface.

Properties of (Fe-B)-doped Sn-1.0Ag-0.5Cu solders prepared by mechanical alloying

To introduce boron (B) into the Sn-1.0Ag-0.5Cu (SAC 105) solder, based on the thermodynamic calculations, iron (Fe) is a competent carrier component for bonding B and Sn. The Sn-Fe-B master alloys were prepared by mechanical alloying initially;then, the SAC 105- 0.05(Fe-B) and SAC 105-0.1 (Fe-B) solder alloys were prepared using 72-h-milling Sn-Fe-B master alloys. The preparation process and the properties of solders were studied in this work. For the Sn-Fe-B master alloys, the results show that with the increase in the ball-milling time, the powder changes illustrate a cold welding-crushingcold welding cyclic process. Moreover, the supersaturated solid solubility of (Fe-B) increases gradually in the alloys, matrix and the lattice distortion increases to 0.167% after 72-h milling. Meanwhile, the alloying degree is increasingly apparent, and after 72-h milling, the content of B in the Sn matrix reaches 2.38 wt%. For the solder alloys, with the (Fe-B) content in creasing, the melting point decreases and a significant grain refinement occurs in the matrix. Compared to the benchmark SAC105, the hardness of SAC105-0.05(Fe-B) and SAC 105-0.1 (Fe-B) solder alloys prepared by this method is improved by 20.65% and 34.79%, respectively. The present research provides a novel approach for introducing the immiscible component into the lead-free solder alloys.

Solder paste metamorphism

Solder paste quality can be improved from microstructure and surface status of the solder powder.In this work,the micro-morphology of solder paste was observed and the particle surface condition was analyzed.Also,the conditions of corrosion and the corrosion products in different organic acid groups(activators)were analyzed.The result shows that the SnO passive film on the solder powder surface reacts with the COO-in the active agent of the solder paste.This reaction led the passivation layer to be peeled off.It also caused the change in solder powders’physical and chemical properties and made the metal boundary to be cold-welded.This is the root cause of solder paste exsiccation and deterioration.The study on the details shows that to obtain high-quality solder paste,one of the key methods is using the solder powder with ideal passivation shell structure and defect-free surface.

Modification of Sn–1.0Ag–0.5Cu solder using nickel and boron

Effects of Ni and B additions on the microstructure and growth behavior of the intermetallic compound(IMC) of Sn–1.0Ag–0.5Cu alloys(SAC105) were investigated in this study. Results show that microadditions of Ni and B result in volume fraction of primary Sn increasing and the grain size decreasing observably. It is found that a large number of fine reinforcement particles with network-like shape are found in the solder, and the thickness of interfacial IMC layer in the solder joint is grew less than that of SAC105 with longer aging time. Shear test results reveal that as-soldered solder joints of microalloyed SAC105 have better shear strength than that of SAC105 solder alloy.