Songbai Xue

Microstructure and properties of Cu/Al joints brazed with Zn−Al filler metals

Abstract The mechanical properties and microstructural distribution of the Cu/Al brazing joints formed by torch-brazing with different Zn–Al filler metals were investigated. The microstructure of the Zn–Al alloys was studied by optical microscopy and scanning electron microscopy, and the phase constitution of the Cu/Al joints was analyzed by energy dispersion spectrometry. The results show that the spreading area of the Zn–Al filler metals on the Cu and Al substrates increases as the Al content increases. The mechanical results indicate that the shear strength reaches a peak value of 88 MPa when Al and Cu are brazed with Zn–15Al filler metal. Microhardness levels from HV122 to HV515 were produced in the three brazing seam regions corresponding to various microstructure features. The Zn- and Al-rich phases exist in the middle brazing seam regions. However, two interface layers, CuZn 3 and Al 2 Cu are formed on the Cu side when the Al content in the filler metals is 2% and more than 15%, respectively. The relationship between intermetallic compounds on Cu side and Zn– x Al filler metals was investigated.

Effects of cerium on Sn-Ag-Cu alloys based on finite element simulation and experiments

Abstract Effect of small addition of rare earth on Sn-Ag-Cu solder was investigated by finite element method based on creep model of low stress and high stress and experiments respectively. It was found that addition of rare earths evidently improved the resistance to creep deformation of the solder, so that the reliability of Sn-Ag-Cu-Ce solder joint could be improved remarkably. Mechanical testing and microstructural analysis results showed that, mechanical properties of alloys bearing Ce were better than that of the original alloy, and the optimum content of Ce was about 0.03wt.%. After aging intermetallic compound between solder joint and Cu substrate was observed and analyzed by X-ray diffraction (XRD), scanning electron micrographs (SEM) and energy dispersive X-ray fluorescence spectrometer (EDX). Results showed that the thickness of intermetallic compound layer would became thinner when the addition of Ce was about 0.03wt.%, and the grains of intermetallic compound became finer, and the microstructure was more homogeneous than that in the original Sn-Ag-Cu/Cu interface.

Effect of Ag on the properties of solders and brazing filler metals

Ag is used as a beneficial alloy element in no matter solders or brazing filler metals. Obviously, the addition of Ag has a positive function on melting temperature, wettability, mechanical property and conductivity of filler metals. Therefore, Ag is still widely used in many researches and production in spite of that Ag is very expensive. Respectively, three kind of typical solders (Sn–Ag–Cu, Sn–Zn and Sn–Bi) and brazing filler metals (Ag–Cu–Zn, Cu–P, and Zn–Al) have been chosen for illustration. This article summarizes research status on the studying of Ag-contained solders and brazing filler metals, also analyses influence rules of Ag addition on the change of filler metals’ physical property, microstructure as well as mechanical property. Moreover, the problems and difficulties in the process of study Ag-contained solders and brazing filler metals have been presented. Synchronously, some suggestions have been put forward which may solve the problems and difficulties mentioned above, which provides theory guide for the follow-up study of Ag-contained solders and brazing filler metals, and their prospects are also looked ahead.

Creep behavior of SnAgCu solders with rare earth Ce doping

Abstract Extensive testing was carried out to study the effects of rare earth Ce doping on the properties of SnAgCu solder alloys. The addition of 0.03% (mass fraction) rare earth Ce into SnAgCu solder may improve its mechanical properties, but slightly lower its melting temperature. The tensile creep behavior of bulk SnAgCuCe solders was reported and compared with SnAgCu solders. It is found that SnAgCuCe solders show higher creep resistance than SnAgCu alloys. Moreover, Dorn model and Garofalo model are successfully used to describe the creep behavior of SnAgCu and SnAgCuCe alloys. The parameters of the two creep constitutive equations for SnAgCu and SnAgCuCe solders are determined from separated constitutive relations and experimental results. Nonlinear least-squares fitting is selected to determine the model constants. The experimental data of the stress-creep strain rate curves are in good agreement with the theoretical ones.

Microstructure and creep properties of Sn-Ag-Cu lead-free solders bearing minor amounts of the rare earth cerium

Purpose – The purpose of this paper is to investigate the effects of minor addition of the rare earth (RE) element cerium, Ce, on the microstructures and creep properties of Sn‐Ag‐Cu solder alloys.Design/methodology/approach – The pure Sn, Sn‐Cu alloy, Sn‐Ag alloy and Cu‐Ce alloy were used as raw materials. Sn‐Ag‐Cu alloys with different contents of RE Ce were chosen to compare with Sn‐Ag‐Cu. The raw materials of Sn, Sn‐Cu alloy, Sn‐Ag alloy, Cu‐Ce alloy were melted in a ceramic crucible, and were melted at 550°C±1°C for 40 minutes. To homogenize the solder alloy, mechanical stirring was performed every ten minutes using a glass rod. During the melting, KC1+LiCI (1.3:1), were used over the surface of liquid solder to prevent oxidation. The melted solder was chill cast into a rod.Findings – It is found that the microstructure exhibits smaller grains and the Ag3Sn/Cu6Sn5 intermetallic compound (IMC) phases are modified in matrix with the addition of Ce. In particular, the addition of 0.03 wt.% Ce to the Sn‐...

Present status of Sn–Zn lead-free solders bearing alloying elements

Recently, the Sn–Zn family of alloys, which possesses many attractive advantages such as relatively low melting point, cheap cost and the environmentally friendly component of Zn, has been widely used in electronic industry as one of the most potential replacements for the traditional Sn–Pb solders. However, there’re still some arguments on its shortcomings about the poor wettability and the weak oxidation resistance, which definitely limits its further application in lead-free electronic manufacturing. In order to overcome these disadvantages and further enhance the properties of Sn–Zn lead-free solders, alloying elements such as RE, Bi, Ag, Al, Ga, Cu, etc. were selected by lots of researchers as alloys addition into the solders. This paper summarizes the effects of alloying elements on the wettability, oxidation resistance, mechanical properties and microstructures of Sn–Zn lead-free solder alloys.

Torch brazing 3003 aluminum alloy with Zn—Al filler metal

Abstract Using Zn—Al filler metal with Al content of 2%–22% (mass fraction) and improved CsF–AlF 3 flux, wetting properties of Zn–Al filler metal on 3003 Al substrate were investigated. The mechanical property as well as the microstructure of the brazed joints was also studied. The results indicate that excellent joints can be produced by means of torch brazing when the Al content is less than 8%. The metallographic structure in the brazing seam is mainly composed of Al based solid solutions and Zn based solid solutions. The high hardness value of brazing seam of the 3003 aluminum alloy is higher than that of the base metal due to the effect of solid solution strengthening. The results also show that three microstructure zones could be found at the brazing interface; i.e., base metal, diffusing zone and interface zone. The distribution of the solid solution in the brazing seam is the main factor of the tensile strength rather than the diffusion zone width near the interface.

Determination of Anand parameters for SnAgCuCe solder

A unified viscoplastic constitutive model, Anand equations, was used to represent the inelastic deformation behavior for Sn3.8Ag0.7Cu/Sn3.8Ag0.7 Cu0.03Ce solders in surface mount technology. The Anand parameters of the constitutive equations for the SnAgCu and SnAgCuCe solders were determined from separated constitutive relations and experimental results. Non-linear least-squares fitting was selected to determine the model constants. Comparisons were then made with experimental measurements of the stress–inelastic strain curves: excellent agreement was found. The model accurately predicted the overall trend of steady-state stress–strain behavior of SnAgCu and SnAgCuCe solders for the temperature ranges from −55 to 125 °C and for the strain rate range from 1% s−1 to 0.01% s−1. It is concluded that the Anand model can be applied to represent the inelastic deformation behavior of solders at high homologous temperatures and can be recommended for finite element simulation of the stress–strain response of lead-free soldered joints. Based on the Anand model, the investigations of thermo-mechanical behavior of SnAgCu and SnAgCuCe soldered joints in fine pitch quad flat package by the finite element code have been done under thermal cyclic loading, and it is found that the reliability of the SnAgCuCe soldered joints is better than that of the SnAgCu soldered joints.

Effects of Ag on Properties of Sn-9Zn Lead-Free Solder

Abstract The influences of different Ag contents on the properties of Sn-9Zn lead-free solder were investigated. The results indicate that Ag plays an important role not only in the solderability and the structure of the solder, but also in the mechanical property of the soldered joint. In particular, adding 0.3% (mass fraction) Ag can improve the oxidation resistance of the solder, so the solderability of the solder is significantly improved. Sn-9Zn-0.3Ag shows finer and more uniform microstructure than Sn-9Zn. Results also indicate that when the content of Ag is 0.3%, the best mechanical property of the soldered joint can be obtained, and the fracture micrographs show that plenty of small and uniform dimples are found on the soldered joints fractures. Some Cu-Zn and Ag-Zn intermetallic compounds appear at the bottom of dimples when the content of Ag is up to 1%, and the mechanical property of the soldered joint is reduced.

Reliability study of Sn–Ag–Cu–Ce soldered joints in quad flat packages

Abstract The reliability of Sn–Ag–Cu–Ce lead-free soldered joints in quad flat packages under thermal cycling was investigated based on finite element simulation and experiments. The stress and strain response of fine pitch QFP device lead-free soldered joints were analyzed using finite element method based on Garofalo–Arrhenius model. The simulated results indicate that the creep distribution is not uniform, the heel of joints is the maximum creep strain concentrated sites. And comparisons were then made with experimental results of the cracks observed in the Sn–Ag–Cu–Ce soldered joints subjected to the temperature cycled experiment. In addition, the relative mechanical and metallurgical factors, which dominate the failure of soldered joints, were utilized to analyze the phenomena. The fracture surfaces indicate that crack initiate and propagate along the interface among bulk Cu 6 Sn 5 phases in Sn–Ag–Cu–Ce soldered joints.