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Mechanical Properties of QFP Joints Soldered with SnAgCu and SnPb Solders

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Chinese Journal of Mechanical Engineering 2011年第4期24卷 596-600页

作者： xue Peng xue songbai ZENG Guang ZHANG Liang DAI Wei College of Materials Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing 210016 China

With the development of lead-free solder alloys, the investiagtion focusing on the relibility of lead-free solders are essential. Since the reliability database of lead-free solder joints needs to be further supplied, the creep behavior of SnAgCu soldered joints on Quad Flat Package （QFP） devices under thermo cycling load are studied in this paper, compared to conventional SnPb solder, by finite element simulation based on Garofalo-Arrhenius creep model. Meanwhile, the mechanical properties of SnAgCu and SnPb soldered joints in the pitches of QFP devices are also carried out by means of tensile test. The results indicate that the values of strain and stress of SnAgCu soldered joints were all smaller than those of SnPb under thermal cycling, and the tensile strength of the joints soldered with SnAgCu solder was higher than that of SnPb, which means the reliability of the joints soldered with SnAgCu solder is better than SnPb soldered joints. As the fracture surface morphology of the soldered joints compared, SnAgCu soldered joint presented ductile fracture, while the fracture mechanism of SnPb solder joints displayed both brittle and ductile fracture. Above all, the experimental results is in accord with that of simulation, which will provide guidance for reliability study and application of lead-free solders.

关键词： creep model finite element analysis Quad flat package (QFP) devices mechanical properties

Diode Laser Soldering Technology of Fine Pitch QFP Devices

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Chinese Journal of Mechanical Engineering 2011年第5期24卷 917-922页

作者： xue songbai ZHANG Liang HAN Zongjie WANG Jianxin YU Shenglin College of Materials Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing 210016 China School of Mechanical and Electrical Engineering Xuzhou Normal University Xuzhou 221116 China The 14th Research Institute China Electronics Technology Group Corporation Nanjing 210013 China

The laser provides a controllable means of supplying localized energy for solder joint formation and is a valuable tool in electronics *** 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 *** 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 *** 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 *** 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 *** experimental results may provide a theory guide for investigation of diode laser soldering.

关键词： diode laser soldering QFP device mechanical properties of micro-joint

EFFECTS OF LEAD WIDTHS AND PITCHES ON RELIABILITY OF QUAD FLAT PACKAGE(QFP)SOLDERED JOINTS

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Chinese Journal of Mechanical Engineering 2007年第4期20卷 40-43页

作者： xue songbai WU Yuxiu HAN Zongjie WANG Jianxin College of Materials Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing 210016 China

The finite element method（FEM） is used to analyze the effects of lead widths and pitches on reliability of soldered joints. The optimum simulation for QFP devices is also researched. The results indicate that when the lead pitches are the same, the maximum equivalent stress of the soldered joints increases with the increasing of lead widths, while the reliability of the soldered joints reduces. When the lead widths are the same, the maximum equivalent stress of the soldered joints doesn＇t decrease completely with the increasing of lead pitches, a minimum value of the maximum equivalent stress values exists in all the curves. Under this condition the maximum equivalent stress of the soldewed joints is relatively the least, the reliability of soldered joints is high and the assembly is excellent. The simulating results indicate the best parameter： The lead width is 0.2 mm and lead pitch is 0.3 mm （the distance between two leads is 0.1 mm）, which are benefited for the micromation of QFP devices now. The minimum value of the maximum equivalent stress of soldered joints exists while lead width is 0.25 mm and lead pitch is 0.35 mm （the distance between two leads is 0.1 mm）, the devices can serve for a long time and the reliability is the highest, the assembly is excellent. The simulating results also indicate the fact that the lead width is 0.15 mm and lead pitch is 0.2 mm maybe the limit of QFP, which is significant for the high lead count and micromation of assembly.

关键词： Quad flat package (QFP) Maximum equivalent stress Soldered joints Assembly optimization Finite element method

Anand Parameters Determination for SnAgCu Solder Bearing Micro-amounts Rare Earth Ce

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Chinese Journal of Mechanical Engineering 2010年第2期23卷 257-262页

作者： ZHANG Liang xue songbai GAO Lili CHEN Yan YU Shenglin SHENG Zhong College of Materials Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing 210016 China Harbin Welding Institute Harbin 150080 China The 14th Research Institute China Electronics Technology Group Corporation Nanjing 210013 China

SnAgCu solder system with the addition of rare earth Ce, which has better thermo-mechanical properties compared to those of SnPb solder, is regarded as one of the promising candidates for electronic assembly. Moreover, the SnAgCuCe solder alloys can provide good quality joints with Cu substrates. However, there is few report of the constitutive model for SnAgCu solder bearing micro-amounts rare earth Ce. In this paper, the unified viscoplastic constitutive model, Anand equations, is used to represent the inelastic deformation behavior for SnAgCu and SnAgCuCe solders. In order to obtain the acquired data for the fitting of the material parameters of this unified model, a series of experiments of constant strain rate test were conducted under isothermal conditions at different temperatures. The Anand parameters of the constitutive equations for SnAgCu and SnAgCuCe solder were determined from separated constitutive relations and experimental results. Nonlinear least-square fitting was selected to determine the model constants. And the simulated results were then compared 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 25℃ to 150 ℃, and the strain rate ranges from 0.01 s^-1 to 0.001 s ^-1. It is concluded that the Anand model can be applied for representing the inelastic deformation behavior of solders at high homologous temperature 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 of SnAgCu and SnAgCuCe soldered joints in fine pitch quad flat package by finite element code were done under thermal cyclic loading, it is found that the reliability of SnAgCu soldered joints can be improved remarkably with addition of rare earth Ce. The results ma

关键词： Anand equations constitutive relations SnAgCuCe solders rare earth reliability

Effect of Thermal Cycling on Properties and Microstructure of SnAgCuCe Soldered Joints in QFP Devices

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Chinese Journal of Mechanical Engineering 2011年第4期24卷 561-566页

作者： ZHANG Liang xue songbai GAO Lili ZENG Guang YU Shenglin SHENG Zhong College of Materials Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing 210016 China School of Mechanical ＆ Electrical Engineering Xuzhou Normal University Xuzhou 221116 China The 14th Research Institute China Electronics Technology Group Corporation Nanjing 210013 China

Increasing global concern about the environment is bringing regulatory （European directives） and consumer （＂green products＂） pressure on the electronics industry in Europe and Japan to reduce or completely eliminate the use of lead （Pb） in products. Among all lead-free solder alloys, SnAgCu solder system, which has better thermo-mechanical properties compared with those of SnPb solder, is proven to be one of the promising candidates for electronic assembly. Previous work also revealed that adding a small amount of rare earth Ce into SnAgCu solder can visibly improve the properties and inhibit the excessive growth of the intermetallic compound layer. Thermal fatigue properties of SnAgCuCe soldered joints in QFP devices under thermal conditions have been investigated by finite element method and experiments. Based on creep model of low stress and high stress, corresponding creep subroutine was established for simulating the stress and strain response of SnAgCuCe soldered joint from -55 ℃ to 125 ℃, and fatigue life was calculated using creep fatigue life prediction equation. Moreover, thermal cycling experiments were conducted, the experimental results were found to be close to the simulated results. In addition, the tensile force of SnAgCuCe soldered joints decreased with increasing number of thermal cycles, and the fracture mechanism transformed from toughness fracture to brittle intergranular fracture. Moreover the tensile force changes and fracture microstructure evolution could benefit the quantitative evaluations of the mechanical performances of lead-free soldered joints under thermal cycling loadings.

关键词： finite element method creep equation thermal cycling fatigue life

Reliability Evaluation of QFN Devices Soldered Joints with Creep Model

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Chinese Journal of Mechanical Engineering 2011年第3期24卷 428-432页

作者： JI Feng xue songbai ZHANG Liang GAO Lili SHENG Zhong DAI Wei College of Materials Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing 210016 China

The solder joint reliability of quad flat non-lead （QFN） package,which has become very popular over the past few years,has received intense *** finite element method （FEM） is essential to evaluate the reliability of QFN *** this paper,Garofalo-Arrheninus model was implemented to simulate the deformation of QFN soldered *** creep strain of the soldered joints was calculated by means of finite element analyses,and was used to evaluate the reliability of QFN *** is found that the critical soldered joint of QFN is located the package corner while the maximum creep strain is obtained at the top interface of peripheral soldered *** creep strain is provided with periodicity and additivity as the thermal *** analysis of QFN package with different lead counts was presented as well,in which the phenomenon that the value of induced creep strain arise as the package size decreasing is ***,SnPb and two lead-free solders,namely,Sn3.5Ag/Sn3.8Ag0.7Cu,were both taken into *** results indicate that the creep strain value of lead-free soldered joints is lower than that of SnPb soldered joints,which can be attributed to the difference of stiffness and coefficient of thermal expansion among three ***-Arrheninus model is used to calculate the creep strain of the QFN device for the first time in this *** results provide an important basis for evaluating the reliability of QFN package.

关键词： finite element analyses reliability lead-free solder creep strain

Investigating Interaction Between Biochanin A and Human Serum Albumin by Multi-spectroscopic and Molecular Simulation Methods

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Transactions of Tianjin University 2017年第4期23卷 325-333页

作者： Zhaohui xue aiqing Cheng Yanni Li Wancong Yu Xiaohong Kou School of Chemical Engineering and Technology Tianjin University Medical Plant Lab Tianjin Research Center of Agricultural Biotechnology

Biochanin A (BCA), the most abundant isoflavone in chickpeas, presents a wide range of biological activities, such as hypolipidaemic, anti-oxidative, anti-proliferative, and estrogen-like effects. We investigated the interaction between BCA and human serum albumin (HSA) via several techniques. UV–Vis absorption spectroscopy verified the conformational variation of HSA after BCA addition, and fluorescence spectroscopy revealed the relevant binding parameters. Circular dichroism spectroscopy was used to estimate the secondary structural changes of HSA with and without BCA. Molecular docking and dynamics simulations were then applied to study the characteristics of HSA with BCA. Energy decomposition analysis was used to prove that Trp214 in subdomain IIA of HSA is the most likely binding site of BCA. Van der Waals forces and hydrophobic interactions may play important roles during the binding process. All of our results showed that BCA presents significant binding affinity to HSA, thus confirming that the role of HSA has as an efficient transporter of biomolecules. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

关键词： Absorption spectroscopy Binding energy Bins Body fluids Dichroism Flavonoids Fluorescence spectroscopy Hydrophobicity Molecular biology Molecular dynamics Van der Waals forces

MECHANICAL PROPERTIES OF FINE PITCH DEVICES SOLDERED JOINTS BASED ON CREEP MODEL

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Chinese Journal of Mechanical Engineering 2008年第6期21卷 82-85页

作者： ZHANG Liang xue songbai HAN Zongjie WANG Jianxin GAO Lili SHENG Zhong College of Materials Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing 210016 China

Nonlinear analyses of quad flat package （QFP） on printed circuit board （PCB） assemblies subjected to thermal cycling conditions are presented. Two different solders are considered, namely, Sn37Pb and Sn3.5Ag. The stress and strain response of fine pitch devices soldered joints was investigated by using finite element method based on Garofalo-Arrheninus model. The simulated results indicate creep distribution of soldered joints is not uniform, the heel and toe of soldered joints, the area between soldered joints and leads are the creep concentrated sites. The similar phenomena of stress curves simulated based on Garofalo-Arrheninus model and Anand equations is confirmed, and the creep strain value of Sn3.5Ag soldered joints is lower than that of Sn37Pb soldered joints. Thermal cycling results show that Sn3.5Ag strongly outperforms Sn37Pb for QFP devices under the studied test condition. This is well matched with the experimental outcome analyzed. In addition, the soldered devices were tested by micro-joints tester, the tensile strength of Sn3.5Ag soldered joints is found to be higher than that of Sn37Pb soldered joints. By analyzing the fracture microstructure of soldered joints, it is found that fracture mechanism of Sn3.5Ag soldered joints is toughness fracture, while fracture mechanism of Sn37Pb soldered joints includes brittle fracture and toughness fracture. The results of this study provide an important basis of understanding the mechanical properties of fine pitch devices with traditional Sn37Pb and Sn3.5Ag lead-free soldered joints.

关键词： Finite element method creep properties tensile strength fracture microstructure

Solderability and intermetallic compounds formation of Sn-9Zn-xAg lead-free solders wetted on Cu substrate

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Rare Metals 2009年第6期28卷 656-660页

作者： CHEN Wenxue xue songbai WANG Hui WANG Jianxin HAN Zongjie College of Materials Science and Technology Nanjing University of Aeronautics and Astronautics Nanjing 210016 China

The eutectic Sn-9Zn alloy was doped with Ag （0 wt.%-1 wt.%） to form Sn-9Zn-xAg lead-free solder alloys. The effect of the addition of Ag on the microstructure and solderability of this alloy was investigated and intermetallic compounds （IMCs） formed at the solder/Cu interface were also examined in this study. The results show that, due to the addition of Ag, the microstructure of the solder changes. When the quantity of Ag is lower than 0.3 wt.%, the needle-like Zn-rich phase decreases gradually. However, when the quantity of Ag is 0.5 wt.%-1 wt.%, Ag-Zn intermetallic compounds appear in the solder. In particular, adding 0.3 wt.% Ag improves the wetting behavior due to the better oxidation resistance of the Sn-9Zn solder. The addition of an excessive amount of Ag will deteriorate the wetting property because the gluti- nosity and fluidity of Sn-9Zn-（0.5, 1）Ag solder decrease. The results also indicate that the addition of Ag to the Sn-Zn solder leads to the precipitation of ε-AgZn3 from the liquid solder on preformed interracial intermetallics （CusZn8）. The peripheral AgZn3, nodular on the Cu5Zn8 IMCs layer, is likely to be generated by a peritectic reaction L ＋ γ-Ag5Zns→AgZn3 and the following crystallization of AgZn3.

关键词： soldering materials lead-free solder wettability intermetallic compounds