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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

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

Several important problems of chemical metallurgy in arc welding

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China Welding 1995年第1期4卷 1-10页

作者： You Aiqing and xue songbai(Harbin Research Institute of Welding)

The following three aspects are discussed:the metallurgical behavior of hydrogen during welding;the oxygen content and the modes of oxide inclusions in weld metal; and the basicity calculation of welding *** metallurgical behaviors of hydrogen during welding are determined according to the results of measuring the hydrogen contents in welding fume, slag and the weld metal with E4303(ilmenite type) and E5015 (low hydrogen type) electrodes *** is verified that hydrogen exists mostly in welding fume in the form of moisture and that secondly in welding *** mechanism of dehydrogenation in MMA welding process is proposed and relevant calculation and experiments have been conducted to verify the course. The total amount of oxygen in weld metal is mainly determined by the amount of oxygen which can be dissociated from various oxides in the molten slag and can be predicted through *** modes of oxide inclusions in weld metal are determined by the structures of the slag.A formula for basicity calculation is proposed which is based on the free energy of the reaction between oxides and the free energy of forming oxide compound. And the basicity of CaF2 is also specified.

关键词： chemical metallurgy hydrogen content oxygen content inclusion basicity

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

Effects of Ga,Al,Ag,and Ce multi-additions on the wetting characteristics of Sn-9Zn lead-free solder

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Rare Metals 2009年第6期28卷 600-605页

作者： WANG Hui xue songbai ZHAO Feng CHEN Wenxue College of Materials Science and Technology Nanjing University of Aeronautics andAstronautics Nanjing 210016 China Department of Materials Loughborough University Leicestershire LEII 3TU UK

An orthogonal method was used to evaluate the effects of Ga, Al, Ag, and Ce multi-additions on the wetting characteristics of Sn-9Zn lead-free solders by wetting balance method. The results show that the optimal loading of Ga, Al, Ag, and Ce was 0.2 wt.%, 0.002 wt.%, 0.25 wt.%, and 0.15 wt.%, respectively. Intermetallic compounds （IMCs） formed at the interface between Sn-9Zn-0.2Ga-0.002Al-0.25Ag- 0.15Ce solder and Cu substrate were investigated by scanning electron microscope （SEM） and energy dispersive spectroscopy （EDS） analysis. The SEM images illustrate that the IMCs can be divided into two portions from the substrate side to the solder side： a planar CusZns layer and an additional continuous scallop-like AgZn3 layer. The EDS analysis also shows that Ga segregates in the solder abutting upon the interface. X-ray photoelectron spectroscopy （XPS） and Auger electron spectroscopy （AES） of the surface components of Sn-9Zn-0.2Ga-0.002Al- 0.25Ag-0.15Ce solder indicate that Al aggregates at the surface in the form of Al203 protective fdm, which prevents the further oxidation of the solder surface. On the other hand, Ce aggregates at the subsurface, which may reduce the surface tension of the solder and improve the wettability in consequence.

关键词： metallography lead-free solder wetting balance method wettability intermetallic compounds