Emerald | Soldering & Surface Mount Technology | Table of Contents http://www.emeraldinsight.com/0954-0911.htm Table of contents from the most recently published issue of Soldering & Surface Mount Technology Journal en-gb Tue, 26 Aug 2014 00:00:00 +0100 2014 Emerald Group Publishing Limited editorial@emeraldinsight.com support@emeraldinsight.com 60 Emerald | Soldering & Surface Mount Technology | Table of Contents http://www.emeraldinsight.com/common_assets/img/covers_journal/ssmtcover.gif http://www.emeraldinsight.com/0954-0911.htm 120 157 Study of IMC at interfaces of Sn3.0Ag0.5Cu3.0Bi0.05Cr/Cu joints during thermal aging http://www.emeraldinsight.com/journals.htm?issn=0954-0911&volume=26&issue=4&articleid=17116814&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The interfacial intermetallic compounds (IMCs) in the Sn3.0Ag0.5Cu3.0Bi0.05Cr/Cu (SACBC/Cu) and Sn3.0Ag0.5Cu/Cu (SAC/Cu) solder joints were investigated comparatively. To find out their differences is the point.<B>Design/methodology/approach</B> - The samples were annealed after isothermal aging at 150? for 0, 168 and 500 hours. and their cross-sections were observed by SEM and EDS.<B>Findings</B> - The interfacial IMC morphology in two joints had significant differences. For the Cu/SAC/Cu joints, the granular and short-rod like Ag3Sn particles attached on the surface and boundary of interfacial Cu6Sn5 grains were detected and they coarsened observably with aging time at 150?, and lastly embedded at the grain boundaries. However, For the Cu/SACBC/Cu joints, there were tiny filamentous Ag3Sn growing on the surface of interfacial Cu6Sn5 grains, and the Ag3Sn had a tendency to break into nano-particles, which would be distributed evenly and cover on the IMC layer, profiting from the Bi and Cr precipitates from solder matrix during aging.<B>Originality/value</B> - The paper implies that the addition of Bi and Cr could effect the IMCs of joint, thereby delay interfacial reactions between Sn and Cu atoms and improve the service reliability. The SACBC solder is a potential alloy for electronic packaging production. Article literatinetwork@emeraldinsight.com (Guokui Ju, Fei Lin, Wenzhen Bi, Yongjiu Han, Junjie Wang, Xicheng Wei) Tue, 26 Aug 2014 00:00:00 +0100 Failure Analysis on Electrolytic Ni/Au Surface Finish of PCB Used for Wire Bonding and Soldering http://www.emeraldinsight.com/journals.htm?issn=0954-0911&volume=26&issue=4&articleid=17116800&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The purpose of this study was to address two kinds of printed circuit board (PCB) failures with Electrolytic Ni/Au as surface finish. One was the weak bondability of gold wires to Ni/Au pads and the other was "dull gold" and weak solder wettability, which both caused great loss for the PCB manufacturer.<B>Design/methodology/approach</B> - The failure samples were studied and analyzed in terms of macro and micro morphology of surface finish, its element composition and thickness by various characterization techniques, such as three-dimensional stereo microscope (3D SM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray fluorescence spectrum (XRF).<B>Findings</B> - Then the causes of the two failures were both found to be the inadequate thickness of gold deposit and other surface finish defects, but these causes played different roles in either failure and the mechanisms differ. Finally their failure mechanisms were discussed and corresponding countermeasures were put forward for prevention.<B>Practical implications</B> - This study not only addresses a practical failure problem, but also provides some clues to a better and further understanding of the effect of PCB process and management on its quality and reliability in manufacturing practice.<B>Originality/value</B> - It sheds light on how the thickness and quality of surface finish affect its wire bonding and soldering performances. Article literatinetwork@emeraldinsight.com (Fei-Jun Chen, Shi Yan, Zhen-Guo Yang) Tue, 26 Aug 2014 00:00:00 +0100 Contamination profile on typical printed circuit board assemblies vs soldering process http://www.emeraldinsight.com/journals.htm?issn=0954-0911&volume=26&issue=4&articleid=17116834&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - Typical printed circuit board assemblies processed by reflow, wave, or selective wave soldering were analysed for typical levels of process related residues, resulting from a specific or combination of soldering process. Typical solder flux residue distribution pattern, composition, and concentration are profiled and reported. The effect of such contaminants on conformal coating was tested.<B>Design/methodology/approach</B> - Presence of localized flux residues were visualized using a commercial residue reliability assessment testing gel test and chemical structure was identified by Fourier transform infrared spectroscopy, while the concentration was measured using ion chromatography, and the electrical properties of the extracts were determined by measuring the leak current using a twin platinum electrode setup. Localized extraction of residue was carried out using a commercial critical contamination control extraction system. <B>Findings</B> - Results clearly show that the amount and distribution of flux residues are a function of the soldering process, and the level can be reduced by an appropriate cleaning. Selective soldering process generates significantly higher levels of residues compared to the wave and reflow process. For conformal coated printed circuit board assemblies, the contamination levels generated from the tested wave and selective soldering process are found to be enough to generate blisters under exposure to high humidity levels.<B>Originality/value</B> - Although it is generally known that different soldering process can introduce contamination on the PCBA surface compromising its cleanliness, no systematic work is reported investigating the relative levels of residue introduced by various soldering process and its effect on corrosion reliability. Article literatinetwork@emeraldinsight.com (Helene Conseil, Morten Stendahl Jellesen, Rajan Ambat) Tue, 26 Aug 2014 00:00:00 +0100 Effects of aging on microstructure evolution and mechanical properties of high-temperature Zn-4Al-3Mg solder http://www.emeraldinsight.com/journals.htm?issn=0954-0911&volume=26&issue=4&articleid=17116796&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The purpose of this paper is to investigate the transformations during aging at 200 oC for different periods on microstructure and mechanical properties of the high-temperature Zn-4Al-3Mg solders.<B>Design/methodology/approach</B> - The solder was melted in a resistance furnace, and its different cooling rates were obtained by changing the cooling medium. Subsequently, all the specimens were aged at 200 oC for 20 h and 50 h, respectively. Scanning electron microscope (SEM) equipped with an energy dispersive X-ray (EDX) detector, X-Ray diffraction (XRD) were used for the observation of microstructures and the determination of the phase composition. Tensile tests and Rockwell hardness (HRB) tests were also performed.<B>Findings</B> - After aging, Zn atoms precipitated from the supersaturated a-Al and the (a-Al + ?-Zn)eutectoid phase with the original fine lamellar structure coarsened and spheroidized to minimize the system energy. Among these solders, the furnace-cooled alloys exhibited the highest thermal stability, largely remaining the original morphology after aging, whereas the collapse and spheroidization of the ?-Zn phase and the coarsening of the ?-Zn dendrites took place in the air-cooled and water-cooled samples respectively. Furthermore, a decrease in tensile strength during aging was attributed to the thermal softening effect. The variation of macro hardness was mainly associated with the microstructural alterations in terms of quantity, morphology and distribution of soft ?-Zn phase and hard intermetallic compounds (IMCs) induced by the aging treatment.<B>Originality/value</B> - The structural stability of eutectic Zn-4Al-3Mg solders solidified at different cooling rates and the effect of aging on mechanical properties were investigated. Article literatinetwork@emeraldinsight.com (Huan Wang, Yongchang Liu, Huixia Gao, Zhiming Gao) Tue, 26 Aug 2014 00:00:00 +0100 Comparing the reliability and intermetallic layer of solder joints prepared with infrared and vapour phase soldering http://www.emeraldinsight.com/journals.htm?issn=0954-0911&volume=26&issue=4&articleid=17116894&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - The reliability of 0603 size resistors’ solder joints formed with Infrared and Vapour Phase soldering was investigated. The intermetallic layer of the joints was analysed based on image processing algorithm automatically.<B>Design/methodology/approach</B> - For the reliability analyses, the aging method was a Highly Accelerated Stress Test with +105 °C maximum temperature, fully saturated (100%) relative humidity on +0.5 atm. overpressure. The joints were characterised based on the thickness of their intermetallic layer and on their shear strength in as-reflowed stage, and after 400, 800, 1200, 1600, 2000 hours of HAST. An image processing algorithm was developed to measure the thickness of the intermetallic layers on cross-sectional Scanning Electron Microscopy images automatically.<B>Findings</B> - The increase of the intermetallic layer thickness is lower in the case of HAST aging compared to other methods. The thickness increment of the Cu6Sn5 layer was higher for Infrared and lower for Vapour Phase soldering; the Cu3Sn layer cannot be inspected even after 2.000h of HAST aging. The results of shear strength measurements show better reliability for Vapour Phase soldered joints.<B>Practical implications</B> - The developed image processing method is applicable to obtain quantitative results about the intermetallic layers in an effective, fast way.<B>Originality/value</B> - There is a lack of information in the literature regarding the reliability comparison of solder joints formed with Vapour Phase and conventional reflow processes. Thus, we performed research about the lifetime of solder joints formed with Vapour Phase and IR reflow method. Article literatinetwork@emeraldinsight.com (Oliver Krammer) Tue, 26 Aug 2014 00:00:00 +0100 Comparing 2D and 3D numerical simulation results of gas flow velocity in convection reflow oven http://www.emeraldinsight.com/journals.htm?issn=0954-0911&volume=26&issue=4&articleid=17116880&show=abstract <strong>Abstract</strong><br /><br /><B>Purpose</B> - With the spread of finer surface mounted devices it is important to understand convection reflow soldering technology more deeply. The paper compares and studies 2D and 3D Computational Fluid Dynamics (CFD) simulation results of gas flow velocity in a convection reflow oven. The aim is to show the differences of the different modelling aspects.<B>Design/methodology/approach</B> - Convection reflow ovens are divided into zones. Every zone contains an upper and a lower nozzle-matrix. The gas flow velocity field is one of the most important parameter of the local heat transfer in the oven. It is not possible to examine the gas flow field with classical experimental methods due to the extreme circumstances in the reflow oven. Therefore, numerical simulations are necessary.<B>Findings</B> - The heat transfer changes highly along the moving direction of the assembly and it is nearly homogeneous along the traverse direction of the zones. The gas flow velocity values of the 2D model are too high due to the geometrical distortions of the 2D model. On the other hand, the calculated flow field of the 2D model is more accurate than in the 3D model due to the finer mesh.<B>Research limitations/implications</B> - Investigating the effects of tall components on a printed wiring board inside the gas flow field and further analysis of the mesh size effect on the models.<B>Practical implications</B> - The presented results can be useful during the design of a simulation study in a reflow oven (or in similar processes).<B>Originality/value</B> - The presented results provide a completely novel approach from the aspect of 2D and 3D simulations of a convection reflow oven. The results also reveal the heat transfer differences. Article literatinetwork@emeraldinsight.com (Balazs Illes) Tue, 26 Aug 2014 00:00:00 +0100