Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

Filters

Reset filters

Settings
Now showing 1 - 10 of 37
  • Publication
    Reduction of voids in solder joints an alternative to vacuum soldering
    ( 2012)
    Diehm, R.
    ;
    Nowottnick, M.
    ;
    Pape, U.
    Voids in solder joints are representing one of the main problems especially for power electronics. A low and homogeneous thermal resistance of solder joints is demanded for a quick and uniform conduction of the heat loss from the power chip. The same applies for the electrical conductivity of solder joints. Enclosed voids can cause a displacement of electrical and thermal paths and a local concentration of power and heat. In addition, gas voids are anxious to form spheres in the solder gap, which could be a cause for tilting of chip components and a wedge-shaped solder gap. This is tightening the problem of patchy distribution of current or heat and is causing stress and cracks. The amount of voids can be influenced by different measures, e. g. a good wettability of metallization, solder pastes with special adopted solvents and an adequate preheating profile. However, a special vacuum process step during soldering is demanded for absolutely void free solder joints. But this vacuum process is associated with some essential disadvantages. Besides of the technical expenses for vacuum pumps and additional locks, the vacuum process excludes the use of gas convection for heating and cooling. Apart from a special vapour phase-vacuum technology, most machines are using infrared radiation or heat conduction for soldering. The same principles as used in vacuum soldering technology are applicable also for a higher pressure level. If the void in the solder joint is arising for an excess pressure, the normal atmosphere pressure could be sufficient for escaping of enclosed gas. Essential for this effect is the pressure difference between inside and outside of solder joint. A benefit of soldering with excess pressure is the possibility of gas convection for heat transfer. This allows the application of conventional components and the realization of the usual temperature distribution and profiles.
  • Publication
    Solder joint reliability in automotive applications: Describing damage mechanisms through the use of EBSD
    ( 2010)
    Steller, A.
    ;
    Pape, U.
    ;
    Dudek, R.
    Due to the large scatter in data that have been gathered over the past years to describe the reliability behavior of lead-free solder joints, a precise correlation of aging condition to the resulting damage appearance could not yet be established. Recent research has shown, that a key to a more profound understanding of damage mechanisms can be offered through the analysis of recrystallization processes in the solder joints. Electron Backscatter Diffraction (EBSD) is a valuable analysis method to obtain quantitative data on grain properties. In this paper the results of detailed EBSD measurements on SnAg3.0Cu0.5 solder joints of chip resistors are therefore presented. Correlations between recrystallization behavior and applied loading profile are generated and verified through FEM-simulations. It is recommended to employ sophisticated data mining tools like Support Vector Machines to support data interpretation of the various parameters offered by EBSD.
  • Publication
    NanoFlux - Doping of Solder Pastes
    ( 2008)
    Zerrer, P.
    ;
    Fix, A.
    ;
    Hutter, M.
    ;
    Pape, U.
    The reliability of automotive electronics depends a great deal on solder joints. After the WEEE and RoHS came into effect the new focus became lead-free solder pastes such as SnAg or SnAgCu (SAC). One approach to improve the thermal fatigue properties of these alloys is to add a third or fourth alloying element SAC + X. Until now, this was always done by metallurgical alloying, requiring special apparatuses, conditions and, exceptional processing expertise. Hence, it is even more difficult and more expensive to produce a powder out of these alloys. The project "nanoFlux", funded by the German federal ministry of research and education, is a new approach to alloy special elements into a solder joint during a conventional retlow process used in SMD technology. A standard powder is mixed with a flux containing Al, Co, Fe, or mixtures of these elements. NanoFlux should not significantly influence the melting point or the pasty range to be used in established lead-free proce sses. This could drastically lower the costs for the manufacturing and storage of special alloys. Recent results already show successful alloying for Co and Fe. The thermal properties were monitored during an insitu reflow differential scanning calorimeter (DSC) experiment. To verify a successful doping, reflowed, cleaned, and dissolved solder balls were analysed by inductively coupled plasma optical emission spectroscopy (ICP OES). Parallel to those experiments, a test board was set up and a thermal cycle test has been conducted. The higher remaining shear strength was linked to the microstructural characteristics of the different solders through scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. It was possible to successfully dope a solder joint with a fourth element by mixing a Co or Fe containing flux with the solder powder.
  • Publication
    Lead free solder joints: reliability and metallurgical reactions
    ( 2008)
    Hutter, M.
    ;
    Schmidt, R.
    ;
    Pape, U.
    ;
    Oppermann, H.
    ;
    Reichl, H.
    The electronics industry has successfully transitioned to lead free soldering for computer and consumer products while in the automotive industry due to the high reliability requirements there this step is still in an ongoing proc-ess. In order to ensure or even enhance the reliability of solder joints, i.e. the board level reliability, in electronic devices besides gaining mechanical data and developing predictive fatigue models research work has already been launched to understand the effect of choice and amount of certain elements the solder alloys comprise. However, the influence of adding certain elements by means of alloying or application of surface coatings on the mechanical properties, strengthening mechanisms and the microstructure is not totally understood. In this work the effect of using an electroplated Fe pad metallization (and for comparison reasons using electroless Ni/P) to-gether with the lead free solders SnAg3.0Cu0.5 (SAC305) and SAC plus Bi, Sb and Ni as well as SnPb37 eutec-tic as reference on the formation and growth of intermetallic phases is discussed.
  • Publication
    Zuverlässigkeit von Lötverbindungen
    ( 2006)
    Hutter, M.
    ;
    Pape, U.
    ;
    Wunderle, B.
  • Publication
    Entwicklung von Weichlotpasten für das Löten mit der Mikrowelle
    ( 2006)
    Nowottnick, M.
    ;
    Pape, U.
    Ein selektiver und gleichzeitig simultaner Reflowlötprozess kann grundsätzlich durch elektromagnetische Felder ermöglicht werden, deren Energie die zu erwärmenden Baugruppen durchdringt und in Abhängigkeit von den Materialeigenschaften nur in bestimmten Bereichen einkoppelt. Die Nutzung elektromagnetischer Felder im Mikrowellenbereich ermöglicht es, unterschiedliche Werkstückgrößen in einem großen Volumen und mit hohem Durchsatz zu behandeln. Konventionelle Lotpasten lassen sich allerdings nur sehr langsam und mit hoher Leistungsdichte durch Mikrowellen erwärmen. Indem der Lotpaste eine definierte Menge eines extrem gut ankoppelnden Materials, dem sog. Suszeptor, zugegeben wird, lässt sich die Effektivität wesentlich erhöhen. Solche Suszeptoren müssen entsprechende polare oder dielektrische Eigenschaften besitzen und können der Lotpaste in fester oder flüssiger Form zugesetzt werden. Auf diese Weise ist es möglich, die Erwärmung des Lotes gegenüber der übrigen Baugruppe erheblich zu beschleunigen, wodurch die benötigte Mikrowellenenergie minimiert werden kann.
  • Publication
    Low temperature processing of highly integrated assemblies by selective microwave heating
    ( 2006)
    Pape, U.
    ;
    Diehm, R.
    ;
    Kempe, W.
    ;
    Nowottnick, M.
    This poster presents the principles and state of the work of a joint research project ?MICROFLOW?, funded by the German Department for Education and Research (BMBF). The usually used simultaneous reflow soldering processes were optimized in the past for a minimum of temperature difference between small and large or heavy components. A further development of soldering processes is demanded because of the increasing requirements for polymer electronics, electrical-optical assemblies or high temperature electronics. The technology developed should allow a direct heating of the solder paste while the components are at a considerably lower temperature. This is possible only by sequentially working selective soldering processes at present. The selective heating method for a simultaneous process presented here is possible using microwaves provided the energy penetrates the assembly and heats certain regions only, depending on specific material characteristics. Today?s conventional solder pastes are already able to be heated with microwave, but only very slowly and using a high power density. It is possible to increase the absorbed heat considerably by mixing additional materials referred to as suszeptors into the solder paste which are absorbing microwave power. A main task for a save microwave application was to guarantee the operators safety and to ensure the electromagnetic compatibility to the printed circuit boards, integrated circuits and other components as well. This was possible by means of minimizing of volumetric microwave power, optimizing microwave frequency and above all the ensuring of field homogeneity.
  • Publication
    A simultaneous and selective microwave supported soldering technology
    ( 2006)
    Nowottnick, M.
    ;
    Pape, U.
    ;
    Scheel, W.
    ;
    Diehm, R.
    ;
    Kempe, W.
    This paper is showing results from a joint research project "MICROFLOW", funded by the German Department for Education and Research (BMBF). Usual simultaneous reflow soldering processes like convection soldering or vapor phase soldering were optimized in the past for a minimum of temperature difference between small and large or heavy components on electronic assemblies. Especially the increasing demands for polymer electronics, for electrical-optical assemblies or high temperature electronics require are further development of soldering processes. Such a process should allow a direct heating of the solder joints up to soldering temperature and have to save all other components at the same time. Today this is possible only by application of sequential working selective soldering processes like hot bar soldering or laser soldering. But for a cost effective industrial application it is necessary to realize a selective and as well simultaneous soldering process, which is indeed not available at present. The wanted selective heating method for an effective simultaneous process is possible in principle by using of electromagnetic fields, when the energy is penetrating the assembly and is launching heat in certain regions, depending on specific material characteristics. Electromagnetic fields in the microwave frequency region are able to treat various sizes and shapes of assemblies with large capacity and with a high throughput. Indeed it is possible to heat conventional solder pastes only with very slowly and with a high microwave power density. It is possible to increase the launched heat considerable by mixing of additional materials, so called suszeptors, into the solder paste, which are absorbing microwave power with a high efficiency. A fundamental task for a save microwave application was the to guarantee the operators safety and to ensure the electromagnetic compatibility of printed circuit boards, integrated circuits and other components as well. This was possible b means of minimizing of volumetric microwave power, optimizing microwave frequency and above all the ensuring of field homogeneity.