Attila Bonyár

Investigation of intermetallic compounds (IMCs) in electrochemically stripped solder joints with SEM

Abstract In this work we compare the microstructures of intermetallic compounds (IMCs) in electrochemically stripped solder joints created by two different soldering methods (vapor phase soldering (VPS), and selective laser soldering with a CO2 laser). After the selective removal of the Sn phase with amperometry, the microstructure and structural composition of the IMC can be revealed in a detailed way, which is unlike any other previously published methods. The differences between the IMC microstructures of the technologically different solder joints were analyzed with optical microscopy and scanning electron microscopy (SEM). Energy dispersive spectroscopy (EDS) measurements were utilized to identify the different intermetallic phases (Ag3Sn, Cu6Sn5). Significant differences were observed in the IMC structures of solder joints prepared by different technologies.

Hybridization chain reaction performed on a metal surface as a means of signal amplification in SPR and electrochemical biosensors

A more specific and intense signal is desirable for most kinds of biosensors for biomedical or environmental applications, and it is especially so for label-free biosensors. In this paper, we show that hybridization chain reaction (HCR) can be exploited for the easily detectable accumulation of nucleic acids on metal surfaces as an event triggered by specific recognition between a probe and a target nucleic acid. We show that this process could be exploited to increase the sensitivity in the detection of nucleic acids derived from a pathogenic microorganism. This strategy can be straightforwardly implemented on SPR biosensors (commercial or custom-built) or on label-free electrochemical biosensors. Together with signal amplification, HCR can serve as a confirmation of the specificity of target recognition, as it involves the specific matching with a separate base sequence in the target nucleic acid. Furthermore, the kinetics of the target binding and the HCR can be easily distinguished from each other, providing an additional means of confirmation of the specific recognition.

Localization factor: A new parameter for the quantitative characterization of surface structure with atomic force microscopy (AFM)

In this work we present the possible application of a new parameter called localization factor for the quantitative characterization of surface structures with atomic force microscopy (AFM). For this purpose contact mode AFM images were taken from technologically different polycrystalline gold thin films and were evaluated according to the following parameters: surface roughness (R(a), R(RMS)), roughness factor (f(r)) and localization factor. The localization factor was compared with the other surface parameters. We demonstrate that this new parameter can be used to identically characterize these gold thin film surfaces with contact mode AFM in the 1-1000 μm(2) scan range. The mathematical background and possible application fields of the localization factor are also discussed in our paper.

Effect of grain orientation on chemical etching

The effect of grain orientation on the effectiveness of pre-etching before color etching was investigated by the help of electron back scattering diffraction and atomic force microscopy in case of cast iron. Strong correlation was found between the angle between the specimen normal and the [001] orientation of the ferrite grains and the depth of the etching. If the angle between the specimen normal and the [001] direction of the ferritic grain is small, then the speed of the etching is low, but the lateral variation of the etching speed within the grain is larger.

Microstructure Comparison of Soldered Joints Using Electrochemical Selective Etching

The microstructure of the commonly used SnAgCu (SAC) lead free solder alloy was investigated. SAC solder bumps were soldered by two different soldering techniques (Vapor Phase Soldering (VPS), Laser reflow). Since the soldering profile of the VPS method is considerably different from the temperature profile of the laser reflow soldering, the created microstructures are expected to be diverse. Selective electrochemical etching was applied on cross sectional samples in order to extract the tin from the cross sectioning plane. In this manner the spatial structure of Cu6Sn5 and the Ag3Sn intermetllic compounds (IMCs) was highlighted. The microstructures of the samples were analyzed with optical microscopy and Scanning Electron Microscope (SEM) on cross-section samples. The composing elements were identified by SEM-EDS.

AFM characterization of the shape of surface structures with localization factor.

Although with the use of scanning probe microscopy (SPM) methods the topographical imaging of surfaces is now widely available, the characterization of surface structures, especially their shape, and the processes which change these features is not trivial with the existing surface describing parameters. In this work the application of a parameter called localization factor is demonstrated for the quantitative characterization of surface structures and for processes which alter the shape of these structures. The theory and optimal operation range of this parameter are discussed with three application examples: microstructure characterization of gold thin films, characterization of the changes in the grain structure of these films during thermal annealing, and finally, characterization of the oxidation processes on a polished tin surface.

Correlation between the Grain Orientation Dependence of Color Etching and Chemical Etching

A gray cast iron specimen was investigated by color and chemical etching with optical and atomic force microscopy, and the effect of grain orientation on the effectiveness of etching was examined. It was proven that the grain orientation dependence of chemical and color etching is just the opposite, and that the specimen surface after color etching is not uniformly smooth. Explanation for the layer structure of the color etched iron specimen is given.

Selective electrochemical etching for the investigation of solder joint microstructures

Hereby we introduce a method called selective electrochemical etching for the investigation of solder joint microstructures. The aim of this technique is to remove the tin from the solder joint, which enables the examination of the remaining intermetallic microstructures in such a detail, which is unlike to any other previously established method. In our work we discuss the importance of intermetallic compound (IMC) investigation and compare the existing methods with our proposed technique. Pilot measurement results are also presented on selectively etched SAC (Sn-Ag-Cu) alloy solder joints. We present the found relationship between 1) the soldering methods and parameters, 2) the resulting microstructures, 3) the amount of the removed charge/Sn phase during the etching and 4) shear test results on the different solder joints. In our paper we will also investigate the effect of the etching conditions (e.g. etching time, electrolyte concentration, etc.) in order to reach the optimal etching depth, considering the detail and integrity of the intermetallic structures.

A custom-developed SPRi instrument for biosensor research

In this paper we present a custom-developed, small, fixed-angle Surface Plasmon Resonance imaging (SPRi) instrument that enables the biochips to be prepared in an array format providing SPR information simultaneously on up to 100 active sites (spots). Besides the presentation of the hardware and software setup of our device we also demonstrate the application with pilot measurement results on different solutions containing NaCl, sucrose, avidin or DNA. The sensitivity of our instrument is calculated in function of the concentration.

Investigation of thermally generated gold nanoparticles with AFM

Gold nanoparticles (Au NPs) were generated by thermally annealing gold thin films (5-30 nm) which were sputtered on glass substrates. The conditions of the thermal annealing (temperature and annealing time) were varied in order to generate nanoparticles in different sizes. The size and distribution of the nanoparticles were characterized by atomic force microscopy (AFM). The Au NP modified surface is intended to be used as sensor transducer element in a surface plasmon resonance imaging (SPRi) instrument. Thus we investigated the size of the generated NPs in function of the annealing parameters in order to reach optimal conditions for the NP signal amplification in the SPRi device.