Tomi Laurila | Aalto University (original) (raw)

Papers by Tomi Laurila

Diamond and Related Materials, 2015

Molecular Neurobiology, 2015

Carbon-based materials, such as diamond-like carbon (DLC), carbon nanofibers (CNFs), and carbon n... more Carbon-based materials, such as diamond-like carbon (DLC), carbon nanofibers (CNFs), and carbon nanotubes (CNTs), are inherently interesting for neurotransmitter detection due to their good biocompatibility, low cost and relatively simple synthesis. In this paper, we report on new carbon-hybrid materials, where either CNTs or CNFs are directly grown on top of tetrahedral amorphous carbon (ta-C). We show that these hybrid materials have electrochemical properties that not only combine the best characteristics of the individual "building blocks" but their synergy makes the electrode performance superior compared to conventional carbon based electrodes. By combining ta-C with CNTs, we were able to realize electrode materials that show wide and stable water window, almost reversible electron transfer properties and high sensitivity and selectivity for detecting dopamine in the presence of ascorbic acid. Furthermore, the sensitivity of ta-C + CNF hybrids towards dopamine as well as glutamate has been found excellent paving the road for actual in vivo measurements. The wide and stable water window of these sensors enables detection of other neurotransmitters besides DA as well as capability of withstanding higher potentials without suffering from oxygen and hydrogen evolution.

Journal of Physics: Condensed Matter, 2015

We present a computational study of spontaneous polarization and piezoelectricity in Sc x Al 1−x ... more We present a computational study of spontaneous polarization and piezoelectricity in Sc x Al 1−x N alloys in the compositional range from x = 0 to x = 0.5, obtained in the context of density functional theory and the Berry-phase theory of electric polarization using large periodic supercells. We report composition-dependent values of piezoelectric coefficients e ij , piezoelectric moduli d ij and elastic constants C ij . The theoretical findings are complemented with experimental measurement of e 33 for a series of sputtered ScAlN films carried out with a piezoelectric resonator. The rapid increase with Sc content of the piezoelectric response reported in previous studies is confirmed for the available data. A detailed description of the full methodology required to calculate the piezoelectric properties of ScAlN, with application to other complex alloys, is presented. In particular, we find that the large amount of internal strain present in ScAlN and its intricate relation with electric polarization make configurational sampling and the use of large supercells at different compositions necessary in order to accurately derive the piezoelectric response of the material.

J. Mater. Chem. A, 2015

In this work, we demonstrate the solution processing of optical and electrochemical dye sensors b... more In this work, we demonstrate the solution processing of optical and electrochemical dye sensors based on 4-(dioctylamino)-4 0 -(trifluoroacetyl)azobenzene and its application in sensing different amine compounds.

Electrochemical detection of different biomolecules in vivo is a promising path towards in situ m... more Electrochemical detection of different biomolecules in vivo is a promising path towards in situ monitoring of human body and its functions. However, there are several major obstacles, such as sensitivity, selectivity and biocompatiblity, which must be tackled in order to achieve reliably and safely operating sensor devices. Here we show that by utilizing hybrid carbon materials as electrodes to detect two types of neurotransmitters, dopamine and glutamate, several advantages over commonly used electrode materials can be achieved. In particular, we will demonstrate here that it is possible to combine the properties of different carbon allotropes to obtain hybrid materials with greatly improved electrochemical performance. Three following examples of the approach are given: (i) diamond-like carbon (DLC) thin film electrodes with different layer thicknesses, (ii) multi-walled carbon nanotubes grown directly on top of DLC and (iii) carbon nanofibres synthesized on top of DLC thin films. Detailed structural and electrochemical characterization is carried out to rationalize the reasons behind the observed behvior. In addition, results from the atomistic simulations are utilized to obtain more information about the properties of the amorphous carbon thin films.

Journal of Polymer Science Part B: Polymer Physics, 2002

The surface free energy of crosslinked photodefinable epoxy (PDE) was evaluated from the advancin... more The surface free energy of crosslinked photodefinable epoxy (PDE) was evaluated from the advancing contact angles measured by the sessile drop method. Poly(tetrafluoroethylene) (PTFE) was used as a reference material in the evaluation of the surface free energies by various models. Pure water, diiodomethane, formamide, ethylene glycol, diethylene glycol, glycerol, 1-bromonaphthalene, decane, and tetradecane were used as the probing liquids. The surface free energies for PDE and PTFE were calculated to be 43.6 and 21.2 mJ/m 2 , respectively. The contact-angle measurements indicated the isotropy of the PDE surface with respect to the surface free energy. The PDE coating was further characterized with scanning electron microscopy and atomic force microscopy. The PDE surface was treated chemically and by reactive ion etching (RIE) to determine their impact on the wettability and adhesion. The treatments resulted in decreased contact angles between the crosslinked PDE surface and water as the polarity of the surface increased from about 9% to 18 and 43% by the chemical and RIE treatments, respectively. On the contrary, the surface free energy of the treated PDEs, as calculated by the geometric mean model, did not change markedly (to 47.4 and 41.8 mJ/m 2 by the chemical and RIE treatments, respectively). Consequently, the contact angles of diiodomethane and the PDE solution on the treated surfaces did not decrease noticeably. The stud-pull test showed improved adhesion strength for PDE that was left less crosslinked and, therefore, had residual affinity against the sequential PDE layer.

Microelectronics Reliability, 2005

Integral nickel-phosphorus (NiP) resistors were fabricated on flexible polyimide (PI) substrates ... more Integral nickel-phosphorus (NiP) resistors were fabricated on flexible polyimide (PI) substrates by electroless NiP deposition. The deposition process was first set up for standard rigid epoxy substrates and then modified for the flexible substrates. The effects of the PI surface modifications on the interfacial adhesion (NiP/PI) were measured experimentally by the pull-off method. The process parameters were optimised to give good adhesion. The mechanical durability of the electrolessly deposited thin film NiP resistors was tested by measuring the electrical resistance during cyclic loading. The results showed the resistors to be mechanically stable. The electrical resistance was also monitored continuously during exposure to corrosive gas environment. The corrosive environment had no significant effect on the resistance of either the electrolessly deposited resistors or the commercial integral resistors used as a reference. The results show that resistors can be fabricated on flexible PI substrate by the described method.

Defect and Diffusion Forum, 2010

Nb 3 Sn growth following the bronze technique, (i.e. by interdiffusion between Cu(Sn) alloy (bron... more Nb 3 Sn growth following the bronze technique, (i.e. by interdiffusion between Cu(Sn) alloy (bronze) and Nb) is one of the important methodologies to produce this superconductor. In this study, we have addressed the confusion over the growth rate of the Nb 3 Sn phase. Furthermore, a possible explanation for the corrugated layer in the multifilamentary structure is discussed. Kirkendall marker experiments were conducted to study the relative mobilities of the species, which also explained the reason for finding pores in the product phase layer. Based on the parabolic growth constant at different temperatures, the activation energy for the growth is determined. We have further explained the dramatic increase in the growth rate of the product phase by changing just one atomic percentage of Sn in the Cu-Sn bronze alloy.

Proceedings of the 5th Electronics System-integration Technology Conference (ESTC), 2014

Scripta Materialia, 2009

Diffusion parameters, such as the integrated diffusion coefficient of the phase, the tracer diffu... more Diffusion parameters, such as the integrated diffusion coefficient of the phase, the tracer diffusion coefficient of species at different temperatures and the activation energy for diffusion, are determined in V 3 Si phase with A15 crystal structure. The tracer diffusion coefficient of Si was found to be negligible compared to the tracer diffusion coefficient of V. The calculated diffusion parameters will help to validate the theoretical analysis of defect structure of the phase, which plays an important role in the superconductivity.

Materials Science and Engineering: R: Reports, 2005

The objective of this review is to study interfacial reactions between pure Sn or Sn-rich solders... more The objective of this review is to study interfacial reactions between pure Sn or Sn-rich solders, and common base metals used in Pb-free electronics production. In particular, the reasons leading to the observed interfacial reactions products and their metallurgical evolution have been analyzed. Results presented in the literature have been critically evaluated with the help of combined thermodynamic-kinetic approach based on the concept of local equilibrium and microstructural knowledge. The following conclusions have been reached: Firstly, the formations of intermetallic compounds in solid/liquid reaction couples are primarily controlled by the dissolution processes of base metals. Other factors that need be considered are the thermodynamic driving force for the formation of intermetallic compounds, their structures and concentration profiles in liquid. Secondly, annealing of solder interconnections in solid state can drastically change the microstructures formed in the solid/liquid reactions, especially if only one of the components in the solder takes part in the interfacial reactions. Thirdly, additional elements can have three major effects on the binary reactions between a base metal and Sn: (i) they can increase or decrease the reaction/growth rates, (ii) the additives can change the physical properties of the phases formed, and (iii) they can form additional reaction products or displace the binary equilibrium phases by forming new reaction products. Finally, if the local stable or metastable equilibrium is established at the interface, stability information together with kinetic considerations can provide a feasible approach to analyze interfacial reactions, which can have significant impact on the reliability of soldered electronics assemblies. #

Microelectronic Engineering, 2004

Interfacial reactions in the Si/TaC/Cu metallization system were investigated by utilizing transm... more Interfacial reactions in the Si/TaC/Cu metallization system were investigated by utilizing transmission electron microscopy and a combined kinetic and thermodynamic analysis. The formation of an amorphous Ta [C,O] layer was observed at the TaC/Cu interface at 600°C. After annealing at the same temperature a thin amorphous layer was detected also at the Si/TaC interface. After annealing at 750°C the thickness of the amorphous layer at the Si/TaC interface had increased and a mixture of crystalline and amorphous phases could be detected inside the TaC layer. This was anticipated to be the preliminary stage of the formation of SiC and TaSi 2 that occurred at 800°C. Overlapping with thickening of the amorphous layer formation of large Cu 3 Si precipitates took place and the layered metallization structure was partially destroyed. In order to obtain more information on the reactions at the Si/TaC interface and the effect of oxygen on the stability of TaC the ternary Si-Ta-C and Ta-C-O phase diagrams were evaluated from the assessed binary data. Activity diagram was also calculated to evaluate the possible reaction sequence at the Si/TaC interface. The observed reaction structure was found to be consistent with the thermodynamics of the ternary system.

Journal of Materials Science: Materials in Electronics, 2012

The effect of Ti on the solid state reactions between Sn and Ni has been investigated in this wor... more The effect of Ti on the solid state reactions between Sn and Ni has been investigated in this work. Based on the experimental results the following statements can be made: Firstly, the presence of Ti does not have measurable effects on the thickness evolution of Ni 3 Sn 4 during solid state annealing. Secondly, the results from long term heat treatments show that there is no marked solubility of Ti to Ni 3 Sn 4 . Rather Ti reacts with Sn to form large Ti 2 Sn 3 platelets inside the solder matrix. The Sn-rich part of the Ni-Sn-Ti phase diagram was assessed in order to rationalize the experimental results. By utilizing this information, the absence of any marked effects of Ti on the growth of Ni-Sn intermetallic compounds (IMC) was analysed. As there is no solubility of Ti to SnAg solder or to Ni-Sn IMC's, Ti cannot change activities of components in the solder nor influence the stability of the IMC layers. Hence, these results throw significant doubts over the concept of trying to influence the Ni-Sn IMC layer thickness or quality by Ti alloying.

Journal of Electronic Materials, 2008

Interfacial reactions between liquid Sn and various Cu-Ni alloy metallizations as well as the sub... more Interfacial reactions between liquid Sn and various Cu-Ni alloy metallizations as well as the subsequent phase transformations during the cooling were investigated with an emphasis on the microstructures of the reaction zones. It was found that the extent of the microstructurally complex reaction layer (during reflow at 240°C) does not depend linearly on the Ni content of the alloy metallization. On the contrary, when Cu is alloyed with Ni, the rate of thickness change of the total reaction layer first increases and reaches a maximum at a composition of about 10 at.% Ni. The reaction layer is composed of a relatively uniform continuous (Cu,Ni) 6 Sn 5 reaction layer (a uniphase layer) next to the NiCu metallizations and is followed by the two-phase solidification structures between the single-phase layer and Sn matrix. The thickness of the two-phase layer, where the intermetallic tubes and fibers have grown from the continuous interfacial (Cu,Ni) 6 Sn 5 layer, varies with the Ni-to-Cu ratio of the alloy metallization. In order to explain the formation mechanism of the reaction layers and their observed kinetics, the phase equilibria in the Sn-rich side of the SnCuNi system at 240°C were evaluated thermodynamically utilizing the available data, and the results of the Sn/Cu x Ni 1-x diffusion couple experiments. With the help of the assessed data, one can also evaluate the minimum Cu content of Sn-(Ag)-Cu solder, at which (Ni,Cu) 3 Sn 4 transforms into (Cu,Ni) 6 Sn 5 , as a function of temperature and the composition of the liquid solders.

Journal of Applied Polymer Science, 2006

Journal of Applied Physics, 2006

The interfacial reactions of near-eutectic Sn-Ag-Cu solder with Ni͑P͒ / Au metal finishes on prin... more The interfacial reactions of near-eutectic Sn-Ag-Cu solder with Ni͑P͒ / Au metal finishes on printed wiring boards as well as in component under bump metallizations have been investigated in this work. With the help of the scanning electron microscopy and transmission electron microscopy it was discovered that the first phase to form was the metastable nanocrystalline ternary NiSnP layer that provided the substrate for the subsequent formation of ͑Cu, Ni͒ 6 Sn 5 . During cooling or in the subsequent reflows the metastable NiSnP layer partially transformed into the columnar Ni 3 P. In this transformation Sn atoms and impurities, which do not dissolve into the Ni 3 P, diffuse towards the remaining NiSnP layer. When the specimens are further annealed in solid state at 170°C the Ni 3 P phase transforms into Ni 5 P 2 implying that some more Ni has diffused towards the solder. However, when Ni͑P͒ / Au finishes with a higher P content were used, only the ternary NiSnP layer was observed. Based on the mass balance and available thermodynamic data on the Sn-P-Ni system the evolution of the observed microstructures in the reactions between the solder and Ni͑P͒ / Au finishes is discussed.

Intermetallics, 2012

Othman et al. (Intermetallics 2012;22:1e6) recently published a manuscript on "Effects of current... more Othman et al. (Intermetallics 2012;22:1e6) recently published a manuscript on "Effects of current density on the formation and microstructure of Sne9Zn, Sne8Zne3Bi and Sne3Age0.5Cu solder joints". We found problems in calculation of diffusion parameters. Even the comment on the formation of Cu 5 Zn 8 instead of Cu 6 Sn 5 is not correct. In this comment, we have explained the correct procedure to calculate the diffusion coefficients. Further, we have also explained the reason for the formation of Cu 5 Zn 8 instead of Cu 6 Sn 5 in the Cu/ Sne9Zn system.

Diamond and Related Materials, 2015

Molecular Neurobiology, 2015

Carbon-based materials, such as diamond-like carbon (DLC), carbon nanofibers (CNFs), and carbon n... more Carbon-based materials, such as diamond-like carbon (DLC), carbon nanofibers (CNFs), and carbon nanotubes (CNTs), are inherently interesting for neurotransmitter detection due to their good biocompatibility, low cost and relatively simple synthesis. In this paper, we report on new carbon-hybrid materials, where either CNTs or CNFs are directly grown on top of tetrahedral amorphous carbon (ta-C). We show that these hybrid materials have electrochemical properties that not only combine the best characteristics of the individual "building blocks" but their synergy makes the electrode performance superior compared to conventional carbon based electrodes. By combining ta-C with CNTs, we were able to realize electrode materials that show wide and stable water window, almost reversible electron transfer properties and high sensitivity and selectivity for detecting dopamine in the presence of ascorbic acid. Furthermore, the sensitivity of ta-C + CNF hybrids towards dopamine as well as glutamate has been found excellent paving the road for actual in vivo measurements. The wide and stable water window of these sensors enables detection of other neurotransmitters besides DA as well as capability of withstanding higher potentials without suffering from oxygen and hydrogen evolution.

Journal of Physics: Condensed Matter, 2015

We present a computational study of spontaneous polarization and piezoelectricity in Sc x Al 1−x ... more We present a computational study of spontaneous polarization and piezoelectricity in Sc x Al 1−x N alloys in the compositional range from x = 0 to x = 0.5, obtained in the context of density functional theory and the Berry-phase theory of electric polarization using large periodic supercells. We report composition-dependent values of piezoelectric coefficients e ij , piezoelectric moduli d ij and elastic constants C ij . The theoretical findings are complemented with experimental measurement of e 33 for a series of sputtered ScAlN films carried out with a piezoelectric resonator. The rapid increase with Sc content of the piezoelectric response reported in previous studies is confirmed for the available data. A detailed description of the full methodology required to calculate the piezoelectric properties of ScAlN, with application to other complex alloys, is presented. In particular, we find that the large amount of internal strain present in ScAlN and its intricate relation with electric polarization make configurational sampling and the use of large supercells at different compositions necessary in order to accurately derive the piezoelectric response of the material.

J. Mater. Chem. A, 2015

In this work, we demonstrate the solution processing of optical and electrochemical dye sensors b... more In this work, we demonstrate the solution processing of optical and electrochemical dye sensors based on 4-(dioctylamino)-4 0 -(trifluoroacetyl)azobenzene and its application in sensing different amine compounds.

Electrochemical detection of different biomolecules in vivo is a promising path towards in situ m... more Electrochemical detection of different biomolecules in vivo is a promising path towards in situ monitoring of human body and its functions. However, there are several major obstacles, such as sensitivity, selectivity and biocompatiblity, which must be tackled in order to achieve reliably and safely operating sensor devices. Here we show that by utilizing hybrid carbon materials as electrodes to detect two types of neurotransmitters, dopamine and glutamate, several advantages over commonly used electrode materials can be achieved. In particular, we will demonstrate here that it is possible to combine the properties of different carbon allotropes to obtain hybrid materials with greatly improved electrochemical performance. Three following examples of the approach are given: (i) diamond-like carbon (DLC) thin film electrodes with different layer thicknesses, (ii) multi-walled carbon nanotubes grown directly on top of DLC and (iii) carbon nanofibres synthesized on top of DLC thin films. Detailed structural and electrochemical characterization is carried out to rationalize the reasons behind the observed behvior. In addition, results from the atomistic simulations are utilized to obtain more information about the properties of the amorphous carbon thin films.

Journal of Polymer Science Part B: Polymer Physics, 2002

The surface free energy of crosslinked photodefinable epoxy (PDE) was evaluated from the advancin... more The surface free energy of crosslinked photodefinable epoxy (PDE) was evaluated from the advancing contact angles measured by the sessile drop method. Poly(tetrafluoroethylene) (PTFE) was used as a reference material in the evaluation of the surface free energies by various models. Pure water, diiodomethane, formamide, ethylene glycol, diethylene glycol, glycerol, 1-bromonaphthalene, decane, and tetradecane were used as the probing liquids. The surface free energies for PDE and PTFE were calculated to be 43.6 and 21.2 mJ/m 2 , respectively. The contact-angle measurements indicated the isotropy of the PDE surface with respect to the surface free energy. The PDE coating was further characterized with scanning electron microscopy and atomic force microscopy. The PDE surface was treated chemically and by reactive ion etching (RIE) to determine their impact on the wettability and adhesion. The treatments resulted in decreased contact angles between the crosslinked PDE surface and water as the polarity of the surface increased from about 9% to 18 and 43% by the chemical and RIE treatments, respectively. On the contrary, the surface free energy of the treated PDEs, as calculated by the geometric mean model, did not change markedly (to 47.4 and 41.8 mJ/m 2 by the chemical and RIE treatments, respectively). Consequently, the contact angles of diiodomethane and the PDE solution on the treated surfaces did not decrease noticeably. The stud-pull test showed improved adhesion strength for PDE that was left less crosslinked and, therefore, had residual affinity against the sequential PDE layer.

Microelectronics Reliability, 2005

Integral nickel-phosphorus (NiP) resistors were fabricated on flexible polyimide (PI) substrates ... more Integral nickel-phosphorus (NiP) resistors were fabricated on flexible polyimide (PI) substrates by electroless NiP deposition. The deposition process was first set up for standard rigid epoxy substrates and then modified for the flexible substrates. The effects of the PI surface modifications on the interfacial adhesion (NiP/PI) were measured experimentally by the pull-off method. The process parameters were optimised to give good adhesion. The mechanical durability of the electrolessly deposited thin film NiP resistors was tested by measuring the electrical resistance during cyclic loading. The results showed the resistors to be mechanically stable. The electrical resistance was also monitored continuously during exposure to corrosive gas environment. The corrosive environment had no significant effect on the resistance of either the electrolessly deposited resistors or the commercial integral resistors used as a reference. The results show that resistors can be fabricated on flexible PI substrate by the described method.

Defect and Diffusion Forum, 2010

Nb 3 Sn growth following the bronze technique, (i.e. by interdiffusion between Cu(Sn) alloy (bron... more Nb 3 Sn growth following the bronze technique, (i.e. by interdiffusion between Cu(Sn) alloy (bronze) and Nb) is one of the important methodologies to produce this superconductor. In this study, we have addressed the confusion over the growth rate of the Nb 3 Sn phase. Furthermore, a possible explanation for the corrugated layer in the multifilamentary structure is discussed. Kirkendall marker experiments were conducted to study the relative mobilities of the species, which also explained the reason for finding pores in the product phase layer. Based on the parabolic growth constant at different temperatures, the activation energy for the growth is determined. We have further explained the dramatic increase in the growth rate of the product phase by changing just one atomic percentage of Sn in the Cu-Sn bronze alloy.

Proceedings of the 5th Electronics System-integration Technology Conference (ESTC), 2014

Scripta Materialia, 2009

Diffusion parameters, such as the integrated diffusion coefficient of the phase, the tracer diffu... more Diffusion parameters, such as the integrated diffusion coefficient of the phase, the tracer diffusion coefficient of species at different temperatures and the activation energy for diffusion, are determined in V 3 Si phase with A15 crystal structure. The tracer diffusion coefficient of Si was found to be negligible compared to the tracer diffusion coefficient of V. The calculated diffusion parameters will help to validate the theoretical analysis of defect structure of the phase, which plays an important role in the superconductivity.

Materials Science and Engineering: R: Reports, 2005

The objective of this review is to study interfacial reactions between pure Sn or Sn-rich solders... more The objective of this review is to study interfacial reactions between pure Sn or Sn-rich solders, and common base metals used in Pb-free electronics production. In particular, the reasons leading to the observed interfacial reactions products and their metallurgical evolution have been analyzed. Results presented in the literature have been critically evaluated with the help of combined thermodynamic-kinetic approach based on the concept of local equilibrium and microstructural knowledge. The following conclusions have been reached: Firstly, the formations of intermetallic compounds in solid/liquid reaction couples are primarily controlled by the dissolution processes of base metals. Other factors that need be considered are the thermodynamic driving force for the formation of intermetallic compounds, their structures and concentration profiles in liquid. Secondly, annealing of solder interconnections in solid state can drastically change the microstructures formed in the solid/liquid reactions, especially if only one of the components in the solder takes part in the interfacial reactions. Thirdly, additional elements can have three major effects on the binary reactions between a base metal and Sn: (i) they can increase or decrease the reaction/growth rates, (ii) the additives can change the physical properties of the phases formed, and (iii) they can form additional reaction products or displace the binary equilibrium phases by forming new reaction products. Finally, if the local stable or metastable equilibrium is established at the interface, stability information together with kinetic considerations can provide a feasible approach to analyze interfacial reactions, which can have significant impact on the reliability of soldered electronics assemblies. #

Microelectronic Engineering, 2004

Interfacial reactions in the Si/TaC/Cu metallization system were investigated by utilizing transm... more Interfacial reactions in the Si/TaC/Cu metallization system were investigated by utilizing transmission electron microscopy and a combined kinetic and thermodynamic analysis. The formation of an amorphous Ta [C,O] layer was observed at the TaC/Cu interface at 600°C. After annealing at the same temperature a thin amorphous layer was detected also at the Si/TaC interface. After annealing at 750°C the thickness of the amorphous layer at the Si/TaC interface had increased and a mixture of crystalline and amorphous phases could be detected inside the TaC layer. This was anticipated to be the preliminary stage of the formation of SiC and TaSi 2 that occurred at 800°C. Overlapping with thickening of the amorphous layer formation of large Cu 3 Si precipitates took place and the layered metallization structure was partially destroyed. In order to obtain more information on the reactions at the Si/TaC interface and the effect of oxygen on the stability of TaC the ternary Si-Ta-C and Ta-C-O phase diagrams were evaluated from the assessed binary data. Activity diagram was also calculated to evaluate the possible reaction sequence at the Si/TaC interface. The observed reaction structure was found to be consistent with the thermodynamics of the ternary system.

Journal of Materials Science: Materials in Electronics, 2012

The effect of Ti on the solid state reactions between Sn and Ni has been investigated in this wor... more The effect of Ti on the solid state reactions between Sn and Ni has been investigated in this work. Based on the experimental results the following statements can be made: Firstly, the presence of Ti does not have measurable effects on the thickness evolution of Ni 3 Sn 4 during solid state annealing. Secondly, the results from long term heat treatments show that there is no marked solubility of Ti to Ni 3 Sn 4 . Rather Ti reacts with Sn to form large Ti 2 Sn 3 platelets inside the solder matrix. The Sn-rich part of the Ni-Sn-Ti phase diagram was assessed in order to rationalize the experimental results. By utilizing this information, the absence of any marked effects of Ti on the growth of Ni-Sn intermetallic compounds (IMC) was analysed. As there is no solubility of Ti to SnAg solder or to Ni-Sn IMC's, Ti cannot change activities of components in the solder nor influence the stability of the IMC layers. Hence, these results throw significant doubts over the concept of trying to influence the Ni-Sn IMC layer thickness or quality by Ti alloying.

Journal of Electronic Materials, 2008

Interfacial reactions between liquid Sn and various Cu-Ni alloy metallizations as well as the sub... more Interfacial reactions between liquid Sn and various Cu-Ni alloy metallizations as well as the subsequent phase transformations during the cooling were investigated with an emphasis on the microstructures of the reaction zones. It was found that the extent of the microstructurally complex reaction layer (during reflow at 240°C) does not depend linearly on the Ni content of the alloy metallization. On the contrary, when Cu is alloyed with Ni, the rate of thickness change of the total reaction layer first increases and reaches a maximum at a composition of about 10 at.% Ni. The reaction layer is composed of a relatively uniform continuous (Cu,Ni) 6 Sn 5 reaction layer (a uniphase layer) next to the NiCu metallizations and is followed by the two-phase solidification structures between the single-phase layer and Sn matrix. The thickness of the two-phase layer, where the intermetallic tubes and fibers have grown from the continuous interfacial (Cu,Ni) 6 Sn 5 layer, varies with the Ni-to-Cu ratio of the alloy metallization. In order to explain the formation mechanism of the reaction layers and their observed kinetics, the phase equilibria in the Sn-rich side of the SnCuNi system at 240°C were evaluated thermodynamically utilizing the available data, and the results of the Sn/Cu x Ni 1-x diffusion couple experiments. With the help of the assessed data, one can also evaluate the minimum Cu content of Sn-(Ag)-Cu solder, at which (Ni,Cu) 3 Sn 4 transforms into (Cu,Ni) 6 Sn 5 , as a function of temperature and the composition of the liquid solders.

Journal of Applied Polymer Science, 2006

Journal of Applied Physics, 2006

The interfacial reactions of near-eutectic Sn-Ag-Cu solder with Ni͑P͒ / Au metal finishes on prin... more The interfacial reactions of near-eutectic Sn-Ag-Cu solder with Ni͑P͒ / Au metal finishes on printed wiring boards as well as in component under bump metallizations have been investigated in this work. With the help of the scanning electron microscopy and transmission electron microscopy it was discovered that the first phase to form was the metastable nanocrystalline ternary NiSnP layer that provided the substrate for the subsequent formation of ͑Cu, Ni͒ 6 Sn 5 . During cooling or in the subsequent reflows the metastable NiSnP layer partially transformed into the columnar Ni 3 P. In this transformation Sn atoms and impurities, which do not dissolve into the Ni 3 P, diffuse towards the remaining NiSnP layer. When the specimens are further annealed in solid state at 170°C the Ni 3 P phase transforms into Ni 5 P 2 implying that some more Ni has diffused towards the solder. However, when Ni͑P͒ / Au finishes with a higher P content were used, only the ternary NiSnP layer was observed. Based on the mass balance and available thermodynamic data on the Sn-P-Ni system the evolution of the observed microstructures in the reactions between the solder and Ni͑P͒ / Au finishes is discussed.

Intermetallics, 2012

Othman et al. (Intermetallics 2012;22:1e6) recently published a manuscript on "Effects of current... more Othman et al. (Intermetallics 2012;22:1e6) recently published a manuscript on "Effects of current density on the formation and microstructure of Sne9Zn, Sne8Zne3Bi and Sne3Age0.5Cu solder joints". We found problems in calculation of diffusion parameters. Even the comment on the formation of Cu 5 Zn 8 instead of Cu 6 Sn 5 is not correct. In this comment, we have explained the correct procedure to calculate the diffusion coefficients. Further, we have also explained the reason for the formation of Cu 5 Zn 8 instead of Cu 6 Sn 5 in the Cu/ Sne9Zn system.