James Rohan - Academia.edu (original) (raw)
Papers by James Rohan
Copper and low dielctric constantant (k) materials are poised to become the dominant interconnect... more Copper and low dielctric constantant (k) materials are poised to become the dominant interconnect scheme for integrated circuits for the future because of the low resistance and capacitance that they offer which can improve circuit performance by more than 30 % over conventional interconnect schemes. This paper addresses the thermomechanical stresses in the CuILow k interconnect scheme through numerical simulation
Nanostructure Science and Technology, 2013
56th Electronic Components and Technology Conference 2006, 2006
This paper reports on the development of a 3D interconnection process leading to the successful a... more This paper reports on the development of a 3D interconnection process leading to the successful assembly of a five-layer 3-D 1mm cube module. This proof of concept module demonstrates the capability for successful integration and interconnection of commercial off the shelf components to fabricate functional modules in 1mm cube dimensions. It also demonstrates that use of established volume scale technologies like Flip-chip, dicing and patterning techniques are viable for fabricating these 1mm modules. The demonstrator consists of LED's bonded to the six sides of the 1mm cube, interconnected and powered up. The work will particularly report on two different processes to fabricate the interconnection pattern using direct Focused Ion Beam (FIB) assisted Pt deposition and electroless metal deposition, which again patterned by FIB. Uniform thickness of the deposit and excellent coverage on all six sides is achieved by electroless nickel deposition. Voltage current characterisation of the deposited Pt shows a resistivity value of 1864 ± 100 µΩ cm, whereas electroless Ni film shows a resistivity of 25 µΩ cm due to boron inclusion. 100 nm Au layer is deposited by chemical displacement reaction to enhance the conductivity and solderability of the film.
This invention features the use of redox reagents, dissolved in non-aqueous electrolytes, to prov... more This invention features the use of redox reagents, dissolved in non-aqueous electrolytes, to provide overcharge protection for cells having lithium metal or lithium-ion negative electrodes (anodes). In particular, the invention features the use of a class of compounds consisting of thianthrene and its derivatives as redox shuttle reagents to provide overcharge protection. Specific examples of this invention are thianthrene and
Proceedings of SPIE - The International Society for Optical Engineering, 2007
Initial results are presented on the electroless deposition of metal contacts to p-type gallium n... more Initial results are presented on the electroless deposition of metal contacts to p-type gallium nitride (GaN). Deposition procedures were developed for the deposition of both nickel and tungsten-cobalt (W-Co) contacts onto p-type GaN. Attempts to deposit platinum on p-type GaN failed, despite the fact that electroless platinum deposition was successfully achieved on other substrate types. Nickel contacts were overlaid with gold and annealed in oxygen ambient to form ohmic contacts with specific contact resistivity values down to 2x10 -2 Ωcm 2 . Measurements at elevated temperatures up to 140 0 C showed that the specific contact resistivity was almost independent of temperature. The tungsten-cobalt contacts showed rectifying behaviour even after annealing at 650 0 C. This makes this contact type a possible candidate for Schottky contacts in high temperature applications.
2013 IEEE 63rd Electronic Components and Technology Conference, 2013
ABSTRACT The paper introduces the trend of integration and miniaturization of power converters wi... more ABSTRACT The paper introduces the trend of integration and miniaturization of power converters with potential for enhanced efficiency, form factor reduction and cost reduction. To demonstrate the concept of highly integrated switched mode power supply with integrated magnetic, a system-in-package DC-DC converter using a stacked co-packaging approach is developed. A system approach was taken to the design, and functional integration, using 3-D packaging for realizing a power supply in package solution (PwrSiP). The target integrated converter is capable of handling an input voltage of 5V and frequencies up to 40MHz. A DC-DC converter IC on a 0.35μm CMOS process was designed to meet this goal. In parallel with the IC design, technology development for on-silicon integrated micro-inductors was completed to achieve small-form factor and extremely low profile. A maximum measured efficiency of 83% and 78% was achieved on the stacked converter operating at 20MHz and 40MHz, respectively. The stacked approach showed a 30% area reduction compared to side-by-side implementation with external discrete inductor.
ECS Transactions, 2009
Abstract Methanesulphonic acid (MSA) is an alternative to sulphuric acid electrolytes. The electr... more Abstract Methanesulphonic acid (MSA) is an alternative to sulphuric acid electrolytes. The electrochemical nucleation and growth of Cu on a glassy carbon (GC) electrode was studied from the methanesulphonate and sulphate baths. The overpotential for Cu deposition was much smaller in the MSA bath compared to the traditional sulphuric acid bath. Cu nucleation occurred at a higher rate in the MSA bath. The measured diffusion coefficient value for Cu deposition from the MSA bath was 6.82 x 10-6 cm2/s. The UV-Vis spectroscopic results ...
Opto-Ireland 2005: Optoelectronics, Photonic Devices, and Optical Networks, 2005
ABSTRACT High brightness LEDs (HBLEDs) have been fabricated on GaN semiconductor material grown o... more ABSTRACT High brightness LEDs (HBLEDs) have been fabricated on GaN semiconductor material grown on sapphire substrate. These devices provide an optical output power in excess of 50 mW at a driving current of 1 amp. For this high current application, large size (1.8 mm × 0.6 mm) GaN LEDs are flip-chip mounted onto a heat sink to provide a low thermal resistance path from the junction to the ambient. For the flip-chip mounting, a Au/Sn/Au solder and a Au/Au thermal compression bonding process have been optimized. The bond strength of the Au/Sn solder joints and the Au-Au bonds is measured through shear testing. Good bond strength results of 224 g/f for the Au/Sn/Au solder and 288 g/f for the solid Au bonds have been achieved. The thermal modeling of the assembly is done with a finite element analysis and the optimum design has been adopted for this high current application. At present these assemblies are under lifetime test and so far nearly 6000 hours of continuous operation has been achieved.
Abstract A direct electrodeposition technique for very high quality Cu nanotube arrays and subseq... more Abstract A direct electrodeposition technique for very high quality Cu nanotube arrays and subsequent conversion of the deposited Cu into Cu2O has been developed. The Cu2O nanotube arrays have high capacity, high cyclability and high rate capability. The cycling performance of Cu2O nanotubes show a high level of structural integrity with capacity retention even after 94 cycles when cycled at 1.67 mA/cm2. The outstanding electrochemical performance of the Cu2O nanotubes comes from high surface area, easy infiltration of ...
Talanta, 2008
The coming decade will see the rapid emergence of low cost, intelligent, wireless sensors and the... more The coming decade will see the rapid emergence of low cost, intelligent, wireless sensors and their widespread deployment throughout our environment. While wearable systems will operate over communications ranges of less than a meter, building management systems will operate with inter-node communications ranges of the order of meters to tens of meters and remote environmental monitoring systems will require communications systems and associated energy systems that will allow reliable operation over kilometers. Autonomous power should allow wireless sensor nodes to operate in a "deploy and forget" mode. The use of rechargeable battery technology is problematic due to battery lifetime issues related to node power budget, battery self-discharge, number of recharge cycles and long-term environmental impact. Duty cycling of wireless sensor nodes with long "SLEEP" times minimises energy usage. A case study of a multi-sensor, wireless, building management system operating using the Zigbee protocol demonstrates that, even with a 1 min cycle time for an 864 ms "ACTIVE" mode, the sensor module is already in SLEEP mode for almost 99% of the time. For a 20-min cycle time, the energy utilisation in SLEEP mode exceeds the ACTIVE mode energy by almost a factor of three and thus dominates the module energy utilisation thereby providing the ultimate limit to the power system lifetime. Energy harvesting techniques can deliver energy densities of 7.5 mW/cm 2 from outdoor solar, 100 W/cm 2 from indoor lighting, 100 W/cm 3 from vibrational energy and 60 W/cm 2 from thermal energy typically found in a building environment. A truly autonomous, "deploy and forget" battery-less system can be achieved by scaling the energy harvesting system to provide all the system energy needs. In the building management case study discussed, for duty cycles of less than 0.07% (i.e. in ACTIVE mode for 0.864 s every 20 min), energy harvester device dimensions of approximately 2 cm on a side would be sufficient to supply the complete wireless sensor node energy. Key research challenges to be addressed to deliver future, remote, wireless, chemo-biosensing systems include the development of low cost, low-power sensors, miniaturised fluidic transport systems, anti-bio-fouling sensor surfaces, sensor calibration, reliable and robust system packaging, as well as associated energy delivery systems and energy budget management.
Solid State Ionics, 2012
ABSTRACT The growth of thin porous anodic aluminum oxide (AAO) films on silicon by anodizing Al o... more ABSTRACT The growth of thin porous anodic aluminum oxide (AAO) films on silicon by anodizing Al on Ti/Au/Si and Ti/Pt/Si substrates in oxalic acid was demonstrated. Removal of the Al2O3 barrier layer was effected by selective chemical etching in H3PO4 and a reversed bias method in the anodizing solution. Ion transport and the influence of the Ti adhesion layer at the oxide–metal interface during the critical stages of anodization and pore opening were investigated. The AAO films may be exploited as templates in the creation of silicon-integrated nanostructured wire arrays. Electrodeposition of Pt into the AAO template yielded a nanowire array with superior methanol oxidation activity that can be integrated in a micro direct methanol fuel cell.
physica status solidi (c), 2005
PACS 78.66.Fd, 81.15.Pq, 85.30.De, 85.60.Jb InGaN based high brightness (HB)-LED chips have been ... more PACS 78.66.Fd, 81.15.Pq, 85.30.De, 85.60.Jb InGaN based high brightness (HB)-LED chips have been fabricated and bonded to substrates that were coated with electroplated Au/Sn/Au solder. The assemblies yielded a forward voltage of 5.6 V and an optical output power of 42 mW when tested at 1,000 mA bias. The electroluminescence distribution was mapped with a CCD camera to determine the current spreading into the p-contact region. Computational fluid dynamics (CFD) was used to check the effect of non-uniform current spreading on the thermal resistance of the assemblies. We show that a good knowledge of the non-uniform heat generation is required to obtain accurate modelling results. The bond strength of the AuSn solder joints exceeded the norm, when shear tested according to MIL-STD-883E (method 2019.5).
Journal of Power Sources, 2008
Solution phase deposition of aligned arrays of carbon nanotubes (CNTs) in a platinum (Pt) matrix ... more Solution phase deposition of aligned arrays of carbon nanotubes (CNTs) in a platinum (Pt) matrix composite is demonstrated. The catalyst material is electrodeposited in an oriented manner on the nanoscale using anodised aluminium oxide (AAO) templates. The catalyst performance of the composite for the oxidation of methanol is shown. The carbon monoxide (CO) tolerance is increased and the catalyst function is improved by minimising the influence of adsorbed CO on the kinetics of the methanol oxidation reaction.
Journal of Power Sources, 2012
Journal of Electronic Materials, 2004
The interfacial reaction between electroless Ni(P) under-bump metallization (UBM) and solders is ... more The interfacial reaction between electroless Ni(P) under-bump metallization (UBM) and solders is studied. A P-rich layer forms in the UBM along the solder side after reflow and thermal aging. Crack formation inside the P-rich layer can sometimes penetrate throughout the entire UBM layer structure. The Ni(P) UBM degradation occurs earlier in the Sn3.5Ag solder than in Sn37Pb because of its higher reflow temperature. Despite the formation of a P-rich layer and cracks inside the UBM, it still keeps its original function within the high-temperature storage period in this study. Explanations for the formation of the P-rich layer and cracks in the UBM are outlined along with explanations for the Ni(P) UBM degradation process.
![Research paper thumbnail of Nanotubes of Core/Shell Cu/Cu[sub 2]O as Anode Materials for Li-Ion Rechargeable Batteries](https://attachments.academia-assets.com/42944322/thumbnails/1.jpg)
](Journal of The Electrochemical Society, 2010
A direct electrodeposition technique for Cu nanotube array fabrication and the subsequent convers... more A direct electrodeposition technique for Cu nanotube array fabrication and the subsequent conversion of the deposited Cu into Cu 2 O was developed. The Cu 2 O nanotube arrays showed high capacity, cyclability, and rate capability. The cycling performance of the Cu 2 O nanotubes showed a high level of structural integrity with capacity retention even after 94 cycles when cycled at 1C to 3C rates. The enhanced electrochemical performance of the Cu 2 O nanotubes came from a high surface area, electrolyte access, high electrical conductivity of Cu core support, and structural integrity of the oxide shell active material.
Journal of The Electrochemical Society, 2010
Methanesulfonic acid ͑MSA͒ is an alternative to sulfuric acid electrolyte for metal deposition. T... more Methanesulfonic acid ͑MSA͒ is an alternative to sulfuric acid electrolyte for metal deposition. The electrochemical nucleation and growth of Cu on a glassy carbon electrode in methanesulfonate was compared with sulfate baths. The overpotential for Cu deposition was much smaller in the MSA bath compared to the traditional sulfuric acid bath, and Cu nucleation occurred at a higher rate in the MSA bath. The measured diffusion coefficient value for Cu deposition from the MSA bath was 6.82 ϫ 10 −6 cm 2 /s. UV-visible spectroscopic results confirmed that the coordination of Cu species was the same in both electrolytes. Cu electrodeposition on Ni sputtered Si substrate from the high efficiency MSA bath was photoresist-compatible with no void formation. One-dimensional Cu nanorods were also deposited through an anodized aluminum oxide template on a Ni evaporated seed layer substrate, showing potential applications as electrical interconnects in ultralarge scale integration ͑ULSI͒ and microelectromechanical systems ͑MEMS͒.
Journal of The Electrochemical Society, 2005
ABSTRACT A zincate-free electroless nickel deposition on aluminum bond pads is investigated. A th... more ABSTRACT A zincate-free electroless nickel deposition on aluminum bond pads is investigated. A three-step, etch, rinse, and electroless plating, is demonstrated for deposition on aluminum bond pads patterned with polyimide. The chemicals used are compatible with this dielectric material. The deposition has been achieved with good selectivity, uniformity, and deposition rate at aluminum bond pads. The adhesion and contact resistance were also determined and improved through anneals in the range 200-400°C for 1 h. The optimized condition for adhesion and contact resistance was an anneal at 400°C. The combination of a nickel hypophosphite reducing agent and the additives used leads to an active plating bath in the early stages of deposition, by comparison with commercial solutions, and hence, good coverage of the aluminum bond pad using the simplified process. © 2004 The Electrochemical Society. All rights reserved.
Copper and low dielctric constantant (k) materials are poised to become the dominant interconnect... more Copper and low dielctric constantant (k) materials are poised to become the dominant interconnect scheme for integrated circuits for the future because of the low resistance and capacitance that they offer which can improve circuit performance by more than 30 % over conventional interconnect schemes. This paper addresses the thermomechanical stresses in the CuILow k interconnect scheme through numerical simulation
Nanostructure Science and Technology, 2013
56th Electronic Components and Technology Conference 2006, 2006
This paper reports on the development of a 3D interconnection process leading to the successful a... more This paper reports on the development of a 3D interconnection process leading to the successful assembly of a five-layer 3-D 1mm cube module. This proof of concept module demonstrates the capability for successful integration and interconnection of commercial off the shelf components to fabricate functional modules in 1mm cube dimensions. It also demonstrates that use of established volume scale technologies like Flip-chip, dicing and patterning techniques are viable for fabricating these 1mm modules. The demonstrator consists of LED's bonded to the six sides of the 1mm cube, interconnected and powered up. The work will particularly report on two different processes to fabricate the interconnection pattern using direct Focused Ion Beam (FIB) assisted Pt deposition and electroless metal deposition, which again patterned by FIB. Uniform thickness of the deposit and excellent coverage on all six sides is achieved by electroless nickel deposition. Voltage current characterisation of the deposited Pt shows a resistivity value of 1864 ± 100 µΩ cm, whereas electroless Ni film shows a resistivity of 25 µΩ cm due to boron inclusion. 100 nm Au layer is deposited by chemical displacement reaction to enhance the conductivity and solderability of the film.
This invention features the use of redox reagents, dissolved in non-aqueous electrolytes, to prov... more This invention features the use of redox reagents, dissolved in non-aqueous electrolytes, to provide overcharge protection for cells having lithium metal or lithium-ion negative electrodes (anodes). In particular, the invention features the use of a class of compounds consisting of thianthrene and its derivatives as redox shuttle reagents to provide overcharge protection. Specific examples of this invention are thianthrene and
Proceedings of SPIE - The International Society for Optical Engineering, 2007
Initial results are presented on the electroless deposition of metal contacts to p-type gallium n... more Initial results are presented on the electroless deposition of metal contacts to p-type gallium nitride (GaN). Deposition procedures were developed for the deposition of both nickel and tungsten-cobalt (W-Co) contacts onto p-type GaN. Attempts to deposit platinum on p-type GaN failed, despite the fact that electroless platinum deposition was successfully achieved on other substrate types. Nickel contacts were overlaid with gold and annealed in oxygen ambient to form ohmic contacts with specific contact resistivity values down to 2x10 -2 Ωcm 2 . Measurements at elevated temperatures up to 140 0 C showed that the specific contact resistivity was almost independent of temperature. The tungsten-cobalt contacts showed rectifying behaviour even after annealing at 650 0 C. This makes this contact type a possible candidate for Schottky contacts in high temperature applications.
2013 IEEE 63rd Electronic Components and Technology Conference, 2013
ABSTRACT The paper introduces the trend of integration and miniaturization of power converters wi... more ABSTRACT The paper introduces the trend of integration and miniaturization of power converters with potential for enhanced efficiency, form factor reduction and cost reduction. To demonstrate the concept of highly integrated switched mode power supply with integrated magnetic, a system-in-package DC-DC converter using a stacked co-packaging approach is developed. A system approach was taken to the design, and functional integration, using 3-D packaging for realizing a power supply in package solution (PwrSiP). The target integrated converter is capable of handling an input voltage of 5V and frequencies up to 40MHz. A DC-DC converter IC on a 0.35μm CMOS process was designed to meet this goal. In parallel with the IC design, technology development for on-silicon integrated micro-inductors was completed to achieve small-form factor and extremely low profile. A maximum measured efficiency of 83% and 78% was achieved on the stacked converter operating at 20MHz and 40MHz, respectively. The stacked approach showed a 30% area reduction compared to side-by-side implementation with external discrete inductor.
ECS Transactions, 2009
Abstract Methanesulphonic acid (MSA) is an alternative to sulphuric acid electrolytes. The electr... more Abstract Methanesulphonic acid (MSA) is an alternative to sulphuric acid electrolytes. The electrochemical nucleation and growth of Cu on a glassy carbon (GC) electrode was studied from the methanesulphonate and sulphate baths. The overpotential for Cu deposition was much smaller in the MSA bath compared to the traditional sulphuric acid bath. Cu nucleation occurred at a higher rate in the MSA bath. The measured diffusion coefficient value for Cu deposition from the MSA bath was 6.82 x 10-6 cm2/s. The UV-Vis spectroscopic results ...
Opto-Ireland 2005: Optoelectronics, Photonic Devices, and Optical Networks, 2005
ABSTRACT High brightness LEDs (HBLEDs) have been fabricated on GaN semiconductor material grown o... more ABSTRACT High brightness LEDs (HBLEDs) have been fabricated on GaN semiconductor material grown on sapphire substrate. These devices provide an optical output power in excess of 50 mW at a driving current of 1 amp. For this high current application, large size (1.8 mm × 0.6 mm) GaN LEDs are flip-chip mounted onto a heat sink to provide a low thermal resistance path from the junction to the ambient. For the flip-chip mounting, a Au/Sn/Au solder and a Au/Au thermal compression bonding process have been optimized. The bond strength of the Au/Sn solder joints and the Au-Au bonds is measured through shear testing. Good bond strength results of 224 g/f for the Au/Sn/Au solder and 288 g/f for the solid Au bonds have been achieved. The thermal modeling of the assembly is done with a finite element analysis and the optimum design has been adopted for this high current application. At present these assemblies are under lifetime test and so far nearly 6000 hours of continuous operation has been achieved.
Abstract A direct electrodeposition technique for very high quality Cu nanotube arrays and subseq... more Abstract A direct electrodeposition technique for very high quality Cu nanotube arrays and subsequent conversion of the deposited Cu into Cu2O has been developed. The Cu2O nanotube arrays have high capacity, high cyclability and high rate capability. The cycling performance of Cu2O nanotubes show a high level of structural integrity with capacity retention even after 94 cycles when cycled at 1.67 mA/cm2. The outstanding electrochemical performance of the Cu2O nanotubes comes from high surface area, easy infiltration of ...
Talanta, 2008
The coming decade will see the rapid emergence of low cost, intelligent, wireless sensors and the... more The coming decade will see the rapid emergence of low cost, intelligent, wireless sensors and their widespread deployment throughout our environment. While wearable systems will operate over communications ranges of less than a meter, building management systems will operate with inter-node communications ranges of the order of meters to tens of meters and remote environmental monitoring systems will require communications systems and associated energy systems that will allow reliable operation over kilometers. Autonomous power should allow wireless sensor nodes to operate in a "deploy and forget" mode. The use of rechargeable battery technology is problematic due to battery lifetime issues related to node power budget, battery self-discharge, number of recharge cycles and long-term environmental impact. Duty cycling of wireless sensor nodes with long "SLEEP" times minimises energy usage. A case study of a multi-sensor, wireless, building management system operating using the Zigbee protocol demonstrates that, even with a 1 min cycle time for an 864 ms "ACTIVE" mode, the sensor module is already in SLEEP mode for almost 99% of the time. For a 20-min cycle time, the energy utilisation in SLEEP mode exceeds the ACTIVE mode energy by almost a factor of three and thus dominates the module energy utilisation thereby providing the ultimate limit to the power system lifetime. Energy harvesting techniques can deliver energy densities of 7.5 mW/cm 2 from outdoor solar, 100 W/cm 2 from indoor lighting, 100 W/cm 3 from vibrational energy and 60 W/cm 2 from thermal energy typically found in a building environment. A truly autonomous, "deploy and forget" battery-less system can be achieved by scaling the energy harvesting system to provide all the system energy needs. In the building management case study discussed, for duty cycles of less than 0.07% (i.e. in ACTIVE mode for 0.864 s every 20 min), energy harvester device dimensions of approximately 2 cm on a side would be sufficient to supply the complete wireless sensor node energy. Key research challenges to be addressed to deliver future, remote, wireless, chemo-biosensing systems include the development of low cost, low-power sensors, miniaturised fluidic transport systems, anti-bio-fouling sensor surfaces, sensor calibration, reliable and robust system packaging, as well as associated energy delivery systems and energy budget management.
Solid State Ionics, 2012
ABSTRACT The growth of thin porous anodic aluminum oxide (AAO) films on silicon by anodizing Al o... more ABSTRACT The growth of thin porous anodic aluminum oxide (AAO) films on silicon by anodizing Al on Ti/Au/Si and Ti/Pt/Si substrates in oxalic acid was demonstrated. Removal of the Al2O3 barrier layer was effected by selective chemical etching in H3PO4 and a reversed bias method in the anodizing solution. Ion transport and the influence of the Ti adhesion layer at the oxide–metal interface during the critical stages of anodization and pore opening were investigated. The AAO films may be exploited as templates in the creation of silicon-integrated nanostructured wire arrays. Electrodeposition of Pt into the AAO template yielded a nanowire array with superior methanol oxidation activity that can be integrated in a micro direct methanol fuel cell.
physica status solidi (c), 2005
PACS 78.66.Fd, 81.15.Pq, 85.30.De, 85.60.Jb InGaN based high brightness (HB)-LED chips have been ... more PACS 78.66.Fd, 81.15.Pq, 85.30.De, 85.60.Jb InGaN based high brightness (HB)-LED chips have been fabricated and bonded to substrates that were coated with electroplated Au/Sn/Au solder. The assemblies yielded a forward voltage of 5.6 V and an optical output power of 42 mW when tested at 1,000 mA bias. The electroluminescence distribution was mapped with a CCD camera to determine the current spreading into the p-contact region. Computational fluid dynamics (CFD) was used to check the effect of non-uniform current spreading on the thermal resistance of the assemblies. We show that a good knowledge of the non-uniform heat generation is required to obtain accurate modelling results. The bond strength of the AuSn solder joints exceeded the norm, when shear tested according to MIL-STD-883E (method 2019.5).
Journal of Power Sources, 2008
Solution phase deposition of aligned arrays of carbon nanotubes (CNTs) in a platinum (Pt) matrix ... more Solution phase deposition of aligned arrays of carbon nanotubes (CNTs) in a platinum (Pt) matrix composite is demonstrated. The catalyst material is electrodeposited in an oriented manner on the nanoscale using anodised aluminium oxide (AAO) templates. The catalyst performance of the composite for the oxidation of methanol is shown. The carbon monoxide (CO) tolerance is increased and the catalyst function is improved by minimising the influence of adsorbed CO on the kinetics of the methanol oxidation reaction.
Journal of Power Sources, 2012
Journal of Electronic Materials, 2004
The interfacial reaction between electroless Ni(P) under-bump metallization (UBM) and solders is ... more The interfacial reaction between electroless Ni(P) under-bump metallization (UBM) and solders is studied. A P-rich layer forms in the UBM along the solder side after reflow and thermal aging. Crack formation inside the P-rich layer can sometimes penetrate throughout the entire UBM layer structure. The Ni(P) UBM degradation occurs earlier in the Sn3.5Ag solder than in Sn37Pb because of its higher reflow temperature. Despite the formation of a P-rich layer and cracks inside the UBM, it still keeps its original function within the high-temperature storage period in this study. Explanations for the formation of the P-rich layer and cracks in the UBM are outlined along with explanations for the Ni(P) UBM degradation process.
Journal of The Electrochemical Society, 2010
A direct electrodeposition technique for Cu nanotube array fabrication and the subsequent convers... more A direct electrodeposition technique for Cu nanotube array fabrication and the subsequent conversion of the deposited Cu into Cu 2 O was developed. The Cu 2 O nanotube arrays showed high capacity, cyclability, and rate capability. The cycling performance of the Cu 2 O nanotubes showed a high level of structural integrity with capacity retention even after 94 cycles when cycled at 1C to 3C rates. The enhanced electrochemical performance of the Cu 2 O nanotubes came from a high surface area, electrolyte access, high electrical conductivity of Cu core support, and structural integrity of the oxide shell active material.
Journal of The Electrochemical Society, 2010
Methanesulfonic acid ͑MSA͒ is an alternative to sulfuric acid electrolyte for metal deposition. T... more Methanesulfonic acid ͑MSA͒ is an alternative to sulfuric acid electrolyte for metal deposition. The electrochemical nucleation and growth of Cu on a glassy carbon electrode in methanesulfonate was compared with sulfate baths. The overpotential for Cu deposition was much smaller in the MSA bath compared to the traditional sulfuric acid bath, and Cu nucleation occurred at a higher rate in the MSA bath. The measured diffusion coefficient value for Cu deposition from the MSA bath was 6.82 ϫ 10 −6 cm 2 /s. UV-visible spectroscopic results confirmed that the coordination of Cu species was the same in both electrolytes. Cu electrodeposition on Ni sputtered Si substrate from the high efficiency MSA bath was photoresist-compatible with no void formation. One-dimensional Cu nanorods were also deposited through an anodized aluminum oxide template on a Ni evaporated seed layer substrate, showing potential applications as electrical interconnects in ultralarge scale integration ͑ULSI͒ and microelectromechanical systems ͑MEMS͒.
Journal of The Electrochemical Society, 2005
ABSTRACT A zincate-free electroless nickel deposition on aluminum bond pads is investigated. A th... more ABSTRACT A zincate-free electroless nickel deposition on aluminum bond pads is investigated. A three-step, etch, rinse, and electroless plating, is demonstrated for deposition on aluminum bond pads patterned with polyimide. The chemicals used are compatible with this dielectric material. The deposition has been achieved with good selectivity, uniformity, and deposition rate at aluminum bond pads. The adhesion and contact resistance were also determined and improved through anneals in the range 200-400°C for 1 h. The optimized condition for adhesion and contact resistance was an anneal at 400°C. The combination of a nickel hypophosphite reducing agent and the additives used leads to an active plating bath in the early stages of deposition, by comparison with commercial solutions, and hence, good coverage of the aluminum bond pad using the simplified process. © 2004 The Electrochemical Society. All rights reserved.