B. Munirathinam | TU Delft Repository

Exploring water and ion transport process at silicone/copper interfaces using in-situ electrochemical and Kelvin probe approaches

Journal article (2021) - Bala Munirathinam, Joost van Dam, Annemarie Herrmann, Willem van Driel, F. De Buyl, S. J.F. Erich, L.G.J. van der Ven, O. C.G. Adan, Arjan Mol

In general, packaging materials which encapsulate light emitting diodes (LEDs) and microelectronic devices offer barrier protection against several environmental hazards such as water and ionic contaminants. However, these encapsulants may provide pathways for water and ionic contaminants to reach the metal/polymer interfaces and provoke local corrosion of electronics, which is a major reliability concern for polymer encapsulated LEDs and microelectronics. As the water and corrosive constituents play a crucial role in their reliability, water uptake kinetics, interfacial ion transport and delamination behaviour of silicone coated copper model system, mimicking a typical microelectronics packaging system, is explored in the present work. Electrochemical impedance spectroscopy (EIS) integrated with attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy studies revealed that water diffusion inside the silicone network is Fickian in nature and the evolution of the observed time constants are related to the diffusion and interfacial reactions. A decrease of impedance magnitude with time was observed in EIS measurements concurrently with water absorption bands shifting towards lower wavenumber in ATR-FTIR measurements, implying the growth of strong hydrogen bonding between water molecules and the silicone network. The estimated diffusion constant of water using the capacitance method was in the order of 7 × 10-12 m2 s−1 and the water absorption volume fraction was in the range of 0% to 0.30%. Scanning Kelvin probe studies elucidated the ion transport process occurring at the silicone/copper interface in a humid atmosphere. The interfacial ion transport process is controlled by the interfacial electrochemical reactions at the cathodic delamination front and the estimated average delamination rate is 0.43 mm h-1/2. This work demonstrates that exploring ion and water transport in the silicone coating and along the silicone/copper interface is of pivotal importance as part of a detailed reliability assessment of the polymer encapsulated LEDs and microelectronics. ...

In general, packaging materials which encapsulate light emitting diodes (LEDs) and microelectronic devices offer barrier protection against several environmental hazards such as water and ionic contaminants. However, these encapsulants may provide pathways for water and ionic contaminants to reach the metal/polymer interfaces and provoke local corrosion of electronics, which is a major reliability concern for polymer encapsulated LEDs and microelectronics. As the water and corrosive constituents play a crucial role in their reliability, water uptake kinetics, interfacial ion transport and delamination behaviour of silicone coated copper model system, mimicking a typical microelectronics packaging system, is explored in the present work. Electrochemical impedance spectroscopy (EIS) integrated with attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy studies revealed that water diffusion inside the silicone network is Fickian in nature and the evolution of the observed time constants are related to the diffusion and interfacial reactions. A decrease of impedance magnitude with time was observed in EIS measurements concurrently with water absorption bands shifting towards lower wavenumber in ATR-FTIR measurements, implying the growth of strong hydrogen bonding between water molecules and the silicone network. The estimated diffusion constant of water using the capacitance method was in the order of 7 × 10-12 m2 s−1 and the water absorption volume fraction was in the range of 0% to 0.30%. Scanning Kelvin probe studies elucidated the ion transport process occurring at the silicone/copper interface in a humid atmosphere. The interfacial ion transport process is controlled by the interfacial electrochemical reactions at the cathodic delamination front and the estimated average delamination rate is 0.43 mm h-1/2. This work demonstrates that exploring ion and water transport in the silicone coating and along the silicone/copper interface is of pivotal importance as part of a detailed reliability assessment of the polymer encapsulated LEDs and microelectronics.

Improved corrosion protection of titanium implant material by crystallographic texturing of Sr doped calcium phosphate electrodeposits

Journal article (2019) - Balakrishnan Munirathinam, Nitesh R. Jaladurgam, J. Magesh, Ramaswamy Narayanan, Johannes M.C. Mol, Lakshman Neelakantan

Nanocrystalline calcium phosphate (CaP) coatings can provide biocompatibility and corrosion protection to biomaterials upon implementation in the human body. While the long term stability of recently developed coatings in biological environment proves to be challenging, the present work tailors the surface by orienting the growth (crystallographic texturing) of strontium doped CaP coatings in order to increase their corrosion resistance. X-ray diffraction (XRD) as well as selected area electron diffraction patterns from transmission electron microscopy reveal that nanocrystalline CaP crystallizes in hexagonal hydroxyapatite structure preferentially oriented along the c-axis. Orientation distribution function obtained from XRD texture studies confirms the presence of a [0001] fiber texture and the estimated texture index indicates the evolution of texture with increasing deposition current density. Polarization studies point out that increasingly textured coatings decrease the corrosion current density by an order of magnitude (from 2.43 × 10 ⁻⁷ to 3.46 × 10 ⁻⁸ A cm ⁻² ). Impedance measurements confirm that oriented growth of film renders improved corrosion resistance. This study demonstrates that oriented growth of electrodeposited films strongly improves the corrosion performance of titanium, which can be employed in design and development of highly corrosion resistive implant materials. ...

An investigation on the hardness and corrosion behavior of MWCNT/Mg composites and grain refined Mg

Journal article (2018) - N. Saikrishna, G. Pradeep Kumar Reddy, Balakrishnan Munirathinam, Ravikumar Dumpala, M. Jagannatham, B. Ratna Sunil

In the present work, multi walled carbon nanotubes (MWCNT) reinforced magnesium (Mg) matrix composite was fabricated by friction stir processing (FSP) with an aim to explore its mechanical and electrochemical behavior. Microstructural observations showed that the thickness of the produced composite layer was in the range of 2500 μm. FSP resulted uniform distribution of CNT near the surface while agglomerated layers in the subsurface. Grain refinement of Mg achieved by FSP improved the hardness but significant enhancement in the hardness value was observed for FSPed MWCNT/Mg composites. Potentiodynamic polarization studies revealed that the increase in corrosion current density was observed for MWCNT/Mg composite compared with grain refined Mg and pure Mg, implying the significance of secondary phase (MWCNT) in decreasing the corrosion resistance of the composite. ...