Intermetallic formation and growth at the interface between copper and Sn-Pb solders and its effects on joint strength

This work details the effect of Lead, a heavy metal toxin, on the interfacial reaction between Cu and Sn-Pb solders and the tensile fracture of solder joints.Doctor of Philosophy (SME

The use of nano-structured hybrid materials for oral drug delivery

We have used a novel hybrid nano-structured sponge to conduct proof of concept studies for the oral delivery of peptides employing insulin as the loaded model drug. The hybrid sponge was synthesized from a modified acid-base neutralization reaction for hydroxyapatitc (HA) incorporating cMtosan (CHT) as the organic counterpart. The trace addition of chitosan during synthesis resulted in a hybrid colloidal suspension which could be dried to from this hybrid sponge. The sponge morphology was unique indicating two levels of structure with assembled nanoparticles combined with nanoporous HA-CHT architecture. These films showed relatively high levels of insulin loading (~700IU/g of carrier) and could be coated with an alginate based gel. Release of insulin in simulated gastric and intestinal fluids (SGF and SIF) indicated that release was predominant in intestinal conditions and that a complex double mode kinetic release profile was inherent in the system. However, we believe at this stage that this characteristic can be rationalized as the combined effect of release from the drug adsorbed onto the nanoparticles and condensed into the nanoporous architecture. Overall the loading and release were promising and further studies are currently underway to incorporate other functional modifications in the sponge and in vitro characterization

Improvement of the wet tensile properties of nanostructured hydroxyapatite and chitosan biocomposite films through hydrophobic modification

Hydrophobic modification of chitosan/hydroxyapatite composites and chitosan films was performed using four n-alkyl acids with varying alkyl chain lengths (6 to 16 carbons), and these films were characterized for their hydrophobicity and tensile properties under wet conditions. Grafting was performed by a heterogeneous reaction in a 2.0 mol L-1 DMF solution of the acid at 80 degrees C for either one or five days. Characterisation by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) verified the introduction of amide functionalities and alkyl chains. The degree of substitution (DS) ranged from 2-5% for the composite films (based on XPS N 1s narrow scans) reflecting the heterogeneous nature of the reaction. Water contact angle measurements and the tensile testing under wet conditions showed, in general, that the grafting time and alkyl chain length had little effect on the surface hydrophobicity and the tensile properties of films, respectively. However, these modifications had a pronounced effect on decreasing the water content of the films, suggesting that the grafting had occurred in the bulk of the film for longer grafting times. In contrast, the tensile properties of the grafted composite films were significantly improved relative to non-grafted films and a modulus of 393 +/- 68 MPa and an UTS of 18.7 +/- 1.5 MPa were reached for composite films grafted for one day. This study provides a simple method to improve the wet tensile properties of chitosan/hydroxyapatite composite films making them more suitable for biomedical applications

In vitro apatite formation and its growth kinetics on hydroxyapatite/polyetheretherketone biocomposites

The formation of biologically equivalent carbonate-containing apatite on the surface of synthetic hydroxyapatite (HA) is an important step leading to good bone healing. In this study, HA-reinforced polyetheretherketone (PEEK) composites were prepared by homogeneous mixing of HA and PEEK powders, compaction, and pressureless sintering. The bioactivity of HA/PEEK composite with 10, 20, 30 and 40 vol% HA was evaluated by immersing the composite disks in the simulated body fluid (SBF) for up to 4 weeks. The surface of composite with 40 vol% HA was covered by a layer of bone-like apatite just after 3 days of immersion, while 10 vol% HA was covered only after 28 days. This apatite layer was characterized by SEM, thin film X-ray diffractometer, attenuated total reflectance–Fourier transform infrared spectrometer (FTIR)/FTIR. Introducing a concept called apatite-forming capacity of SBF, growth kinetics of the apatite layer on the surface of the composite disks was carried out. The growth rate constant increased with HA volume fraction of the composite, suggesting that the bioactivity of the HA/PEEK composite increases with increasing HA volume fraction in the composite. ; ; ;

Isothermal and thermal cycling aging on IMC growth rate in lead-free and lead-based solder interface

The growth of interfacial intermetallic compounds (IMC) between Pb-free and Pb-based solders with different surface finish (Cu and Ni/Au) metallization is a major concern for long-term solder joint reliability performance in electronic assemblies. The growth rate of the IMC layer can affect the solder joint reliability. Analysis of solid-state diffusion mechanism for the growth of IMC between solder-to-substrate interface for Pb-free and Pb-based solders subject to isothermal and thermal cycling aging were conducted. Experimental study of IMC layer growth between Sn3.8Ag0.7Cu and Ni/Au surface finish by isothermal aging versus thermal cycling (TC) aging was investigated to develop a framework for correlating IMC layer growth behavior. An integrated model for IMC growth was derived to describe the Ni-Cu-Sn IMC growth behavior subject to TC aging. Comparison of modeling and test results showed that IMC layer growth rate under TC aging was accelerated. It is noted that IMC layer growth study from various references showed different experimental data and growth kinetic parameters for both liquid-state and solid-state reactions

An organic matrix-mediated processing methodology to fabricate hydroxyapatite based nanostructured biocomposites

An amorphous calcium phosphate precursor phase, which forms by adding orthophosphoric acid to a calcium hydroxide suspension, is transformed into crystalline hydroxyapatite by introducing polymer solutions. The nanostructured composite films formed by a solvent casting technique from the concentrated hybrid suspension are characterised for structure and mechanical properties

Development of encoded particle-polymer arrays for the accelerated screening of antifouling layers

A multiplexed screening methodology for the rapid development of antifouling polymer surfaces is presented. An array of protein resistant polymer layers with high grafting (> 100 mg m(-2)) were polymerized on optically encoded particles. Multiplexed analysis showed a 97% reduction in nonspecific protein adsorption for all polymer layers created