Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Ume, I. Charles; Committee Member: Danyluk, Steven; Committee Member: Goyal, Deepak; Committee Member: Lu, Jye-Chyi(JC); Committee Member: Michaels, Thomas; Committee Member: Sitaraman, Suresh. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (MEng) - School of Engineering and Science, Swinburne University of Technology, 2008. / Thesis submitted for the degree of Master of Engineering, School of Engineering and Science, Swinburne University of Technology, 2008. Typescript. Includes bibliographical references (p. 98-101).

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: Ronald L. Panton. Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (Ph.D.)--Lehigh University, 1994. / Adviser: Michael R. Notis. Includes bibliographical references.

The systems engineering approach was used to implement conformal solder mask in the manufacture of printed wiring boards (PWBs) at the AT&T Microelectronics Richmond Plant. Existing solder mask had a planar surface causing low soldering process yields on PWBs using Surface Mount Technology (SMT). SMT reduced product cost by allowing 50% more components per unit area of a PWB. Conformal solder mask processing reduced the mask thickness applied, and allowed future SMT PWBs to be manufactured. Coating methods to apply solder mask were evaluated. Two methods, curtain coating and electrostatic spray (ESS) f were chosen since no method satisfied all operational requirements. Ciba Geigy's Probimer process was implemented to meet short term revenue and capacity requirements. Probimer was an industry standard but had performance limitations. ESS met all requirements but required additional development to select a solder mask material and obtain customer approval. / Master of Science

The thermocyclic fatigue behavior of the low-melting solder 43Sn/43Pb/14Bi has been investigated and compared to that of standard 60Sn/4OPb solder via metallographic analysis (using scanning electron microscopy) and evaluation of the degree of fatigue development (using a fatigue scale as a function of thermocycles). Specimens were subjected to shearing strains imposed by several hundred fatigue thermocycles. Both solder types fatigue by the same microstructural failure mechanism as described by other workers. The mechanism is characterized by a preferential coarsening of the solder joint microstructure at the region of maximum stress concentration where cracks originate.

Lead corrosion in premise plumbing systems from materials, such as lead pipes, soldered joints, and brass, can cause elevated lead in drinking water. This work examined mechanisms by which galvanic corrosion of lead solder:copper joints is accelerated by high chloride, low sulfate, and high nitrate in the water. Galvanic corrosion studies conducted using simulated copper plumbing joints showed lowered pH and concentrated anions at the lead solder surface. A combination of low pH and high chloride can prevent passivation of the solder surface, indefinitely sustaining high corrosion rates and lead contamination of potable water supplies. The mass of lead leached to water correlated with predictions based on Faraday's law, although a portion of the oxidized lead remained attached to solder in a scale layer. When the level of sulfate in water increased relative to chloride, galvanic currents and associated lead contamination could be greatly reduced. The impact of chloride-to-sulfate mass ratio (CSMR) on lead leaching from 50:50 lead:tin solder galvanically coupled to copper was examined at the bench scale.The CSMR can be affected by coagulant changeover, use of desalinated water, anion exchange, brine leaks, and other treatment changes. Consistent with prior experiences, increasing the CSMR in the range of 0.1 to 1.0 produced dramatic increases in lead leaching from this source. Above this range, while lead leaching was generally very high, there was little correlation between lead release and CSMR. The impact of nitrate was tested at the bench scale using synthesized water. Results consistently showed that increasing nitrate in the range of 0 to 10 mg/L NO??N, could dramatically increase lead leaching from simulated soldered pipe joints. Although higher nitrate slightly increased the galvanic current, the main factor affecting lead release appears to be initiation of non-uniform corrosion, with small pieces of solder detaching into the water. Under some circumstances, the decay of chloramine after it leaves the treatment plant, and formation of nitrate via nitrification, can markedly increase corrosivity of distributed water to lead solder. The bench scale experiments conducted in this work illuminated many issues related to accelerated lead corrosion of solder. However, future research is necessary to further elucidate the mechanisms behind nitrate-accelerated corrosion, as well as methods for inhibition of corrosion due to chloride and nitrate. / Master of Science

Conventional tin-lead solder alloys have been widely used in electronics interconnection owing to their properties such as low melting temperature, good ductility and excellent wettability on copper and other substrates. However, due to the worldwide legislation addressing the concern over the toxicity of lead, the usage of lead-containing solders has been phased out, thus stimulating substantial efforts on lead-free alternatives, amongst which eutectic Sn-Ag and Sn-Cu, and particularly Sn-Ag-Cu alloys, are promising candidates as recommended by international parties. To meet the increasing demands of advanced electronic products, high levels of integration of electronic devices are being developed and employed, which is leading to a reduction in package size, but with more and more input/output connections. Flip chip technology is therefore seen as a promising technique for chip interconnection compared with wire bonding, enabling higher density, better heat dissipation and a smaller footprint. This thesis is intended to investigate lead-free (eutectic Sn-Ag, Sn-Cu and Sn-Ag-Cu) wafer level solder bumping through electrodeposition for flip chip interconnection, as well as electroplating lead-free solderable finishes on electronic components. The existing knowledge gap in the electrochemical processes as well as the fundamental understanding of the resultant tin-based lead-free alloys electrodeposits are also addressed. For the electrodeposition of the Sn-Cu solder alloys, a methanesulphonate based electrolyte was established, from which near-eutectic Sn-Cu alloys were achieved over a relatively wide process window of current density. The effects of methanesulphonic acid, thiourea and OPPE (iso-octyl phenoxy polyethoxy ethanol) as additives were investigated respectively by cathodic potentiodynamic polarisation curves, which illustrated the resultant electrochemical changes to the electrolyte. Phase identification by X-ray diffraction showed the electrodeposits had a biphasic structure (β-Sn and Cu6Sn5). Microstructures of the Sn-Cu electrodeposits were comprehensively characterised, which revealed a compact and crystalline surface morphology under the effects of additives, with cross-sectional observations showing a uniform distribution of Cu6Sn5 particles predominantly along β-Sn grain boundaries. The electrodeposition of Sn-Ag solder alloys was explored in another pyrophosphate based system, which was further extended to the application for Sn-Ag-Cu solder alloys. Cathodic potentiodynamic polarisation demonstrated the deposition of noble metals, Ag or Ag-Cu, commenced before the deposition potential of tin was reached. The co-deposition of Sn-Ag or Sn-Ag-Cu alloy was achieved with the noble metals electrodepositing at their limiting current densities. The synergetic effects of polyethylene glycol (PEG) 600 and formaldehyde, dependent on reaching the cathodic potential required, helped to achieve a bright surface, which consisted of fine tin grains (~200 nm) and uniformly distributed Ag3Sn particles for Sn-Ag alloys and Ag3Sn and Cu6Sn5 for Sn-Ag-Cu alloys, as characterised by microstructural observations. Near-eutectic Sn-Ag and Sn-Ag-Cu alloys were realised as confirmed by compositional analysis and thermal measurements. Near-eutectic lead-free solder bumps of 25 μm in diameter and 50 μm in pitch, consisting of Sn-Ag, Sn-Cu or Sn-Ag-Cu solder alloys depending on the process and electrolyte employed, were demonstrated on wafers through the electrolytic systems developed. Lead-free solder bumps were further characterised by material analytical techniques to justify the feasibility of the processes developed for lead-free wafer level solder bumping.

As the world moves towards eliminating lead from consumer products, the microelectronics industry has put effort into developing lead-free solder paste. The major drawback of lead-free solder is the problems caused by its high reflow temperature. Variable frequency microwave (VFM) processing has been shown to allow some materials to be processed at lower temperatures. Issues addressed in this study include using VFM to reduce the solder reflow temperature, comparing the heating rate of different size solder particles, and comparing the reliability of VFM reflowed solder versus conventionally reflowed solder. Results comparing the effect of particle size on the heating rate of solder showed that the differences were negligible. This is due in part to the particle sizes overlapping. Many lead-free solder pastes reflow around 250℃. Results indicate that when using the VFM, lead-free solder paste will reflow at 220℃. The reliability of solder that was reflowed using the VFM at the reduced temperature was found to be comparable to solder reflowed in a conventional manner. Based on these findings, VFM processing can eliminate the major obstacles to making lead-free solder paste a more attractive option for use in the microelectronics industry.