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

Lead is a toxic heavy metal that has been extensively used in modern society, causing widespread environmental contamination, even in isolated parts of the world. There is now overwhelming evidence associating lead exposure with wideranging health effects, including reductions in intelligence scores, hyperactivity, shortened concentration spans, poor school performance, violent/aggressive behaviour, hearing loss, delayed onset of puberty, anaemia, and in severe cases, coma and death. In recent years consensus has been reached in respect of the absence of a threshold of safety for key health effects associated with lead exposure, and the permanent and irreversible nature of many of the health and social consequences of exposure to lead. The public health problem of environmental lead exposure has been widely investigated in developed countries such as the United States of America where, since the 1970s, policies and interventions have been followed by significant reductions in blood lead levels amongst children. In developing countries, and in African countries in particular, there is a relative dearth of information on the sources, mechanisms of exposure and blood lead distributions in children, and little action has been taken to protect children against lead poisoning. This study was undertaken to determine the current distribution of blood lead concentrations, and associated risk factors, amongst selected groups of first grade school children in the South African urban settings of Cape Town, Johannesburg 7 and Kimberley, a lead mining town (Aggeneys) and two rural towns in the Northern Cape province. A further objective of the study was to compare blood lead distributions determined in the current study with the findings of similar studies undertaken prior to the introduction in 1996 of unleaded petrol in South Africa. The results show that over the past decade, blood lead concentrations amongst first grade school children have declined considerably, but that large proportions of children, especially those living or attending school in impoverished areas, continue to have intolerably high blood lead concentrations, within a range that puts them at risk of detrimental health and social outcomes. The major sources of exposure to lead in the samples studied were leaded petrol, lead-based paint used to decorate homes and schools, lead solder used in “cottage industries” and other home-based lead-related activities, as well as the transfer of lead particles from lead-related work settings into homes. Recommendations for policy and relevant interventions for the South African context are discussed.

Microelectronic systems are subjected to thermal cycling, power cycling, and vibration environments in various applications. These environments, whether applied sequentially or simultaneously, affect the solder joint reliability. Literature is scarce on predicting solder joint fatigue failure under such multiple loading environments. This thesis aims to develop a unified modeling methodology to study the reliability of electronic packages subjected to thermal cycling, power cycling, and vibration loading conditions. Such a modeling methodology is comprised of an enriched material model to accommodate time-, temperature-, and direction-dependent behavior of various materials in the assembly, and at the same time, will have a geometry model that can accommodate thermal- and power-cycling induced low-cycle fatigue damage mechanism as well as vibration-induced high-cycle fatigue damage mechanism. The developed modeling methodology is applied to study the reliability characteristics of ceramic area array electronic packages with lead-based solder interconnections. In particular, this thesis aims to study the reliability of such solder interconnections under thermal, power, and vibration conditions individually, and validate the model against these conditions using appropriate experimental data either from in-house experiments or existing literature. Once validated, this thesis also aims to perform a design of simulations study to understand the effect of various materials, geometry, and thermal parameters on solder joint reliability of ceramic ball grid array and ceramic column grid array packages, and use such a study to develop universal polynomial predictive equations for solder joint reliability. The thesis also aims to employ the unified modeling methodology to develop new understanding of the acceleration factor relationship between power cycling and thermal cycling. Finally, this thesis plans to use the unified modeling methodology to study solder joint reliability under the sequential application of thermal cycling and vibration loading conditions, and to validate the modeling results with first-of-its-kind experimental data. A nonlinear cumulative damage law is developed to account for the nonlinearity and effect of sequence loading under thermal cycling, power cycling, and vibration loading.

The aim of this masterś thesis is to investigate properties of lead-free low-temperature solders after termal aging. The theoretical part is focused on various types of lead - free solders, pastes used for the manufacture of electrical circuits by thick-film technology and methods of testing the properties of the soldered joints. The practical part deals with the design and production of test substrates for testing the solder joints formed between the SMD component and the ceramic substrate. Two solder bismuth-containing solder was selected for testing, the SAC solder was selected as the reference. After aging with temperature cycling from -30 ° C to 115 ° C, the data obtained by testing the mechanical strength of the solder joint by the shear test is evaluated.

The project deals with the overall design and construction of equipment called the desiccators for brazing in a protective atmosphere. The device was designed and manufactured cooling and heating element. For the soldering various temperature profiles have been defined and adjusted, as for SnPb as well for lead-free solders. There was a realization of samples were measured and analyzed. Finally were realized micro sections for lead free solder.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / Eutectic (63% tin-37% lead) or near-eutectic (40% tin-60% lead) tin-lead solder is widely used for creating electrical interconnections between the printed wiring board (PWB) and the components mounted on the board surface. For components mounted directly on the PWB mounting pads, that is, surface mounted components, the tin-lead solder also constitutes the mechanical interconnection. Eutectic solder has a melting point of 183°C (361°F). It is important to realize that its homologous temperature, defined as the temperature in degrees Kelvin over its melting point temperature (T(m)), also in degrees Kelvin, is defined as T/T(m). At room temperature (25°C = 298K), eutectic solder's homologous temperature is 0.65. It is widely acknowledged that materials having a homologous temperature ≥ 0.5 are readily subject to creep, and the solder joints of printed wiring assemblies are routinely exposed to temperatures above room temperature. Hence, solder joints tend to be subject to both thermal fatigue and creep. This can lead to premature failures during service conditions. The geometry, that is, the lead configuration, of the joints can also affect failure. Various geometries are better suited to withstand failure than others. The purpose of this paper is to explore solder joint failures of dual in-line (DIP) integrated circuit components, leadless ceramic chip carriers (LCCCs), and gull wing and J-lead surface mount components mounted on PWBs.