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Predictive and Analytical Tools in Design
Published in Ali J Jamnia, Khaled Atua, Executing Design for Reliability within the Product Life Cycle, 2019
In addition to the two main mechanical and electrical influences on failure, a third and, to some extent, less considered influence, is chemical and electrochemical factors. This may be divided into two broad categories: Corrosion is a natural two-step process whereby a metal loses one or more electrons in an oxidation step resulting in freed electrons and metallic ions. The freed electrons are conducted away to another site where they combine with another material in contact with the original metal in a reduction step. This second material may be either a nonmetallic element or another metallic ion. The oxidation site where metallic atoms lose electrons is called the anode, and the reduction site where electrons are transferred is called the cathode. In electromechanical systems, corrosion is often caused by galvanic cells, which are formed when one of the following two criteria is satisfied: two dissimilar metals exist in close proximity or the metal is a multiphase alloy in the presence of an electrolyte.Migration is a process by which material moves from one area to another area. If migration happens between two adjacent metals such as copper and solder, it is called diffusion. If it happens as a result of internal stresses and in the absence of an electric field, it is called whiskering. Finally, if it happens in the presence of an electric field and between similar metals, it is called dendritic growth. Two factors have given this topic relevance in PCB and system package design. The first factor is that as the PCBs are more densely populated, it becomes exceedingly difficult to clean and wash away all the processing chemicals. The presence of the pollutants along with an electric field provides an ideal environment for electromigration and dendritic growth. The second factor is more related to legislation and a lead-free environment. Pure tin solder, which is a natural replacement for a leaded solder, has a tendency to grow conductive needles, known as whiskers, in an out-plane direction (z-axis).
Design for X
Published in Ali Jamnia, Introduction to Product Design and Development for Engineers, 2018
In addition to the two main mechanical and electrical influences on failure, a third and, to some extent, less-considered influence is chemical and electrochemical factors. These may be divided into two broad categories: Corrosion is a natural two-step process whereby a metal loses one or more electrons in an oxidation step, resulting in freed electrons and metallic ions. The freed electrons are conducted away to another site where they combine with another material in contact with the original metal in a reduction step. This second material may be either a nonmetallic element or another metallic ion. The oxidation site where metallic atoms lose electrons is called an anode, and the reduction site where electrons are transferred is called a cathode. In electromechanical systems, corrosion is often caused by galvanic cells that are formed when one of the following two criteria is satisfied: two dissimilar metals exist in close proximity or the metal is a multiphase alloy in the presence of an electrolyte.Migration is a process by which material moves from one area to another. If migration happens between two adjacent metals such as copper and solder, it is called diffusion. If it happens as a result of internal stresses and in the absence of an electric field, it is called whiskers. Finally, if it happens in the presence of an electric field and between similar metals, it is called dendritic growth. Two factors have given this topic relevance in printed circuit board and system package design. The first factor is that as the PCBs are more densely populated, it becomes exceedingly difficult to clean and wash away all the processing chemicals. The presence of the pollutants along with an electric field provides an ideal environment for electromigration and dendritic growth. The second factor is more related to legislature and lead-free environments. Pure tin solder, which is a natural replacement for a leaded solder, has a tendency to grow conductive needles, known as whiskers, in an out-plane direction (z-axis).
Anticipating and preventing complications in spinal cord stimulator implantation
Published in Expert Review of Medical Devices, 2023
Steven M. Falowski, Hao Tan, Joseph Parks, Alaa Abd-Elsayed, Ahmed Raslan, Jason Pope
Of all possible SCS-related complications, lead migration is the most common. Lead migration is undesirable as it reduces the efficacy of SCS and increases the risk for other complications [3,20], potentially requiring explant should more serious complications develop [23]. In an earlier 2008 review, Falowski et al. noted that migration occurs in anywhere between 11% and 45% of implanted SCS systems [24]. However, the incidence of lead migration seems to have decreased over the years. Studies from 2010 onward report figures in the ballpark of roughly 5% or less [12,18,25–27].