A medical device is considered “implantable” if it’s partly or totally introduced into the human body via surgery or another medical intervention, and it’s intended to stay there for a long period of time. According to the American Medical Association (AMA), approximately 10 percent of Americans will receive an implantable device during their lifetimes. To serve consistent, often life-sustaining functions, implantables require high-reliability components that guarantee long-term performance.

When constructing multilayer ceramic capacitors (MLCCs), there are two classes of dielectrics electrical engineers typically select from depending on the application – Class 1, which consists of non-ferroelectric materials such as C0G/NP0, and Class 2, which are ferroelectric materials such as X5R and X7R. One key difference between these materials comes in the form of capacitance stability as voltage and temperature increase. With Class 1 dielectrics, capacitance will remain stable when DC voltage is applied and operational temperature increases. On the other hand, Class 2 dielectrics, which have a higher dielectric constant (K), are less stable with regards to temperature, voltage, frequency, and time.

High reliability – this is what the industry demands for some of the world’s most important devices. From implantable devices going into the human body, to space and military devices, these applications are built to last under extreme conditions. To do so, they are made of high-quality components with appropriate additional testing to ensure long-term reliability.

Standards are a form of technical infrastructure, and their influence is felt throughout the electronics industry. For example, formed in 1924, the Electronic Industries Alliance (EIA) was an American standards organization that established an alliance of trade associations in the United States electronics manufacturing industry. Their collaboration ensured that electronic equipment produced by different manufacturers was compatible and interchangeable. The EIA formally dissolved in February 2011, dividing by sector.

Designing medical implantable devices for high reliability is crucial for a variety of reasons. First, given the life-critical functions performed by many medial implantable devices, and the invasive procedure required to implant medical equipment properly in the human body, it is imperative that all medical devices are designed to function reliably throughout their entire lifetime. Furthermore, since patient safety is paramount, any precautions to reduce the possibility of potentially life-threatening malfunctions, recalls, and replacement surgeries are necessary. And, beyond preventing patient safety issues, there may also be severe economic and legal implications for device manufacturers if an implantable device fails.

Multilayer ceramic capacitors (MLCCs) are made up of two materials—ceramic dielectric material and metal electrode material. Layering metal electrodes and ceramic dielectrics (Figure 1.) achieves voltages that are capable of producing high electric fields that ultimately allow MLCCs to regulate current flow and prevent electromagnetic interference between components. There are two common electrodes used in MLCCs: precious metal electrodes (PMEs), containing palladium silver, and base metal electrodes (BMEs), containing nickel or copper. Each electrode type holds a spot in the capacitor world for a reason.

In an ideal world, capacitors could be designed in a way where they would exhibit no resistance. However, this is physically impossible to achieve as there will always be some type of internal resistance in a capacitor that appears in series with the capacitance of the device. Known as equivalent series resistance (ESR), the level of this resistance will vary across capacitors depending on a variety of factors including the dielectric materials used, frequency of the application, leakage, and quality and reliability of the capacitor. The two graphs in Figure 1 show an example of how ESR can change as frequency increases across various capacitances on two different classes of ceramic dielectrics.

Impedance, measured in ohms, extends the concept of “opposition” to alternating current (AC) applications. It accounts for resistance, the opposition of current flow, and reactance, the measure of opposing alternating current – an effect of inductance and/or capacitance. In direct current (DC) applications, we talk in terms of resistance, not reactance. Chances are: This isn’t new information. But there’s a reason we wanted to cover this topic – impedance values play an important role in capacitor selection.

Space missions present a unique set of environmental challenges that demand high reliability down to the smallest electronic components. Mission failures could cost human lives. From in-flight systems to power supplies, every single system contributes to the success of a space project, so they must maintain high quality and safety standards for long durations.

There are two main mounting schemes for placing components on a printed circuit board (PCB): through-hole technology (THT) and surface-mount technology (SMT). Given its popularity over the last few decades, it’s no surprise that designers default to SMT, but there are advantages to both schemes that are worth exploring, especially for high-reliability application designs.