Tech Spotlight: The Benefits of Ultra Flat Bulk Capacitors for Compact Electronic Devices

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Introduction

The rapid development of portable computer technology and electronics has contributed to the exponential increase of mobile data and global data traffic. The functions of digital devices like tablet PCs, POS (point of sale) devices, and smartphones have become more diverse, with a corresponding increase in performance. Portable devices demand a greater number of functions, along with increased computing power that must be condensed into their compact and ultra-thin housing. The relentless trend towards mega-functional, ultra-miniaturized, and high-performance systems has spurred the need for newer, superior materials leading to low-profile components, thin interconnections, and high-density interconnect substrates. This article provides an overview of the challenges and solutions that engineers may encounter when designing compact electronic devices. It also elaborates on the benefits of using Ultra Flat Bulk capacitors in compact electronic devices.

The Challenges of Designing Ultra-Thin Portable Devices

Portable electronic devices have many uses, spanning healthcare, military, instrumentation, security, field operations, and other industries. Strict requirements accompany contemporary portable devices in the context of size, weight, and power. These three factors either individually or together can make design a challenge for field-appropriate devices. Designers should concentrate on compact electronic components, specific parts, and feature selection; they should also use careful hardware management, and pick power-efficient electronic components.  The correct selection reduces PCB real estate and BOM counts. Mega-functional systems suffer from power supply and management bottlenecks, as power components fail to scale down in tandem with the other system components, resulting in bulky, independent power modules. Among all power components, thin-film capacitors present maximum integration challenges, due to multiple manufacturing concerns. Aluminum electrolytic capacitors continue to be a bulwark in electronic power circuits, due to their ability to offer bigger bulk storage, high energy density, and high voltage. However, in an increasing number of applications, their onboard height or profile limits their functionality. Capacitors are generally among the tallest components on a printed circuit board (PCB). The introduction of surface-mount (SMT) capacitors, spanning multiple dielectric technologies, has helped to shrink the populated board height. Multiple capacitors must be banked on the PCB to accomplish high capacitance or voltage using SMTs. Such an approach, unfortunately, consumes substantial board real estate, particularly in high capacitance holdup applications. Ultra-Flat Aluminum Electrolytic Capacitors save circuit board space, and thus solve this problem. These capacitors substitute large SMT capacitor arrays.

Ultra-low-profile (ULP) Series Aluminum-Electrolytic Capacitors

To meet the challenges of low-height profile, circuit board footprint reduction, long life, and improved system reliability, Cornell Dubilier Electronics (CDE) has developed an ultra-low-profile (ULP) family of aluminum-electrolytic capacitors, as shown below in Figure 1. These can replace large arrays of SMT solid tantalum capacitors. The ULP series is designed specifically for applications requiring bulk capacitance and the lowest board profiles, and offers considerably higher energy density than arrays of SMT capacitors. This design allows engineers to use a single component to save space, weight, and cost, while also improving reliability. With energy density exceeding 0.4 J/cc, a single ULP capacitor provides much greater bulk storage in a smaller footprint than a bank of low-profile SMT capacitors. Capacitance values range from 500 µF to 24,000 µF. Working voltages range from 4 to 63 WVDC, with an operating life of 3,000 hours at 85°C without voltage derating. Unlike solid tantalum capacitors, ULP capacitors do not require voltage derating. The ultra-thin package concept allows a much more dense concentration of foil and electrolyte, as well as higher capacitance density due to high-gain foils, and a unique packaging and seal system. The primary seal is a heat-sealed polymer with no rubber gaskets or grommets, and this primary seal is near hermetic. For longer life, an outer metal casing is also sealed and provides a layer of physical protection. They have robust construction, with a 10g vibration rating, a sealed, robotically laser‐welded nickel‐silver case, REACH/RoHS Compliant and lightweight. The ULP family is offered in package heights of 2.2 mm and 3.2 mm. With flat ribbon-lead–style terminations, it is possible to mount the device off-board for added design flexibility.

Figure 1: Ultra-low-profile (ULP) aluminum-electrolytic capacitors (Image Source: CDE)

Applications

The lightweight ULP series Ultra-Flat Aluminum Electrolytic Capacitors are ideal for use in portable devices and are well suited for a wide range of applications where height profile, board space, weight, and reliability comprise critical design factors. Examples of such applications include bulk storage in portable devices, disk drives, portable instruments, medical monitors, IoT remote monitoring devices, compact power supplies, drones and remotely Piloted Vehicles (RPVs), video monitors, and displays.

As mentioned in the preceding paragraph, thin-film capacitors are difficult to integrate due to multiple manufacturing concerns. A majority of dielectric technologies use multilayer technology to accomplish low-profile SMT chip packages, and surface-mount (SMT) capacitors spanning multiple dielectric technologies are now being introduced. Conventional aluminum electrolytics utilize wound capacitor elements inside their SMT packages. Such cylindrical windings are fitted into cylindrical metal containers and then mounted vertically on rectangular mounting pads. Thus, SMT aluminum electrolytics are known as V-chips, short for vertical chips. These cylindrical packages hold a liquid electrolyte that should be sealed by composite or rubber seals to prevent any electrolyte leaks. For SMT devices, this design suffers from a serious flaw, as the capacitor occupies an abnormally large portion of the entire package volume. A typical SMT aluminum electrolytic wastes up to 60% of the capacitor’s volume due to materials like space-wasting end-seal gaskets.

Figure 2: A ULP series aluminum electrolytic capacitor (Image Source: CDE)

As illustrated in Figure 2, designers can use ULP series aluminum electrolytic capacitors to store the bulk amounts of energy required for low-temperature operation, with fewer components as compared to alternative approaches. Such an advancement is achieved with the replacement of space-consuming flexible seals with the new ULP series aluminum electrolytic capacitors, complete with vibration-resistant packaging and welded seams. These configurations permit engineers to achieve better reliability while conserving space, weight, and operating life, along with reduced loaded-board cost.