Technical Library

Chip-Type Aluminum Electrolytic Capacitors:
Latest Technology Trends

NICHICON CORPORATION

1. Introduction

With advances in electronics technology comes the need for PC board level parts that are small, highly efficient, have long-life, and are reliable enough to cope with rising ambient temperatures.
Although the electronics market is coming out of a temporary slump, we still cannot let down our guard. While demand prospects have brightened somewhat, full recovery will take more time. One area of steady growth is in-vehicle electronics, where the market for environmentally friendly cars such as EVs (electronic vehicles) and HVs (hybrid vehicles) is expanding.
In in-vehicle electronics, companies are racing to make on-board products that are compact enough to give car manufacturers freedom of design, and this is spurring advances in high-density mounting technology using surface mounting. High-density mounting technology is not limited to the in-vehicle electronics field; it is also making inroads into digital equipment and information and communications appliances. Against this background, the market is moving away from lead-type capacitors and towards surface-mounted-type (chip-type) capacitors, which require increasingly higher performance.
Using Nichicon products as examples, letís take a look at the latest trends in chip-type aluminum electrolytic capacitors.

2. Aluminum Electrolytic Capacitors

Today, aluminum electrolytic capacitors are an all-purpose electronic component incorporated into many types of electronic equipment. They have a higher capacitance per volume than other types of capacitors, and their main material, aluminum, is relatively inexpensive.
Aluminum electrolytic capacitors use as their dielectric material an aluminum oxide (Al2O3) coating, which is formed onto a highly pure aluminum foil surface. The dielectric oxide coating can be formed into a much thinner and more uniform layer than can other dielectric materials. Another advantage is its high relative permittivity, which allows higher capacitance
Looking at the structure of an aluminum electrolytic capacitor, it contains an element made up of an anode and a cathode foil around which is wrapped separator paper. This element is impregnated with electrolyte and sealed inside an aluminum case. The capacitance of an aluminum electrolytic capacitor is proportional to the surface area of the dielectric material. To achieve higher capacitance, the electrode foil undergoes a chemical erosion process called etching that increases its effective surface area. The separator between the electrodes acts as an insulator. An element not impregnated with electrolyte has a very low capacitance, but impregnating the element allows the separator to retain electrolyte, and this results in the oxide coating functions effectively as the dielectric material. In other words, the electrolyte actually functions as the cathode. Because the property of the electrolyte will influence the various properties of the aluminum electrolytic capacitor. An appropriate electrolyte is chosen depending on the capacitorís intended rating, temperature range, and application.
Because chip-type aluminum electrolytic capacitors must be able to withstand reflow soldering, they use a highly heat-resistant electrolyte and sealing material. They also have a resin-molded plate (seat) attached so as to improve stability and heat-resistance during substrate molding. This type (JIS 32) is the main kind of chip-type aluminum electrolytic capacitor in use today. (Figure 1)

Figure 1 Structure of chip-type aluminum electrolytic capacitor

Figure 1 Structure of chip-type aluminum electrolytic capacitor

3. Compact, High-Capacitance, Low-Impedance CM Series

Photo 1 CM Series chip-type aluminum electrolytic capacitor: compact, high-capacitance, and low-impedance

Photo 1 CM Series chip-type aluminum electrolytic capacitor: compact, high-capacitance, and low-impedance

Nichicon developed the CM Series of chip-type aluminum electrolytic capacitors (photo 1), which guarantee operation for 2,000 hours at 105℃ and which boast high capacitance and the industryís lowest impedance. This series was developed in response to the increasingly advanced needs of in-vehicle electronics and other areas of digital equipment and information and communication appliances. Capacitors used in the secondary side and control systems of equipment need superior qualities for low noise and low impedance. And in addition to high-density mounting, capacitors must be compact, have high capacitance, and low impedance to meet the demands of the increasingly smaller and higher performance products that they will be incorporated into.
Nichiconís years of technological expertise has gone into the development of the CM Series, which is designed for products of optimal structure. The thin separator of this series has been proven highly reliable thanks to its low ESR (equivalent series resistance) and high density. Because of the thinness of the separator, it can be wrapped around the two electrodes to form a compact cylindrical element. Put another way, more of the thinner electrode foil can be wrapped into the same space as conventional thicker foil, which means more surface area of electrode foil. Furthermore, the anode foil uses high-capacity electrode foil.
Using the technologies just described, Nichicon has made the new CM Series significantly smaller per rated voltage than its current CL Series. (Figure 2) The CM Series can thus help manufacturers make their set equipment smaller, lighter, and less complex.
The CM Series comes in six different product dimensions (φ4 to φ6.3×5.8L, φ6.3×7.7L, φ8×10L, φ10×10L), a rated voltage range of 6.3 to 50V, and a rated capacitance range of 10 to 2,200μF.

Figure 2 Comparison of sizes of CL Series and CM Series

Figure 2 Comparison of sizes of CL Series and CM Series

4. Low-Temperature ESR Specification CX Series with Long-Life Operation at 135℃

Photo 2 CX Series chip-type aluminum electrolytic capacitor: low-ESR specifications and guaranteed operation of 2,000 hours at 135℃

Photo 2 CX Series chip-type aluminum electrolytic capacitor: low-ESR specifications and guaranteed operation of 2,000 hours at 135℃

In fields such as in-vehicle electronics, there is a growing need for highly reliable capacitors with low-ESR specifications after endurance testing. Such capacitors must withstand the extreme high-temperature conditions in a carís engine compartment and be able to operate in cold climates. The CX Series offers the industry's first guaranteed long-life operation at 135℃ as a low-ESR product after endurance testing. Its outstanding features are the longest operation time in its class at 135℃, low-ESR specifications, and vibration-resistant construction, all of which make it ideal for use in peripheral equipment operating in the extreme conditions of a carís engine compartment. Compared to Nichiconís current CZ Series (resistance up to 125℃), the CX Series uses an electrolyte that gives stability in higher temperature environments, uses highly reliable sealing material and high amplification foil, and has an optimal structure, all of which gives it the ability to operate at 135℃ for 2,000 hours (guaranteed low-ESR time: 1,000 hours). (Figure 3)
The CX Series comes in three different product dimensions (φ6.3×10L, φ8×10L, φ10×10L), a rated voltage range of 6.3 to 35V, and a rated capacitance range of 47 to 470μF. The φ6.3×10L size is new to the lineup and compatible with high-density mounting. (Photo 2)

Figure 3 Rise in ESR over time of CZ Series and CX Series (125℃ correction)

Figure 3 Rise in ESR over time of CZ Series and CX Series (125℃ correction)

5. Prospects for Aluminum Electrolytic Capacitors

Technology advances in so many fields come thanks to electronic components that offer greater space savings, efficiency, and performance.
Digital equipment typifies this trend, becoming not only smaller with higher performance with each passing year, but also becoming an increasingly integral part of our lives.
In the field of in-vehicle electronics, manufacturers are striving to incorporate electrical drives into environmentally friendly cars such as EVs and HVs, place ECUs (engine control units) in the engine compartment to create a more pleasant car interior, simplify systems, and decrease overall costs. Examples of this trend include increasingly more advanced and multifaceted drive assistance and GPS systems.
To continue to keep ahead of the constant advances in electronics technology, it is essential that we focus on developing products that offer added value and customization. It is also essential that we not just build on existing technology but also come up with new product lineups born of completely new innovations. Such innovations, like those made possible through the development of our CM Series and CX Series, will provide the basis for future high-performance products from Nichicon.

 

NICHICON CORPORATION
From the Dempa Shimbun, Aug. 8, 2013

 
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