Technical Library

Latest Technological Trends for
Conductive Polymer Aluminum Solid Electrolytic Capacitors

 
NICHICON CORPORATION
 

1. Introduction (Overview)

 FPCAP molded-resin VA, VB, UA Series

FPCAP molded-resin
VA, VB, UA Series

Conductive polymer aluminum solid electrolytic capacitors, which use conductive polymers for the cathode material, have low equivalent series resistance (ESR) and are thus widely used in PCs and PC peripherals, game consoles, and other digital equipment.
As exemplified by the Ultrabook, recent years have seen dizzying advances in digital devices that have become thinner, lighter, and less expensive. Additionally, conductive polymer aluminum solid electrolytic capacitors have had to meet critical low profile size requirements. Also, since digital equipment operates at increasingly higher frequencies, there have been increasingly greater needs for capacitors to have lower ESR and ESL (equivalent series inductance) to raise the current rejection efficiency.They must also have high voltage resistance for use as the primary-side input for DC-DC converters. In this article, we will look at the latest technologies in resin-molded conductive polymer aluminum solid electrolytic capacitors developed to meet these market demands.

 

2. Structure, Features

Figure 1 shows the internal structure of a wound-type conductive polymer aluminum solid electrolytic capacitor. The difference between a wound-type conductive polymer aluminum solid electrolytic capacitor and a wound-type aluminum electrolytic capacitor is as follows: the polymer uses a conductive polymer for the cathode electrolyte and the more common aluminum electrolytic uses an electrolytic solution. They share basically the same elemental structure: a separator wound between an anode electrode foil and cathode electrode foil attached by a lead wire. Since the structure is the same, conductive polymer aluminum solid electrolytic capacitors can be manufactured using the same production technologies as aluminum electrolytic capacitors. The latest resin-molded conductive polymer aluminum solid electrolytic capacitors from Nichicon make the most of this advantage. They were developed to offer low-cost production of low-profile conductive polymer aluminum solid electrolytic capacitors.
Table 1 compares the materials and structures of the newly developed Nichicon capacitors with typical laminated resin-molded conductive polymer aluminum solid electrolytic capacitors. Figure 2 shows a simplified structural comparison. The newly developed product incorporates conventional production technology: a separator wound between an anode electrode foil and cathode electrode foil attached by a lead wire. But because it is wound elliptically to achieve a thinner element and the element is formed with a proprietary method, despite having a wound structure, it achieves a low profile similar to the internal element of the laminated method. As well, for symmetrical extraction of the lead wire of both electrodes, like in laminated conductive polymer aluminum solid electrolytic capacitors and tantalum solid electrolytic capacitors, the cathode lead wire protrudes out of the side opposite to the anode lead wire and connected to the cathode electrode foil. Then, an element forming the conductive polymer is mounted on the lead frame and molded shut with epoxy resin. The structure in which the conductive polymer is mounted on the lead frame and molded shut with epoxy resin is the same as that for laminated conductive polymer aluminum solid electrolytic capacitors and tantalum solid electrolytic capacitors. However, symmetrical extraction of the lead wire of both electrodes allows the lead wire and lead frame to be connected to both electrodes, meaning that no expensive conductive adhesives are used for connecting; this it where it differs from laminated construction and this is the main feature of Nichicon's resin-molded conductive polymer aluminum solid electrolytic capacitors. Regarding the connections, because aluminum is used for the lead wire of both electrodes, and because the lead frame is specially processed, Nichicon has achieved connecting technology that offers energy efficiency, space efficiency, and stable connecting quality (strength, resistance), even using resistance welding. In the past, stable connection quality had been difficult to achieve.
With these technologies, Nichicon has been able to use existing materials and production technologies and equipment for wound-type conductive polymer aluminum solid electrolytic capacitors. By combining these existing technologies with innovations such as directly welding the lead wire onto the lead frame to eliminate the need for expensive conductive adhesives, we have developed simply structured products that we can offer for a reasonable price.
The newly developed products are the standard VA Series in sizes of 7.3 × 4.3 × 2.8mm (max. height of 3mm); the low-ESR VB and VC Series; the low-profile UA Series in sizes of 7.3 × 4.3 × 1.9 mm (max. height of 2mm); and the low-ESR UB Series. (See Table 2)

Figure 1: Internal Structure of Wound-Type Conductive Polymer Aluminum Solid Electrolytic Capacitors

Figure 1: Internal Structure of Wound-Type Conductive Polymer Aluminum Solid Electrolytic Capacitors

Table 1: Comparison of Conductive Polymer Aluminum Solid Electrolytic Capacitors

  Aluminum case rubber sealed Epoxy resin sealed
  Standard product New product Standard product
Element structure Wound Wound Laminated
Cathode extraction Aluminum foil lead wire Aluminum foil lead wire Conductive adhesive
(carbon and silver)
External wire Lead wire Lead frame Lead frame
Cost Low ← High

Figure 2: Simplified Structure (Comparison with Laminated Conductive Polymer Aluminum Solid Electrolytic Capacitor)

Figure 2: Simplified Structure (Comparison with Laminated Conductive Polymer Aluminum Solid Electrolytic Capacitor)

Table 2: Product Lineup
VA, VB, VC Series 7.3 × 4.3 × 2.8mm (max. height of 3mm)
UA, UB Series    7.3 × 4.3 × 1.9mm (max. height of 2mm)

Note: Figures in parentheses are ESR standard values(mΩ)

Rated voltage[V]/Capacitance[µF] 2.0 2.5 4 6.3 16 25
15          

VA (60)

UA / UB
(70 / 40)
27        

VA / VB
(55 / 30)

UA / UB
(55 / 40)
VA / VB
(60 / 30)
33         VA / VB
(55 / 30)
 
47         VA / VB
(55 / 30)
 
100      

VA / VB
(25 / 20)

UA (25)
   
150    

VA / VB
(20 / 15)

UA (20)
VA / VB
(25 / 20)
   
220 UA / UB
(15 / 9)
VA / VB / VC
(20 / 15 / 9)
VA / VB
(20 / 15)
     
330 VA / VB / VC
(20 / 15 / 9 )
         


3. High Voltage Resistance

With increasing use of high ripple current capacitors, in order to raise the current rejection efficiency, Nichicon has developed technology that allows it to maintain the low-ESR feature of conductive polymer aluminum solid electrolytic capacitors while achieving high voltage resistance. With this technology, we have developed and released wound-type conductive polymer aluminum solid electrolytic capacitors with a rated voltage of 125V. A big part in achieving high voltage resistance capacitors was played by the conductive polymer formation method and the separator. Under conventional methods of formation using chemical polymerization, there was the problem of unreacted substances and by-products remaining in the conductive polymer; these substances would pass through defects in the dielectric oxide film, causing electrical contact which reduced the voltage resistance. That is why in developing these new capacitors, Nichicon used technology for forming highly pure conductive polymer material, thus preventing unreacted substances and by-products and making possible capacitors with high voltage resistance. As well, by optimizing the separator for material quality, density, and thickness, we were able to improve the voltage resistance performance. Manufacturers of set equipment select capacitors with a rated voltage based on the voltage resistance safety margin they set in relation to the circuit voltage. There is thus strong demand for high-voltage-resistance, low-profile conductive polymer aluminum solid electrolytic capacitors for use as the primary-side input for DC-DC converters in products such as notebook PCs. These newly developed capacitors from Nichicon come in a lineup with a rated voltage of 25V, the highest level for a molded-resin chip-type product using aluminum electrode foil. This makes these capacitors ideal for use as the primary-side input as high voltage resistance products become more widespread.

 

4. Low ESR

Because laminated conductive polymer aluminum solid electrolytic capacitors have parallel connection (lamination) of multiple capacitor elements, it is relatively easy to give them low ESR for the structure (circuit). With these newly developed capacitors, Nichicon has in particular optimized the separator and the conductive polymer formation method, achieving low ESR for the wound element itself. The result is the VC Series in sizes of 7.3 × 4.3 × 2.8mm (max. height of 3mm); and the low-profile UB in sizes of 7.3 × 4.3 × 1.9 mm (max. height of 2mm). These products have an ESR of 9 mΩ at a rated voltage of 2.5V. Advancements in the speed and functionality of CPUs mean accompanying increases in operating frequencies. Therefore, capacitors used in the power circuits must have a low ESR so that they can discharge the electric charges that accumulate instantaneously; this will allow stabilization of the potential. To continue meeting the needs for increasingly lower ESR, we will look to improve the wound element structure (materials used) and optimize the conductive polymer formation method.

Figure 3: Comparison of Frequency Properties

EV Power Station
 

5.Future Development Efforts

Electronic equipment will continue to get thinner, lighter, and cheaper. Price drops have been particularly dramatic for common products like PCs and TVs. It will be crucial for manufacturers of electronic components to offer not only quality but also products that will allow set manufacturers to offer even lower prices to consumers. Conductive polymer aluminum solid electrolytic capacitors boast superb ESR properties and superior stability under high temperatures. Besides use for power circuit smoothing and current rejection in PCs, they are seeing use in a range of other types of circuits as well. Nichicon is looking to supplement conventional markets by tapping into potential new fields, making use of the product properties mentioned here to develop capacitors that offer further improvements in low profile, high capacity, high voltage resistance, and low ESR.

 

NICHICON CORPORATION
From the Dempa Shimbun, Jan. 31, 2013

 
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