One feature of aluminum electrolytic capacitors is that they can be produced relatively inexpensively and in high volume. They also have a wide range of rated voltages, from approximately 2 to 700V, making them convenient for use in a wide range of applications. They also come in different types: chip type, lead type, snap-in terminal type, and screw-terminal type (Photo 1).
The capacitor experiencing the greatest increase in demand is the chip-type aluminum electrolytic capacitor. One reason for this growth is that increasingly smaller substrates are necessitating higher degrees of integration, and the substrate surface mount method is the most suitable way to mount highly miniaturized components. Lead-type capacitors are either hand-soldered to the substrate or they are wave soldered (a method in which the capacitor is provisionally fixed on the substrate with adhesive and then immersed in a bath of liquid solder). Chip-type capacitors, however, are soldered using a reflow method in which solder paste is applied to the connection points on the substrate, the capacitor is mounted on top of this, and the substrate is put through a high-temperature oven. Chip-type capacitors are shaped to make them easier to mount to substrates subjected to the reflow method.
The various applications for chip-type aluminum electrolytic capacitors include electronic car components, flat-panel displays, PC motherboards, and game consoles. Electronic car component applications have shown remarkable growth in recent years, and this will be our focus as we look at the latest trends in chip-type aluminum electrolytic capacitors.
[Photo 1] Types of aluminum electrolytic capacitors
Electronic components are becoming more prevalent in cars. One major reason is society’s demand for cars that are more energy efficient and environmentally friendly, features that can only be attained through the use of electronic components that control the various mechanisms of the car. Demands for energy efficiency and environmental performance in cars are only going to get more stringent, so it is safe to say that these demands will be met with an increasingly wide range of new electronic control devices. Automotive electronic components come in a wide variety, each of which must perform a specific function depending on the electronic equipment they are incorporated into.
For example, for the control and monitoring of the battery unit in EVs (electronic vehicles) and HEVs (hybrid electric vehicles), aluminum electrolytic capacitors with a relatively high rated voltage are required. The ECU (engine control unit), which operates near the car engine, requires aluminum electrolytic capacitors that can withstand the constantly high temperatures of the engine compartment. Other capacitors must have properties that guarantee they will operate in the low-temperature environment of extremely cold regions. In addition, the capacitors must not only have the electrical properties of low ESR (equivalent series resistance) and high-ripple-current resistance; they must also have a vibration-resistant structure to withstand engine vibration. Here we will look in particular at how capacitors meet the performance needs of the ECU.
- (1) Resistance Over a Wide Temperature Range
In recent years, cars are using increasingly fewer components and packing more parts into smaller spaces, the result being that parts like the ECU tend to be placed in close proximity to the engine. This makes it crucial for the ECU to employ aluminum electrolytic capacitors that can withstand high temperatures. For aluminum electrolytic capacitors to be stable under high temperatures, they must use a low-transpiration electrolyte and heat-resistant rubber sealing material. A major structural characteristic of aluminum electrolytic capacitors is the electrolytic paper, which has been impregnated with electrolyte, and is between the anode foil and cathode foil. The electrolyte plays a crucial role in that it restores the anodic oxide film that is subject to ion conductance and deterioration over time. As current flows, the electrolyte undergoes electrical decomposition and evaporation due to heat, gradually escaping through the seal. Once the electrolyte drops to a certain level, the aluminum electrolytic capacitor’s capacitance rapidly decreases, while loss tangent (tanδ) rapidly increases (Figure 1). This phenomenon is called electrolyte dry up and is a factor in aluminum electrolytic capacitor breakdown and shortened service life. Because electrolyte evaporation increases with higher temperatures, dry up also occurs relatively quickly. The rubber sealing also generally deteriorates more quickly in high temperature environments, reducing its sealing ability and further hastening the evaporation of electrolyte. Low-transpiration electrolyte generally exists as a solid or near-solid at low temperatures and this therefore raises the ESR. Therefore, while the electrolyte is becoming gradually more low-transpiration, this is necessitating more favorable low temperatures properties. A currently desirable temperature range would be -40 to 125°C (as high as 135°C or 150°C in some cases).
[Figure 1] End-of-life property behavior of aluminum electrolytic capacitors
- (2) Low ESR, High-Ripple-Current Resistance
When ripple current flows, aluminum electrolytic capacitors heat up, causing the electrolyte to evaporate and deteriorate, and consequently shortening capacitor life. Because most of the heat generated due to ripple current is joule heat, the greater the aluminum electrolytic capacitor’s resistance, the larger the heat generated at the same ripple current. So by using electrolyte and materials with a low specific resistance to achieve low ESR, and by minimizing the change in properties caused by heat generation, we have achieved a capacitor with low ESR and high-ripple-current resistance.
- (3) Vibration Resistance
To meet vibration-resistance demands in engine environments, chip-type aluminum electrolytic capacitors have been given two structural modifications. Photo 2 shows two types of capacitors: one with vibration-resistance construction and another without. For the first modification, the height of the wall around the seat has been raised to control vibration. For the second, an auxiliary electrode has been placed on the seat to improve anchoring with the substrate. Thanks to these modifications, capacitors provide vibration resistance of 30G (10 to 2,000Hz).
Photo 2: Regular and vibration-resistant chip-type aluminum electrolytic capacitors
In response to the aforementioned needs, Nichicon has developed a wide-ranging lineup of product series: the UCD, UCM, and UCL (resistance up to 105°C, low impedance), and the UUE, UCX, and UBC (resistance up to 125°C, 135°C, and 150°C, respectively). In the next section, we will look at the expanded UCZ (resistance up to 125°C, low-temperature ESR specifications).
The UCZ (Photo 3) had previously been offered in product sizes up toφ10×10L but in October 2014, we expanded the series to include products ranging in size toφ12.5×13.5L toφ18×21.5L.
[Photo 3] UCZ of chip-type aluminum electrolytic capacitors
- (1) Features
- Capacitors for use in under-the-hood applications and extremely cold regions must be resistant to high temperatures and exhibit stable low-temperature characteristics. In response, Nichicon developed a proprietary electrolyte providing low transpiration while also maintaining stable properties at low temperatures. Figure 2 shows an example of changes in capacitor characteristics in a 125°C environment with the rated voltage applied, and changes in ESR characteristics at -40°C.
[Figure 2] Example of characteristics of UCZ (at 25V, 1,000µF, φ12.5×13.5L)
Chip-type capacitors are soldered using a reflow method. If the capacitor is made larger, most of the heat during the reflow process is absorbed by the aluminum electrolytic capacitor’s main unit, which means that not enough heat goes towards fusing the solder to the terminal section. Larger capacitors sizes thus make anchoring to the substrate difficult. Also, because heat is absorbed by the main unit, the characteristics of the aluminum electrolytic capacitor are affected. This puts limits on the size of chip-type aluminum electrolytic capacitors as compared to lead-type capacitors. Increasing the capacity of chip-type aluminum electrolytic capacitors therefore presents a major challenge. To overcome this obstacle, Nichicon, , employed in-house-developed high-capacity electrode foil and thin electrolytic paper with low-ESR performance, in the UCZ. Compared to Nichicon’s UUE, the UCZ has four times the capacitance (Table 1).
Capacitance and loss tangent characteristics measured over time upon return to room temperature.
ESR measured at -40°C.
[Table 1] Capacitance comparison of UCZ and UUE (at same size)
- (2) Specifications
The major specifications of the UCZ are as follows. (Expanded series information is in parentheses.) Nine types in case sizes from φ6.3 X 5.8L to φ18 X 21.5L (φ12.5×13.5L to φ18×21.5L), category temperature range of -40 to 125°C, endurance of 1,000 to 4,000 hours at 125°C (3,000 hours for φ8 to 12.5, 3,500 hours for φ16 and φ18 X 16.5L, and 4,000 hours for φ16 and φ18 X 21.5L), rated voltage range of 10 to 100V (25 to 100V), and rated capacitance range of 10 to 3,300µF (82 to 3,300µF).
Electronic car components are likely to be the main application field for chip-type aluminum electrolytic capacitors. Not only are electronic components becoming increasingly prevalent in cars, as stated earlier in this article; with the spread of EVs, HVs, FCVs (fuel-cell vehicles), and other vehicles with electrical drive systems, the electronic equipment controlling these is playing an increasingly important role and taking on a greater variety of forms and functions. Consequently, the parts that make up this control equipment will need to have increasingly specialized performance. Idling stop systems becoming standard in cars represent an example of such specialized performance. When the car is stopped, the engine shuts off and the fan cooling the engine compartment also shuts off temporarily. When this occurs, the electronic components are subject to higher temperatures than they would be when the car is moving. Aluminum electrolytic capacitors must therefore be able to withstand these momentary high temperatures. We can predict that there will be even more specialized performance demands to match the way cars are operated and used.
To continue meeting user expectations, Nichicon will develop new products that anticipate future needs.