From Design, Trial to Mass Production of Capacitor and PC Board, We will supply Electronic Device all over the world

With advances in electronic equipment, aluminum electrolytic capacitors have been found in an increasingly broad range of applications from televisions, VCRs, other household products, PCs, portable terminals, other data communications products, air bags, engine controllers, and other vehicle-mounted electronic equipment. The development of surface-mount components requiring smaller, thinner, and lighter components, has special importance providing a richer range of functions. Ultimately, the capacitors have been designed to physically resemble computer chips.

Aluminum electrolytic capacitors are structured by inserting into an aluminum case an element made from a 3-layer role. This role is comprised by the anode foil, the cathode foil, and the electrolytic paper between the two, with the coil impregnated with the electrolytic solution for driving the device. The capacitor is then sealed with a rubber plug. While this structure provides higher capacitance at lower cost than other types of capacitors, this structure is difficult to make into the physical form factor of a computer chip. Despite this problem, the development of electrolytic fluids with high levels of temperature, durability, and rubber plugs with excellent sealing performance, has led to the rapid development of chip-type capacitors that can endure the reflow process. Presently, the flagship product is the vertical chip-type capacitor such as shown in Figure 1. This capacitor is equipped with a resin seat to ensure stability when the capacitor is mounted on the wiring board. Also, the resin seat protects the capacitor from heat during the reflow process.

Movements in Technology

Figure 2 summarizes the types of performance sought in chip aluminum electrolytic capacitors. High capacitance and high voltage are necessary to make electronic products smaller and thinner. High impedance is required to reduce energy losses in electronic products and to stabilize the equipment while increasing the allowable ripple current. The long life span is required for high-reliability electronic equipment and for the types of electronic equipment that emphasize long-term reliability. Thus, the product can be termed "maintenance free." Additionally, with the recent increase in electronically-controlled equipment in automobiles. There are demands for vibration resistance levels that are quite different from the requirements for televisions and PDAs. These electronic control devices have special performance requirements demanding endurance for the relatively large vibrations from the springs, engine, and other equipment. Also, the ability to withstand heat is required by the electronic equipment. Especially, equipment that must function under harsh temperature conditions such as an engine compartment of an automobile. Elna Company, Ltd. has prepared a variety of chip-type aluminum electrolytic capacitor series that fulfill these performance requirements. Figure 3 shows the product line.

In the section below, we will focus on the technical elements that have been developed through years of effort at Elna Company Ltd., and other new technologies as well. There will be discussions regarding the RTK series of vertical chip aluminum electrolytic capacitors for vehicle-mounted electronic equipment as an example of the Elna products.

Photograph 1:

RTK Series Vertical-type Chip Aluminum Electrolytic Capacitors for Vehicle-mounted Electrical Equipment

Photograph 2:

The New RYK Series of Ultra High Vibration Resistant Horizontal Chip-type Aluminum Electrolytic Capacitors for Vehicle-mounted Electronic Equipment Use

Figure 1: Structural Diagram of a Typical Vertical-type Chip Aluminum Electrolytic Capacitor (2-terminal type)

Approach to High Vibration Durability

In the normal vertical-type chip aluminum electrolytic capacitor, shown in Figure 1, the lead terminals from the body of the capacitor are shaped, cut, and used as the electrodes. However, this structure does not provide a tight contact between the body of the capacitor and the seat;

the capacitor is secured to the printed wiring board by these two electrode terminals. Graph 1 shows the results of a study where this structure was subjected to a broad range of vibrational frequencies to search for the point of resonance. At approximately 300Hz, a 10G peak acceleration was observed, approximately 10 times that of the 1G applied vibration. This observation assumes that if a 10G vibration were applied then accelerations of 100G would be achieved near the resonant frequency of the 300Hz. The normal vertical-type chip aluminum electrolytic capacitor unequivocally was discovered to be weak structurally when enduring a broad range of vibrational frequencies. This structure had the terminal leads formed as described above and wherein the capacitor is secured to the printed circuit board by the electrode leads alone. In this normal vertical-type aluminum electrolytic capacitor, relatively strong vibrations will cause the capacitor to shift back and forth relative to the circuit board. The shifting will likely cause problems with broken leads at the root part of the electrode leads. Structurally, the root is the most likely place for the most stress. Given this, at Elna we have focused our attentions on creating a tight bond between the printed wiring board and the surface-mounted aluminum electrolytic capacitor. Also, our focus has created a tight bond between the body of the capacitor and the seat. As can be seen in the structure in Figure 4, the tight bond between the body of the capacitor and the seat was created by using an adhesive resin to adhere the aluminum case to the seat, The resin completely bonded the two together. Additionally, the tight bond between the chip-type aluminum electrolytic capacitor and the printed wiring board was ensured by providing two in-mold supplemental terminals. These two terminals are fabricated as part of the seat so that the tight bond can be secured using the total of 4 terminals (the in-mold supplemental terminals and the electrode leads).

Figure 2: Map of Required Performance

Figure 3: System Diagram of the Surface Mount Chip-type Aluminum Electrolytic Capacitor Series

Figure 4: Structural Diagram of the Chip-type Aluminum Electrolytic Capacitor for Vehicle-mounted Electrical Equipment (4-terminal type)

Graph 2 is the result of the aforementioned resonant frequency search over the broad frequency range. It is clear that the resonant frequency near 300Hz, seen with the normal vertical-type chip aluminum electrolytic capacitor to which no countermeasures had been applied, was passed without problems. The resonant frequency shifted to a high frequency range and the peak acceleration had a confirmed reduction of approximately 75%. Because of this, the RTK series, which was developed as a series of chip aluminum electrolytic capacitors for use in vehicle-mounted electronic equipment, can be described as more rigid after mounting on a printed wiring board then the normal vertical-type chip aluminum electrolytic capacitor.

The above findings mean that the stresses on the root of the electrode leads, the place where the stresses are most likely to accumulate, have been reduced. In this way we successfully confirmed high reliability levels with overall resistance to vibration after the component has been mounted on a printed wiring board.

Graph 1: The Peak Acceleration at the Resonant Frequency (2-terminal type)

Graph 2: The Peak Acceleration at the Resonant Frequency (4-terminal type)

Approach to High Temperature Durability

Aluminum electrolytic capacitors have a structure that is impregnated with an electrolyte made from an organic solvent, where a rubber is used to seal the capacitor. The keys to handling higher temperatures are to increase the air-tightness of the seal to control the high-temperature durability of the electrolyte and to control the escape of vapors when the electrolytic fluid swells the rubber plug. Although the rubber plug swells when contacting the organic solvent, the following can be said about this swelling:

  1. 1.The higher the cross-link density the less the swelling.
  2. 2.Because the filler does not cause swelling, the greater the proportion of filler, the less the swelling.
  3. 3.Because reinforcing carbon black powder plays the role of cross linking, the amount of swelling changes proportionally.

In comparison to conventional materials, Elna, Ltd. developed improved materials that substantially reduce the amount of vapor osmosis from the electrolytic solutions. By optimizing the cross-link density in order to improve the air tightness of the rubber plug, Elna created a high-seal rubber plug. Additionally, Elna has developed and currently uses electrolytes that are resistant to chemical changes in the electrolytic solution from high temperature environments. These electrolytes have high levels of dissociation in the organic solvent, thereby, increasing the electrical conductivity of the electrolytic fluid. These electrolytes were effective in reducing the ESR of the aluminum electrolytic capacitors. This makes it possible to increase the amount of tolerable ripple current.

Other Prospects

There are advancements in automotive electronic control equipment. This equipment was developed while keeping environmental friendliness foremost in mind on a global perspective, by providing higher safety levels during operation, and increasing the comfort of the ride. The capacitor requirements for this broad range of electrical equipment are also diverse. Because of this, Elna, Ltd. was the first in the world to develop, mass produce, and sell five series of chip-type aluminum electrolytic capacitors created to secure high levels of resistance to vibrations. In recent years the demand for these capacitors has increased dramatically. The product specifications for each of the series are given in Table 1.

Table 1

Type Vertical Horizontal
Temperature range of use -40°C - 125°C -55°C - 105°C -55°C - 105°C -40°C - 85°C -40°C - 125°C
Rated voltage range 10V - 63V 6.3V - 100V 6.3V - 35V 6.3V - 100V 6.3V - 63V
Capacitance range 10μF - 330μF 10μF - 470μF 47μF - 470μF 10μF - 1000μF 82μF - 820μF
High temperature load characteristics 125°C
Guaranteed for 1250 hours
Guaranteed for 2000 hours
Guaranteed for 2000 hours
Guaranteed for 2000 hours
Guaranteed for 1000 hours