Digital control technologies for electronic devices are diffusing into a wide variety of areas ranging from familiar mobile devices, such as smartphones to infrastructure equipment for traffic, communication, and others as well as space-related equipment, and now digitization is playing a vital role in human lives. This trend also applies to audio areas; digitization is progressing for sound sources, such as high-resolution audio, and reproduction devices and circuits, as part of that trend. As most of these devices are being miniaturized, electronic components mounted in devices are required to offer compatibility with digital circuits, or more specifically, capability for miniaturization and surface mounting, while maintaining sound quality.
The Rubycon PMLCAP product line is a series of film capacitors that do not require voltage derating at operating temperatures of up to 125ºC because of using a new dielectric material, guaranteeing high-temperature operation. Moreover, PMLCAP capacitors are surface-mount components that are manufactured using a unique thin-film formation technology and that, therefore, are very small but have a very large capacitance as compared to conventional products. Thus, the capacitors are being brought into markets where conventional capacitors of this kind have not been delivered.
The MU Series is a set of products that have a new terminal structure, thereby offering improved compatibility with digital audio equipment and other audio applications, while maintaining such characteristics and advantages of PMLCAP.
This document describes distinctive features of the PMLCAP MU Series—low distortion, mountability, and safety. In addition, it provides a future technological outlook for PMLCAP.
|Capacitance||0.0001 ～ 22µF||0.001 ～ 0.1µF|
|Temparature||-55 ～ +125ºC|
An MLCC, multi-layer ceramic capacitor, which is a common surface-mount capacitor with a small size and a large capacitance, tends to have a high harmonic distortion rate due to the piezoelectricity of its dielectric ceramic material. In a circuit of audio equipment, this high-distortion characteristic could result in inhibiting reproduction of original sound, and so the use of MLCCs is often avoided particularly in high-end audio equipment that prioritizes sound quality.
In contrast, as shown in Fig. 1, the PMLCAP MU Series has very low distortion, because it has a structure that provides high interlayer adhesiveness thanks to the use of a lamination technology by which a dielectric layer and an internal electrode layer are successively formed through vapor deposition in a vacuum, and also because it consists of dielectric material with no piezoelectricity and external electrodes free from magnetic material.
In the design of audio circuits, discrete electronic components are employed in some cases in order to enhance sound quality, and substrates where both discrete components and surface mount components are mounted are often used.
Because of its new structurally robust electrodes, as shown in Table 2, the PMLCAP MU Series is compatible with various mounting methods such as reflow, flow, and hand soldering, and can improve flexibility in designs with such substrates, and contribute to miniaturization of devices.
With the thermally hardened polymer as dielectric material, the series has very high heat resistance as compared to general surface-mount multi-layer film capacitors.
Fig. 3 shows images of products placed in contact with a soldering iron for five seconds assuming that the user accidentally brought it into contact with them during an actual mounting process. When its contact melts, a normal multi-layer film capacitor causes a short circuit, but the PMLCAP MU Series can retain its characteristics.
For audio equipment, particularly for in-car types, the safety of individual components is one of the most important factors. The PMLCAP MU Series, as described later, has self-healing ability and has low risk of emitting smoke and igniting; therefore, it ensures security while maintaining sound quality, and can considerably contribute to reducing risk to users.
One of the technologies of the PMLCAP for ensuring reliability is self-healing ability. When a momentary excessive voltage or large current is applied to a capacitor, dielectric material and surrounding electrode material are eliminated at a defective or weak part due to Joule heat, restoring insulation properties. Also, even if a microfracture mode develops there, no short circuit occurs and a certain level of resistance is maintained to prevent the circuit from breaking down completely.
Figs. 3 and 4 show waveforms of a momentary voltage applied in far excess of the rated voltage of a capacitor and those of the voltage monitored between terminals of a PMLCAP when the momentary voltage is applied to the PMLCAP via a resistor with a resistance of 2Ω.
As clearly shown in Fig. 4, at the moment when the voltage is applied, the voltage between the terminals of the PMLCAP temporarily drops (insulation loss), but instantaneously returns to the original level (self-healing).
Also, it is known that capacitors of some other types may produce heat, ignite, burn, or emit smoke, causing a risk of fire, when an excessive voltage or current is applied to them. This is because they use dielectric material that is easily intensely oxidized.
The dielectric material employed in the PMLCAP is thermal-hardened polymer that starts weight loss behavior at around 400ºC, and therefore has high thermal resistance.
Figs. 5 and 6 provide an example of behavior shown when a high-frequency current is increasingly applied to a manganese-dioxide tantalum electrolytic capacitor and a PMLCAP.
As shown here, while the compared capacitor burns with intense fire, the PMLCAP itself does not ignite despite emitting a little smoke, causing an open fault. An open fault is caused by a meltdown due to local heat from the resistance of the connection between the internal electrodes (evaporated aluminum) and the external electrode metal, or by the disconnection between electrodes due to deformation stress from the thermal volume expansion of the device (Fig.7).
【Future Technological Outlook】
The PMLCAP MU Series is a line of products that have a capacitance conforming to the E6 Series capacitance range, along with rated voltages of 16 to 100V, and are available in six JIS sizes (1608, 2012, 3216, 3225, 4532, and 5750). The series is highly flexible in terminal formation because of its manufacturing process, it can respond to a request for exceptional specifications (e.g., LW-reverse products) according to customers’ requirements.
Also, the development of highly environmental durable products is underway through further improvement of humidity resistance, in order to bring products into new markets. Samples of these products are scheduled to be available in the first quarter of 2015.
* This article was published in the column "High technology" on the Dempa Shimbun dated on Aug. 21, 2014 with some additions and amendments made later on.
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