By Norm Mamada, Taiyo Yuden (U.S.A.), Inc.
The latest wrinkle in BME (base metal electrode) Multilayer Ceramic Capacitor (MLCC) design is the emergence of the multiple-circuit "array" form factor. Typically available in two- and four-circuit configurations (Figure 1), Nickel-based (Ni) MLCC arrays provide significant production efficiencies over single-circuit devices that make the former extremely attractive to OEM designers. By integrating the functionality of multiple components into a single physical package, capacitor arrays materially contribute to even further size reduction-and lower cost of manufactured goods of cell phones, notebook PCs, PDAs and other electronic devices.
For example, an 0805 size MLCC Array combining the performance capability of four 0402 size capacitors reduces the necessary PCB real estate by approximately 1/3rd when the landing pad is considered. Another big advantage of the arrays is the ability to significantly reduce the number of components required to meet design performance parameters. Designers of high-density circuits can design four landing patterns in a row as shown in Figure 2. This design allows manufacturers the flexibility of using either four 0402 capacitors or two 0504 two-circuit arrays in the same circuit design. Using the arrays will reduce mounting operations by 50% as well as lower carrying costs by reducing the number of components kept in stock. Similarly, a four-circuit array reduces component count and number of components carried by 75%.
The savings generated by lower component counts are easily calculated using an industry-accepted estimate for the cost of an individual pick-and-place operation. With installed cost, placement time, stocking costs, equipment depreciation and all the other variables factored in, this cost typically ranges from $0.005 to $0.02, with $0.01 being the most commonly used estimate. Considering that modern cellular telephones require upwards of 200 MLCCs, the cost saving that may be realized by using MLCC arrays in lieu of single-circuit capacitors is anything but insignificant.
Figure 1. Typical components now entering the market include an 0504 1.0 mF two-circuit capacitor array with X5R temperature rating, a 2.2 mF two-circuit 0805 size array, also in X5R, and a 0.1 mF capacitance value 0805 case size four-circuit capacitor array with X5R temperature rating.
Ni-MLCC vs. Ta and AE CapsFor OEM designers responding to the market's miniaturization trend, the Ni-MLCC, both individually and in an array configuration, provides superior performance from a smaller, lower profile package, and at a lower unit cost, than alternative technologies. Important advantages over equivalent Tantalum (Ta) and Aluminum Electrolyte (AE) caps include non-polarized electrodes for easier manufacturability and mounting. Ni-MLCCs also provide advantages over Palladium (Pd) and Silver-Palladium (Ag-Pd) caps, lower resistivity, lower degree of migration and lower unit cost.
To sum up the most important advantages over equivalent Ta and AE caps, the Ni-MLCC provides:
Higher capacitance relative to case size
Lower impedance at higher frequencies
Lower ESR with less power loss and heat generation
Non-polarization for simpler mounting and easier manufacturability
Smaller case size and lower profile vs. equivalent voltage/capacitance types
Lower unit cost
Lower Impedance at Higher Frequencies
Figure 2. (above) Two 0504 arrays can be used to replace four 0402 capacitors, saving valuable PCB real estate in the ever increasing miniaturization of cell phones, camcorders, PDAs and other consumer electronics.
Ni-MLCCs offer advantages over Ta and AE caps in a power source bypass (decoupling) application to attenuate a specific noise frequency band. Figure 3 compares the relative impedance versus frequency for a 10 μF Ta and a 2.2 μF Ni MLCC. The 10 μF Ta offers lower impedance from about 100 kHz - 10 MHz but gains impedance in the higher frequencies. In the 100 kHz - 10 MHz band, the Ni MLCC is clearly superior and remains so beyond 100 MHz.
At any frequency of interest in that whole band, especially in the 1 - 10 MHz range, a Nickel-based MLCC of one-tenth the capacitance rating of the AE type provides significantly lower impedance, thus shunting away the unwanted noise more effectively than either alternative.
Lower ESR, Power Loss and Heat Generation
Figure 3. (right) Ideal for smoothing and bypass (decoupling) applications, Ni-MLCCs offer lower impedance at higher frequencies.
The special attention paid to the design and manufacturability of the Ni-MLCC results in a very low equivalent series resistance (ESR). Because of this, and minimal inductance, the impedance of the Ni-MLCC is lower at higher frequencies than is either of the higher-capacitance alternatives. Two natural by-products of the lower ESR are lower power loss and less generated heat.
Ideal capacitors have only capacitance and cause no power loss. However, actual capacitors have resistance, which causes power loss in the form of ripple currents that flow during the charge/discharge cycle and generate heat. As the frequency increases, the impedance decreases because of its inverse relationship to capacitance. Note in the following table how resistance and inductance are both lower with the Ni MLCC than with either alternative. Both ESR and parasitic inductance add to the total impedance as described by the following formula.
ConclusionMLCC manufacturers, like Taiyo Yuden Co., Ltd., have opted to decrease board space requirements in a number of ways, the most cost-effective being the design of high-capacitance MLCC arrays. While maintaining the performance of individual components, MLCC arrays dramatically reduce board space requirements, lower production costs and allow OEM designers to obtain higher performance from ever smaller form factor components.
Norm Mamada is an Engineering Manager for Taiyo Yuden (U.S.A.), Inc., located in . Mr. Mamada can be contacted at firstname.lastname@example.org.