APLIKACIJSKI ČLANKI APPLICATION ARTICLES TANTALUM CAPACITOR REPLACEMENT WITH CERAMIC CAPACITOR Iztok Šorli, MIKROIKS, Ljubljana High Capacitance MLCC For several years we have been facing periodic variations of availability and price of Tantalum capacitors. In the past this behaviour was due to political and economical strategies. Today it is the poor supply of Tantalum raw material that drives the Tantalum capacitor crisis. At present we see a price growth of 50% (from 0.2 USD to 1.0 USD) for normal Tantalum capacitors; the forecast is for a further hike in the next year. Murata can help to solve this problem by offering many ceramic capacitors that directly replace electrolytic and Tantalum types. Before we discuss about electrical characteristics, part numbers etc., let us briefly summarize some basic concepts of high capacitance usage. Figure 1 shows principal circuits that need high capacitance values. Smoothing The function of CI and C2 is to smooth ripple and voltage fluctuations at the input and output of the LDO (Low Drop Out Regulator). C2's ESR and ESL are most important because they are responsible for the purity of the output voltage. In the past high value Ta capacitors were used; now it is possible to use ceramic capacitors at 1 /2 to 1 /10 of the Ta values used. Bypassing 03 creates a "virtual" ground for the transistor which "believes" it is working at ideal conditions. The static and dynamic parameters are satisfied and the active device is properly used. Also in this case the ESL of the capacitor is of the most importance since a low value avoids self - oscillation problems. Coupiing In order to link two stages (for example pre amp to power amp) 04 is basic. This capacitor transfers only the signal and does not modify the DO parameters. For the example mentioned, it is the most important that the capacitor is not polarized in order to avoid signal distortion. What better solution than a ceramic capacitor? Smoothing LDO CI C2 Bypass Coupiing R2 Q2 C4 /q3 R3 Figure 1: Examples of principal circuits where capacitors with high capacitance values are mostly used Technical Aspects of Multi Layer Ceramic Capacitors Despite the simple construction, monolithic ceramic capacitor provides both high-speed response and an excellent high-frequency characteristics; the capacitance range has generally reached just approximately 1|aF until now. However, with recent advancements in the thin-layer/multilayer forming technology for dielectrics, as well as the technology for using base metal for internal electrodes, the capacitance range now exceeds 1 |iF Moreover, capacitors with capacitance of up to lOOjiF have been developed and are now being used. Multilayer Ceramic Capacitors (MLCC) are built as a kind of "sandwich", composed of conductive layers separated by a dielectric (ceramic). Two conductive terminations are added to provide solderability, figure 2. The mathematical formula that relates all the mechanical and electrical parameters to the capacitance values is as follows: £ xg^xSxn where eo: dielectric constant of vacuum 8: dielectric constant of ceramics S: active area per layer n: number of ceramic layers * d: thickness of a layer With this equation in mind, the means of obtaining high value multilayer ceramic chip capacitors are: * thinner dielectric layers * increased number of dielectric layers * increased active area increased dielectric constant The most important parameter that can enable an increase in the capacitance of monolithic ceramic capacitors is the thickness of the dielectric element. Year by year, the dielectric element thickness becomes ever smaller. Currently, products with a dielectric element of 2 ~ 3 |i.m thick are on the market, and recent products with dielectric elements only 2|.im thick or less have been developed. The core technologies for supporting thin-layer products include technologies for ultra-fine graining and low-temperature firing of ceramics, non-reduction material technology, and technologies for graining and dispersing the electrode material, as well as using base metal for the electrode material. These technologies are much advanced compared to more conventional ones. Consequently, the delicacy of a MLCC design is clear. A good capacitor is the result of a good balance between materials, thickness and dimensions. This demonstrates the difficulties to be overcome in order to obtain small, high value capacitors with good temperature performance and high working voltages. Reliability Superiority of Ceramics over Tantalum A A. t TERMINATION CERAMIC UNIT INNER ELECTRODE A - A'CROSS SECTION B Breakdown voltage In figure 3 there are two important points that must be observed: * considerably higher actual breakdown voltage of ceramic capacitors compared to tantalums enormous safety factor between stated working voltage and actual breakdown voltage of ceramic capacitors This only means that the ceramic capacitor is more reliable and that can safely operate at the stated working voltage; it would also seldom fail due to overvoltage spikes which would kill tantalum capacitor. Fugure 2: Structure of a ceramic capacitor A) device cross section B) physical cross section as seen on electron microscope; the graph Is showing how higher capacitances ofX7R and Y5Vceramic capacitors can be obtained by thinning dielectric layers and by Increasing their number Sample (1) MLCX7R 1/iF 10V{GRM40X7R105K10) (2) MLC Y5V 4.7 F 16V (GRM42-6Y5V475Z16) (3) MLC Y5V 4.7^ F 16V (GRM230Y5V475Z16) (4) MLC Y5V 10/i F 16V (GRM235Y5V106Z16) (5) TA1 //F 16V (A case) (6) TA4.7/JF 16V(Bcase) (7) TA 10;(F 16V (C case) o > z O Q 200 100 O - a . MLCX7R 1a; F 10V S MLC Y5V I 4.7;. F 16V ■ MLC Y5V MLC Y5V 4,7;-F16V 10/.F 16V TA TA V F 16V TA lO/iF 16V 4,7//F lOV I Z 5 (2) (3) (4) (5) (6) (7) Figure 3: Comparison among measured breal 5[V] - AV=3[V) DUTY=60(%1 2 [|i secj ->1 AV=64 [mV] MLC 1|.lF f (GRM42-6 X7R 105K 16) k MEASURING CIRCUIT O-Wr- 50 ohm 0 PULSE GENERATOR; HP 8112A DIGITIZING OSiLLOSCOPE: HP 54111D TA 10uF s ALlOuF 4V=69 [mV] AV=233 [mV] Input Pulse j Input Pulse Freq Voltage 10kHz 100kHz Output ripple voltage (nnV) AL TA i MLCC 534 336_ 332 __204_ 64_ 38 30 196 16_ 12 3 FFT Analysis result shows MLCC's superiority in terms of noise absorption in High Frequency range. S ^fii AL10nF TA 10nF MLCC lOpF "1 'Jtilll hjlit-M Figure 9: Generai noise absorption comparison data Null rpsonance tv|>o lorwarcl method DC - OC eonvei ter. ••«^rw; ;.S(H'C> Iniiiil : nVTK Olilpiil ; 5\ ! 2A (UIW) Smoothing Capacitor: MLC 22|iF Smoothing Capacitor TA 22SIF Figure 8: Puise response of MLCC versus Ta/Ai capacitors CoiTiparing Ml.C'C and TA . MLCC can reduce ripple iioi.sc bv !/.> ill Forward method l^C ~ DC convertei'. Figure 10: Exampie of Ta/AI repiacement in smoothing application Table I: performance comparison among MLCC, tantalum and aluminum capacitors TALand Pattern MLCC TA AL Hiiig freq. Capacitance - frequency Exelent Fair Poor Imedance - frequency Exelent Fair Poor Reliability Break down Voltage Exelent Fair Fair Life Exelent Fair Fair Temp, rise Exelent Fair Poor Noise absorption Exelent Fair Poor Polarity Exelent Poor Poor Size Exelent Good Fair Ottler Temp. Capacitance X7R X5R Y5V Good Fair Good Fair Voltage Capacitance X7R X5R Y5V Good Good Fair Fair 1 The Murata answer In figure 11 you will find the most important values of MLCC that Murata is able to supply. The dielectric types, the capacitance values, the working voltages and the sizes of capacitors currently in production are shown. Please, note that this list is being constantly updated as new capacitor types are being added on the regular basis. As well, figure 12 allows you to find the right MLCC size to match the existing land pattern of the Ta being replaced. On the left there are the most common Ta pad designs for reflow soldering, on the right there are basic MLCC sizes for those pads. To find equivalent size of MLCC just drag its symbol over the Ta land pattern. IS :T)io Land Patterns are referred :fo advised Tantalum pad. for ■Reflov/ Soider 1 iThe termination dimensions are icaicuiated considering the ;minfmum iolierance value. Figure 12 . MLCC to Ta matching sizes Continued development will see continued decreases in the thickness of the dielectric element. Using thin-layer forming technology allows ceramic capacitors to be further reduced. With increased semiconductor density, semiconductor components use lower voltages. Accordingly, electric and electronic circuits are driven at lower voltages. If a ceramic capacitor appears with a rated voltage of 4 V or 2.5 V, there is a great possibility that applications will be found for it. The current situation is favorable especially for thin-layer monolithic ceramic capacitors. Likewise, the technology has grown enough to meet the needs for products with more than 100 f.iF, 220 |i,F, or higher capacitance. In addition, low-profiled products that can be used in thinner equipment are available. Step by step, product thickness of 1.35 mm or more will be reduced to 1.35 mm or less (1.25+0.1 mm), to 0.95 mm or less (0.85 mm±0.1 mm), and then to 0.7 mm or less (0.6 mm+0.1 mm). As described above, it is expected that high-capacitance monolithic ceramic capacitors will be further developed in a variety of directions - through downsizing, upsizing, capacitance increase, rated voltage increase, and more - all based on the ceramic thin-layer forming technology. REFERENCES /1/ MURATA mail, no.4, spring 2001 /2/ muRata internal communication /3/ Denpa Shinbun, Part 2, High Tectinoiogy, Aug. 21, 2000 Figure 11: List of high capacitance MLCC that can be supplied by muRata Iztok Sora M IKRO I KS d. o. o. Stegne 11, 1521 Ljubljana Tel.01 5112 221, fax.01 5112 217