High Cap Replacement

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1 High Cap Replacement Richard Tse and Takashi Chiba TDK Components USA, Inc. Abstract This paper explains fundamental component performance differences between MLCCs and other types of capacitors. A brief history of MLCC development is explained as well as electrical characteristics. An example analysis is shown to show real world applications of the theories and static data discussed. March 00

High Capacitance Replacement By Richard Tse & Takashi Chiba Advancement of MLCC s: As technology improves, the market demands smaller products that are faster, consume less power, and offer many more

The purpose, of course, is to provide the tools to allow the design engineer to build denser PCB s. Multilayer ceramic capacitors (MLCCs) were developed for surface mount applications.

2 High Capacitance Replacement By Richard Tse & Takashi Chiba Advancement of MLCC s: As technology improves, the market demands smaller products that are faster, consume less power, and offer many more features. Due to this, PCB s have reduced in size and are packed more densely. The component industry has met these demands by offering space saving devices such as ASIC s and SMD passive components. The purpose, of course, is to provide the tools to allow the design engineer to build denser PCB s. Multilayer ceramic capacitors (MLCCs) were developed for surface mount applications. Initially, MLCCs these were only available in small capacitance values and provided a great alternative to leaded capacitors. Now the MLCC is evolving to the next step by increasing capacitance to enter the tantalum (Ta) and aluminum (Al) area. TDK s thin layer technology is exemplified in the thin layer advancements made on the 36 (06) case size capacitors. Fig. 0 shows the rapid increase in number of layers, and capacitance, over the past several years. With the success of these advancements, TDK is number in the high capacitance market. Fig 0: Cross Section showing thin layer technology of TDK 0 0µF Thin Layer Development (36) Layers Capacitance (µf) Layers 330 Layers 0 5 Layers 60 Layers In order to achieve high capacitance value MLCCs (HCV), the number of active layers in the MLCC must be increased. At the same time, the layer thickness must be decreased. The reasons for these changes become obvious when looking at the general equation for capacitance. (Eq. 0) 0 Layers 0 Layers C= Year Fig. 0: Thin layer technology for TDK 36(06) εαn t Eq 0: General capacitance formula Where: eε:dielectric constant TDK has been pushing the envelope by being the first to develop not only highest capacitance MLCCs but simultaneously decreasing its size. An example of this is TDK's 00µF MLCC in 5750 (0) case size which was almost immediately followed by the 00µF MLCC in 453 (8). As higher capacitance is achieved, TDK then developed the 0µF MLCC in a 0 (0805) case size. (Fig. 0) A :area n :number of layers t :layer thickness At one time, palladium (Pd) was used as the electrode material for MLCCs. Over the past several years the cost for this precious metal has skyrocketed. (Fig. 03) With the number of layers increasing, the cost of a HCV will also increase and this poses a second challenge. Page of 7 Rev. March 00

3 Source: NYMEX No. Name Material Class I Class II Pd TME Pd TME Dielectric TiO CaZrO3 BaTiO3 US$/Troy Oz. 3 4 Electrode Termination Pd Ag or Ag/Pd Ni Cu Nickel (Ni) Pd Ag or Ag/Pd Ni Cu 5 00% Tin (Sn) Fig. 03: Cost of Palladium has skyrocketed! The solution to this problem is the development of transition metal electrode (TME) technology. TME is sometimes also referred to as BME, which stands for base metal electrode. It is sometimes also referred to as nickel (Ni) since it is the actual metal used. Historically, palladium (Pd) was the dominant electrode material used. Palladium is a precious metal and the price has skyrocketed. One benefit in TME is that Ni offers less electro-migration as compared to Pd (Fig. 04) but the primary advantage is the low material price. For these reasons, TDK has worked very hard to develop and refine TME technology for HCV and eventually completely replace Pd MLCCs Comparison of Metal Migration : Deionized water : 0.0mol% NaCl water Above 60000sec Test Conditions : 60 At the tip Fig. 05: MLCC Material System TDK has been leading the industry in development of TME. TDK was the first to develop TME for mass production in class II dielectrics. TDK is also the first company to offer class I MLCCs (C0G/NPO) with TME. The amount of surface mount products in use is increasing every year. Due to this, many companies tried to compete in the capacitor market but only a few have been successful. This is especially true in the area of high capacitance. TDK recognized the demand for high capacitance and responded with its thin layer technology. As TDK enters the Ta and Al high capacitance arena, it is necessary to compare MLCCs with Ta and Al in order to understand the benefits of using MLCCs. These high capacitance replacement, or set analysis, studies are currently large focus areas for many design engineers. Gap:300um Time to short(sec) Substrate AlO3 Voltage across the gap 30V : (00V/mm) Water : Deionized : 0.0 mol% NaCl water MLCC vs. Tantalum and Aluminum 0 Ag Ag-Pd (7 : 3) Cu Pd Ni Fig. 04: Analysis shows Ni has lower electro migration than Pd. One of the challenges of using TME technology is that parts of the production process are more difficult. It is necessary to co-fire the ceramic and electrode material using reduction gas in order to prevent oxidation of the Ni. The formulation of the ceramic material must be changed to not only match the physical properties of Ni but must also be compatible with the reduction gas. This different material system is the result of years of research and testing performed by TDK to develop TME. (Fig. 05) MLCCs clearly offer performance advantages compared to alternate technologies such as tantalum and aluminum electrolytic capacitors. However, MLCCs historically did not offer high capacitance values and therefore could not be used in many of the high capacitance applications. During the past few years, thin layer technology has allowed TDK MLCCs to be competitive with tantalums and aluminum. In most cases, a direct capacitance value replacement from tantalum (or aluminum) to MLCC is not the best way to approach a high cap replacement effort. Instead, the circuit needs to be tested to verify the best replacement value. First, there are certain rules of thumb that should be applied when performing a set analysis based on the circuit function of that capacitor. Second, MLCCs outperform Ta and Al in many performance Page of 7 Rev. March 00

4 characteristics including impedance/esr, voltage withstanding, ripple current, and temperature stability. With a better understanding of the performance differences between MLCCs and other types of capacitors, the design engineer can then select the best MLCC based on performance and price. This section will briefly explain the performance advantages for MLCCs. It is important to understand at least the basics of these performance differences before approaching a cap replacement. This also helps in understanding the basis for the replacement rules of thumb. The next section will go through an example analysis and explain in more details various aspects of the procedure and rules of thumb. () Impedance and ESR Characteristics Decoupling is the most common application for these high value capacitors. Low impedance is required for effective noise suppression at the noise frequency. MLCCs exhibit high frequency response performance in the high frequency area. Characteristic impedance between Ta, Al, and MLCCs show that Ta has slightly lower impedance over frequency than Al but MLCCs offer a significantly lower impedance as shown in a log-log graph. (Fig. 06) The lower impedance of the MLCC is due to the electrode material, which is metal. In the case of a tantalum capacitor, a portion of the electrode material is typically MnO, which is a type of semiconductor and therefore has higher resistance. In the case of an aluminum capacitor, the electrode material is a form of an electroconductive liquid, which has low conductivity and therefore poor impedance characteristics..0e+0 Impedance Characteristics Tant. 0uF/6.3V/A case Alminum 0uF/6V C36X5R0J06K ESR(ohm).0E+0.0E+0.0E+00.0E-0.0E-0.0E-03 ESR Characteristics.0E+03.0E+04.0E+05.0E+06.0E+07 Fig 07: ESR Characterisitcs Frequency(Hz) () Surge Voltage Withstanding Tant. 0uF/6.3V/A case Alminum 0uF/6V C36X5R0J06K Voltage withstanding is also referred to as breakdown voltage. When high voltage above the manufacturers rated voltage is applied to a capacitor, the capacitor breaks. Typically, to measure voltage withstanding, the DC voltage across the capacitor is raised at a controlled rate until the capacitor fails. The maximum DC voltage is recorded as the breakdown voltage. The engineer needs to consider application voltage and surge voltage when designing a circuit. Typically, when using tantalum capacitors, a derating rule must be applied to ensure the tantalum can withstand the surge voltage. If the application voltage is 5V then a 50V tantalum must be used. In the case of a MLCC, a 5V-rated capacitor is more than enough for a 5V application so the derating rule does not apply. Fig. 8 shows typical breakdown voltages of MLCCs are much higher than that of tantalum. This means that MLCCs have a higher reliability over voltage surges in circuit compared to tantalum. In the case of Al capacitors, the selected capacitor must be rated to at least twice the actual ripple current..0e+0 Impedance(ohm).0E+00.0E Breakdown Voltage.0E-0.0E-03.0E+03.0E+04.0E+05.0E+06.0E+07 Fig 06: Impedance Characterisitcs Frequency(Hz) Breakdown Voltage (VDC) The ESR also follows a similar trend where the ESR for an Al capacitor is slightly higher than the ESR for a Ta. Again, the ESR for a MLCC starts lower and continues to decrease until it reaches the selfresonant frequency (SRF). (Fig. 07) C36X7RE05K C36X7RE5K C36X5RC475K Ta, 4.7uF,0V Ta, 0uF,6.3V (A case) (A case) Fig 8: Surge/Breakdown Voltage Page 3 of 7 Rev. March 00

5 (3) Ripple Current Performance When using capacitors in smoothing circuits, ripple current flows through the capacitor. Heat is generated due to the equivalent series resistance (ESR) of the capacitor.(eq. 0) Since MLCCs have the lowest ESR, they also have a significantly lower change in temperature as ripple current increases. (Fig. 9) This is one of the reasons why MLCCs are commonly used in smoothing circuits. 6 5 P = V wctand = I ESR Ripple 00kHz Eq. 0: Consuming Power IMPEDANCE (ohm) 00K 0K K Z -f Characteristics of Al Elect. Cap (6V, 0uF) -55C -5C 0C 0C 5C 55C 85C 5C 00 K 0K 00K M 0M Frequency (Hz) Fig. : Temperature Stability for Al O T ( C) K Z - f Characteristics of MLCC (6V, 0uF) Fig 9: Ripple Current (4) Temperature Stability Due to the electrode material used, MLCCs have a much more stable impedance with temperature change. For an Al capacitor, impedance decreases more at higher temperatures than at lower temperatures. The difference in impedance can typically be greater than orders of magnitude between 55 and +5 o C. The temperature stability of a Ta capacitor is more stable that that of Al but at higher frequencies there is still some deviation at different temperatures. In the case of the MLCC, not only is the impedance significantly lower than Ta or Al at higher frequencies, but it is also the most stable across the temperature range. (Fig. 0-) IMPEDANCE (ohm) 00K 0K K Z - f Characteristics of tantalum (6.3V, 0uF) 00 Fig. 0: Temperature Stability for Ta Current (A) K 0K 00K M 0M Frequency (Hz) -55C -5C 0C C36X7RC05K C36X7RA5K C36X7R0J335K Ta 4.7mF 0V Ta 0mF 6.3V 0C 5C 55C 85C 5C IMPEDANCE (ohm) 0K K K 0K 00K M 0M Frequency (Hz) Fig. : Temperature Stability for MLCC -55C -5C 0C 0C 5C 55C 85C 5C High capacitance MLCCs have entered the market to compete with tantalum and aluminum capacitors. In addition to capacitance, MLCCs also offer improved performance and stability. So far, only the static performance characteristics have been discussed. The next section will go through a high cap replacement (set analysis) example. This will show the performance advantages of a MLCC in an actual application. High Cap Replacement Example The best way to compare the performance advantages of MLCCs is by example. The following set analysis was performed on an ADSL modem. (Fig. 3) The purpose of this analysis is to replace the existing tantalum capacitors with MLCCs. (It should be noted that the portions of the analysis are reproduced here with the permission of the customer.) Page 4 of 7 Rev. March 00

6 C0 C08 C0 Pk-Pk = 7.mV C0: Ta 0 mf, VDC =.6V XYZ Corp. Fig. 3: ADSL Modem for Set Analysis Pk-Pk = 5.mV Waveform measurements are taken across each capacitor. For the purpose of this example, analysis of three capacitors are shown from Fig. 3; C0, C08, & C0. These waveforms are measured using an oscilloscope while the target circuit is driven based on the customer s recommendation. These initial waveforms are used as the baseline to compare the performance of the original capacitor(s) against the TDK MLCCs. The goal is to determine the MLCC which will yield equal or better performance. Based on the circuit function, several rules of thumb are used to determine the initial minimum replacement capacitance. One capacitor is selected and replaced with an MLCC. After comparing the MLCC performance with the original tantalum performance, the peak to peak voltage is compared to determine if the selected MLCC provides enough capacitance. If not, it is replaced with a larger value MLCC and the measurement and the performance is measured again. This replace and measure step is repeated until a suitable capacitor is found. For C0, the original waveform shows a peak to peak voltage of 7.mV using a 0mF tantalum. The tantalum is replaced with a mf MLCC. Fig. 4 shows that using a MLCC with 0% the nominal capacitance of the original Ta gives similar results! After completing analysis on this component, the original tantalum is returned to the PCB and this single replacement analysis it focused on the next targeted capacitor. Similar results are shown for C08 and C0. (Fig. 5 & Fig. 6 respectively.) C0: MLCC mf, VDC =.6V Fig. 4: Single replacement for C0 Pk-Pk =.8mV C08: Ta 0 mf, VDC = 3.V Pk-Pk = 8.4mV C08: MLCC mf, VDC = 3.V Fig. 5: Single replacement for C08 Page 5 of 7 Rev. March 00

7 Pk-Pk = 3.mV majority of the cases, the basic procedures are typically the same. (Fig. 7) First, the PCB must be characterized. This involves taking a component inventory from the bill of material (BOM) and verification of the capacitance, actual operating voltage, and other critical parameters. This initial characterization is complete after determining the circuit function for each capacitor. C0: Ta 0 µf, VDC = 0.8V Set Analysis Flowchart Characterize Original Capacitor Performance Replace Original Cap with MLCC MLCC Measure and Performance Pk-Pk = 4.0mV Is performance of selected MLCCs acceptable? No C0: MLCC µf, VDC = 0.8V Yes Fig. 6: Single replacement for C0 Is analysis complete? No Continue with next component. Once analysis on all targeted capacitors are completed, the PCB is completely replaced with the recommended MLCCs and performance is once again measured and compared against the original tantalum performance. As shown in the above examples, it is typical to replace a tantalum or aluminum capacitor with a lower value MLCC Several rules of thumb are used when determining the initial replacement MLCC part numbers. The first step is to determine the maximum operating voltage of the circuit. The second step determines the minimum capacitance based on circuit application. For example, in a decoupling application, MLCCs down to 0% of the original tantalum capacitor value can be used. These rules of thumb should only be used as guidelines. Actual performance should always be verified before deciding on a replacement value. It is never a good idea to simply take the original capacitor and replace directly. Set Analysis Service Set analysis is a service that can be performed by TDK to evaluate cap replacement opportunities. In the Yes Report Results Fig. 7: Set Analysis (High Cap Replacement) Flowchart After the characterization is complete and the targeted capacitors have been identified, analysis is performed on one component. The original capacitor is replaced with a MLCC and the performance is measured. Several MLCC values can be tested in order to find the best capacitance value that offers equal or better performance. The original capacitor is then soldered back to the original location on the PCB and then next targeted capacitor is analyzed. Once analysis has been completed, TDK will generate a table of recommended MLCCs for consideration. This procedure overview is of course very general. Specific concerns and test conditions vary case by case. In order to perform a Set Analysis, TDK also needs additional information from the customer. This information includes but is not limited to the following: Page 6 of 7 Rev. March 00

8 . Design Engineer(s) Contact Information. BOM 3. Schematic 4. Assembly Drawing 5. Power/Installation Instructions 6. Test/Load Conditions 7. Diagnostic Software 8. Areas of specific Concern Of course some of the items listed above may not apply or are not available for a specific module but the more information that is provided is very helpful for successful analysis. Conclusion The development of TDK s thin layer technology coupled with TME technology has allowed TDK to enter the high capacitance area that was typically dominated by Ta and Al capacitors. MLCCs offer lower impedance and ESR over frequency compared to Ta and Al. Additionally, MLCCs offer better voltage and temperature stability. This static performance is confirmed when looking at an actual high cap replacement (Set Analysis) study. Typically the procedures in a Set Analysis are the same from one board to the next. Depending on the circuit function, the recommended MLCC can be as low as 0% of the original capacitor value. By following some rules of thumb, the minimum potential replacement value can be easily determined but it will obviously need to be verified in circuit. It is not recommended to simply make a direct replacement without testing. The interest in replacing high capacitance parts with MLCCs has been desirable for many customers for various reasons. Some of the attention is due to the low availability of tantalum. Some manufacturers are moving away from through hole (Al) due to assembly cost and cycle time. In addition to the performance advantages, MLCCs offer many other advantages over other types of capacitors. Some of these added benefits include the following:. Improved Performance. Higher Reliability 3. No Polarity 4. Reduced real estate 5. Reduced component count on BOM 6. MLCCs are surface mount (as opposed to Al) TDK also offers Set Analysis service where TDK can perform the initial cap replacement analysis for the customer and return a list of recommended replacement part numbers. Page 7 of 7 Rev. March 00

9 End of Report Contact one of the following TDK sales offices for further information or visit our TDK CORPORATION OF AMERICA 600 Feehanville Drive, Mount Prospect, IL 60056, U.S.A. Phone: Fax: ATLANTA Sales Office 80 Satellite Blvd., Suite 400 Duluth, GA Phone: Fax: AUSTIN Sales Office 900 Metric Blvd., Suite J-44 Austin, TX Phone: Fax: CHICAGO District Office 600 Feehanville Drive, Mount Prospect, IL Phone: Fax: DALLAS District Office 5 E. Carpenter Freeway, Suite 690 Irving, TX 7506 Phone: Fax: DENVER Sales Office Suite 4, 94 Broadway Ave. Boulder, CO 8030 Phone: Fax: DETROIT District Office 3870 Seven Mile Road, Suit 340 Livonia, MI 485 Phone: Fax: FLORIDA Sales Office 800 Fairway Drive, Suite 9 Deerfield Beach, FL 3344 Phone: Fax: GREENSBORO District Office 600 Green Valley Road, Suite 07 Greensboro, NC 7408 Phone: Fax: HUNTSVILLE District Office 50 Finney Road, Huntsville AL 3584 Phone: Fax: INDIANAPOLIS District Office 405 West Vincennes Road Indianapolis, IN 4668 Phone: Fax: LOS ANGELES Office 37 Warland Drive, Cypress CA Phone: Fax: NEW ENGLAND Sales Office 0 Trafalgar Square Nashua, NH Phone: Fax: NEW JERSEY District Office 99 Wood Ave. South 5th Floor Iselin NJ Phone: Fax: PORTLAND Sales Office 00 S.W. Fifth Avenue, Suite 00 Portland, OR 9704 Phone: Fax: SAN DIEGO District Office 665 Greenwich Drive, Suite 50 Sand Diego, CA 9 Phone: Fax: SAN JOSE District Office 98 Ridder park Drive, Sutie 00 San Jose, CA 953 Phone: Fax:

MLCC Application Notes

MLCC Application Notes What is the Capacitance of this Capacitor? Frequently asked questions regarding aging and its effect on capacitance. Steve Maloy TDK Components USA, Inc. Abstract TDK recognizes