T498

Product Update – T498 High Temperature (+150°C) Tantalum SMT Capacitors KEMET Electronics Corp. P. O. Box 5928 Greenville, SC 29606 (864) 963-6300 www.kemet.com The tantalum SMT capacitor in its solid-state structure is typically rated as capable of 125°C applications. The T498 tantalum surface mount capacitor has a maximum temperature rating of 150°C. The difference between the T498 and the standard tantalum capacitors lies within its material set and design. The materials changed include the carbon, the silver epoxy, the silver paint, the plastic molded encapsulant, and the leadframe. These materials 1 still contain no lead and are fully RoHS compliant. The standard finish on the leadframe is a matte tin plating over nickel, and the device is capable of the 260°C reflow pro2 files as defined in J-STD-020C . A gold or tin-lead finish is also available. dot matrix pattern. The effect does not create a coloration change, but creates a surface abrasion as the laser removes the reflectivity of the plastic surface in the desired pattern. Figure 2. Photograph of “D” case, T498 SMT capacitors. Through oblique lighting and vision systems, the markings can be quite revealing as shown in Figure 2. An explanation for the pattern with the markings is shown in Figure 3. Figure 1. Structure of new T498 tantalum capacitor. The appearance of this device is radically different from the previous SMT tantalum capacitors from KEMET, in that the color is no longer gold with brown lettering. The gold material has a heat activation of color change from yellowish gold to brown created in the presence of a controlled surface temperature rise. A laser flash through a mask is used to create the polarity and identifying marks on the gold plastic. Using this material and process in the presence of higher heats created an effect where the entire surface of the package was turning brown, and the markings became indiscernible. The black compound has no discernable change in coloration when exposed to extended temperatures above 125°C. The marking on the package for the polarity stripe, capacitance code, voltage rating, the KEMET logo, and the print week code (PWC) are still created with a laser in a Figure 3. Component marking diagram for T498 capacitor. ©2005 KEMET Electronics Corp. May 2005 The carbon, conductive epoxy, and the silver paint materials were chosen for the best offerings that would allow the device to exist in the 150°C environment without degradation. The tantalum anode structure, the tantalumpentoxide, and the MnO2 cathode system have been proven to withstand this temperature exposure without degradation. Application Derating We will use the guidelines established with the long history of the commercial tantalum product to fix the recommended application at no more than 50% of the rated voltage. For a T498 rated at 50 VDC, this would create a recommended application of 25 VDC. This application would then apply up to 85°C, at which point the temperature-voltage derating requirements effectively lower the voltage rating of the part. At 150°C, this 50 VDC has a temperature-voltage derated rating down to 33 VDC, and following the 50% application guides, the recommended maximum application is the 17 VDC. It is very important to consider the failure rate at rated voltage and 150°C is listed as 0.5% per thousand-piecehours; but that application derating will allow for an appreciably reduced failure rate. Using the voltage factor 3 calculations from MIL-HDBK-217F , at rated voltage the multiplying factor for the failure rate is 5,909. Compared to “50% of rated” factor of 1.045, then the improvement in failure rate at 150°C would be down from the 0.5% level to 884 parts per billion-piece-hours. Remember though, the rated voltage is changing with temperature as shown in Figure 4. At temperatures up through 85°C, the recommended application voltage is 50% of nameplate voltage. Above 85°C, the recommended application voltage is 50% of the temperature-voltage derated level. For a standard tantalum at 125°C, the recommended application voltage is 50% of 67%, or 33% of the nameplate voltage. For a T498 at 125°C and 150°C, the application becomes 40% and 33%, respectively, of nameplate voltage (Figure 5). Voltage Rating The voltage rating of a component is fixed so as to create an acceptable failure rate at accelerated life conditions. Inability of a device to meet that criteria may cause the voltage rating of the component to be reduced, or the component to be redesigned (thicker dielectric) to allow for that failure rate to be achieved. Accelerated life testing of this component at 150°C and with 2/3 nameplate voltage applied has shown the failure rate to be less than 0.5% per thousand-piece-hours. Failures were designated by positional fuse failure or parametric shifts beyond the initial limits. The temperature-voltage derating of this device is slightly different from the standard tantalum SMT capacitor. These devices were created using thicker dielectrics for the voltage ratings than is required for the standard product line. Figure 4. Voltage-temperature derating for standard and T498 capacitors. For both the T498 and the standard tantalum capacitors, the voltage rating up through 85°C is the same as the nameplate voltage for the capacitor. For the standard capacitors above 85°C, the voltage rating is linearly reduced from 100% of nameplate voltage at 85°C, down to 2/3rd (67%) of nameplate voltage at 125°C. For the T498 capacitors, the voltage rating is linearly reduced from 100% of nameplate voltage at 85°C, down to 2/3rd (67%) of nameplate voltage at 150°C. This allows the 125°C rating for the T498 to be about 80% of nameplate voltage. Figure 5. Recommended application voltages versus temperature. Power Rating The power rating for capacitors is reflective of the allowable heat generated in the device and there is a direct correlation between these two. Without a standard temperature rise defined, the majority of manufacturers use the ©2005 KEMET Electronics Corp. May 2005 +20°C internal rise and an arbitrary figure in defining the power capability for these devices. This arbitrary rise added to the ambient temperature creates the absolute internal temperature of the component. Since capacitors are life tested under DC or static stress, there is no temperature rise at the maximum rated temperature of the device. Only by using the positive tolerance of +2°C at this temperature, can we define a “tested capability” at this temperature extreme. We then need to look at the difference between the temperature extreme and the assigned or arbitrary rise of +20°C, to calculate the point at which a power derating is applied. For 150°C, and an allowable rise of +20°C, the power derating must begin at 130°C. The power capability (allowing a +20°C rise) for this device is the same from -55°C through 130°C. If the case power is defined as 150mW, then the power capability is defined as 150mW for this temperature range. There is a linear reduction in that power capability then applied from 100% at 130°C, down to 15 mW (10% or 2°C/20°C) at 150°C. Figure 6 shows this delineation. ture of 100% of the case defined power. Consider that these are two “D” case units and the actual power capability here is 15 mW for the standard and 150 mW for the T498. For devices of equal capacitance and ESR, the ripple capability for the T498 would increase by a factor of 3.16 (square root of 10). Application Areas The ideal applications for these components begin where the standard products’ end. At temperatures between 115°C and 140°C, these applications would still allow a 10°C margin or better, between the rating and the application. New under hood or in system applications may be considered with the T498 that were previously thought to be too precarious for the standard tantalum. 1 RoHS –“Restriction on the use of certain Hazardous Substances in Electrical and Electronic Equipment” (European Union directive 2002 / 95 / EC) 2 J-STD-020C – IPC/JEDEC Joint Industry Standard – Moisture/Reflow Sensitivity Classification 3 MIL-HDBK-217F – Notice 2, Reliability Prediction of Electronic Equipment, Department of Defense, December 2, 1991, Washington, DC. Figure 6. Power derating to maximum temperatures. The allowable temperature rise is arbitrary and two considerations must be weighed when choosing this figure. First, the internal temperature rise plus the ambient must never exceed the maximum temperature plus 2°C. To do so would create an environment in which there is no reliability data to justify this application. Second, the rise must be considered as a potential thermal shock condition when the device is at ambient temperature and immediately after power is applied. Deltas in excess of +50°C may lead to thermal gradients that could induce stresses high enough to cause an internal fracture and failure. It is evident from the plot of Figure 6 that the difference in these two types of capacitors creates entirely different power capabilities between 105°C and 125°C. For example, the power dissipation for the standard tantalum at 125°C is down to 10% of the case defined power capability, while the T498 shows a capability at this tempera©2005 KEMET Electronics Corp. May 2005