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5.5 Reliability of Low-Voltage Tantalum Polymer Capacitors

CARTS USA 2005 March 21-24, 2005 Palm Springs, CA. Reliability of Low-Voltage Tantalum Polymer Capacitors Erik K. Reed, Jeffrey N. Kelly, Jonathan L. Paulsen KEMET Electronics Corporation PO Box 5928. Greenville, SC 29606. Tel:864-963-6300. Fax: 864-228-4333. Abstract normal operating conditions. For 100 F, 6V. Tantalum Polymer Capacitors in an EIA 3528-21. This paper briefly reviews earlier work which first case, the test data suggest typical capacitor assessed the Reliability of 6V Tantalum Polymer lifetimes approaching 1,000 years at rated voltage Capacitors . A physics-based acceleration formula and 85oC. that better models the interaction of voltage and temperature stress is presented and discussed. New The accelerated testing strategy and acceleration observations are made about the original test data models employed in this initial assessment of in light of the physics-based acceleration model as Reliability of Tantalum Polymer Capacitors were well as new testing done on 6V Capacitors since the borrowed from accelerated testing work done on original paper was presented.

CARTS USA 2005 March 21-24, 2005 Palm Springs, CA Reliability of Low-Voltage Tantalum Polymer Capacitors Erik K. Reed, Jeffrey N. Kelly, Jonathan L. Paulsen

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Transcription of 5.5 Reliability of Low-Voltage Tantalum Polymer Capacitors

1 CARTS USA 2005 March 21-24, 2005 Palm Springs, CA. Reliability of Low-Voltage Tantalum Polymer Capacitors Erik K. Reed, Jeffrey N. Kelly, Jonathan L. Paulsen KEMET Electronics Corporation PO Box 5928. Greenville, SC 29606. Tel:864-963-6300. Fax: 864-228-4333. Abstract normal operating conditions. For 100 F, 6V. Tantalum Polymer Capacitors in an EIA 3528-21. This paper briefly reviews earlier work which first case, the test data suggest typical capacitor assessed the Reliability of 6V Tantalum Polymer lifetimes approaching 1,000 years at rated voltage Capacitors . A physics-based acceleration formula and 85oC. that better models the interaction of voltage and temperature stress is presented and discussed. New The accelerated testing strategy and acceleration observations are made about the original test data models employed in this initial assessment of in light of the physics-based acceleration model as Reliability of Tantalum Polymer Capacitors were well as new testing done on 6V Capacitors since the borrowed from accelerated testing work done on original paper was presented.

2 Then the focus is multilayer ceramic Capacitors by various shifted to accelerated lifetesting of 4V and researchers. In summary, the testing strategy is to Tantalum Polymer Capacitors . apply much higher than normal stress ( voltage and temperature) of various intensities to Capacitors , Accelerated lifetest data for 4V and and then precisely record the times-to-failure of Capacitors are presented and are compared and devices in representative test samples. Failure is contrasted with the 6V data. Similarities and defined as blowing a 1 ampere fuse in a low- differences in the behavior of the lower- voltage impedance lifetest circuit, and all test samples are devices with respect to each other and the 6V drawn from one large, randomized population of devices are discussed.

3 The physical bases of these Capacitors . The relative times-to-failure observed similarities and differences are explored, and at the various stress levels are compared with each conclusions are reached regarding the expected other, and are then fitted to mathematical models long-term Reliability of Low-Voltage Tantalum for voltage and temperature acceleration so that Polymer Capacitors . times-to-failure at voltages and temperatures lower than those used in the investigation can be Introduction extrapolated. The data from accelerated lifetesting of 6V It was found that typical times-to-failure were Tantalum Polymer Capacitors were first published shorter when the voltage stress was raised or when one year It was found that the times-to- the test temperature was increased.

4 Also it was failure of the test samples were tightly distributed found that the relative time-distribution of these and could be accurately predicted for given stress failures (the shape of a percentile plot of failures levels of voltage and temperature. While the tight versus time) was not altered as the voltage and distribution of failures suggests the presence of temperature were changed over a wide range. This distinct wear-out mechanisms, it also suggests that behavior was interpreted to mean that no new device lifetime can be accurately predicted, not failure mechanisms were being activated at any of only at accelerated conditions, but also at more the stress conditions employed in the investigation. 189. Finally it was found that if the times-to-failure of have failed.

5 These t50 statistics were fit to the same the various test samples were plotted on a common empirical voltage acceleration model and graph, the individual plots were uniformly spaced Arrhenius temperature acceleration model that as the stress level ( voltage or temperature) was have been successfully used to describe the changed. This boosted confidence that the data Reliability of ceramic ,3. could be fit to appropriate mathematical models for , 85 C. voltage and temperature acceleration. , 105 C 125 C 105 C 85 C. , 125 C. 99% , 145 C. 95%. , 145 C 90%. Normal Percentile , 145 C 80%. , 145 C 70%. 99% , 145 C. , 145 C 50%. 95%. 90% 30%. Normal Percentile 20%. 80%. 70% 10%. 5%. 50%. 30% 1%. 20% 145 C. 10% 5%. 1% 1 10 100 1000. Time (hours). Figure 2. Lognormal Plot of Failure Percentile 1 10 100 1000.

6 Versus Time-To-Failure at 85 C, 105 C, 125 C, Time (hours). and 145 C for Tests Performed at on 100 F, Figure 1. Lognormal Plot of Failure Percentile 6V Tantalum Polymer Capacitors . versus Time-To-Failure at , , , , and for Tests Performed at 145 C on 100 F, 6V Tantalum Polymer Capacitors . The empirical voltage acceleration model employed in the initial investigation is the power Figure 1 contains representative time-to-failure law relationship given by Equation 1, where is an data from the original investigation that were empirically-derived exponent. recorded at various test voltages at a constant temperature of 145oC for 100 F Tantalum Polymer . Capacitors rated at 6V. These data clearly t V . demonstrate (1) shorter lifetimes at higher A = 1 = 2 (1). voltages, (2) similarly shaped failure distributions, t2 V1.

7 And (3) uniform, predictable spacing as the voltage is changed. For the 100 F, 6V Tantalum Polymer Capacitors tested in the original investigation, it was found Figure 2 contains representative time-to-failure that the t50 times fit the empirical model of data from the original investigation that were Equation 1 well at each temperature, but that the recorded at various test temperatures at a constant value of was different at each temperature. voltage of for Capacitors rated at 6V. These Specifically, it was found that =19 at 85oC, data clearly demonstrate (1) shorter lifetimes at = at 105oC, = at 125oC, = at higher temperatures, (2) similarly shaped failure 145oC and = at 165oC. It is clear from these distributions, and (3) uniform, predictable spacing. results that the voltage acceleration process is temperature dependent.

8 Moreover, the For each of the test samples subjected to a specific temperature dependence likely fits some combination of voltage and temperature, a single mathematical model, but that model was not statistic was assigned to quantify the relative identified during the investigation. performance of the samples at the specific cumulative stress level. Since the times-to-failure In Figure 3, the t50 times appear on a log-log plot were found to be log-normally distributed in time, that produces straight lines from the model of the chosen statistic was median life, denoted as t50, Equation 1. The log-log plot provides graphical which is the time when 50% of the test samples means to discover the value of at each 190. temperature (the slope of the line), and to Specifically, it was found that Ea= at , extrapolate t50 times at voltages outside the original Ea= at , Ea= at , range of test voltages.

9 Ea= at , and Ea= at It is clear from these results that the temperature Two data points in Figure 3 that correspond to (1) acceleration process is voltage dependent. rated voltage at 145oC and (2) times rated Moreover, the voltage dependence likely fits some voltage at 125oC fell below the lines fit to the other mathematical model, but that model was also not data points at those temperatures. It was identified during the investigation. subsequently determined (and verified by means of 10. 7. independent testing of similarly processed Corrected Lines Capacitors ) that these samples saw a different, *See Text*. harsher reflow profile during board mounting than 10. 4. did the other test samples. The correct data points X. Median Life [t50] (hrs). X. (based on additional testing) are marked on the graph with the letter X.

10 10. 1. 7. 10. 1027yr 165 C, = -2. 145 C, = 10. 125 C 125 C, = 23yr 105 C, = 105 C 85 C, = 5. 10 (85 C) y= -19. 85 C 165 C 145 C 125 C 105 C 85 C. (105 C) y= 10. -5. Median Life [t50] (hrs). (125 C) y= (145 C) y= -3 -1. (165 C) y= Inverse Absolute Temperature, 1/T (10 , K ). 3. 10 X. 650hr X. Figure 4. Plot of Median Life versus Inverse Absolute Temperature at , , , 1. , , , , , and on 10. Semi-Log Scale for 100 F, 6V Tantalum Polymer 165 C Capacitors . 145 C. -1. 10. In Figure 4, the t50 times of the investigation appear Multiple of Rated voltage on a semi-log plot that produces straight lines from Figure 3. Plot of Median Life versus Test voltage the Arrhenius temperature acceleration model of at 85 C, 105 C, 125 C, 145 C, and 165 C on Log- Equation 2. The semi-log plot provides graphical Log Scale for 100 F, 6V Tantalum Polymer means to discover the value of Ea at each voltage Capacitors .


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