AVX固体钽电容漏电流分析.doc

固体钽电容漏电流分析ANALYSIS OF SOLID TANTALUM CAPACITOR LEAKAGE CURRENT固体钽电容漏电流分析Abstract:摘要The leakage current of a solid tantalum capacitor is the sum of several independent factors. From measurements of leakage over a range of test conditions some degree of separation of these components of the current can be achieved and so the relative importance of factors leading to high leakage can be assessed. There is a background level present directly related to dielectric absorption and it contributes to the loss factor of the capacitor. It is not a true leakage. On top of this absorption current there are other components, most of which are essentially by-passing the bulk of the dielectric. These can be moisture or manganese dioxide tracks or breakdown sites in the dielectric layer. These typical behavior patterns are described in detail.固体钽电容器的漏电流是几个独立因素之和，对各种条件下漏电流的测量，可以一定程度将这些漏电流成分分开，因此相对重要的大漏电流因素可以评估出来。有直接的背景涉及到介质吸收，它对电容器的损耗因子有贡献。它不是真正的漏电流。另外，紧接着吸收电流的是其它成分，大多数在本质上是介质本体的旁路电流。这些可能是潮汽或二氧化锰轨迹或介质层的击穿点造成的。这些典型的行为方式也会详细介绍。The leakage current of a solid tantalum capacitor is the sum of several independent factors. From measurements of leakage over a range of test conditions some degree of separation of these components of the current can be achieved and so the relative importance of factors leading to high leakage can be assessed.固体钽电容的漏电流是几个独立因素的总和， 在一定测试条件范围内对漏电流可以得到某种程度的分开的量值，所以，可以对导致漏电流大的重要因素进行评估。There is a background level present equivalent to a dielectric resistivity of about 1016 ohm cm. This background is directly related to dielectric absorption and it contributes to the loss factor of the capacitor. It is not a true leakage insofar as it can be recovered when the capacitor is discharged. It is proportional to voltage and, over the period usually employed for leakage current measurements, is inversely proportional to time.这里有一个大约为1016cm介质电阻率的参考背景。此背景直接与介质吸收相联系，并对电容器的损耗因子有贡献。它并不是真正意义上的漏电流，因为在电容器放电时可以恢复。它与电压成正比，并在测量漏电流期间与时间成反比。On top of this absorption current there are other components, most of which are essentially by-passing thebulk of the dielectric. These can be moisture or manganese dioxide tracks or breakdown sites in the dielectric layer. The dependence of these on the measuring voltage ranges from ohmic to an extreme sensitivity. Moisture tracks can be identified by their behavior at high and low temperatures. Leakage at breakdown sites usually exhibit a strong dependence on voltage. On the other hand manganese dioxide tracks are normally ohmic.在吸收电流的最大值中，存在其它的成分，绝大多数情况下主要是电介质体的旁路电流。这些情况可能是潮气或二氧化锰轨迹或介质层有穿破点。这决定于测量电压，范围从欧姆级到极端敏感的值。潮湿的原因可以通过在高低温时，电容器的行为特性鉴别出来。介质层有穿破点发生的漏电流很大程度上地决定于电压。另一方面二氧化锰轨道一般为欧姆级的电流。Some typical behavior patterns are described in detail.下面会详细介绍一些漏电流典型的表现模式。Introduction简介The leakage current of a solid tantalum capacitor is normally expressed as a single value measured at room temperature, at rated voltage, and after 3 or 5 minutes. This value is classed as high or low in comparison with a selection limit of typically 10nA/FV (e.g., 3.3A for a 33F 10V capacitor). The capability limit of a low leakage solid capacitor is in the region of 0.01nA/FV; in terms of insulation resistance this equates to 100,000 megohm microfarads and in terms of resistivity to higher than 1016 ohm cm.钽电容的漏电流测量一般在室温、额定电压、3-5分钟后以专一的值表示。与选定的一般极限10nA/FV(例如：33F10V为3.3A) 做比较，可以分类为高漏电流或低漏电流。低漏电流电容的能力极限在0. 01nA/FV的范围内。用绝缘电阻的话，等于1000，000兆欧微法，相当于高于1016欧姆厘米电阻率。In any production batch there is a range of leakage current values extending from the region of 0.1nA/FV or lower, up through the selection limit. Those near or above this limit are removed on final test. The manufacturer needs a procedure for analyzing the causes of these rejects as well as for improving the general level of performance and for examining failures on life test and in the field. This paper outlines results obtained in such analyses.在任何一个产品批中，漏电流值的范围从0. 1nA/FV或更低，高到选定的极限值。那些接近或超过此极限值的产品在最后的测试中被剔除。制造商需要分析剔除的原因，并改善一般产品的性能，以及为寿命故障试验和生产现场制定一个程序。这篇文章概括了从这样的分析中得到的结果。Leakage Distribution漏电流分布情况A typical distribution of leakage currents within a production batch is shown in Fig. 1.在一个产品批内典型的；漏电流分布情况见图1：批能力极限选定的极限一批中的数量短路漏电流10nA/FV10.010.01 Figure 1. Batch distribution图1：批分布There is a lower limit below which no values occur; this is the capability limit for that particular anodedesign and production process. In a perfect batch all the leakage currents would cluster close to that limit. In practice there is a tail to the distribution, some capacitors being only slightly above the normal levels and others with values extending through to short circuits with resistance values down to below 10 ohms.漏电流有一个低的不能更低的极限值，这是具体阳极设计和生产工艺能力的极限。在一个理想的生产批中，所有漏电流会集中在此极限的周围。实际上，分布有一个尾状形，一些电容器只是稍高于正常水平，另一些的值扩大到电阻值低于10欧姆的短路。In order to understand leakage current behavior it is necessary to characterize the current at the capabilitylimit and then correct for this background level.为了理解漏电流的行为特征，有必要对能力极限时的漏电流的特性进行描述，然后，对该背景漏电流水平进行恰当的说明。As a simplifying assumption, it is suggested that the contributions to the total leakage current are essentially additive, and so once the capability level has been established for a batch, that amount can be deducted from the total. The behavior pattern of the residual component of the current can then be compared with known characteristics of typical current carrying mechanisms. This residual component will be called the “fault current” as it would not be present in a perfect capacitor free from any flaws in the dielectric or external insulation.作为一个简化的假设，建议把总的漏电流看成是各部分漏电流相加的。所以一旦一批产品的能力极限水平已经建立，各种漏电流的数量可以从总数中减去。然后余下的漏电流成分的行为方式可以与典型的电流运载机制已知特性相比较。其中余下的成分被成为“故障电流”，因为它在完好的电容器中不存在，流经介质或外绝缘的漏电流除外。Leakage Current Characteristics漏电流特性Even though it is normally quoted as such, leakage current is not one single value; it varies markedly withtime, voltage, and temperature, and also has a distinct history dependence (Fig. 2).尽管一般都这样引用，但是，漏电流不是孤立的值。它随时间、电压和温度有显著的变化，并且显然也与过去的情况有关（图2）。 10漏电流(A)13时间 （分）54210漏电流(A)1010.1温度 806040200.1漏电流(A)0.010.0011525电压 V0201510Figure 2. Typical plots of leakage current against time,voltage, and temperature图2 典型漏电流对时间、电压和温度的关系By relating these characteristics to known mechanisms, probable causes of high currents can be deduced.通过讲述这些已知机制，可以推导出高漏电流的原因。Effect of time时间的影响The plot of leakage current (I) against time (t) for the first 5 minutes of electrification can often be approximated as the sum of three components (a) the charging current (log I = A Bt); (b) a current which is inversely proportional to time (It = constant); and (c) a current which changes only slowly with time. The charging current drops logarithmically with time and is usually negligible after a few seconds except for the highest capacitance values. In any case, it can be calculated from the capacitance and the charging resistance and so allowed for in the analysis.充电5分钟漏电流（I）对时间(t)的图常常可以近似为3个成分的和：(a)充电电流（logI=A-Bt）,（b）一个反比于时间的电流(It=常数)，(c)一个随时间变化很慢的电流。充电电流以时间的对数下降；除非很高的电容量，一般在几秒钟后可以忽略不计。在任何情况下可以通过容量和充电电阻来计算，并且可以进行分析。Within any batch the It term tends to be similar from one capacitor to another. The fault current, which iswhat remains after deducting the charging current and the It current for the total leakage current, is the value which varies most between capacitors.在任何产品批中，It条件各个电容是相似的，扣除充电电流以后的故障电流以及总电流的It电流，不同的电容变化是最大的。When the time scale is extended beyond five minutes, it is seen that this residue is not actually constant; normally it slowly drops with time although, in some instances, it can increase. As a first approximation the leakage can be split into the two components for further analysis as in Fig. 3.当时间超过5分钟后，可以看出剩余部分并不是常数，一般随时间慢慢下降，在一些情况，它可能会增加。作为第一个近似值，漏电流可以分解成两个成分进一步分析，如图3所示：电流（F）47F35V1总漏电流It电流0.1故障电流0.01时间（分）1010.1Figure 3. Analysis of leakage/time plot图3：漏电流时间分析A simple addition to the leakage/time measurement throws up an immediate explanation of the It term. Ifat the end of the test period the power supply is short circuited, current flows back out of the capacitor, again obeying an It = constant relationship. This discharge current is of the same order as the It component of leakage current. In other words, that part is not a true leakage as it does not pass through the dielectric, only into it to be stored there. It is in effect dielectric absorption. For a really low “leakage current capacitor, almost all the current is stored in the dielectric ready to be released when the capacitor is shorted. This can be seen in Fig. 4.简单地添加一个漏电流 / 时间测量，立即产生一个It术语的说明，如果测试阶段结束时，将电源短路，电容从电容器中流回，再次服从It=常数关系。这些放电电流与漏电电流的It成分在同一数量级。换句话说，这一部分不是真正的漏电流，因为它并没有通过电介质，它只是储存在里面。它被介质有效地吸收。对一个真正的低“漏电流”电容器，几乎所有的电流储存在电介质中，当电容器短路时随时准备释放。这可以从图4中看到。充电It电流电流（A）0.1放电电流0.011时间（分）201050.1Figure 4. Comparison of currents图4： 充放电流比较The input of charge is terminated arbitrarily after five minutes, but the recovery of charge, the dischargecurrent, has no such truncation and is capable of flowing for extended periods. In order to make a strictcomparison of the quantity of charge flowing in the two directions, it would be necessary to integrate It from zero time to either the charge time or to infinity. However, such a calculation yields infinity for the charge! Obviously the It relationship cannot apply at either very short or very long times. If the shortest time for the integration is taken as an arbitrary figure of 10 seconds and the longest is either 300 seconds for charging or 1200 seconds for discharging, the quantity of current flowing in Figure 4 is 21 micro coulombs and 18 micro coulombs, respectively.充电输入在5分钟后很快就终止了。但是电流的恢复放电电流没有这样快断，并有能力流更长的时间。为了严格比较两个方向上的电量，有必要集中It从零时间到充电时间或到无穷大。但是这样计算产生无限的电荷！显然，It关系不适用于非常短或非常长时间。如果将最短集中时间武断地取为10秒，并充电最长取为300秒或放电为1200秒，图4中流过的电荷分别是21微库仑和18微库仑。It should be noted that the capability limit is when the fault current is negligible and all the current is due to this dielectric absorption effect. By choosing capacitors near the capability limit for the batch, the behavior of this component of the current can be determined with a fair degree of accuracy.必须注意的是，性能极限发生在故障电流被忽略，并且全部电流是由于受介质吸收的影响时。通过选择性能极限接近于此的该批电容器，此电流成分的行为特性可以在相当精确的程度上做出决定。Effect of Voltage电压影响From what is known already about dielectric absorption, it could be assumed that the discharge current isdirectly proportional to voltage. This has in fact been found to be true (Fig. 5)从已经知道的介质吸收，可以假设放电电流正比于电压，实际上从图5中已经发现真实的情况：放电电流（A）标准化电流（A）11150F16V16V8V0.10.14V2V标准化2-16V0.010.010.1110Figure 5. Effect of test voltage图5：测试电压的影响Generally, the fault current is more sensitive to voltage, increasing typically 100 to 1000 fold for a 10-fold voltage increase. This difference in voltage sensitivity can result in situations where the leakage at rated voltage is mainly due to the fault current while that at 0.1 x rated voltage is mainly dielectric absorption (Fig. 6).通常，故障电流对电压更敏感，电压增加10成，电流一般增加100-1000成。这种对电压敏感性的差别可以从这种场合得到：额定电压的漏电流主要是故障电流，而在0.1额定电压主要是介质吸收。（图6）。10图6电压敏感性分析漏电流总漏电流1DA(介质吸收)电流0.1故障电流0.010测试电压1UR0.80.60.40.2Unless the two components are separated, the true effect of voltage cannot be assessed.除非将两种漏电流分开，否则，不能对电压的真正影响做评估。Another aspect of voltage is the relationship to the rated voltage of the capacitor. In the measurements onour own product, the discharge current has been found to be lower in terms of nA/FV the higher the rated voltage. Data in support of this statement will be found in Table 1.另一面是电压对电容器额定电压的关系。在对我们自己的产品测试时发现，放电电流在额定电压较高时比nA/F条件为低。在表1中的数据可以支持此说法。Table 1. Effect of Time, Temperature, and Rated Voltage表1 时间、温度和额定电压的影响容量/电压放电电流（nA/FV）比率85/RT比率1m/5m室温851分钟5分钟1分钟5分钟1分钟5分钟室温8547/6.30.380.0846.40.7517958150/6.30.230.0433.60.45161058680/6.30.310.0613.50.461185868/100.170.0322.80.37161158220/100.200.0352.70.3414106810/160.150.0381.630.231164733/160.170.0381.590.189559150/160.220.0421.830.21855922/250.140.221.440.201096768/250.100.0160.790.084856968/250.110.0150.530.0545471068/250.150.0280.520.0544251068/250.150.0240.660.0604361110/350.0910.0170.560.063645910/350.0860.0170.480.057635822/350.0820.0170.330.03442510Effect of Temperature温度的影响The effect of temperature is complicated by significant deviations from the It = constant relationship athigh temperature (Fig. 7).温度的影响在高温时由于大大偏离It=常数的关系变得复杂化。（图7）10放电电流851图7：温度的影响200.1105时间（分）1Also the ratio of discharge current at 85 to that at room temperature decreases with increasing rated voltage (Table 1). Points to note in this Table are:1. The discharge current drops as the rated voltage increases2. The ratio between the 85 and the room temperature readings drops as the rated voltage increases(note, however, the wide range within the 25V batches)3. The ratio between the 1 minute and 5 minute readings at room temperature are close to 5 as expectedfrom It = constant4. The ratio between the 1 minute and 5 minute readings at 85 average about 8而且在85时，放电电流比率在室温下随额定电压的增加而减少(表1)。表中要指出的是：1、充电电流随额定电压的增加而下降。2、85和室温之间的读数比率随额定电压的增加而下降。（但是，注意，在25V这批产品中广泛存在这种情况）。3、在室温下，1分钟和5分钟的读数比率正像从公式It=常数所预期的，接近为5。4、在85下，1分钟和5分钟的读数比率平均大约为8。When this discharge current is used to split out the fault current components from the total leakage current, even wider variations in the temperature coefficient are found. This can be of great value in pinpointing causes of high leakage as it allows the true behavior pattern of the fault current to be determined.当这些放电电流从总的漏电流中分离出故障电流，可以发现温度系数平缓而宽的变化范围。在微秒的高漏电流因素中，这可能是有重要价值的，因为它使这种故障电流真正的行为方式得到确定。Causes of High Leakage Current高漏电流原因To summarize the position so far: A single valued leakage current is of no value for fault analysis The leakage current must be measured under a range of conditions of time, voltage, and temperature The leakage current must be corrected to remove the effect of dielectric absorption, which is a consistent property of all solid tantalum capacitors The dielectric absorption current can be estimated from the discharge current Unless the above correction is made, the true effect of the measurement conditions on the importantcomponent of the high current will be obtained到此为止要总结：一单值漏电流对故障分析是无价值的。漏电流必须在一定时间、电压和温度条件下测试。漏电流必须去掉介质吸收的影响加以纠正，这符合所有固体钽电容的情况。介质吸收电流可以从放电电流中估算出来。做了上述纠正，可以得到测量条件对高电流的重要影响。Although the study of the currents at the capability limit are very interesting from the scientific viewpoint,and although many more results are available for publication at some time, the main area of practical interest must be the fault current. This current could be through the bulk of the dielectric, through flaws in the dielectric, or in route bypassing the dielectric and bridging between the positive and negative contacts. Each of these paths could be further subdivided as in the following incomplete list:从科学的观点出发，虽然研究电流在能力极限这点上是非常有趣的。并且同时可以从发表的文章中得到更多的结果，但是特别有兴趣的主要领域是故障电流。此电流可以穿过介质的体积，通过介质中裂纹或者旁路通过介质，以及在正极和负极之间搭桥。这些成因的每一个可以进一步细分如下面的并不完全的清单：bulk effects semiconduction in the tantalum oxide due to heat treatments excess carriers due to previous reverse polarizationflaws impurity centers electrical breakdown sites mechanical damagebypassing manganese dioxide on anode wire conductive volatiles (usually moisture) flux residues本体(Bulk)的影响由于热处理在氧化钽中生成的半导体性。 由于先前保存的极化造成的超载流子。裂纹 杂质中心。 电击穿处。 机械损坏。旁路 钽丝上的二氧化锰。 传导挥发物（通常为潮汽）。 焊剂残余物。Some of these mechanisms have very definite characteristic behaviors. For instance a manganese dioxidebridge from the outer layers on the anode to the positive terminal wire gives an ohmic behavior; i.e., the fault current is directly proportional to voltage, is constant with time, and it has a low temperature coefficient (about 2-fold for 60 rise).其中的一些机制已经有非常明确的特性行为，例如从阳极外层到正端引线的二氧化锰桥给出欧姆级的行为，即故障电流正比于电压，不随时间变化，它有低的温度系数。（上升60大约为2-fold折）。Volatiles show up readily on a temperature plot. The current starts to rise, but above about 60 it begins todrop and usually finishes with a lower value at 85 than at room temperature (Fig. 8).挥发在温度曲线中可以容易地发现，电流开始上升，但是大约高于60开始下降，通常在85以较低值结束且比室温时低。（图8）图8 挥发的影响漏电流10.10.010.00111温度 806040200-20Cooling quickly down to room temperature drops the value even further. Cooling to sub-zero temperatures can also show sudden drops in leakage as the moisture path freezes, but there are practical difficulties with such testing. Flux residues can have some unusual, and as yet not understood, behavior. When this mechanism occurs in a metal cased capacitor, piercing a small hole in the can sometimes causes a high current to drop almost instantaneously to a low level. It is not clear whether this is due to a volatile material passing out through the hole or something going in to counteract the flux residues.快速冷却到室温使漏电流值进一步下降。冷却到0以下也可以显示漏电流的突然下降，因为潮汽通道冻结。但是做这种实验有实际的困难。焊剂残余可能有一些不寻常的的并且还未被理解的行为。当这种机制出现在金属包装的电容器时，在罐中刺一个小孔有时会引起高的电流下降，几乎瞬间达到一个低的水平。不清楚是否挥发材料穿出通过此孔或有一些进入去抵消此焊剂残余物。