钽电容器的技术概述和使用指南培训教材之五.doc

参考目录序号内容页码备注1钽和氧化铌电容器的技术概述和使用指南2引言2第一部分 电气特性和术语解释8第二部分 交流工作、波纹电压和波纹电流 24第三部分 可靠性和故障率计算34第四部分 钽和氧化铌电容器应用指引44第五部分 电容器的机械和热特性50第六部分 环氧树脂的可燃性52第七部分 产品的认证情况522片式钽电容器中的材料54附录1：摘自其它材料3钽电容器的一些知识55附录2：摘自其它材料4片式钽电容器的正确使用57附录3：摘自其它材料5钽电容器使用中的注意事项62附录4：摘自其它材料INTRODUCTION导言Tantalum capacitors are manufactured from a power of pure tantalum metal. The typical particle size is between 2 and 10 μm.钽电容器是由纯钽金属制成的一般钽粉颗粒的大小为2-10μmFigure below shows typical powders. Note the very greatdifference in particle size between the powder CVs/g.下面的图介绍了典型的钽粉。

注意各种比容粉颗粒大小有很大的差别4000μFV20000μFV 50000μFVFigure 1a. Tantalum powde图1a 钽粉Figure 1b. Niobium Oxide powder图1b 氧化铌粉The power is compressed under high pressure around a Tantalum wire (known as Riser Wire) to form a “pellet”. The riser wire is the anode connection to the capacitor.钽粉通过高压，压在钽丝（称为引出线）的周围，形成一个“钽块”，引出线是电容器阳极的接线This is subsequently vacuum sintered at high temperature (typically 1200-1800℃) which produces a mechanically strong pellet and drive off any impurities within the power. During sintering the power becomes a sponge like structure with all the particles interconnected in a huge lattice.接下来是在真空下的高温（一般为1200-1800℃）烧结，产生一种有机械强度、密度的钽块，并且驱除了钽粉中的所有杂质。

在烧结过程中，钽粉变成像海绵体一样的结构，所有颗粒在无限的格子内互相连接This structure is of high mechanical strength and density, but is also high porous giving a large internal surface area (see Figure 2)..该结构有高的机械强度和密度，但是也有高度的多孔性，在内部产生大的表面积（见图2）Figure 2. Sintered Anode图2 烧结后的阳极The larger the surface area the larger the capacitance. Thus high CV/g (capacitance voltage product per gram) powers, which have a low average particle size, are used for low voltage, high capacitance parts.表面积越大，容量就越大因此高比容（CV/g）（每克容量电压的乘积）的钽粉，具有小的平均颗粒尺寸，用在低压大容量的产品上。

By choosing which power and sinter temperature is used to produce each capacitance / voltage rating the surface area can be controlled. 通过选择钽粉和烧结温度，可以控制表面积，以产生各种不同容量 / 额定电压的产品The following example uses a 220μF 6V capacitor to illustrate the point.通过220μF，6V的电容器为例，来说明这一点C=(ε0εr A)/dWhere: ε0is the dielectric constant of free space(8.855×10-12 Farads/m)这里 ε0是自由空间的介质常数(8.855×10-12法拉/m) εris the relative dielectric constant =27×10-12 Farads/m for Tantalum Pentoxideεr是相对介质常数，对五氧化二钽（Ta2O5）=27×10-12法拉/m d is the dielectric thickness in metals.d 是金属介质的厚度C is the capacitance in FaradsC是容量，单位是法拉A is the surface area in metersA是金属的表面积Rearranging the equation gives:重新安排等式得到：A=Cd/ε0εrThus for a 220μF 6V capacitor the surface area is 346 square centimeters, or nearly one and half the size of the page.因此，对于一个220μF/6V的电容器，其表面积为346平方厘米，接近于一张半纸那样大。

The dielectric is then formed over all the Tantalum surface by the electrochemical process of anodization. To activate this the “pellet” is dipped into a very weak solution of phosphoric acid.The dielectric thickness is controlled by the voltage applied during the forming process. Initially the power supply is kept in constant current mode until the correct thickness of dielectric has been reached (that is the voltage reaches the “forming voltage”), it then switches to constant voltage mode and the current decays to close to zero.The chemical equations describing the process are as follows:通过对阳极进行电化学工艺的处理，在所有钽表面形成了介质，为了激化钽块，将它浸到非常稀的磷酸溶液中，介质厚度是通过形成（赋能）过程中施加电压的大小来控制的。

起初采用电源电流保持不变的模式，直到达到了正确的介质厚度为止（电压达到了“形成电压”）然后转换到电压不变的模式，电流衰减到接近为零为止，描述该过程的化学方程式如下：Tantalum Anode: 2Ta→2Ta5+ + 10e-钽阳极22Ta5+ + 10 OH-→Ta2O5 + 5H2ONiobium Oxide Anode:氧化铌阳极 2 NbO → 2 NbO3+ + 6 e-2 NbO3+ + 6 OH-→ Nb2O5 + 3 H2OCathode: 阴极：Tantalum:钽10 H2O – 10 e → 5H2 + 10 OH-NiobiumOxide:氧化铌6 H2O – 6 e- → 3H2 + 6 OH-The oxide forms on the surface of the Tantalum, but it also grows into the material. For each unit of oxide two third grows out and one third grows in. It is for this reason that there is a limit on the maximum voltage rating of Tantalum capacitors with present technology powers.The dielectric operates under high electrical stress. Consider a 220μF 6V part:在钽的表面形成氧化物，但是氧化物也在材料的内部生成。

一单位的氧化物，三分之二在外部生成，三分之一在内部生成这就是为什么现在技术的钽粉，在钽电容器的最大额定电压受到限制的原因介质在高的电场强度下工作举一个220μF6V的产品为例子：Forming voltage = Forming Ratio × Working Voltage形成电压 =形成比×工作电压= 3.5 × 6= 21 VotsThe pentoxide (Ta2O5) dielectric grows at a rate of 1.7×10-9m/V 五氧化二钽（Ta2O5）介质的生长率为1.7×10-9m/VDielectric thickness (d) =21×1.7×10-9=0.036μm介质厚度(d) Electric Field strength =Working Voltage /d=167KV/mm电场强度 =工作电压/d=167KV/mm每毫米16万七千伏Niobium Oxide:氧化铌：The niobium oxide (Nb2O5) dielectric grows at a rate of2.4 x 10-9 m/V氧化铌(Nb2O5)介质的生长率为2.4×10-9m/VDielectric thickness (d) = 21 x 2.4 x 10-9= 0.050 μm介质厚度(d) = 21 x 2.4 x 10-9= 0.050 μmElectric Field strength = Working Vo。