EIA ECA-797-2014 Aluminum-Electrolytic Capacitor Application Guideline.pdf

1、 EIA STANDARD Aluminum-Electrolytic Capacitor Application Guideline EIA/ECA-797 August 2014 EIA/ECA-797 ANSI/EIA-797 Approved: August 7, 2014 NOTICE EIA Engineering Standards and Publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and pu

2、rchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for his particular need. Existence of such Standards and Publications shall not in any respect preclude any member or nonmember of ECIA

3、from manufacturing or selling products not conforming to such Standards and Publications, nor shall the existence of such Standards and Publications preclude their voluntary use by those other than ECIA members, whether the standard is to be used either domestically or internationally. Standards and

4、 Publications are adopted by ECIA in accordance with the American National Standards Institute (ANSI) patent policy. By such action, ECIA does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties adopting the Standard or Publication. This EIA Standard i

5、s considered to have International Standardization implication, but the International Electrotechnical Commission activity has not progressed to the point where a valid comparison between the EIA Standard and the IEC document can be made. This Standard does not purport to address all safety problems

6、 associated with its use or all applicable regulatory requirements. It is the responsibility of the user of this Standard to establish appropriate safety and health practices and to determine the applicability of regulatory limitations before its use. (From Standards Proposal No. 5257, formulated un

7、der the cognizance of the P-2.2 Committee on Paper, Film, Mica, and Wet Electrolytic Capacitors Standards). Published by Electronic Components Industry Association 2014 Engineering Department 2214 Rock Hill Road, Suite 265 Herndon, VA 20170 PLEASE! DONT VIOLATE THE LAW! This document is copyrighted

8、by the ECIA and may not be reproduced without permission. Organizations may obtain permission to reproduce a limited number of copies through entering into a license agreement. For information, contact: IHS 15 Inverness Way East Englewood, CO 80112-5704 or call USA and Canada (1-877-413-5184), Inter

9、national (303-397-7956) iCONTENTS Page Foreword v Clause 1 Introduction 1 1.1 Aluminum-electrolytic construction 1 1.1.1 Overview 1 1.1.2 Etching 2 1.1.3 Forming 2 1.1.4 Slitting 3 1.1.5 Winding 3 1.1.6 Connecting terminals 3 1.1.7 Impregnation 4 1.1.8 Sealing 4 1.1.9 Aging 5 1.2 Comparison to other

10、 types of capacitors 5 1.2.1 Ceramic capacitors 5 1.2.2 Film capacitors 6 1.2.3 Tantalum capacitors 6 1.2.3.1 Solid 6 1.2.3.2 Wet 7 2 Characterization 7 2.1 Circuit model 7 2.2 Primary parameters 8 2.2.1 Temperature range 8 2.2.1.1 Operating temperature range 8 2.2.1.2 Storage temperature range 9 2.

11、2.2 Rated capacitance 9 2.2.2.1 Capacitance tolerances 9 2.2.2.2 Capacitance method of measurement 9 2.2.2.3 Capacitance temperature characteristics 9 2.2.2.4 Capacitance frequency characteristics 9 2.2.3 Dissipation factor 9 2.2.3.1 Dissipation factor method of measurement 10 2.2.3.2 Dissipation fa

12、ctor temperature characteristics 10 2.2.3.3 Dissipation factor frequency characteristics 10 2.2.4 Equivalent series resistance (ESR) 10 2.2.4.1 Equivalent series resistance method of measurement 10 2.2.4.2 Equivalent series resistance temperature characteristics 10 2.2.4.3 Equivalent series resistan

13、ce frequency characteristics 11 2.2.5 Impedance 112.2.5.1 Impedance method of measurement 11 2.2.5.2 Impedance temperature characteristics 11 2.2.5.3 Impedance frequency characteristics 12 2.2.6 DC leakage current 12 2.2.6.1 DC leakage current method of measurement 12 2.2.6.2 DC leakage current temp

14、erature characteristics 12 2.2.6.3 DC leakage current voltage characteristics 13 2.2.7 Voltage 13 2.2.7.1 Rated DC voltage 13 2.2.7.2 Rated surge voltage 13 2.2.7.2.1 Surge-voltage method of measurement 13 CONTENTS (continued)ii 2.2.7.3 Reverse voltage 13 2.2.7.4 Transient overvoltage 13 2.2.8 Rippl

15、e current 14 2.2.8.1 Ripple current method of specification 14 2.2.8.2 Ripple current temperature characteristics 14 2.2.8.3 Ripple current frequency characteristics 15 2.3 Secondary parameters 152.3.1 Inductance 15 2.3.2 Low-temperature impedance 15 2.3.3 Self-resonant frequency 152.3.4 Dielectric

16、absorption 15 2.3.5 Insulation and grounding 16 2.4 Mechanical the dielectric is the insulating aluminum oxide on the anode foil; the true negative plate is the conductive, liquid electrolyte, and the cathode foil merely connects to the electrolyte. This construction delivers colossal capacitance be

17、cause etching the foils can increase surface area more than 100 times and the aluminum-oxide dielectric is less than a micrometer thick. Thus the resulting capacitor has very large plate area and the plates are awfully close together. These capacitors routinely offer capacitance values from 0.1 F to

18、 3 F and voltage ratings from 5 V to 500 V. They are polar devices, having distinct positive and negative terminals, and are offered in an enormous variety of styles which include molded and can-style SMT devices, axial- and radial-leaded can styles, snap-in terminals styles and large-can, screw-ter

19、minal styles. Representative capacitance-voltage combinations include: a) 330 F at 100 V, 1000 F at 50 V and 6800 F at 10 V for SMT devices; b) 100 F at 450 V, 6,800 F at 50 V and 10,000 F at 10 V for miniature-can styles; c) 1200 F at 450 V and 39,000 F at 50 V for snap-in can styles; d) 9000 F at

20、450 V and 390,000 F at 50 V for large-can screw-terminal styles. If two, same-value, aluminum electrolytic capacitors are connected in series, back-to-back with the positive terminals or the negative terminals connected, the resulting single capacitor is a nonpolar capacitor equal in capacitance to

21、half the capacitance of either of the original pair at rated voltage. See 3.5 for more on nonpolar capacitors. Figures 1-3 show typical nonsurface-mount aluminum electrolytic capacitor constructions. Figure 1 Miniature, radial-leaded type capacitor Figure 2 Snap-in type capacitor EIA/ECA-797 Page 2

22、a) Conventional construction b) Pitchless construction Figure 3 Large-can, screw-terminal type capacitors 1.1.2 Etching The anode and cathode foils are made of high purity, thin aluminum foil, 0.02 mm to 0.1 mm thick. To increase the plate area and the capacitance, the surface area in contact with t

23、he electrolyte, is increased by etching the foils to dissolve aluminum and create a dense network of billions of microscopic tunnels penetrating the foil. Etching involves pulling the aluminum foil on rollers through a chloride solution while applying an AC, DC or AC-and-DC voltage between the etch

24、solution and the aluminum foil. Surface area can increase as much as 100 times for foil in low-voltage capacitors and 20 to 25 times for high-voltage capacitors. 1.1.3 Forming The anode foil carries the capacitors dielectric. The dielectric is a thin layer of aluminum oxide, Al2O3, that is chemicall

25、y grown on the anode foil during a process called “formation.” Formation is accomplished by pulling the anode foil on rollers through an electrolyte bath and continuously applying a DC voltage between the bath and the foil. The voltage is 135% to 200% of the final capacitors rated voltage. The thick

26、ness of the aluminum oxide is about 1.4 nm to 1.5 nm for each volt of the formation voltage, e.g., the anode foil in a 450 V capacitor may get a formation voltage in excess of 600 V and have an oxide thickness of about 900 nm. Thats less than a hundredth the thickness of a human hair. Formation redu

27、ces the effective foil surface area because the microscopic tunnels are partially occluded by the oxide. The tunnel etch pattern is adjusted by choice of foil and etching process so that low-voltage anodes have dense tunnel patterns compatible with thin oxide and high-voltage anodes have coarse tunn

28、el patterns compatible with thick oxide. The cathode foil is not formed and it retains its high surface area and dense etch pattern. 1.1.4 Slitting EIA/ECA-797 Page 3 Foil is etched and formed in jumbo rolls of 40 cm to 50 cm wide and then slit into various widths according to the lengths of the fin

29、al capacitors. 1.1.5 Winding The capacitor element is wound on a winding machine with spindles for one-to-four separator papers, the anode foil, another set of one-to-four separator papers and the cathode foil. These are wound into a cylinder and wrapped with a strip of pressure-sensitive tape to pr

30、event unwinding. The separators prevent the foils from touching and shorting, and the separators later hold the reservoir of electrolyte. Before or during winding aluminum tabs are attached to the foils for later connection to the capacitor terminals. One method is by cold-welding of the tabs to the

31、 foils. The tab locations are microprocessor controlled during winding so that the capacitor elements inductance can be less than 2 nH. Another method of attachment is by staking. This is a process of punching the tab through the foil and folding down the punched metal. There is some evidence that c

32、old welding reduces short-circuit failures and performs better in high-ripple current and discharge applications. Wound-capacitor elements are shown in figure 4. Figure 4 Wound capacitor elements 1.1.6 Connecting terminals In SMT capacitors and miniature capacitors with rubber-bungs, extensions of t

33、he tabs are the capacitor terminals. But in large-can capacitors like snap-ins and screw-terminal styles, the tabs are riveted or welded on the underside of the capacitor tops to terminal inserts. Welding produces the lowest contact resistance and highest current handling. Both resistive welding and

34、 ultrasonic welding are used. The up to 12 tab pairs that may be used in large screw-terminal capacitors often require more mechanical support during assembly so the tabs in such capacitors may be both riveted to post extensions on the terminals and then welded. In an axial-lead capacitor the cathod

35、e tab is welded to the can before sealing. EIA/ECA-797 Page 4 1.1.7 Impregnation The capacitor element is impregnated with electrolyte to saturate the paper separators and penetrate the etch tunnels. The method of impregnation may involve immersion of the elements and application of vacuum-pressure

36、cycles with or without heat or, in the case of small units, just simple absorption. The electrolyte is a complex blend of ingredients with different formulations according to voltage and operating temperature range. The principal ingredients are a solvent and a conductive salt a solute to produce el

37、ectrical conduction. Common solvents are ethylene glycol (EG), dimethylformamide (DMF) and gammabutyrolacetone (GBL). Common solutes are ammonium borate and other ammonium salts. EG is typically used for capacitors rated 20 C or 40 C. DMF and GBL are often used for capacitors rated 55 C. Capacitor-e

38、lement materials are shown in figure 5. Figure 5 Capacitor-element materials Water in the electrolyte plays a big role. It increases conductivity thereby reducing the capacitors resistance, but it reduces the boiling point so it interferes with high temperature performance, and it reduces shelf life

39、. A few percent of water is necessary because the electrolyte maintains the integrity of the aluminum oxide dielectric. When leakage current flows, water is broken into hydrogen and oxygen by hydrolysis. The oxygen is bonded to the anode foil to heal leakage sites by growing more oxide. The hydrogen

40、 escapes by passing through the capacitors rubber seal. 1.1.8 Sealing The capacitor element is sealed into a can. While most cans are aluminum, phenolic cans are often used for motor-start capacitors. In order to release the hydrogen the seal is not hermetic. The seal is usually a pressure closure m

41、ade by rolling the can edge into a rubber gasket, a rubber end-plug or into rubber laminated to a phenolic board. In small capacitors molded phenolic resin or polyphenylene sulfide may replace the rubber. Too tight a seal causes pressure build up, and too loose a seal shortens the life by permitting

42、 drying out, loss of electrolyte. EIA/ECA-797 Page 5 1.1.9 Aging Here the capacitor assembly comes full circle. The last manufacturing step is “aging” during which a DC voltage greater than the rated voltage but less than the formation voltage is applied to the capacitor. Usually the voltage is appl

43、ied at the capacitors rated temperature, but other temperatures and even room temperature may be used. This step also reforms the cut edges and any damaged spots on the anode foil and covers any bare aluminum with aluminum oxide dielectric. Aging acts as burn-in and reduces or eliminates early life

44、failures (infant mortals). Low, initial DC leakage current is a sign of effective aging. 1.2 Comparison to other types of capacitors 1.2.1 Ceramic capacitors Ceramic capacitors have become the preeminent, general-purpose capacitor, especially in SMT chip devices where their low cost makes them espec

45、ially attractive. With the emergence of thinner-dielectric, multilayer units with rated voltages of less than 10 V capacitance values in the hundreds of microfarads have become available. This competes with traditional, high-capacitance aluminum electrolytic capacitors. Ceramic capacitors are availa

46、ble in three classes according to dielectric constant and temperature performance. Class 1 (NPO, COG) is suitable for low capacitance, tight tolerance applications in the range of 1 pF to a few mF. Class 2 (X7R) has 20 times to 70 times as much capacitance per case size, but capacitance typically va

47、ries about 10% over its 55 C to + 125 C temperature range. The maximum change is 15 %. Class 3 (Y5V) with about 5 times the capacitance of class 2 has wild swings of capacitance with voltage and temperature. The temperature range is 30 C to + 85 C, and capacitance varies about + 20%, 65% over the ra

48、nge. Ceramic chip capacitors are brittle and sensitive to thermal shock, so precautions need to be taken to avoid cracking during mounting, especially for high-capacitance large sizes. The typical temperature range for aluminum electrolytic capacitors is 40 C to + 85 C or 105 C. Capacitance varies a

49、bout + 5%, 40% over the range with the capacitance loss all at cold temperatures. Capacitors rated 55 C generally only have 10 % to 20 % capacitance loss at 40 C. Cold temperature performance for rated voltages of 300 V and higher is often worse, and temperature performance varies by manufacturer. Thus class 1 and 2 ceramic capacitors perform better than aluminum electrolytic capacitors at cold temperatures, and class 3 ceramic capacitors perform worse at all temperatures. Aluminum electrolytic capacitors readi