Long-Term Storage of Aluminum Electrolytic Capacitors Virginia Manor Rd Ste 290, Beltsville MD

Transcription

1 Lng-Term Strage f Aluminum Electrlytic Capacitrs Virginia Manr Rd Ste 290, Beltsville MD

2 What are Aluminum Electrlytic Capacitrs? Aluminum Electrlytic Capacitrs (als knwn as Al Caps) are ne f the ldest capacitr technlgies in use by the electrnics industry Al Caps cnsists f tw aluminum fils, ne cathde and ne ande, with a paper spacer infused with liquid electrlyte The tw fils and the spacer are stacked like a sandwich and then tightly wund int a rll The rll is placed inside an aluminum can and then sealed with a rubber (EPDM typically) r epxy bung 9000 Virginia Manr Rd Ste 290, Beltsville MD

3 What are Aluminum Electrlytic Capacitrs? (cnt.) The capacitance cmes frm a thin layer f aluminum xide frmed n the ande fil that has been etched/rughened The greater the degree f etching/rughness, the larger the surface area f the aluminum xide (Al2O3), the higher the capacitance The cathde fil als has an aluminum xide layer, but it is relatively insignificant and is designed t nt effect the cnductivity between the cathde fil and the electrlyte slutin 9000 Virginia Manr Rd Ste 290, Beltsville MD

4 Aluminum Oxide Frmatin The cathde film tends t be frmed in mist air Creates a prus xide, very lw electrical resistance, with a crystalline structure The ande film is frmed thugh immersin in an electrlyte slutin Fr lw vltage (less than 100V) capacitrs, electrlyte is typically a prprietary cmbinatin f water, ethylene glycl, weak rganic acids, and ther additives 9000 Virginia Manr Rd Ste 290, Beltsville MD

5 WARNING: Tradeff Alert! Capacitance is a functin f dielectric cnstant (e), dielectric area (A), and thickness (t) C = ε A t (fr Al-Caps, specifically C = 8.8e 8 A (in cm 2 ) t (in cm) ) Al 2 O 3 has a limited dielectric cnstant (see belw) Plyethylene, Plyprpylene, Plystyrene (Film Capacitrs): 2 3 Aluminum Oxide (Aluminum Capacitrs): 7 10 Tantalum Dixide (Tantalum Capacitrs): ~100 Barium Titanate (Ceramic Capacitrs): 1,000 10,000 but the etching and frming prcess can create a very thin (10 t 100 nm) cating with a large surface area (thusands f square centimeters) Tradeff Alert: The thinner the dielectric and the greater the degree f etching, the lwer the vltage breakdwn strength f the capacitr 9000 Virginia Manr Rd Ste 290, Beltsville MD

6 Why Al-Caps? Selectin f liquid Al-Caps vs ther capacitr types (ceramic, tantalum, plymer, film) tends t be driven by a cmbinatin f cst, vltage, capacitance, and ESR Liquid Al-Caps have sme f the highest capacitance f any capacitr technlgy They can prvide that capacitance at relatively lw cst and at relatively high vltage Capacitance is als relatively stable ver a range f vltages and temperature Equivalent series resistance (ESR) tends t be higher, but the impedance is stable as a functin f frequency 9000 Virginia Manr Rd Ste 290, Beltsville MD

7 ESR vs. Impedance 9000 Virginia Manr Rd Ste 290, Beltsville MD

8 Hw d Al-Caps Fail? Mst critical cmpnent in regards t limited lifetime Failure mde is typically evapratin f liquid electrlyte thrugh the rubber seal/stpper Evapratin predictin has been based n standard relatinship Dubling f lifetime with every 10C drp in temperature (nte: This is nt Arrhenius!) L x = L x 2 (T-Tx) /10 Hwever, there are variatins frm manufacturer t manufacturer in regards t this equatin 9000 Virginia Manr Rd Ste 290, Beltsville MD

9 Capacitr Lifetime Calculatins (Nichicn) Lr is rated lifetime Tr is rated temperature T is ambient temperature Ir is rated ripple current I is actual ripple current Dtr is the temperature rise due t rated ripple current Dt is the temperature rise due t actual ripple current a and K are cefficients L = L r 2 T r T 10 1 B n B n = 2 α I 2 r 2 T r T 30 I L = L r 2 T r T 10 2 α 1 I 2 r I 2 T r T 30 L = L r 2 T r T t r I r I K Miniature w/ ripple Miniature w/ ripple 2 Large can 9000 Virginia Manr Rd Ste 290, Beltsville MD

10 Capacitr Lifetime Calculatins (Nippn Chemi-Cn) Lr is rated lifetime Tr is rated temperature T is ambient temperature Ir is rated ripple current I is actual ripple current Dtr is the temperature rise due t rated ripple current Dt is the temperature rise due t actual ripple current A and Kv are cefficients L = L r 2 T r T 10 2 t 5 L = L r 2 T r T 10 2 t r t 5 L = L r 2 T r+5 T t A Miniature w/ ripple Miniature w/ ripple Kv Large can 9000 Virginia Manr Rd Ste 290, Beltsville MD

11 Capacitr Lifetime Calculatins (Rubycn) Lr is rated lifetime Tr is rated temperature T is ambient temperature Ir is rated ripple current I is actual ripple current Dtr is the temperature rise due t rated ripple current Dt is the temperature rise due t actual ripple current Vr is rated vltage V is actual vltage A and Kv are cefficients L = L r 2 T r T 10 2 t r t r L = L r 2 T r T 10 2 t r 10 t 10 V r V t t Miniature 2.5 Large can 9000 Virginia Manr Rd Ste 290, Beltsville MD

12 Capacitr Lifetime Calculatins (Panasnic/Sany) Lr is rated lifetime Tr is rated temperature Ta is cre temperature Ir is rated ripple current I is actual ripple current Dtr is the temperature rise due t rated ripple current Dt is the temperature rise due t actual ripple current Vr is rated vltage V is actual vltage A and Kv are cefficients L = L r 2 T r T a 10 All 9000 Virginia Manr Rd Ste 290, Beltsville MD

13 E-Cap Life Predictin Majr prblem: Like all limited life cmpnents, predictins are extraplated frm manufacturers ratings The basis f these ratings, lifetime and temperature, is nt always clear Issues Failure definitin can vary Lifetime can be with r withut ripple current Prbability f failure after lifetime is never defined (test t zer failures) Different appraches t extend lifetime Large vlume f electrlyte Higher biling pint electrlyte / lwer vapr pressure Better seal Ability t perate at lwer electrlyte vlumes Degradatin f seal due t temperature r temperature cycling is never addressed 9000 Virginia Manr Rd Ste 290, Beltsville MD

14 E-Cap Life Predictin (cnt.) A better apprach wuld be t establish a physics-based equatin derived frm Electrlyte biling pint Vlume f electrlyte Critical vlume Evapratin rate Embrittlement rate f rubber/plastic stpper Unfrtunately, mst capacitr manufacturers cnsider this infrmatin prprietary 9000 Virginia Manr Rd Ste 290, Beltsville MD

15 Hw d Aluminum Electrlytic Capacitrs Fail in Strage? Because f their cnstructin and the way they are manufactured, aluminum electrlytic capacitrs are especially susceptible t degradatin during strage (als knwn as shelf life) There are tw degradatin mdes in regards t lng-term strage f aluminum electrlytic capacitrs assembled t printed circuit bards. Electrlyte Evapratin Dielectric Disslutin Nte: Mdern electrlyte frmulatins are extremely stable and shuld nt experience any change in perfrmance ver reasnable strage times and temperature 9000 Virginia Manr Rd Ste 290, Beltsville MD

16 Electrlytic Evapratin Fr lw vltage capacitrs (apprximately less than 100V), the degradatin rate f this mechanism is the same whether the capacitr is charged r nt The apprximatin f 2X lifetime fr every 10C belw manufacturer s rating is still valid The different manufacturers frmulas theretically are all the same when vltage and ripple current g t zer It is very imprtant t nte that mst capacitr manufacturers will nt guarantee lifetimes beynd 15 years due t cncerns regarding degradatin f the stpper/bung 9000 Virginia Manr Rd Ste 290, Beltsville MD

17 Dielectric Disslutin The aluminum xide dielectric is frmed thrugh the applicatin f a vltage bias (als knwn as frming vltage) If there is n bias applied fr lng perids f time, the dielectric will slwly disslve back int the slutin due t dielectric plarizatin caused by impurities which exist in the aluminum frm manufacturing In this case, the time fr disslutin is much shrter than the rated lifetime Typically n mre than 1000 hurs at rated temperatures Virginia Manr Rd Ste 290, Beltsville MD

18 Prir Wrk There is very limited published data n strage lifetime f aluminum electrlytic capacitrs Greasn and Critchley, 1986, IEEE CHMT E. Wynne, 2002, Thesis Greasn identified leakage current up t 136X higher than the starting leakage current after 3000 hrs at 85C at lw vltage (1V applied n a 50V rated capacitr)) Wynne evaluated radial and axial capacitrs stred fr 10 years in an uncntrlled warehuse (40 t 140F) Measured leakage current, ESR, and capacitance f 28 samples frm each capacitr type All 56 capacitrs were within manufacturer s specificatins 9000 Virginia Manr Rd Ste 290, Beltsville MD

19 Strage Guidance frm United Chemi Cn After 1 year at 40C Capacitance drps by 2% Leakage current increases by apprximately 2X Tan delta stays the same After 2 years at 40C Capacitance drps by 5% Leakage current increases by apprximately 5X Tan delta stays the same 9000 Virginia Manr Rd Ste 290, Beltsville MD

20 Strage Guidance frm Nichicn Recmmends n mre than 2 years at 35C befre frming is required Hwever, its data claims n degradatin after 3 years Recmmends recnditin at rated vltage with 1kW resistr in series fr 30 minutes 9000 Virginia Manr Rd Ste 290, Beltsville MD

21 Strage Guidance frm Rubycn Prvides n guidance, but shws degradatin results frm shelf life test at 85C Fr 50V/10uF/5x11 capacitr 30% reductin in capacitance after 7000 hurs Stable leakage current after initial 1000 hurs 9000 Virginia Manr Rd Ste 290, Beltsville MD

22 Strage Guidance frm Hitachi N mre than 3 years at 35C 9000 Virginia Manr Rd Ste 290, Beltsville MD

23 Strage Guidance frm TDK/EPCOS 1000 hurs at maximum rated temperature At least tw years at 35C Sme mdel numbers can be stred up t 15 years (SIKOREL) 9000 Virginia Manr Rd Ste 290, Beltsville MD

24 Strage Guidance frm Crnell Dublier The fllwing time limits apply t shelf life at 35 C 60%RH fr all styles f CDE Aluminum Electrlytic capacitrs After 3 years, recmmend testing befre use t determine if refrming is required t meet leakage specificatins After 4 years, refrming is usually required befre use After 5 years, refrming is almst always necessary After 10 years, near r at end f useful shelf life Recmmend refrming prcedure Perfrmed at rm temperature with either a 10K hms (fr 75VDC) r 100K hms (abve 75VDC) resistr in series After reaching rated vltage, cntinue t apply rated vltage fr a minimum f 4 hurs Virginia Manr Rd Ste 290, Beltsville MD

25 Strage Guidance frm Kemet Frmerly RIFA These are higher vltage, higher capacitance capacitrs Mre fr industrial pwer applicatins Electrlyte tends t be slvent based, which is mre resistance t dielectric disslutin States 10 years at 40C withut the need fr recnditining 9000 Virginia Manr Rd Ste 290, Beltsville MD

26 Strage Guidance frm Panasnic After 12 mnths (temperature nt defined), recnditin at rated vltage with 1kW resistr in series fr 30 minutes 9000 Virginia Manr Rd Ste 290, Beltsville MD

27 Cnclusin Review f published literature indicates that there currently is a knwledge gap in regards t shelf life f aluminum electrlytic capacitrs Primarily in regards t dielectric disslutin As a general rule f thumb, literature suggests that mdern electrlytic capacitrs shuld be able t have a shelf life f three (3) years withut the need fr refrmatin Dielectric disslutin can almst always be reversed thrugh refrmatin 9000 Virginia Manr Rd Ste 290, Beltsville MD

28 Cnclusin (cnt.) The questins nt currently answered What is the effect f temperature n dielectric disslutin? Fr assembled capacitrs, hw t determine if the circuit wuld be sufficient t successfully refrm the capacitr? Fr assembled capacitrs, what is the maximum leakage current befre the system culd be damaged during pwer up? 9000 Virginia Manr Rd Ste 290, Beltsville MD

29 Disclaimer & Cnfidentiality ANALYSIS INFORMATION This reprt may include results btained thrugh analysis perfrmed by DfR Slutins Sherlck sftware. This cmprehensive tl is capable f identifying design flaws and predicting prduct perfrmance. Fr mre infrmatin, please cntact sales@dfrslutins.cm. DISCLAIMER DfR represents that a reasnable effrt has been made t ensure the accuracy and reliability f the infrmatin within this reprt. Hwever, DfR Slutins makes n warranty, bth express and implied, cncerning the cntent f this reprt, including, but nt limited t the existence f any latent r patent defects, merchantability, and/r fitness fr a particular use. DfR will nt be liable fr lss f use, revenue, prfit, r any special, incidental, r cnsequential damages arising ut f, cnnected with, r resulting frm, the infrmatin presented within this reprt. CONFIDENTIALITY The infrmatin cntained in this dcument is cnsidered t be prprietary t DfR Slutins and the apprpriate recipient. Disseminatin f this infrmatin, in whle r in part, withut the prir written authrizatin f DfR Slutins, is strictly prhibited. Frm all f us at DfR Slutins, we wuld like t thank yu fr chsing us as yur partner in quality and reliability assurance. We encurage yu t visit ur website fr infrmatin n a wide variety f tpics. T help us cntinually imprve, please send any feedback r cmments t is@dfrslutins.cm. Best Regards, Dr. Craig Hillman, CEO 9000 Virginia Manr Rd Ste 290, Beltsville MD