MSB660 36.8 MSB665 Pulse Load Multilayer Ceramic Capaci
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Pulse Load Multilayer Ceramic Capacitors
Introduction
General introduction Multilayer Ceramic Capacitors (MLCCs) increasingly being used applications which electrical load becomes critical. This publication particularly concerned with susceptibility MLCCs electrical fields electrical fields various frequencies, pulse loads resistance these types load important application areas such automotive lighting switched-mode power supplies. elevated temperatures some applications adds further demands. This application note presents typical data that help application engineer selecting optimal product. present general rules concerning immunity given electrical loads. MLCC insulation resistance used criterion check immunity against given electrical load. data, however, relevant applications recommend that customers application questionnaire Annex, special questions. Before going into details various tests, present some general information important proper understanding various failure mechanisms. First shall describe MLCC construction present structural parameters that determine resistance electrical breakdown. Three types breakdown mechanism then discussed: dielectric breakdown, electro-thermal breakdown electro-mechanical breakdown. Construction MLCC comprises several layers non-fired stacked ceramic foils which electrode material printed. These foils pressed sintered obtain compact multilayer structure. capacitance MLCC depends capacitive area each electrode (Ae), number inner electrodes (Ne), thickness ceramic dielectric relative dielectric constant ceramic material
MLCCs series with given rated voltage have related minimum dielectric thickness. dielectric thickness greatest high-voltage products also larger low-capacitive MLCCs general. Figure shows typical construction. electrical load will give rise electric field across dielectric well across various creepage paths (margins). three types margin are: margin, side margin cover layer thickness (see Fig.1). magnitude these margins great compared with dielectric thickness. Hence only dielectric layers form potential breakdown pathway.
margin cover layer thickness dielectric thickness
side margin
CONTENTS Introduction load load Pulse load pulses Automotive pulses Surge pulses ANNEX Application Questionnaire
inner electrodes ceramic material
MSB651
terminations
Fig.1
Construction ceramic multilayer capacitor
Dielectric breakdown MLCC show dielectric breakdown very strong field strengths. component fail because limited intrinsic dielectric strength ceramic material. This failure mechanism related only quality ceramic dielectric material also dielectric thickness (the field strength inversely proportional area dielectric. With actual MLCC constructions given voltage series referred above), there simple relation between dielectric breakdown capacitance. lower capacitances, larger dielectric thickness higher total effective capacitive surface have opposing effects dielectric breakdown voltage. Electro-thermal breakdown High local temperatures caused power dissipation result electro-thermal breakdown. ambient temperature important factor here. Additionally, electro-thermal breakdown influenced heat generated inside MLCC heat flow surroundings. heat generated inside MLCC depends dissipation factor (which function temperature, frequency, voltage construction), voltage amplitude, voltage-time relation (e.g. frequency load) capacitance.
heat flow surroundings MLCC take place conduction, radiation convection. depends MLCC geometry, thermal conductivities various materials (ceramic, terminations, solder, print board material), flow, radiation, temperature gradients heat-transfer coefficients. special type electro-thermal breakdown occur when voltage difference between terminations high enough cause discharges (corona). These discharges outer surface MLCC lead high local currents that destroy regions MLCC itself (`burning spots'). Factors influencing this are: form electrodes. Sharp points result high electrical field gradients which damaging. Sharp points result soldering. humidity surface condition (presence conductive surface contamination, e.g. from human skin). distance between terminations. This distance increases order 0402 0603 0805 1206 1210 1808 1812 Electro-mechanical breakdown When piezoelectric materials exposed electric field they deformed. This become known inverse piezoelectric effect. polycrystalline ferroelectric materials, used Phycomp type MLCCs (dielectric Y5V), below Curie point crystallites take tetragonal symmetry. charge sites coincide, resulting electric dipoles. material said composed Weiss domains. Within Weiss domain, dipoles aligned, giving dipole moment domain. directions polarization between neighbouring domains within crystallite differ 180°. Exposing material strong electric field below Curie point will result growth domains most nearly aligned with field expense other domains. material will also lengthen direction field. this change dimension takes place slowly, resulting stresses material relaxed. However, fast field changes, i.e. high dV/dt other words high currents, stresses exceed critical threshold value result electro-mechanical breakdown. Electro-mechanical breakdown ferro-electric properties ceramic material does occur MLCCs with type ceramic material (NP0).
Power dissipation general equation power dissipation upon stressing MLCC with fields ^CV2RMStan
thermal equilibrium, power generated inside MLCC equals heat transferred environment. This means that Rth.
Note that maximum load equivalent voltage rating, which usually times lower. first case, breakdown levels refer behaviour ambient temperatures, while voltage rating MLCC determined behaviour elevated temperatures (maximum specified temperature both type MLCCs) over extended periods (1000 times rated voltage) order meet international CECC requirements.
(DC) (kV)
MSC950
MSC952
(DC) (kV)
which thermal resistance heat transfer environment conduction, radiation convection temperature rise MLCC From equations follows that temperature rise MLCC caused load voltage given frequency will, theory, proportional V2RMS. This been found type MLCCs, type MLCCs, which function only frequency also applied voltage temperature.
10-1
(nF)
Fig.4
instant breakdown voltage function capacitance, rated voltage size MLCCs. Curves through cumulative defect points given
MSC953
load
MLCC loaded increasing voltages will finally break down because limited dielectric strength. This failure mechanism been treated preceding chapter. Figures present experimental data instant breakdown voltage. these figures, exposure time about Breakdown after prolonged exposure will somewhat lower. Corona effects occur higher voltage levels, especially when testing smaller sized products such 0603 0805. Typical breakdown voltages products with rated voltage above above products. type products with construction comparable type products turn have superior immunity. expected, immunity better products with large dielectric thickness. This case high-voltage products (rated voltage kV), because their construction, also case capacitive products general. Fig.3 Comparable sometimes improved breakdown voltages reached larger product sizes (1812 compared with 1206), capacitance, dielectric thickness type ceramic material same. Additionally, avoid corona effects advisable MLCCs with larger termination separation lengths 1812 1808 1206), especially when using lowcapacitance MLCCs. Fig.2
10-1
(pF)
cumulative survival
instant breakdown voltage function capacitance, rated voltage size MLCCs. Curves through cumulative defect points given
MSC951
cumulative survival
(DC) (kV)
Fig.5
Typical instant breakdown voltage curves MLCCs. nF/1206/50 nF/1206/50 pF/1206/50 pF/1206/500 nF/1808/1
load
(DC) (kV)
immunity levels presented below specified represent typical values. breakdown observed strong drop insulation resistance. voltage level used indicator only, because related. Figures show breakdown curves function MLCC capacitance. There very close correspondence between data presented here immunity data presented previous chapter.
Typical instant breakdown voltage curves MLCCs. pF/0805/200 nF/1206/50 nF/1812/50 pF/1206/500 pF/1812/3 pF/1808/3
Also here, increased immunity found lower capacitance MLCCs higher rated voltages. type MLCCs comparable construction superior type MLCCs. Figures show breakdown levels function frequency. instant breakdown curve function frequency divided into regions: frequencies (below roughly kHz), breakdown level nearly independent frequency. Breakdown occurs because limited dielectric strength ceramic material possibly because electro-mechanical effects. instant breakdown level about instant breakdown level. frequencies roughly above kHz, breakdown occurs decreasing voltage levels because energy dissipation. Figure shows temperature rise function voltage higher frequencies 0805 MLCCs. temperature rise MLCCs less than that MLCCs under same conditions. This lower loss factor capacitors. Note that types, temperature rise more less proportional frequency square voltage given equations (3). temperature rise types deviates from this behaviour. data suggests that decreases with temperature applied field which indeed been found types. Note: both loads, higher rated voltage MLCCs (200 generally recommended instead standard products.
Vbr(RMS) (kV)
MSC954
Vbr(RMS) (kV)
MSC955
VBR,rms (kV)
MSC958
Pulse load
This section discusses immunity MLCCs various types transient. Three different groups transient considered: rise-time fast slow energy level (µJ-mJ) medium (1-10 high (1-100 relevant test automotive pulses surge tests
10-1
(pF)
(Hz)
Fig. instant breakdown voltage function capacitance, rated voltage size MLCCs. frequency: Curves through cumulative defect points given
VBR,rms (kV)
MSC956
slow (0.1-10
VBR,rms (kV)
MSC959
various pulses cover whole spectrum from fast low-energy pulses slow high-energy pulses. pulses Electrostatic Discharge (ESD) persons electricallyloaded objects well known threat optimal behaviour electronic equipment.
(Hz)
(Hz) Fig. instant breakdown voltage function frequency MLCCs. Curves through cumulative defect points given. 0805, 1206
VBR,rms (kV)
MSC957
temperature rise
MSC960
Nowadays, equipment brought onto market, into operation already production countries within European Union must comply with (ElectroMagnetic Compatibility) requirements both emission immunity. immunity requirements concerns ESD. Although there such requirement components, their behaviour will influence behaviour equipment which they operate. immunity MLCCs pulses well characterized. Tests were therefore performed analyze effect these fast low-energy pulses. Pulse tests were performed according standards: MIL-STD 883C (Human Body Model) UZW-BO/FQ-B302 (Machine Model) developed Philips. These standards were originally developed testing semiconductors have adapted test methods make them suitable MLCCs. tests were performed adapted Verifier test apparatus. MLCCs soldered onto substrates were subjected positive pulses test run. These pulses were applied direct contact rather than discharge. discharging step, specified original standards, added between each pulse. (Negative pulses were applied owing apolarity MLCCs). When subjected pulses, low-capacitance MLCCs sometimes exhibited corona effects without internal damage. these cases, products were immersed (Dow Corning fluid 550) obtain immunity data.
(Hz)
0805 0805 (Vrms)
10-1
(pF)
Fig. instant breakdown voltage function frequency MLCCs. Curves through cumulative defect points given. 0805, 1206
Fig.6
instant breakdown voltage function capacitance, rated voltage size MLCCs. frequency: Curves through cumulative defect points given
Fig.10 Example MLCC temperature rise function voltage 0805 MLCCs
Human Body Model pulses according MIL-STD 883C. These pulses simulate discharge electricallyloaded human body using discharge circuit with capacitor resistance inductance (not specified standard derived from pulse characteristics). Figure shows typical pulse form. pulse rise time less than delay time peak current 1.25 (short circuit) (short circuit). caused ringing must less than peak current. voltage level Fig.12 immunity been given type MLCCs tested according MIL-STD 883C standard.
MSB660
Machine Model pulses according Philips standard UZW-BO/FQ-B302. These pulses simulate discharge electricallyloaded machine using discharge circuit with capacitor resistance only inductance (not specified standard, derived from pulse characteristics). typical pulse form presented Fig.13. calibration-current waveform charged voltage first peak current damping Ip1/Ip2 1.4. resonant frequency MHz. voltage level
MSB662
MSC962
voltage (kV)
25/50
Single pulses, pulse typical pulse form given Fig.15(a). vehicle power supply voltage rise time general pulse voltage -100 (pulse -200 (pulse +100 (pulse pulse duration cycle time number pulses 5000 higher. Pulse train, pulse typical pulse form given Fig.15(b). vehicle power supply voltage rise time pulse voltage +100 (pulse +200 (pulse -150 (pulse -200 (pulse pulse duration cycle time pulse train duration (100 pulses). delay time duration test hour longer (36000 pulse trains).
MSB664
10-1
(pF)
Fig.14 Experimental data immunity MLCCs based Machine Model pulses according Philips standard UZW-BO/FQB302. Size 0805 1206
36.8
(ns)
Automotive pulses Other pulses relevant MLCC applications so-called automotive pulses. Compared with pulses, treated previous section, these pulses characterized slower rise times higher energies. Automotive pulses generally characterized international standards 40839, ISO/TR 7637/1 J1113. immunity tests these standards aimed determining ability various electrical devices withstand transients that normally occur motor vehicles. Transients added standard electrical voltage caused, example, release stored energy during start turn vehicles. These general tests, MLCCs only. defects were found after testing products with minimum rated voltage size 1206 larger. This concerns test pulses mentioned various standards. With exception offset Fig.15), these pulses were produced with Schaffner 500/B14 pulse generator. maximum absolute value peak voltage mentioned standard documents single pulses pulse trains. tests were able over stress samples level average dV/dt V/µs, without failure. automotive pulses according 40839 part ISO/TR 7637/1 J1113 characterized follows:
Fig.13 Typical pulse based Machine Model according standard UZW-BO/FQ-B302 developed Philips Figure gives data immunity type MLCCs tested according Machine Model standard. Several types products ceramic were measured. products were resistant least pulses. 0805 1206 products showed same behaviour. advantage high-voltage products (rated voltage clear when comparing data with data since higher immunity levels obtained high-voltage products.
MSB665
Fig.11 Typical pulse based Human Body Model according MIL-STD
voltage (kV)
MSC961
MSB666
50/200
25/200
10-1
(pF)
Fig.12 Experimental data immunity MLCCs size 0805 1206 based Human Body Model pulses according MILSTD 883C
experimental data presented Figs show that energy dissipation highest (and breakdown voltage level lowest) when tested MLCC capacitance close capacitance discharge circuit. This line with model calculations. Moreover, figures show that data seems shifted somewhat higher capacitance values compared with data. This voltage-dependent capacitance products, which causes lowering capacitance higher voltage levels. Additionally, immunity products found lower than that products with same capacitance rated voltage.
Fig.15 Automotive pulses. single pulses, pulses pulse train, pulses
Surge pulses Surge pulses high-energy pulses caused switching inductive capacitive loads less importance multilayer capacitors) lightning. standardized pulse so-called 1.2/50 surge pulse. pulse rise time roughly comparable single automotive pulses treated above. pulse duration voltage level, much higher than voltage level used automotive pulses. 1.2/50 surge pulses standardized according 1000-4-5. called 1.2/50 pulses given with typical pulse form shown Fig.16. front time equals 1.67 time half value voltage ranges from pulse repetition frequency products rated voltage size 1206, products rated voltage size 0805, 1206 1812 were treated with 1.2/50 surge pulse. pulses were generated TEST immunity-test generator. Figures give surge immunity level products referred function capacitance dielectric thickness respectively. Long-term treatment expected result somewhat lower immunity levels. usual picture arises from initial breakdown experiments, also seen after load i.e. higher immunity levels obtained lower capacitance products, higher rated voltage MLCCs (greater dielectric thickness), products compared with products with identical dielectric thickness.
MSB667
ANNEX Application Questionnaire Pulse Testing MLCCs
have found clear relationship between breakdown peak voltage dielectric thickness measured products.
surge breakdown level (kV)
MSC963
Please complete much detail can.
General Capacitance: Tolerance: Rated voltage Application Termination: Dielectric material: Size: AgPd/NiSn NP0/X7R
Maximum peak voltage: Maximum peak-to-peak voltage: Maximum voltage: Maximum peak current: Maximum peak-to-peak current: Frequency (main period) Voltage waveform
Starting intermittent .Vp-p .VRMS .Ip-p
Continuous operation .Vp-p .VRMS .Ip-p Current waveform
10-2
10-1
(nF)
Fig.17 Instant breakdown peak voltage function capacitance products treated with 1.2/50 surge pulses. products: rated voltage size 1206; products: rated voltage sizes 0805, 1206 1812. straight line shows result linear combined data
surge breakdown level (kV)
MSC964
Pulse application Automotive pulses according 40839 pulse number: 1/2/3a/3b .voltage level: pulses according MIL-STD 883C Human Body Model number pulses: .voltage level: pulses according Machine Model number pulses: .voltage level: Surge pulses according 1000-4-5, type 1.2/50 number pulses: .voltage level: General number pulses: .maximum dV/dt: .V/µs maximum current: maximum dI/dt: .A/µs Climatic requirements Ambient temperature: .minimum
dielectric thickness (mm)
Average
maximum
Fig.18 Instant breakdown peak voltage function capacitance products subjected 1.2/50 surge pulses. straight line shows result linear combined data
Remarks Name: Company: Address: Tel.: Fax: Email:
Fig.16 1.2/50 surge pulses
Headquarters Sales Europe Phycomp France S.A.S. Salvador Allende 92000 Nanterre France Tel: (0)1 (0)1
Headquarters Sales Asia Pacific Phycomp Taiwan Ltd. No.223-1, Pao-Chiao Road Hsin-Tien, Taipei Taiwan, R.O.C. Tel: +886 (0)2 2917 Fax: +886 (0)2 2917
Headquarters Sales Phycomp USA, Inc. 16750 Westgrove Drive suite Addison 75201 Tel: 2020 Fax: 2019
General Headquarters Phycomp Holding B.V. Bredeweg 6042 Roermond Netherlands Tel: (0)475 Fax: (0)475
Phycomp Holding B.V. rights reserved. Reproduction whole part prohibited without prior written consent copyright owner. information presented this document does form part quotation contract, believed accurate reliable changed without notice. liability will accepted publisher consequence use. Publication thereof does convey imply license under patent- other industrial intellectual property rights.
Printed Netherlands
Document order number: 9398 31011
Date release: September 2001
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