Third Generation Press-PackIGBTs and Diodes forMegawatt Applications

14 HIGH-POWER SEMICONDUCTORS www.westcode.com

Issue 6 2010 Power Electronics Europe www.power-mag.com

Press-pack IGBT technology has come of age with the introduction of the latest generation of soft punchthrough die. Background to the evolution of the new generation and its enhanced characteristics areintroduced for the largest member of the product family. With high reliability and low losses, the new deviceis ideal for today’s demanding environment of high efficiency and renewable energy sources. A. Gollandand F. Wakeman, Westcode Semiconductors Ltd, Chippenham, UK

First introduced twelve years ago, as a high reliability solution for hostileenvironments, the press-pack IGBT hasevolved towards the product of choice inmany high power applications. The firstEuropean made devices were targeted atinduction heating power supplies, a 1.8kVmedium frequency device, offered as asolution to overcome the punishingthermal stress of such applications. Thesenew introductions were both expensive toproduce and very application specific.However, the robust nature of the designattracted wider appeal and new productswere introduced with higher voltage andless application specific characteristics. A first generation high voltage device,

with current rating up to 900A, saw favourin traction applications [1]. Limitations ofdie technology meant these early highvoltage devices, required snubbers andwere more suited to GTO thyristor circuittopologies. A second generation of 4.5kVdie followed, based on soft punch throughtechnology, which offered more classicalIGBT characteristics giving a wide appealfor a broader range of applicationsincluding drives, traction and utilityapplications. Now a third generation dieset is launched with improved forwardvoltage and SOA performance. This newdie set, in conjunction with larger packageoptions, is an ideal solution for the needsof the latest generation of mediumvoltage drives.

Press-pack encapsulation of smalldieThe concept behind the press-packhousing is to keep it simple; all pressurecontact, no solder or bonded joints [2].However, to achieve this takes a greatdeal of control of materials and themanufacturing process. The key elementof the press-pack IGBT evolution was the

introduction of the single die cell with thefirst generation of high voltage devices [3].Each individual IGBT die is mounted in itsown cell, which can be pre-tested beforeassembly into the package, under cleanroom conditions. Among the latest

generation of products the largest deviceboasts a 125mm contact electrode and42 individual dies in hard parallelconfiguration (Figure 1). The multichipbondless technology offers unrivalledruggedness, with thermal cycling

Figure 1: Latest generation of IGBT press-packs boasting a 125mm contact electrode and 42 individualdies in hard parallel configuration

Figure 2: Turn-on transient of the IGBT under nominal switching conditions

www.westcode.com HIGH-POWER SEMICONDUCTORS 15

www.power-mag.com Issue 6 2010 Power Electronics Europe

Careful optimisation of the deep lowconcentration buffer and anode gives apositive temperature coefficientthroughout the entire current range, whichis important for very large area devicesand also ensures excellent short circuitperformance, well in excess of typicalrequirements. We are now able to offertechnology with on-state losses broadlycomparable to that available with typicaltrench designs, while retaining thesuperiour Reverse Bias Safe OperatingArea (RBSOA), Short Circuit SafeOperating Area (SCSOA), soft switchingbehaviour and easy driving characteristicsassociated with our planar technology.Similarly, a new diode chip complementsthe new IGBTs in our reverse conductingparts, along with our third generation HPSonic-FRD monolithic diodes to supportthe asymmetric parts and clampingapplications.

2400A / 4500V asymmetric deviceperformanceTo fully evaluate and qualify theT2400GB45E IGBT, an extensive range of

measurements has been carried out. Thedevice has a nominal current rating of2400A, which equates to a current densityof 57A/cm2, and nominal DC-link voltageof 2.8kV, with RBSOA testing carried outup to 4800A and 3200V. All switchingwaveforms are shown with anE2400TC45C freewheeling diode andunclamped (stray) inductance ofapproximately 180nH. Junctiontemperatures are 125°C for the IGBT and150°C for the diode unless statedotherwise.Figure 2 shows the turn-on transient of

the IGBT under nominal switchingconditions with a gate resistor of 1.6�

and additional gate-emitter capacitance of267nF. The very low input capacitance ofthe enhanced planar cell provides a fastvoltage fall time. In this case we are ableto further optimise the switchingconditions for both the IGBT and diode bycombination of gate resistance andadditional external capacitance. Underthese conditions typical turn-on losses are7.2J. Figure 3 shows the turn-off transient of

the IGBT under nominal switchingconditions with a gate resistor of 1.5�

and additional gate-emitter capacitance of267nF. The highly rugged cell allows highswitching speed, while the carefullyoptimised buffer ensures a soft turn-offtransient with no voltage disturbances oroscillations, even at high DC-link and strayinductance levels. Under these conditionstypical turn-off losses are 7.85J.Figures 4 and 5 show the turn-on and

turn-off transients respectively underRBSOA conditions. The device can clearlybe seen in figure 7 to be sustaining alarge amount of energy in the dynamicavalanche mode, evident by the self-limiting of dv/dt and clamping of the peakinduced turn-off voltage for a period ofapproximately 1.8µs; no external voltageclamps or snubbers are applied. RBSOA

capabilities beyond that of larger bondlessmonolithic devices or alternative multichippackaging concepts [4]. The fully hermeticdouble side cooled package makes thedevice suitable for all cooling systems; air,liquid and even full immersion. Also failureto short circuit and a predictable rupturerating give more options in systemprotection.

Improved die technologyThe new chipset technology is the latestevolution of our soft punch through planarcell design, which has been proven inpress-pack applications over the last sevenyears. The new enhanced cell designfeatures the addition of an N-enhancement layer, along with furtheroptimisation and tight control of theemitter structure. This gives a significantlyimproved carrier concentration under theemitter. The more favourable carrierdistribution leads to 25% reduction inVce(sat) (typically 3.6V at nominal currentand Tj max) without any appreciableincrease in the turn-off losses, whencompared to the previous generation.

Figure 3: Turn-off transient of the IGBT under nominal switching conditions

Figure 4: Turn-on transient of the IGBT under RBSOA conditions Figure 5: Turn-off transient of the IGBT under RBSOA conditions

16 HIGH-POWER SEMICONDUCTORS www.westcode.com

Issue 6 2010 Power Electronics Europe www.power-mag.com

does not increase linearly with devicevoltage and for high voltage devices thisparameter becomes technicallychallenging. Furthermore as the device current

increases, the insertion and therefore totalcommutation loop inductance tends toincrease due to larger package size andlarger busbar requirements; this in turndramatically increases the energy stored inthe unclamped inductance that eachindividual die must sustain (in an ideal

situation the inductance would reducelinearly as the number of die increases tomaintain the same effective inductanceper die or per ampere). The advanced lowloss technology combined with thesuperiour thermal performance of thepress-pack construction change thefundamental limits for typical inverterdesigns. No longer are designs limited byaverage current, rather commutation orpeak currents (RSOA) become the limitingfactor. Figure 6 shows switching loci of a

double pulse RBSOA test overlaid on thedevice data sheet limit characteristic.Figure 7 shows an additional RBSOA testconducted as a burst of 10 pulses at afrequency of 10kHz from an initial voltageof 3.6kV with current increasing to 4kA,further demonstrating the outstandingrobust nature of these devices.Figure 8 shows a typical type I short

TOSHIBA’S COMPACT SUPER JUNCTIONPOWER MOSFETS - LOWEST RDS(ON) x QgAND RUGGED CHIPSToshiba’s innovative new family of DTMOS II power MOSFETs are now available not only witha maximum VDSS rating of 600V but also with 650V. The range makes your solutions moreefficient, thanks to faster switching speed, linked with lowest RDS(ON) x Q(g) performance.

Our compact smart isolation TO220SIS package combined with the copper connectortechnology, have made the new Toshiba DTMOS II MOSFETs hard to resist. And, if youneed higher power, our TO-3P(N) package are available too.

VViissiitt uuss ttooddaayy aatt wwwwww..ttoosshhiibbaa--ccoommppoonneennttss..ccoomm//ppoowweerr

Figure 6: Switching loci of a double pulseRBSOA test overlaid on the device data sheet

limit characteristic

Figure 7: Additional RBSOA test conducted as aburst of 10 pulses at a frequency of 10kHz froman initial voltage of 3.6kV

Figure 8: Typical type I short circuit testwaveform at DC-link voltage of 3kV andnominal pulse width of 13µs

17www.westcode.com HIGH-POWER SEMICONDUCTORS

www.power-mag.com Issue 6 2010 Power Electronics Europe

Supplier of

customized

shunts

Substitute for transformers – 5 letters

SMD shunt resistors save spaceand offer a number of advantages:

High pulse loadability (10J) High total capacity (7W) Very low temperature dependency over

a large temperature range Low thermoelectric voltage Customer-specific solutions (electrical/mechanical)

Areas of use:

Power train technology (automotive and non-automotiveapplications), digital electricity meters, AC/DC as wellas DC/DC converters, power supplies, IGBT modules, etc.

Telephone: +49 (27 71) 9 34-0 sales.components@isabellenhuette.de

www.isabellenhuette.de

Innovation from tradition

circuit test waveform at DC-link voltage of3kV and nominal pulse width of 13µsusing a soft turn-off gate resistor of 10�.The device is able to withstand both type Iand II short circuit events with gatevoltages up to 18V across the fulloperating temperature range.

Multi-megawatt applicationsThe high current rating and high DC-linkrating make this device a natural fit formedium applications in the multi-megawatt power range. In particular thepress-pack construction lends its self wellfor multilevel water-cooled converterswhere extremely high power density isachievable. Figure 9 shows a typical phaseleg arrangement for a 1600A, 3.3kVneutral point clamped inverter phase legand Figure 10 shows the possibleconfiguration of an 18MW, 6.6kV variablespeed drive. These ratings fit well to awide range of applications including highperformance motor drives, high-speedlocomotive traction, railway interties, utilityscale VAr and power quality compensatorsand renewable grid converters, to name afew. Of specific emerging interest is the

current trend toward medium voltagemachines for the next generation ofwind turbines. Particularly in offshoreapplications, where ratings of 6-8MWare in development employing full-scale power conversion at 3.3kV, forboth machine and grid sideconnection. The very high powerdensity converter solutions possiblewith the press-pack IGBT, combinedwith high reliability and fully hermeticconstruction make this an extremelyattractive solution to the uniquechallenges of these next generationturbines.

Literature[1] F. Wakeman & A. Golland, “Press-

pack IGBTs for traction applications”,Power Electronics Europe, issue 1, 2004.

[2] F. Wakeman, K. Billett, R. Irons &M. Evans, “Electromechanicalcharacteristics of a bondless pressurecontact IGBT” APEC 1999, pp312-317.

[3]. F. Wakeman, G. Li & A. Golland,“New family of 4.5kV Press-pack IGBTs”PCIM Europe 2005.

[4] F. Wakeman, D. Hemmings, W.Findlay & G. Lockwood, “Pressurecontact IGBT, testing for reliability”,PCIM Europe 2000. Figure 9: Typical phase leg arrangement for a

1600A, 3.3kV neutral point clamped inverterphase leg

Figure 10: Possible configuration of an 18MW,6.6kV variable speed drive