ST AN1597 Application note
AN1597
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APPLICATION NOTE
HIGH CURRENT POWER MODULES FOR AUTOMOTIVE
USING Max247™ PACKAGE WITH IMS SUBSTRATE
M. Melito
1. ABSTRACT
Hybrid Electric Vehicles (HEVs) combine the internal com bustion engine of a conventional vehicle w ith
the battery and electric mot or of an electric one. This c ombination offers the extended range and rapid
refuelling that consumers expect from a conventional vehicle, together with a significant portion of the
energy and environmental benefits of an electric vehicle.
The practical benefits of HEVs include improved fuel economy and lower emissions compared to
conventional vehicles. HEVs are safety critical systems and demand high standards of safety and
reliability . A t the same time high power cost-effective power switches are required. But until now, the high
power switch portfolio has not be en well suited for automotive applications: cost is high and reliability
characteristics are not the desired ones.
An innovative techniqu e is proposed to design and m anufacture power electronic modules, using high
performances cost-effective IGBTs assembled in plastic package. This techniq ue allows optimizing both
the power switching devices and the converter, in terms of power handling, reliability and cost. This
design is well adapted to mass production required by automotive applications.
2. Introd uct i on
The serious deterioration of urban air requires cleaner cars. HEVs will reduce sm og-forming pollutants
over the current average. However, hybrids will never be true zero-emission vehicles because of their
internal combustion engine. But the first hybrids on the market will cut emissions of global-warming
pollutants by a third to a half, and later models may c ut emi ssions by even more. Mo re efficient cars can
make a big difference to society in terms of environmental benefits.
The ecological objectives include fuel economy improvement, green house effect reduction, polluting
gases emission reduct ion and pure electric mode within town centers. Addi tional targets for improved
driving comfort are: stopping and starting the motor at traffic lights, increasing the electric power when
the vehicle starts or changes gear, and applying continuous torque to the wheels.
November 2002
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Figure 1: Basic Architecture of a Parallel HEV
Fig.1 depicts the basic arc hitecture of a parallel HEV. Parallel means that the mechanical p ower of ICE
and that of the e lectric mo tor are added in parallel to prov ide torque t o the wheels. For a s hort distance,
pure electric mode is possible. For a long distance, ICE provides the necessary autonomy. When a peak
transient torque is required to boost the vehicle, the two torques are added.
Fig. 2 reports the functional schematic.
Figure 2: Functional Schematic of a Parallel HEV
Internal
Combustion
Engine (ICE)
HV Battery
Clutch
Electric
Machine
CONTROL
Inverter
HV BUS
Gearbox
DC/DC
Converter
Wheels
LV
Battery
The suggested imp rovement has been o btained in the inverter block which houses the active s witches
required to drive the electric motor.
Main goals for power electronic equipment in electric vehicles are: low cost, high reliability and low total
volume. It is a true cha llenge. In terms of cost and reliability, there is a huge gap bet ween low-cost and
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highly reliable standard discrete plastic packages for power transist ors and costly high power modules.
These modules usually exhibit lower reliability due to complex assembly and low volume production.
For surface mount devices, this gap is even larger. Particularly for low-cost applications, module
techniques are not suitable. On the other hand high-volume automotive applications require an AQL
(Average Quality Level) of < 1 ppm and extremely low-cost devices.
A new surface mount plastic package, using m ass -production t ooling able to house l arge dies (c a. 300 x
400 mils
cost reduction by lowering the labor cost for assembly and will increase reliability by improving the
process control. This assembly technique is modular and gives more independence from module
suppliers.
In this paper we show a new module using surface mount technology. The module has been realized
thanks to a new specially designed IGBT housed, toge ther with a high-speed diode, in a high-power
plastic package. This solution realizes a complete bi-directional current switch component with high
reliability and low cost mass production. The c omplete m odul e, rea lized with IM S technol ogy us ing 2 x 8
Max247 in parallel,it is a 400A, 600V power arm bridge unit for automotive applications.
This work has been developed within the INMOVE (Integrated Modular electric propulsion system for
parallel hybrid Vehicles) project founded by EC BRITE EURAM.
2
), will dramatically r educe the package cost. In addit ion, surface mounting will bring addit ional
3. Overview of the Device Technology
The elemental devices are punch-thro ugh IGBTs (PT-IGBTs) with a breakdown v oltage of 600V (50 A
rated current). The devices belong to the last IGBT generation which are manufactured in the mesh overlay technology, i.e. a strip-based concept realized from a p-doped mesh st ructure (the body of th e IGBT )
where directly diffused n+ doped strips substitute the cells, and represent the emitter of the IGBTs.
This particular technological solution allows the IGBTs to be easily made with a reduced on-state voltage
drop through a reduct ion of the on-s tate resistance (up t o 20 % ). Moreov er, the presence of a deep body
p+ avoids the trouble of static latch-up, as the resistance of the bo dy extending under the n+ source is
reduced.
An improved ruggedness, useful fo r paralleling connections, has been reached by mean s of the ballast
resistance technique, by using an "H" type layout structure. The cross section of the manufactured
device with the ballast resistance is shown in Fig. 3.
The extension of the p+ layer over the metallic contact increases the path of the electron current, thus
creating a ballast resistance Rb. During conduction condition, the current through the source of
the MOSFET causes, through Rb, a negative feedback on the gate-source voltage, and the gain is consequently reduced.
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