Infineon AN2019-05 User Manual
AN2019-05
About this document
Scope and purpose
This application note replaces AN2010-02, “Use of Power Cycling Curves for IGBT4” [1] and is applicable for
the following products: industrial power modules (with/without base plate), Intelligent Power Modules
(IPM), and discrete devices.
It provides all required information on the use of Infineon’s power and thermal cycling diagrams and how to
apply the rainflow-counting algorithm for proper cycle counting.
Table of Contents
About this document .................................................................................................................................................................................. 1
Table of Contents......................................................................................................................................................................................... 1
1 Introduction ......................................................................................................................................................................... 2
2 Power cycling ....................................................................................................................................................................... 3
2.1 Key definitions and terms .............................................................................................................................................. 3
2.2 Application examples ....................................................................................................................................................... 8
3 Thermal cycling ................................................................................................................................................................. 11
4 Rainflow-counting algorithm for calculating lifetimes ...................................................................................... 13
5 References ........................................................................................................................................................................... 16
Revision History ........................................................................................................................................................................................ 16
Application Note Please read the Important Notice and Warnings at the end of this document
www.infineon.com page 1 of 17
Revision 2.1
2021-02-19
Introduction
1 Introduction
Different load conditions with varying thermal conditions can lead to different levels of thermal stress in
applications using the same type of industrial power module, IPM module, and/or discrete device.
Specification is a necessary procedure to warrant the required lifetime of a power semiconductor device.
Load-generated stress should not exceed the limits defined by the corresponding diagrams.
There is a distinction between two types of cycling capability, the junction temperature ∆T
cycling (PC), and the solder joint and case temperature ∆T
-related thermal cycling (TC).
C
-related power
vj
This application note provides a better understanding of the underlying failure mechanisms, and the
corresponding power and thermal cycling diagrams.
In particular, the application note discusses in detail the use of both power and thermal cycling diagrams for
industrial power modules.
With regard to IPM modules and discrete products, the application note focuses exclusively on the power
cycling diagrams. Hence, the thermal cycling information discussed in the document is not applicable for these
products.
Therefore, as the application note covers different type of products that differ in construction, current density,
size, and semiconductor technology, for example, it is important to use the specific reliability curves for the
selected product.
Application Note page 2 of 17
Revision 2.1
2021-02-19
Power cycling
Industrial power module (with base plate) Intelligent power module (IPM) Discrete
device
2 Power cycling
Typically, the wire-bonding process is used for the electrical interconnections of the specific products
discussed in this document, i.e. industrial power modules, IPMs, and discrete devices, as illustrated in Figure
1.
For instance the IGBT power module sample shown in Figure 1 comprises approximately 450 wires together
with 900 wedge bonds. For many years, the reliability of this contact technology had been a concern.
Figure 1 Internal view of an industrial power module with base plate, intelligent power module (IPM), and
co-pack IGBT discrete device (typical appearance)
Considerable work has been concentrated on accelerated power-cycling tests, analysis of failure mechanisms,
and improvements in bonding and die attach technology. Developments in the composition of wire, the shape
of bonding tools, bonding parameters, chip metallization, and the mold compound as well as the introduction
of improved die attach processes, such as diffusion soldering and sintering, have led to considerable
improvements in the reliability and lifetime
of the power semiconductor devices.
Power cycling raises and lowers the chip-junction temperature at relatively short intervals in a timeframe of
seconds. It mainly puts stress on the bond wires on the silicon chips, and the soldered joints below the silicon
chips. The power-cycling capability of power semiconductor devices is dependent on the absolute junction
temperature T
, the temperature swing ∆Tvj, the duration t
vj
this case, during the power cycling test the same conditions such as load current and T
and the on-time ton of the cycle. Typically, as in
cyc
are periodically
vjmax
repeated.
In case of products not having the on-time t
PC curve like IPM, the time-dependent PC impact can be omitted
on
for simplification.
2.1 Key definitions and terms
Definition of Tvj
The junction temperature Tvj is the temperature of the semiconductor junction region. Since the junction
temperature can only be determined either by indirect measurement or calculation, it is termed “virtual
junction temperature.”
Definition of T
Application Note page 3 of 17
vj,max
Revision 2.1
2021-02-19
Power cycling
Example of power-cycling capability for an IGBT power module
The maximum junction temperature T
is the maximum allowed value for the specific device to be reached
vj,max
during the temperature cycles shown in the power-cycling diagram. The higher the maximum junction
temperature T
Definition of T
The mean junction temperature T
the power cycling test, i.e. T
Definition of t
The time t
is the period without load. It is adjusted so that the temperature Tj drops down to the level needed
off
to achieve the desired ∆T
, the higher is the stress on the device, which results in a reduced number of cycles.
vj,max
vj,mean
is the arithmetic mean value of the minimum and maximum Tvj during
vj,mean
= 0.5 * (T
vj,mean
off
. The typical t
j
off
vj,min
+ T
vj,max
).
time is in the same range as the heating time ton.
Definition of ton
The turn-on time t
steady temperature rise of T
is the period during which power losses are generated in the device, resulting in a
on
e.g. during the acceleration phase of a motor drive. The longer the turn-on
vj
period, the higher the temperature rise and the corresponding stress to the device, which results in a
reduced number of cycles during lifetime. This can be explained by the viscoplastic deformation energy in
the material layers that undergo thermomechanical cycling for longer turn-on periods. For instance, for
industrial power modules, a typical t
Definition of t
The time t
cyc
is the period of one power cycle of ton + t
cyc
time for the short cycle PCsec test is 1.5 s.
on
. For industrial power modules, a typical t
off
time for
cyc
short-cycle PCsec tests is 3 s.
The following Figure 2 shows an example of a power-cycling diagram. It displays the achievable stress (=
number of temperature cycles) vs. temperature swing during the lifetime of the bond contacts described
above. The junction temperature, which can be measured either under lab conditions or simulated under
application conditions, is used as a measure.
Application Note page 4 of 17
Revision 2.1
2021-02-19
Power cycling
Figure 2 This diagram depicts an example of the number of cycles versus the junction temperature rise for
power-cycling stress at maximum junction temperature
For a repetitive junction temperature swing of e.g. ∆Tj=60 K, we can read from the diagram that the device
can withstand 300,000 cycles. For a correct interpretation of such diagrams from different manufacturers, it
is important to know the underlying conditions.
Definition of I
nom
In the case of discrete devices, the current through the device has a significant impact on the power-cycling
test. Hence, an additional power-cycling diagram is provided as a function of nominal current, I
nominal current is the amplitude value of the current through the device during the t
period in the power-
on
nom
. The
cycling test.
Furthermore, the nominal current corresponds to the chosen current by design for device characterization. It
serves as a reference for specifying main electrical parameters in the data sheet such as V
operating area (SOA) for IGBT devices and R
for MOSFET devices. Very often, in the case of IGBT devices,
DS(on)
and safe
CEsat
the nominal current value is included in the name of the product and specified as the DC collector current
parameter at T
= 100°C in data sheets as well.
C
Note that for co-pack IGBT discrete devices (IGBT and diode die in the same package, similar to the sample
shown in Figure 1.) the nominal current I
for the diode is the same one as the IGBT regardless of the diode
nom
current rating.
In order to find the corresponding power-cycling diagram the applicable nominal current I
is equal to the
nom
RMS current through the device.
Application Note page 5 of 17
Revision 2.1
2021-02-19
Power cycling
Power-cycling capability: typical dependency on ton
What is the failure criterion?
Infineon uses an increase of the R
by 20% or an increase of the on-state voltage by 5% as a failure indicator.
th
With this, the parameters of a "failed" device are still within the limits of the data sheet for products with a 0h
value close to the typical value.
What is the
temperature level for which the curve is valid?
Infineon shows "worst-case" curves, assuming that every temperature swing reaches the maximum allowed
junction temperature T
What is the
failure rate?
jmax
.
The failure rate is the probability with which devices in the field will show any failure according to the above
criterion. Typically, Infineon uses a failure rate of 5% for determining the PC curves. However, in the case of
discrete devices, there are PC curves released showing 1%, 5% and 10% failure probabilities.
What are the
Specifically for industrial power modules, the tests at Infineon are performed with cycle times of t
s. Infineon’s investigation cover t
cycle times which should be considered relevant for PC?
times from 0.1s ... 60s. For this regime, a typical dependency can be given
on
on
+ t
off
= 3
as shown in Figure 3. As an approximation, the derating factors reached at the limits of the 0.1 … 60s interval
should be used also for t
extending the regime. For shorter cycles this would be regarded as a conservative
cyc
approach; for longer cycles, the approximation is based on the assumption that viscoplastic deformation
saturates for t > 60 s.
Figure 3 This diagram depicts the typical dependency of the cycling capability on the turn-on time t
Power-cycling diagrams from competitors might depict higher number of cycles without naming the
“disguised” conditions and applied failure criterias. This is a common practice and may therefore not allow a
direct comparison. Ways to virtually “improve” test results and the corresponding reliability diagrams:
Application Note page 6 of 17
IGBT4 industrial power modules
raise the failure criterion to the level of real malfunction
for
on
Revision 2.1
2021-02-19
Loading...