IEEE Power Electronics Magazine Compendium - March 2018 - 110

Table 1. The FPM in reliability of power electronic components [1].
load

Focus Points

Climate + Design ≥ Stressor

Active Power Components

Passive Power
Components

Ambient

Product
Design

Stressors

Die

LASJ

Wire
bond

Cap.

Relative
humidity
-RH(t)
Temperature
-T(t)

-Thermal
system
-Operation
point
-ON/OFF
power
P(t)

Temperature
swing ΔT

Average
temperature T

dT/dt

Ind.

Control Circuitry, IC, PCB, Connectors
Solder
Joint

MLCC

PCB

Connectors

X
X

Water
Relative
humidity

Pollution

Tightness

Pollution

Mains

Circuit

Voltage

Cosmic

Circuit

Voltage

Mounting

Mechanical

Chock/
vibration

x
x

LASJ: large-area solder joint; MLCC: multilayer ceramic capacitor; IC: integrated circuit; Cap.: capacitor; Ind.: inductor. Level of importance (from high to low): X-X-X-x.

[7]-[11]. However, it is continuously challenged as new materials and devices are appearing on the market.
In a typical power electronic system, power semiconductor devices, capacitors, gate drivers, connectors,
printed circuit boards (PCBs), and fans are considered
as the vulnerable components, especially the insulatedgate bipolar transistor (IGBT) modules in medium- to
high-power applications and capacitors for ac filtering
and dc-link applications. A focus point matrix (FPM) was
presented in [1] to show the critical stressors for different components, which are represented in Table 1. The
steady-state temperature, temperature swings, humidity, voltage, and vibrations have different levels of impact
on semiconductor devices, capacitors, inductors, and
low-power control boards.
As two of the most vulnerable power electronics components with respect to reliability, the failure mechanisms of IGBT modules and capacitors are surveyed in
[12] and [13], respectively. Thermal cycling (i.e., temperature swings inside or outside the devices) is one of
the most critical stressors in power electronics components [10], [11], [14], [15]. It is widely accepted that the
temperature fluctuation on different materials with mismatched coefficients of thermal expansion may cause
disconnection at the material boundaries, thus leading
to wear-out failures of the devices. Similarly, it has been
found that the thermal-related failures also exist in the
capacitor and PCB, and they are claimed to be one of the
most important root causes of failures in these power
electronics components [10]. Different types of capacitors, such as electrolytic capacitors, film capacitors, and
ceramic capacitors, also have thermal-related failure

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IEEE PowEr ElEctronIcs MagazInE

z December 2016

mechanisms. The degradation of electrolytic capacitors
is temperature and voltage dependent. Besides these two
critical stressors, humidity and vibration are critical to
film capacitors and ceramic capacitors, respectively. The
reliability of these capacitors for dc-link applications is
discussed in [13] in detail.

Stress Analysis and Translation from Mission Profiles
After the reliability-critical components and the major failure mechanisms are identified for a power electronics
system, the major stress of the components can be comprehensively evaluated by modeling the loading conditions in a
specific application with a given converter design. The target of this group of analyses is to establish models that can
translate the mission profiles and converter design to the
quantified stresses that will trigger the failure of devices
under a failure mechanism.

challenges of Mission Profiles translation
The correct modeling of stress in power electronics components could be a challenging task. As previously mentioned,
the device loadings are closely related to the mission profiles of the whole converter system, which includes complicated models not only for the electrical system but also for
environmental conditions and the mechanical system. The
typical signal flows and model block diagram to assess the
thermal stress of power electronics components in a gridtied inverter are illustrated in Figure 5, where the disturbances, feedback loops, and relationship between physical
domains can be identified [16]. When translating the mission
profiles to the stress of components, multidisciplinary models have to be involved with different analyzing methods

Table of Contents for the Digital Edition of IEEE Power Electronics Magazine Compendium - March 2018