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New Functions
Power cycle test system with thermal analysis capability
using structure function. (1)Test mode and Specimen failure
There are two modes in a power cycle test: ⊿Tj Power cycle that changes the junction temperature (Tj Temperature) inside of the power
semiconductor device specimen (specimen) and ⊿Tc Power cycle that changes the temperature of the specimen's case (Tc Temperature).
(Test purpose)
To evaluate the specimen failure rate in the market through an accelerated life test.
The following describes the test modes and failure sites.
(Test mode 1: ⊿Tj Power cycle)⊿Tj Power cycle is a test that heats or cools the Tj temperature in a short period of time, and mainly evaluates the life of aluminum wirebonding area on the silicon chip in the specimen, and the solder bonding area beneath the silicon chip.
(Test mode 2: ⊿Tc Power cycle)⊿Tc Power cycle test applies and interrupts the power until the Tc temperature rises or drops to the given upper or lower limit of thetemperature, and mainly evaluates the life of the solder bonding area beneath the silicon chip and solder bonding area between theinsulating substrate and copper base in the specimen.
(Specimen failure)
When each power cycle test is conducted, shearing strain due to the difference in the linear expansion coefficient of each structure partwill generate cracks in the bonding area of each structure part. When the crack continues to widen, the temperature of the bonding arearises, resulting in destruction of the part.
(Failure analysis)
In a power semiconductor device, presence or absence of failure, life, and reliability are closely related to the temperature during operation.
Thermal resistance is used to analyze and calculate the rise in temperature.

Internal temperature ofthe device
125℃
25℃ ⊿Tj (=Tj max - Tj min) insemiconductor chip

Several S Several minOFFOFFONONOFFON

Semiconductor chip
SolderInsulating substrate
Cu base (heat sink)半田
Cu base (heat sink)Heating site in the device

Insulating substrate
Cu base (heatSemiconductorchip

Wire bonding
SolderCrack

Failure site in the device

Solder

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New Functions
Power cycle test system with thermal analysis capability
using structure function. (2)Transient thermal resistance andStructure function(Thermal resistance)
There are two types of thermal resistance: "stationary thermal resistance" in a state where the specimen adequately saturates, or for direct
current; and "transient thermal resistance" for short-term power pulse application.
(Measurement method)
Power semiconductor devices vary in shape. The heat discharging time from chip to the external air also varies by each structure part, andthe effect is seen in the measurement data of transient thermal resistance.
There are two methods for measuring transient thermal resistance: heating method (dynamic method) and cooling method (static method).
Both of those measurement methods were prescribed in 1990 by EIAJ (Electronic Industries Association of Japan).
(Structure function)
Structure function is a graphical representation of data, which is obtained by converting a graph of time/temperature rising characteristics ofa power semiconductor device in measurement of transient thermal resistance into a graph of thermal resistance characteristics and heat
capacity characteristics. The structure function enables evaluation of thermal characteristics of each structure part and shows the change offailure site over time in a graphical representation.
Semiconductor chip
Bonding agent

Rth 1

Rth 2

Rth 3

Rth 4

Cth 2

Cth 3

Cth 4

Cth 5

Rth 5

ConvertInsulating substrate
Bonding agent

Cth 1

Heat sink

Example of cross-section structure of
power semiconductor device

Heat absorption andheat rise due tothermal capacity ofsemiconductor chip

Semiconductor chiptemperatu
reTj [K]Heat equivalent circuit of heat dissipation path ofpower semiconductor device

Heat absorption
from insulating
substrate to heatsink

Heat absorption
from semiconductor
chip to insulating
substrate

Heat absorption toinsulating substrate

Heatcapacity
Cth [J/W]
Heat
absorption ofheat sink

Time t(s)Data of measurement result(Relationship between time andtemperature rising characteristics inshort-term phenomena)●Easy to conduct heat
=Large thermal resistance=>Small inclination(Bonding agent, grease, etc.)●Hard to conduct heat
=Small thermalresistance=>Large inclination(Metal, Si chip, etc.)

ConvertEasy to see with the emphasized
inclination
Thermal resistanceRth [K/W]

Structure function(Relationship between thermalresistance and heat capacity)

Page 3/5

New Functions
Power cycle test system with thermal analysis capability
using structure function. (3)Heating method and Cooling method(Static method)(Dynamic method)(Heating method [Dynamic method])
The measurement method is based on the actual use environment, and the measured data of transient thermal resistance is shown on theapplication note of the power semiconductor device.
Measurement of short-term range has limits in the capability for turning ON the sample's Gate and device's power-application capacity.
There will also be switching noise; however, Espec's original technology for Gate control circuit and noise control enable high-speed andstable measurement.
(Cooling method [Static method])
By smoothing the measurement result, noise can be eliminated and data can be corrected; however, in the case of a power semiconductor
device with multiple heat dissipation paths, it will lead to errors in measured values due to the difference between temperature risingcharacteristics and temperature falling characteristics.
In addition, countermeasures against heat of structure system will be required to saturate the temperature in accordance with thepower-application capacity.
The following pages describes the two methods in more detail.

Heating method(Dynamic method)

Cooling method(Static method)

Applicabledevice

Device with multiple heat flux paths(IGBT, etc.)

Device with one main heat flux path(LED, etc.)

Stressapplication

Application by pulse(Width: several 10mS)

Turn OFF the stress application after
the temperature saturates fromcontinuous application of stress.

Test time

Pulse width × Number of ON/OFFcycles

Heat saturation time + Cooling time

Data acquisition

Measure the data with interval of a few
mS after applying pulse.

Measure the data with interval of 1μS
immediately after turning OFF thestress application.

Coolingmechanism

Temperature saturation is not required.

Cooling mechanism is needed to attainsaturation temperature.

Item
Specimen

Test
Condition

StructurePage 4/5

New Functions
Power cycle test system with thermal analysis capability
using structure function. (4)Heating method (Dynamic method)
This method continuously applies a constant power pulse while gradating the pulse width, and calculates the temperature change andthermal resistance based on the temperature dependence of voltage at the PN joint area inside the power semiconductor device, which canbe obtained at each constant power pulse.

Test procedure (MOSFET)
1) Acquire temperature coefficient of the power semiconductor device.
Apply measured current (lm) to the drain that attains linearity with gate-source voltage (Vgs) and junction temperature (Tj temperature)of the power semiconductor device in advance, use the test chamber to let the Tj temperature change, and observe the relationshipbetween Vgs and Tj temperature under Im.
2) Measure the low temperature before application of constant power pulse.
Switch the circuit of the device to measuring system, and measure the Vgs with Im being applied. From the relationship between Vgs
and Tj temperature in Step 1), convert the figure to a temperature to obtain the low temperature Tj1.
3) Measure the high temperature during and immediately after the application of power pulse.
Switch the circuit of the device to stress system, and apply a power pulse for an arbitrary unit of time. Then, immediately after thepower pulse stops, switch the circuit to the measuring system and measure the Vgs with the Im being applied. From the relationshipbetween Vgs and Tj temperature in Step 1), convert the figure to a temperature to obtain the high temperature Tj2.
4) Calculate the transient thermal resistance.
Calculate the thermal resistance based on the temperature difference ⊿Tj between Tj1 and Tj2 obtained in Step 2) and 3), andapplied power.
5) Repeat the above steps 2) through 4).
Repeat Steps 2) to 4) with an arbitrary constant power pulse width, measure the thermal resistance at each point and plot the data ona graph. Measure the thermal characteristics of each structure part by obtaining measurement points in small intervals.
IsVg

VdIm

Gate-On voltage

Specimen

Gate-Off voltage

Vs

Power-supply device

Measuring system

Stress system

Current

Constant power ON/OFFTime

Temperature⊿ＴTimeTransient Thermal Resistance (℃/W)

Circuit diagram of measuring system of the device

Calculate the thermal resistance at eachpulse, and plot the points on the graph.

Pulse Width （S）Power pulse
Vgs (1)application time
(0.01 - 1000S)

Vgs (2)

Schematic of measurement with heating (dynamic) method

Schematic graph of thermal resistance measurement data

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New Functions
Power cycle test system with thermal analysis capability
using structure function. (5)Cooling method (Static method)
This method continuously applies power to the power semiconductor device, and after interrupting the power upon reaching temperaturesaturation, it measures the transient phenomenon where the voltage-temperature characteristics of the PN joint area in the power
semiconductor device gradually changes. Then, it calculates the temperature change and thermal resistance based on the temperaturetransient response characteristics.
In a radiation structure with heat flow in a single direction, the temperature rising characteristics can be equated to the falling characteristic.
This method uses these characteristics, and is specified by JEDEC (Joint Electron Device Engineering Council) as JESD51-14.
Test procedure (MOSFET)
1) Obtain the temperature coefficient of the power semiconductor device.
Apply measured current (lm) to the drain that attains linearity with gate-source voltage (Vgs) and junction temperature (Tj temperature)of the power semiconductor device in advance, use the test chamber to let the Tj temperature change, and obtain the relationshipbetween Vgs and Tj temperature under Im.
2) Apply power and heat the device until the temperature reaches saturation.
Switch the circuit of the device to stress system, apply the power, and adequately heat the power semiconductor device until it reaches
thermal equilibrium.
Obtain the saturated temperature Tj1.
3) After the temperature saturates, interrupt the power supply and perform high-speed measurement of temperature reduction
characteristics.
After the temperature saturates, suspend the application of power, switch the circuit of the device to measuring system, and perform
high-speed measurement of Vgs with the Im being applied.
1) Convert the relationship between Vgs and Tj temperature into temperature, and obtain continuous data of Tj2 while the temperature
is falling.
(* In MOSFET or IGBT, the measurement starts 1ms after the power interruption due to the transient response characteristics ofGate voltage.
Meanwhile, there is no gate voltage for the diode element , and high-speed measurement of transient response characteristics
of forward voltage Vf can be performed in 1μS.)
4) Calculate the transient thermal resistance.
Calculate the thermal resistance based on the temperature difference ⊿Tj between Tj1 and Tj2 obtained in Step 2) and 3), andIs
applied power.
Vg

Gate-On voltage
Gate-Off voltage

VdIm
SpecimenVs

Power-supply unit

Measuring system

Stress system

Circuit diagram of measuring system of the device

Current

Im: Measured current
TimeMeasurement

Temperature

Transient Thermal Resistance [℃/W]

0.07

Ih: Heating current

0.06

t1

t2

grease_ave

0.05
0.04
0.03
0.02
0.01
0
1.E-06t0

greaseless_ave.

1.E-04

1.E-02
1.E+00Time[sec]

1.E+02

1.E+04

Time

Schematic graph of thermal resistance measurement data
Schematic of measurement with cooling (static) method