This document describes a hardware-software complex for quality control of LEDs according to thermal characteristics. The complex measures the thermal impedance and resistance of LEDs through a method that applies harmonic heating pulses and measures the temperature response. It can test LEDs from the semiconductor junction to the heat sink and ambient environment. The complex provides accurate thermal measurements, analysis of results, and has found customers in LED manufacturing.

1. KOTELNICOV INSTITUTE
of Radio Engineering and Electronics
of the Russian Academy of Sciences
(Ulyanovsk Branch)
Unique Systems
and Technologies
Hardware-software complex
for quality control of LEDs according
to thermal characteristics
CeBIT-2014

2. Typical construction of semiconductor devices
on the radiator

3. Thermal model of semiconductor devices
a.)
b.)
Figure 2. Simple model of a real
physical structure
Figure 3. Foster (a.) and Cauer (b.)
type representation of physical
structures with finite time constants

4. Standard methods
of thermal resistance measurement




Method on Russian Standard
Method on EIA/JEDEC Standard
Method on NIST Standard (US)
Method on MIL Standard (US)

5. Fundamental documents
The following documents are recommended reading for reference and test method standard description
purposes:

Mil Std 883C Method 1012.1
Thermal Characteristics of Microelectronic Devices

SEMI Test Method #G43-87
Test Method, Junction-to-Case Thermal Resistance Measurements of Molded Plastic Packages

SEMI Test Method #G38-87
Still and Forced Air Junction-to-Ambient Thermal Resistance Measurements of Integrated Circuit
Packages

SEMI Test Method #G42-88
Specification, Thermal Test Board Standardization for Measuring Junction-to-Ambient Thermal
Resistance of Semiconductor Packages

SEMI Test Method #G30-88
Junction-to-Case Thermal Resistance Measurements of Ceramic Packages

SEMI Test Method #G32-86
SEMI Guideline for Unencapsulated Thermal Test Chip

SEMI Test Method #G46-88
Thermal Transient Testing for Die Attachment Evaluation of Integrated Circuits

EIA JEDEC EB-20
Accepted Practices for Making Microelectronic Device Thermal Characteristics Test

NIST Special Publication 400-86
Semiconductor Measurement Technology: Thermal Resistance Measurements

6. Diagrams, described the method
of JEDEC Standard 51-1
EIA/JEDEC Standard No. 51-1
Page 10
VH
V
0
Time
VFD
IH
I
Time
0
t0 t1
t2
t3

7. Thermal transient tester T3Ster
(Analog, produced by MicRed Co, cost about $100 000)
An automated photometric/radiometric measurement setup with a Peltier-cooled
LED fixture, used in connection with the T3Ster thermal transient tester

8. Heating curve of LED in logarithmic scale
Step responses
Simulated thermal impedance plots at the three junctions
of the LED module in still air, green LED driven

9. Device for measuring thermal impedance
of light emitting diodes LED-meter

10. Functional scheme of LED meter

11. Principal of thermal impedance determination
Thermal impedance is based on transmitting the electric
pulse through the light emitting diode with the pulseduration that is modulated according to harmonic law,
and measuring the corresponding changes
of the heterojunction temperature relative to the case
or ambient.
On the basis of calculating the magnitude and phases
of the first harmonics of heating power and temperature
of heterojunction the module of thermal impedance
is determined, as well as the phases shift between
the temperature and the heating power.

12. Principal of thermal impedance determination
Thermal impedance is based
on transmitting the electric pulse
through the light emitting diode
with the pulse-duration that
is modulated according
to harmonic law, and measuring
the corresponding changes
of the heterojunction temperature
relative to the case or ambient.
On the basis of calculating the magnitude and phases of the first harmonics
of heating power and temperature of heterojunction the module of thermal
impedance is determined, as well as the phases shift between the temperature
and the heating power.

13. Diagrams of measurement signals

14. Features




The measurement of module and phase of the thermal
impedance with different heating currents and frequencies
of switching the heating power.
The measurement of thermal resistance of all the links
of the thermal path of light emitting diodes: heterojunction
– heat sink – circuit plate (soldering point) – radiator –
ambient. This provides an opportunity to design lighting
products with the most effective heat sink.
The measurement of overheating temperature
of the crystal relative to the ambience medium.
The presentation of the measurement results in the form
convenient for analysis and saving the results
in the computer memory.

15. Computer interface of LED meter

16. Technical characteristics








Range of thermal impedance –
from 0,1 up to 1000 K/W
Magnitude of the heating impulses of current –
from 10 mA up to 1100 mA
Frequency of switching the heating power –
from 0,001 Hz up to 800 Hz
Measurement error of thermal impedance – 2%
Power supply 220 V through the adaptor with output voltage +48 V
Wattage – less than 20 W
The overall device size –190x140x40 cm
The weight together with adapter – 0,6 kg
Technical specification and User's Guide:
http://ctt.ulstu.ru/cebit_2014/ust-control_LEDs.pdf

17. Electrothermal model of structure
of a heterojunction light-emitting diode
Structure
Model
electric
power
heat sources
0
substrate
[Al2O3]
Lx
q(T, J)
Ly
Lz1
y
heterostructure
[InGaN/GaN]
heat sink
Lz2
z
The equations of an electrothermal feedback:
Restrictive condition:
x

18. Solution and calculated results
J, А/мм2
10
1 -  = 0;
2 -  = (J,T);
3 -  = (T);
4 -  = (J);
5 -  = const;
1
2
3
5
4
8
6
4
0.05
0.1
0.15
0.2
0.25
0.3
RTj-c, К/W
7
6
Current dependences of thermal
resistance of power LED
5
4
3
0
100
200
300
400
500
600 I, mA

19. Customers, partners and awards
The device was ordered by:
 Concern JENOPTIC (Germany);
 JSC Svyaz Engineering (Moscow);
 Institute of Physics and Technology of RAS (Saint-Petersburg);
 Research Institute of Semiconductors (Tomsk);
 Moscow State University, Faculty of Physic;
 Ulyanovsk State Technical University
AWARDS:
 Gold Medal at the International Exhibition 2012, IENA
 DIPLOMA at the at the International Exhibition 2012, Moscow
 Grant 2012 START Program

20. Awards on international exhibitions

21. Contacts
Small Innovative Enterprise
“Unique Systems and Technologies”
Mr. Vyacheslav Sergeev,
E-mail: sva@ulstu.ru
Ulyanovsk Centre for Technologies Transfer
Phone, fax: (8422) 77-81-92
E-mail: ctt@ulstu.ru, http://ctt.ulstu.ru
32, Severny Venets st., Ulyanovsk, Russia,
432027.