Evaluation of Pressureless Silver Sintered High Power Semiconductor Devices by Measurement of Thermal
Impedance
Martin Beierlein, Michael Kaloudis
University of Applied Sciences Aschaffenburg Faculty of Engineering
Packaging and Interconnection Laboratory
Advanced Packaging Conference Dresden 08.10.2013
08.10.2013 Martin Beierlein
Agenda
Motivation Sintering of power semiconductors Measurement of thermal impedance Results of the measurements Summary
08.10.2013 Martin Beierlein
Motivation
Miniaturization of semiconductors Semiconductor devices based on SiC Reliability of solder alloys RoHS compliance Fast, non-destructive quality assurance
08.10.2013 Martin Beierlein
Conventional assembly and example of application
Internal view of a Conventional power module assembly 1 Heat sink, 2 Solder, 3 Copper, 4 Ceramic, 5 Die, 6 Bond wire
Ref. [1]
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What is silver sintering?
Silver sintering is the process of compacting a paste of silver particles and organics by the use of thermal energy.
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Pressureless sintering process
Dispensing/ Printing
Positioning
Heating
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Typical power cycling test of soldered and sintered diodes
Number of power cycles Ref. [2]
Cum
mul
ativ
e fa
ilure
Typical power cycling test between +45 and +175 °C
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Thermal impedance Zth
Resistances and capacitances represents the different materials.
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Test object & conducting
3cm
3cm
Substrate Layout Conducting 1 Thermocouple, 2 Heat sink, 3 DCB-substrate, 4 Sinterlayer, 5 Die, 6 Spring contacts
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Typical linear calibration curve of diodes
Ref. [4]
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Measurement setup for Zth
Heating current IH= 25 A for 20 s Measuring current IM = 50 mA Measuring of VF for 100 s
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Test matrix I
Varied parameter: sintering time Wet layer thickness of about 75 µm
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Computer tomography of test objects
A B C
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Results of Zth Measurements
-A -B -C
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Test matrix II
Varied parameter: sintering time Wet layer thickness of about 100 µm
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Computer tomography of test objects
A B C
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Results of Zth Measurements
-A -B -C
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Discussion of Zth Measurements
A: Good die attach with high density silver layer
B: Higher micro porosity causes higher thermal impedance
C: Partially connected die leads to higher thermal impedance
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Summary
Correlation between porosity and Zth
Measurement method allows a non-destructive evaluation of the die attach quality
Outlook: Optimization of the experimental setup Quantitative correlation between porosity and Zth
08.10.2013 Martin Beierlein
References
[1] Perpina, X. and Jorda, X. and Vellvehi, M. and Rebollo, J. and Mermet Guyennet, M. Long-Term Reliability of Railway Power Inverters Cooled by Heat-Pipe-BasedSystems. 58(7):2662-2672, 2011. Available under: http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=5601771
[2] Knoerr, M.; Kraft, S.; Schletz, A.: Reliability assessment of sintered nano-silver die attachment for power semiconductors, S. 56–61. Available under: http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=5702605
[3] Dr. Thomas Schütze. Thermische Ersatzschaltbilder: An 2008-03 application note v1.0 Infi neon Technologies AG, 16.06.2008..
[4] Department of Defense. Test Method Standard Test Methods for Semiconductor Devices, chapter Thermal Impedance Response Testing of Diodes. METHOD 3101.3. in MILSTD-750D. 30.07.2013.