Control of Electromagnetic Radiation from
Integrated Circuit Heat sinks
-Cristian Tudor and Syed Bokhari
Problem of Heat Sink radiation
• Indirect radiation
(near field)
•Concentration of high
speed signals on IC
periphery
•Area in the periphery
of heat sink is prime
real estate
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Methods for Control
1. Optimize heat sink geometry
• 10+ dB suppression possible
• Limited freedom and is Frequency selective
2. Absorber material surrounding heat sink
• Significant broad band suppression possible
• Consumes large area around heatsink
3. Multi-point grounding
• 10+ dB suppression possible
• Frequency selective
• More suppresion requires more grounds
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Resistive loading
Slide 4
DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
2D Model Approximation and analysis
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Impedance and Near field radiation – 2D model without fins
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
2D Model with fins
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Impedance and Near field radiation – 2D model with fins
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Heat sink Excitation Model and IC encapsulation
•
•
•
Slide 9
Small square loop with a 1 V delta gap voltage source
Located between ground plane and Heat sink bottom
Loop center offset from origin (2 mm,2mm,2mm)
DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Peak Radiation from Excitation alone
0
Reference
Max Near Etotal (dB)
-10
-20
-30
-40
-50
1
2
3
4
5
6
Frequency (GHz)
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Bi-directional Heatsink with a low fin density
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Peak Near field without Resistive loading
0
Reference
Ungrounded
Max Near Etotal (dB)
-10
4 Grounds
-20
-30
-40
-50
1
2
3
4
5
6
Frequency (GHz)
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Peak Near field with Resistive loading
-10
4 Grounds
5 Ohms
25 Ohms
-20
50 Ohms
Max Near Etotal (dB)
75 Ohms
100 Ohms
-30
-40
-50
1
2
3
4
5
6
Frequency (GHz)
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Bi-directional Heatsink with a high fin density
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Peak Near field with and without Resistive loading
10
Max Near Etotal (dB)
0
4 Grounds
50 Ohms
-10
-20
-30
-40
-50
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
Frequency (GHz)
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Magnitude of surface current distribution of ungrounded heatsink
(2.3 GHz)
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Magnitude of surface current distribution of grounded heatsink
(3 GHz)
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Effect of shunt capacitance of resistors
-10
0 pF
2 pF
-20
Max Near Etotal (dB)
1pF
0.5 pF
-30
-40
-50
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
Frequency (GHz)
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Omnidirectional Heat sink
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Peak Near field without Resistive loading
10
Reference
Ungrounded
Max Near Etotal (dB)
0
4 Grounds
-10
-20
-30
-40
1
2
3
4
5
6
Fre quency (GHz)
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Peak Near field with Resistive loading
10
4 Grounds
0
2.5 Ohms
Max Near Etotal (dB)
10 Ohms
25 Ohms
-10
50 Ohms
-20
-30
-40
-50
1
2
3
4
5
6
Frequency (GHz)
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Magnitude of surface current distribution of grounded omnidirectional
heatsink(4 GHz)
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Omni-directional heatsink with wide fins
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Peak Near field with and without Resistive loading
0
4 Grounds
50 Ohms
Max Near Etotal (dB)
-10
-20
-30
-40
-50
1
2
3
4
5
Frequency (GHz)
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
6
Conclusion
1. Actual heat sink geometry must be simulated to
determine type of resonance
2. Microstrip cavity type resonances can be suppresed
with resistive loading
3. Optimum resistance values are in the range of 50 Ω
4. Resistors of low shunt parasitic capacitance are
required
5. Where heat dissipation requirements are met with a
bi-directional heat sink, do not use Omni-directional
heat sinks
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Authors’ Biographies
Cristian is currently a senior signal integrity engineer with Fidus
Systems, Ottawa. His work includes analog simulations of high
speed interfaces, interconnect modeling, characterization and
optimization. He is also engaged in the design and characterization
of power distribution networks, SSO analysis, jitter analysis both at
board as well as microcircuit level. Prior to joining Fidus, Cristian
was part of the engineering staff at Nortel Networks and Chipworks
Inc. He was involved in signal integrity and patent analysis related
to integrated circuits. Cristian holds a M.Sc diploma in Electrical
Engineering from the Polytechnic University, Bucharest, Romania.
Cristian Tudor, cristian.tudor@fidus.com
Tel: 1.613-828-0063 Ext: 382
Syed Bokhari received a Ph.D degree in Electrical Engineering from the
Indian Institute of Science, Bangalore, India. He is currently a Lead
Signal Integrity and EMC specialist at Fidus Systems inc. He has over
20 years experience, primarily in the area of electromagnetic modeling.
His previous academic employers include Ecole Polytechnic Federale
de Lausanne in Switzerland, and the university of Ottawa in Canada. He
has worked in the industry at the Indian Space Research Organization,
and at Cadence Design Systems (Canada) Ltd.
He has over 50 publications, contributed to chapters in books and holds
one patent. He is a senior member of the IEEE and is the chairman of
the Ottawa EMC chapter. His areas of current interest include
interconnect modeling for SI and EMC, and RFID antenna design.
Syed Bokhari, syed.bokari@fidus.com
Tel: 1.613-828-0063 Ext: 377
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DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Contact Information
Fidus Systems Headquarters
900 Morrison Drive, Suite 203
Ottawa, ON K2H 8K7 Canada
1-866-88-FIDUS (34387)
info@fidus.com
www.fidus.com
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Fidus California Design Centre
2900 Lakeside Drive, Suite 225
Santa Clara, CA, 95054 USA
1-408-307-4562
mike.shamshirian@fidus.com
DesignCon 2009: Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari