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Control of Electromagnetic Radiation from Integrated Circuit Heat Sinks
Authors: Dr. Syed Bokhari and Cristian Tudor
Copyright 2009 Fidus Systems
Problem of Heat Sink Radiation
• Indirect radiation (near field)
•Concentration of highspeed signals on IC speed signals on IC periphery
•Area in the periphery of heat sink is prime real estate
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 2
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 heat sink
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 3
• Consumes large area around heat sink
3. Multi-point grounding• 10+ dB suppression possible• Frequency selective • More suppression requires more grounds
Resistive Loading
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 4
2D Model Approximation and Analysis
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 5
Impedance and Near field radiation – 2D model without fins
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 6
2D Model with Fins
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 7
Impedance and Near field radiation – 2D model with Fins
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 8
Heat sink Excitation Model and IC Encapsulation
• 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)
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 9
Peak Radiation from Excitation Alone
-20
-10
0M
ax N
ear
Eto
tal (
dB
)
Reference
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 10
-50
-40
-30
1 2 3 4 5 6
Frequency (GHz)
Max
Nea
r E
tota
l (d
B)
Bi-directional Heat sink with a Low Fin Density
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 11
Peak Near field without Resistive Loading
-20
-10
0
Max
Nea
r E
tota
l (d
B)
Reference
Ungrounded
4 Grounds
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 12
-50
-40
-30
1 2 3 4 5 6
Frequency (GHz)
Max
Nea
r E
tota
l (d
B)
Peak Near field with Resistive Loading
-30
-20
-10
Max
Nea
r E
tota
l (d
B)
4 Grounds
5 Ohms
25 Ohms
50 Ohms
75 Ohms
100 Ohms
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 13
-50
-40
-30
1 2 3 4 5 6
Frequency (GHz)
Max
Nea
r E
tota
l (d
B)
Bi-directional Heat sink with a High Fin Density
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 14
Peak Near field with and without Resistive Loading
-20
-10
0
10
Max
Nea
r E
tota
l (d
B)
4 Grounds
50 Ohms
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 15
-50
-40
-30
-20
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
Frequency (GHz)
Max
Nea
r E
tota
l (d
B)
Magnitude of surface current distribution of ungrounded heat sink (2.3 GHz)
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 16
Magnitude of surface current distribution of grounded heat sink (3 GHz)
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 17
Effect of shunt Capacitance of Resistors
-30
-20
-10
Max
Nea
r E
tota
l (d
B)
0 pF
2 pF
1 pF
0.5 pF
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 18
-50
-40
-30
1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
Frequency (GHz)
Max
Nea
r E
tota
l (d
B)
Omni-directional Heat sink
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 19
Peak Near field without Resistive Loading
-10
0
10
Max
Nea
r Eto
tal (
dB
)
Reference
Ungrounded
4 Grounds
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 20
-40
-30
-20
1 2 3 4 5 6
Frequency (GHz)
Max
Nea
r Eto
tal (
dB
)
Peak Near field with Resistive Loading
-20
-10
0
10
Max
Nea
r E
tota
l (d
B)
4 Grounds
2.5 Ohms
10 Ohms
25 Ohms
50 Ohms
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 21
-50
-40
-30
-20
1 2 3 4 5 6
Frequency (GHz)
Max
Nea
r E
tota
l (d
B)
Magnitude of surface current distribution of grounded omni-directional heat sink(4 GHz)
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 22
Omni-directional Heat sink with Wide Fins
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 23
Peak Near field with and without Resistive Loading
-20
-10
0
Max
Nea
r E
tota
l (d
B)
4 Grounds
50 Ohms
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 24
-50
-40
-30
1 2 3 4 5 6
Frequency (GHz)
Max
Nea
r E
tota
l (d
B)
Conclusion
1. Actual heat sink geometry must be simulated to determine type of resonance
2. Microstrip cavity type resonances can be suppressed with resistive loading
3. Optimum resistance values are in the range of 50 Ω
Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. BokhariSlide 25
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
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, [email protected]: 1.613-828-0063 Ext: 382
Slide 26 Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari
Dr. 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 Federalede 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, [email protected]: 1.613-828-0063 Ext: 377
Contact Fidus
Slide 27 Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari