Control of Electromagnetic Radiation from Integrated

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, cristian.tudor@fidus.comTel: 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, syed.bokari@fidus.comTel: 1.613-828-0063 Ext: 377

Contact Fidus

Slide 27 Control of Electromagnetic Radiation from Integrated Circuit Heat sinks - Cristian Tudor & S. Bokhari