physics and modeling of vias in printed circuit boards · physics and modeling of vias in printed...

Physics and Modeling of Vias in Printed Circuit Boards

Jan Birger Preibisch & Christian Schuster

Institute of Electromagnetic Theory

Hamburg University of Technology (TUHH)

18th European IBIS Summit Meeting

May 13th, 2015 Berlin, Germay

Jan Preibisch & Christian Schuster – 2

(1) The Problem with Vias

(2) Physics of Vias

(3) Models for Vias

(4) Application Example

(5) Conclusions

Outline


(2)

The Problem with Vias


The Problem with Vias …

Power Plane Ground Plane

Driver Via

Receiver DC Power Supply

PCB


Signal Integrity Problems:

Attenuation, Reflection, Dispersion, Interference, Crosstalk



Power Integrity Problems:

Voltage Drop, Switching Noise, Crosstalk



Electromagnetic Compatibility Problems:

Near Field Coupling, Radiated Emissions



(2)

Physics of Vias


Currents on Via Structures

Figures by R. Rimolo-Donadio

Via current Port 1

Conduction

return current

Ground

via

Displacement

return Current

Via (Signal) Current

Conduction Return Current

Displacement Return Current


Electric Fields Between Plates

Top View, 5th Cavity

Excitation: Gaussian pulse (fmax = 40 GHz)



Electric Fields Between Plates

Top View, 5th Cavity

Infinite Planes Finite Planes

Top View, 5th cavity



Influence of Ground Vias

1 Ground Via:

1 GND via

GND Via

SIG Via



2 Ground Vias:



4 Ground Vias:



6 Ground Vias:



Frequency [GHz]

Magnitude o

f S

12 [dB

]

1 GND vias

2 GND vias

4 GND vias

6 GND vias



Effect of location

of ground vias:

4 GND Vias, s=80 mil 4 GND Vias, s=40 mil

4 GND Vias, s=160 mil No GND Vias

GND Via

s


Physics of Vias – Summary

Vias „live“ within a parallel plate environment

Shape and size of the plates have an impact

Ground vias can be used to control that impact

Return currents are a mixture of displacement

and conduction currents

!


(3)

Models for Vias


PCB Teardown

Picture courtesy IBM Yorktown (Y. Kwark)

Power Planes

Stripline

Signal and

Power Vias

Transmission

Line Models

Planar Circuit

Models

Via Models


A “Physics-Based” Model for Vias

Via Cross Section

l

l

u

u

i

ipp

i

i

i

vZ

i

v

10

1

u

u

uu

u

i

i

pi

i

i

v

Zi

v

1/1

01

'

'

l

l

ll

l

i

i

pi

i

i

v

Zi

v

'

'

1/1

01

Cp

Zpp

Cp

viu

vil

iiu

iil

v'il

i'iu

i'il

vi

Cp

Cp

Zpp

Current

Current


A “Physics-Based” Model for Vias

Zpp

~60 fF

~60 fF

C

C

Port 1

Port 2

Port 1

Port 2

PMC

360x360 mil

8mil

r=4.4

tan=0.02

Via centered:

Radius 5mil

Antipad 10mil

Simple example:


Planar Circuit Model I

x

y

z

(0,0,0) (a,0,0)

(a,b,0)

(a,b,d)

Port i Port j (xi,yi)

Open

Plane

Edges

Voltage

Current

(xj,yj)

Filling with and m

CRM

m

kb

nk

a

mk

ynxm,,

otherwise 2 and 0,for 1 , nmCCnm

0 0

222

22pp)cos()cos()cos()cos(

)(

m n ynxm

jynjxmiynixm

nmij

kkk

ykxkykxkCC

ab

djZ

m


x

y

z

Separation d


No

Plane

Edges Voltage

Current

(xj,yj)

Filling with and m

)(

)(

2)(

0

)2(

1

)2(

0

0

pp

m

kH

kHjdZ

ij

ij

m k,dist.port,radiusport00

RWM

Planar Circuit Model II


25

x

y

z

Separation d


Any

Open

Plane

Edges Voltage

Current

(xj,yj)

Filling with and m

CIM

jikaHkaJ

jikRHkaJkaJ

j

akU

ii

jij

ij)2(

10

)2(

010

jikaHkaJ

jikRHkaJkaJdkH

ii

ji

ij)2(

00

)2(

000

2

HUZ

1pp

Planar Circuit Model III


Effect of Multiple Scatterings

Fields “seen by” CRM & RWG Fields “seen by” CIM

X. Duan, R. Rimolo-Donadio, S. Müller, K. Han, X. Gu, Y. Kwark, H.-D. Brüns, C.

Schuster, „Impact of Multiple Scattering on Passivity of Equivalent-Circuit Via

Models“, IEEE Electrical Design of Advanced Package & Systems Symposium

(EDAPS), Hangzhou, China, December 12-14, 2011.


Trace between planes:

2 Modes: Stripline + Parallel Plate

Stripline Mode

Parallel Plate Mode (pp)

Including Striplines


Complete Model for One Cavity

tlYkk

tlYkk

tlYkk

tlYkk

tlYk0

0tl

Yk

)()(

)()(

)( 22

22

1

vl

vu

Y0

0Y

l

u

I

I

T T

1uv

1ui

2uv

2ui

3uv

3ui

1lv

1li

2lv

2li

3lv

3li

u

uI

V

l

lI

V

pppp

pppp

YY

YY

Ztl Ztl

Zpp Zpp Zpp Zpp

l

u

V

V

vC

vC

vC

vC

vC v

C

R. Rimolo-Donadio, X. Gu, Y. H. Kwark, M. B. Ritter, B. Archambeault, F. D. Paulis, Y.

Zhang, J. Fan, H.-D. Brüns, C. Schuster, “Physics-based via and trace models

for efficient link simulation on multilayer structures up to 40 GHz,” IEEE Trans.

on Microwave Theory and Techniques, vol. 57, no. 8, pp. 2072-2083, August 2009.


Complete Model for Full PCB

Cavity

representation S-Parameter

Matrix

Port 1 Port n

Cavities merged

using

segmentation

techniques

Zpp Ztl

Decap

Linterc.

Zpp Ztl

Decap

Linterc.

Decap

Linterc.

Decoupling capacitor model

Cavity

representation

Port 1 Port n

Port k






6 Vias, 4 traces case

Centered striplines at two

levels, and thru vias in a 6

cavity stackup

Full-wave model

Comparison with Full-Wave Results

Mag

nit

ud

e of

S12 [

dB

]

Frequency [GHz]

Model

FEM simulation

FIT simulation Full-wave model M

agn

itu

de

of

S14 [

dB

]

Frequency [GHz]

Model

FEM simulation

FIT simulation


Comparison with Full-Wave Results





Computation is 2 to 3 orders of magnitude faster in comparison

to general-purpose numerical methods!

3D Model required

Field information available

High level description (text-based)

Network Parameters


• 119 vias (76 signal,

43 ground)

• 14 differential

striplines (2D)

• 6 cavities

• Terminations

Comp. time: < 3 min

Assumption

of infinite

plates

Comparison with Measurements






Models capture the salient features of the

hardware response despite simplifications

|S13| [dB] - FEXT |S12| [dB] - IL

Link 10 -

S3 Stripline

Link 17 -

S5 Stripline

Link 10 -

S3 Stripline

Link 17 -

S5 Stripline

Measurement Link 10

Measurement Link 17

Model Link 10

Model Link 17




Horizontal Eye Opening [ps] (10 ps/div)

Vert

ical E

ye O

penin

g [V

]

Model

0.598 V

65.63 ps

tr=10 pS

15 Gbps

Measurement

0.552 V

65.63 ps

Link L5

Simulation of the time domain link performance up to

15 Gbps within 10% accuracy!


Models for Vias – Summary

Physics based via models can predict SI, PI,

and EMC issues on PCBs up to tens of GHz

They do this (very) efficiently

They do this (quite) accurately

… but limitations exist with regard to shape,

size, and proximity of vias!

!


(4)

Application Example


1. Design of Controlled Vias

Calculation of Ground and Displacement Return Currents using CIM



Effect of Number of Ground Vias



Engineering Rules for Design



Application Example

The via shows a typical transmission line behavior (reflection)

The transmission is above -1dB up to 40GHz 13 layers


Application Examples – Summary

Physics based via models can be used to

mitigate common SI and PI issues

They are especially useful for pre-layout analysis

Due to their efficiency PCB layout automation

and optimization become „viable“

!


For More Information

Published in IEEE Transactions on Components, Packaging,

and Manufacturing Technology, vol. 3, no. 3, March 2013


Contact Information

Jan Birger Preibisch,

Prof. Dr. sc. techn. Christian Schuster

Institut für Theoretische Elektrotechnik

Technische Universität Hamburg-Harburg

Harburger Schloss Str. 20

21079 Hamburg, Germany

Tel: +49 40 42878 3116

WWW: http://www.tet.tu-harburg.de/

E-Mail: [email protected], [email protected]

physics and modeling of vias in printed circuit boards · physics and modeling of vias in printed...

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