Analysis of Test Coupon Structures for the Extraction

of High Frequency PCB Material Properties

Heidi Barnes

Bob Schaefer

Jose Moreira

‘SPI 20131

AGENDA

2 ‘SPI 2013

� EM Simulation and PCB Material Properties

� 2-Line Segment ( dK, loss tan, conductivity)

� Resonant Beatty Structure (dK height, trace width)

� Measurement Based Parameter Tuning Results

Measurement Based Verification of EM Simulation

3 ‘SPI 2013

EM Simulations are

only as accurate as the

PCB specifications

Simple Series Resonant Change in Impedance

Frequency Domain

EM Simulation Fails to Match Measurement

Time Domain

PCB Conductor and Dielectric Material Properties

4

‘SPI 2013

+

+=Ζ

tw

tb

r8.0

2ln

60

εο

Z0, characteristic impedance (Ohm)

b, the dielectric height between reference planes (mil)

t, copper thickness of the PCB trace (mil)

w, trace width (mil)

, dielectric constant

, is the speed of light in vacuum

, loss tangent

rε

dielconddB ααα +=

fwZ

cond

0

36=α

r

o

diel fc

εδπ

α tan=

oc

δtan

PCB Frequency Dependent Losses

can be separated into Conductor

and Dielectric Losses

Stripline Dielectric Losses only

require 1 line length to determine

dielectric loss and electrical delay.

Stripline Conductor Losses require

more then 1 line width to determine

dielectric height and trace width.

5 ‘SPI 2013

Typical Method for Measured PCB Material Properties

Two PCB Test Structures with Different Line Lengths

� Excellent for determining T-Line loss and delay characteristics

� Does not provide information on as-built trace width and dK height.

FIXTURE AS-PARAMETERS

FIXTURE BS-PARAMETERS

SYMMETRICAL 2x FIXTURE THROUGH PATH

Splitting of the

S-Parameters

Agilent PLTS AFR Algorithm

Step 1

FIXTURE

DE-EMBED

FIXTURE + ADDITIONAL LINE LENGTHT-LINE LENGTH

MATERIAL PROPERTIES

T-Matrix

Step 2

6 ‘SPI 2013

Additional PCB Resonant Beatty Structure

Beatty Style Series Resonant Change in Impedance Test Structure

� Enables estimation of as-fabricated dK height and trace width.

� Only requires one additional test structure on the PCB.

� Simple layout construction.

T-Line Change in ZFabrication Properties

FIXTURE

DE-EMBED

T-Matrix

Step 3FIXTURE + Resonant Beatty Structure

FIXTURE

DE-EMBED

Step 3

S-Parameters before Fixture De-Embed Measured S-Parametersafter Fixture De-Embed

7 ‘SPI 2013

VarEqn VAR

VAR6

t=0.6

TanD=0.0058328 {t}

W=9.4 {t}

sigma=42936000 {t}

W_tol=-1.1 {t}

b=7.9 {t}

Er=3.22 {t}

Dielectric Constant

Loss Tangent

Dielectric Height

Trace Width

Etching Tolerance

Trace thickness

Copper Trace Conductivity

As-Fabricated

Material Properties

Tune Model Variables

to Match Measurement

Enables Estimate of Trace Width and DK Height

Series Resonant Beatty Structure

8 ‘SPI 2013

2-Step Process: Fast Tuning with 2D-Planar Model then Fine Tune with EM Simulator

Fast Tune 2D-Planar Model Parameters to Match Measured Data

* Simple T-Line model with out the complexity of fixture connections

9 ‘SPI 2013

Matching Measured Data – Time and Frequency

Transmission Line Through Segment Series Resonant Beatty Structure

10 ‘SPI 2013

Final 3D EM Model vs. Measurement

Frequency Domain

Fine Tune EM Model Parameters to Match Measured Data

• Dielectric Constant

• Dielectric Height

• Trace Width

• Etching Tolerance

• Loss Tangent

• Copper Trace Conductivity

Parameters for Tuning

Time Domain

3D EM Model

11 ‘SPI 2013

Comment on Measured Data Accuracy

Measurement Accuracy

Quality of the Fixture

Measured vs 3D-EM Simulated

Requires Symmetry

Measure

Model

Conclusion

12 ‘SPI 2013

� Matching Measurement with Simulation needs PCB Test Structures

� Transmission line losses only require 2 test coupon structures

� The addition of a series resonant structure enables estimates of as

fabricated dimensions for accurate EM simulations

� PCB test structures validate both PCB fabrication requirements as well as

simulation set-ups.