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Substrate permittivity Substrate permittivity

Substrate permittivity - PowerPoint Presentation

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Substrate permittivity - PPT Presentation

measurement for PCB Printed Technology Circuits 20162017 José Carlos Martínez Durillo Index Background Importance and implications of in PCB design Methods ID: 598993

results pcb substrate design pcb results design substrate connection implications importance comparison experimental process methods http www factor resonant

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Presentation Transcript

Slide1

Substrate permittivity measurement for PCB

Printed Technology Circuits – 2016/2017José Carlos Martínez DurilloSlide2

Index

BackgroundImportance and implications of

in PCB

design

MethodsSetting up the substrate. Connection processTheoretical resultsExperimental Results. Comparison.ConclusionsReferences

 Slide3

Background

data is provided

by

the manufacturer  

Not

too

accurate

sometimes.

specs. for Bungard FR4 susbtrate

 

Manufacturer, substrate…

Depending

on

€€Slide4

Importance and implications of

in PCB design 

Velocity

Factor

 

Ratio of

the

speed

at

which

a

certain

signal passes through a medium, such as a PCB.

The

higher

the

slower the signal passes through the PCB Slide5

Importance and implications of

in PCB design 

Also

,

if affects to…

Impedance

Capacitance

Strip

width

…Slide6

Importance and implications of

in PCB design 

Also

,

if affects to…

Impedance

Capacitance

Strip

width

…Slide7

Importance and implications of

in PCB design Slide8

Importance and implications of

in PCB design 

Given

a

choice, lower permittivity is nearly always BETTER

Usual

assumption

unvarying

with

f

 

WRONGSlide9

Importance and implications of

in PCB design 

Example

of

dispersion with frequency Slide10

Importance and implications of

in PCB design 

Design

phase Design requirements

Signal

type

Low

loss

Steady behaviourSimulation & analysis

measurement

 More accurateRefine requirementsDesign prototype…

Methods

…Slide11

Methods

Capacitance method ->

Very

size-dependant

->

Hard

to

get

acceptable

results

Resonant cavity-like treatment -> PCB≈2D open-sided cavity

Using an oscilloscope -> Voltage across a resistor between supply and capacitor is measured -> Complex procedure

Time Domain Reflection -> By using reflectometry, velocity factor is estimated and from it, permittivity.Slide12

Methods

Resonant

cavity-like

treatment

Based

on

treating

the substrate like a 2D open-sided cavity

Each resonance corresponds to an integral “wave number” or “mode number” in each direction (length and width)Slide13

Methods

Depending

on

the

dimensions

of

the

substrate, resonances will vary

L and W

equal -> First two resonances fall at the same f -> 2nd resonance with p=0 and q=1… 

Countless

combinations

Does

not affect the results! Slide14

Methods

Measuring

f

for

a

given

p and q,

:

 

Improved

accuracy

Howell

& Wang

Correction

factor to

take

losses into account

Neglectable

if Q>100Slide15

Methods

Measuring

f

for

a

given

p and q,

:

 

Improved

accuracy

Howell

& Wang

Correction

factor to

take

losses into account

Neglectable

if Q>100Slide16

Setting up the substrate

We

will

measure

FR4

substrate

of 1.5748 mm

width

.

Substrate

is cut of 284x35.60 mm using LPKF S62 PCB Prototyping Milling MachineSlide17

Connection process

Again

,

different

possibilities

:

Needs

two

SMASlide18

Connection process

Again

,

different

possibilities

: Slide19

Connection processSlide20

Connection processSlide21

Connection processSlide22

Connection process

For

simplicity

,

we

try

the

simplest

and

cheapest one: reflection

SMA

Connection in a cornerSlide23

Theoretical results

We

asume

=4

 Slide24

Experimental Results. Comparison.

We

must

calibrate

the

network

analyzer before:

Open, short and loadSlide25

Experimental Results. Comparison.

Measured

AdjustedSlide26

Experimental Results. Comparison.

is

calculated

with

:

 

Mean: 3.963Slide27

Experimental Results. Comparison.

resonant

frequency Slide28

Experimental Results. Comparison.

resonant

frequency Slide29

Experimental Results. Comparison.

To

evaluate

the

accuracy

of

the

results

, theoretical frequencies are calculated again, considering =3.963 

0.227 %

deviationSlide30

Conclusions

Keeping

in

mind

the

importance

of

the

permittivity is a vital matter when designing PCB. Depending on the quality of the substrate, the tolerance given by the manufacturer may not be accurate enough.Measurement techiques

must be carried then, to ensure a

correct behaviour of the substrate. This paper has gone through some of them.Slide31

References

http://www.ce-granollers.com/placa_virgen1.htm

FR4

Datasheet

: http://www.bungard.de/images/downloads/ipc4101d.pdf

http

://www.wetterlin.org/sam/SA/Operation/PCB_Diel_Const.pdf

Electromagnetic

Waveguides, S.F. Mahmoud, 1991.

http

://www.sglabs.it/public/SgLabs_HP_85036B_5.JPG

Wang, “Determining Dielectric Constant and Loss-Tangent in FR-4”, UMR, 2000.Slide32

Any

questions

?