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