Title
Author One° , Author Two+ , Author Three*
Affiliation One, Dept of Electrical Engineering, University of L’Aquila, L’Aquila, Italy
e-mail: xxxxx@ing.univaq.it
+
UAq EMC Laboratory, Dept of Electrical Engineering, University of L’Aquila, L’Aquila, Italy
e-mail: yyyyyy@ing.univaq.it
*
Affiliation Three, Dept of Electrical Engineering, University of L’Aquila, L’Aquila, Italy
e-mail: yyyyyy@ing.univaq.it
°
Abstract – In this paper a methodology for taking into
account the frequency dependence of a possible referencing
(grounding) techniques in LTCC boards for satellite
applications is presented. The aim of this work is to analyze
and compare the input impedance and S-parameters values
for different strategies of inter connection of the reference
planes among them.
The numerical analysis presented has proven the
importance of the lateral metallization set up in the LTCC
board working into a metal housing. For board used stand
alone the lateral metallization can be replaced by an
adequate density of vias stitching among the planes. The
modelling agrees well with real grounding solution.
I. INTRODUCTION
Due to the increasing of the bit rates and the decreasing
of the voltage and noise margins, it is known that a
correct design of the power delivery network of hybrid
digital/RF systems is becoming a critical issue.
For all PCB a correct design of the voltage reference
system (very often referred as Ground or GND) [1] is
fundamental either to maintain a correct balance and
stability of the supply voltage used to supply the active
devices and to control the impedance of the passive
interconnections.
A nowadays used technique to achieve these goals is to
connect all reference planes to each other with the aim to
make the reference system almost totally equipotential at
least in a defined range of frequencies.
The way to do this changes from application to
application. In satellite systems, due to the requirements
of reliability, this is done by the combination of internal
stitching vias between the reference (GND) planes and an
external lateral metallization of the full edges of the
LTCC substrate as represented in Fig. 1
The limit of this technology is the impossibility to
automate it and this implies an increase of the associated
costs and time of production.
Because of this there is the need to explore other
solutions for the connections of reference planes in order
to reduce their production costs ensuring adequate
electrical performances.
In this paper is carried out an analysis of the electrical
performances of cheaper technological solution: the
replacement of the lateral metallization by a properly
designed array of internal and external stitching vias
among the reference planes. This solution allows one to
save time, eliminating the straining and drying operations
for the metallization gold around the LTCC substrate.
A three dimensional (3D) electromagnetic analysis, based
on the Finite Integration Technique [3,4] is used to
characterize the electrical performances of the structures
considered.
The paper is organized as follows: in Section II the
geometric details of the considered configurations are
presented along with the figures of merits used to
establish the differences between the proposed solutions.
In Section III the performances’ analysis is carried out for
different densities of the stitching vias. In this Section is
also performed a comparison between the performances
of the actual and proposed configuration. In section IV it
is explored the impact of the metal housing of the LTCC
board on the performances of the proposed configuration
with stitching vias. Finally section V offers some
concluding remarks.
Fig. 1- An LTCC board with lateral metallization.
II. THE CONSIDERED CONFIGURATIONS AND
FIGURES OF MERIT
The figures of merit chosen to measure the goodness of
the interconnection among reference planes by using the
classic solution of lateral metallization or the proposed
one with internal and external stitching vias are:
 the input impedance Zin looking into the board from a
port localized between the first two planes for
different configuration of the reference planes
connections
 the scattering parameter (and in particular S21) of a
microstripe for different configurations of the
connections of the strip’s reference plane to the other
planes.
(a)
(b)
Fig. 2 – SMA connectors: (a) lateral view and (b)
perspective view with waveguide port [4].
After having developed the computational model as
described above a new computation of the S-parameters
between the IN and OUT connectors (see Fig. 14) is
performed.
The results are shown in Fig. 17a and 17b for the usual
three configurations defined in Section III as:
I. full metalized (see Fig. 8 a)
II. stitching (see Fig. 8b)
III. metalized only at the front ends (see Fig. 8c)
[dB
As expected the presence of the housing, of the
connectors and of the bonding changes the shape of the
S-parameters and in particular of |S21|.
The full metalized and metalized only at the front end
models are quite similar with a maximum difference of
0.5 dB at around 10 GHz.
Different consideration should be done for the stitching
model: the partial inductance introduced by the stitching
vias causes at certain frequencies (12.5 GHz in Fig. 17b
for example) significant peaks due to the resonance with
the distributed capacitance of the planes. Resonances
peaks, as shown in Fig.17b.
For the case considered, below 10 GHz, there is an
almost perfect overlapping among the three
configurations considered.
III. CONCLUSIONS
A detailed analysis has been carried out in order to
identify the better figures of merit to quantify the effects
of the connection of multiple reference planes in real
configurations of LTCC board used in satellite
applications.
Input impedance of the planes’ cavities and the Sprameters of interconnections using the reference planes
have been identified and computed by means of three
dimensional full wave electromagnetic simulations.
Multiple conneting strategies have been considered and
from the total amount of results obtained it turns out that
an adequate density of internal vias, stitching the planes
among them, is equivalent to the costly (in terms of time
and money) solution of the full lateral golden
metallization.
This result opens interesting technological scenarios in
the production of these boards.
ACKNOWLEDGMENTS
Frequency [GHz]
(a)
This work was supported by the Italian Ministry of
University (MIUR) under a Program for the Development
of Research of National Interest (PRIN grant #
2006095890).
REFERENCES
[dB
[1]
I. , III.
II.
Frequency [GHz]
(b)
Fig. 3 –LTCC board inside the metal box: (a) frequency
spectrum of |S11| and (b) frequency spectrum of |S21|.
B. Archambeault, PCB Design for Real-World EMI Control,
Kluwer Academia Publisher, Boston, USA, 2002
[2] J.L.Drewniak at All., “An experimental procedure for
characterizing interconnects to the DC power bus on a multilayer
printed circuit board”, IEEE Trans. on Electromagn.
Compatibility, vol. n. 39, n. 4, November 1997.
[3] T. Weiland, “A Discretization Method for the Solution of
Maxwell’s Equation for Six Component Fields”, Electronics and
communication, (AEÜ), Vol. .31 (1977), p. 116.
[4] CST STUDIO SUITE 2008, available at www.cst.com