Abstract
Design and manufacturing techniques of printed circuit boards
(PCB's) have advanced from early one or two-layer structures
to the multilayer boards where ten or more layers are no longer
uncommon. These give additional routing space, potential decrease
in device size and various design possibilities like solid ground
and power planes. Unfortunately multilayer boards are vulnerable
to high coupling between signal vias especially due to PCB resonances.
In this study via crosscoupling is investigated on multilayer
PCB's. Special attention is given to the coupling due
to resonances and vertically aligned blind vias. Problem is approached
from the electromagnetic compatibility (EMC) point of view and
high accuracy of measurements or models is not the objective. Instead
ways to increase isolation are considered important. EMC is considered
to include internal functionality of the device.
Analytical methods are used to calculate resonant frequencies,
fields and quality factors for simple rectangular structures. The
PCB cavity is reduced to two-dimensions for numerical calculation
of same quantities. Aplac finite-difference time-domain simulator
is used to model coupling due to PCB resonances. Isolation between
vertically aligned blind vias is estimated analytically. A quasi-static
numerical model is used to study a coaxial via structure. Multilayer
test boards are constructed for measurement purposes. Simplified
resonator structures on two-layer boards are used to test different
methods to increase isolation.
Measurements show that high coupling between vias may occur
due to PCB resonances. This leads to the situation, where previously
used isolation methods between vias are not necessarily effective
enough. Several means to reduce effects of PCB resonances are described
in this study. Measured and modelled results agree well from an
EMC point of view. Coupling due to vertically aligned blind vias
is also shown to be high. A simple capacitance model may be used
to approximate this up to frequencies where the dynamic wave nature
of the board starts to be important. From a PCB designer's
point of view these results mean that when the board size is not
small compared to the wavelength, there is a possibility of resonances
and reduction methods have to be taken into account. Also placement
of the vias have to be carefully selected especially if blind or
buried vias are used.
| Identifer | oai:union.ndltd.org:oulo.fi/oai:oulu.fi:isbn951-42-5189-X |
| Date | 23 March 1999 |
| Creators | Tarvainen, T. (Timo) |
| Publisher | University of Oulu |
| Source Sets | University of Oulu |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess, © University of Oulu, 1999 |
| Relation | info:eu-repo/semantics/altIdentifier/pissn/0355-3213, info:eu-repo/semantics/altIdentifier/eissn/1796-2226 |
Page generated in 0.0021 seconds