M2031 Datasheet, PDF (1/2 Pages) M/A-COM Technology Solutions, Inc. – Printed Circuit Board Design for LSM1 VCO’s

Application Note
M2031
Printed Circuit Board Design
for LSM1 VCO’s
Introduction
To achieve the best performance from M/A-COM’s
LSM1 VCO series, it is critical that good design
practices are used in the layout of the printed cir-
cuit board. This application note describes the pad
footprint recommended for solder attachment and
some of the electrical and thermal considerations
to incorporate into the pcb design.
Footprint Guidelines
The pad footprint defined on the pcb must be the
correct size to ensure a proper solder connection
interface between the board and the package.
With the correct pad geometry, the packages will
self align when subjected to a solder reflow proc-
ess and will also allow for just enough excess sur-
face area for adequate solder filleting. The follow-
ing pad footprint is a recommended guideline only
and may require additional ground plane areas for
electrical and/or thermal considerations. When an
increase in pad or ground plane size such as this is
implemented, the additional copper area should be
covered by a solder resist mask so as to leave only
the recommended pad footprint available for at-
tachment. This will contain the solder reflow and
eliminate any alignment problems during reflow
soldering.
Rev. V4
Electrical and Thermal Considerations
The circuit board used in the LSM1 VCO package
is FR-4 material with a thickness of 0.8 mm (0.032
inch). The package interconnection pads are 1 oz.
copper with a finish of 0.15 µm gold flash over 5
µm nickel plate.
The electrical performance of the VCO may be im-
proved by extending the ground plate area beyond
the pad footprint. For example, a continuous
ground plane under the base of the VCO linking up
all of the defined ground areas will improve ground-
ing of the VCO and reduce phase noise. It is im-
portant to cover any additional pcb ground area
with a solder resist mask so as to maintain the rec-
ommended attachment footprint. Depending on
the output frequency of the VCO, additional via
holes may also be necessary in the ground plane
of the pcb to minimize unwanted ground reactance.
The RF output track on the circuit board should be
designed as a 50 ohm impedance microstrip line
where the width of the line is calculated in accor-
dance with the dielectric constant and thickness of
the pcb used. The RF output should operate into a
50 ohm load with VSWR less than 1.5:1 at a mini-
mum distance from the VCO.
LSM1 Footprint
1
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