20-30GHz SHP Mixer
Application note
CHM1290REF
The design of the motherboard has a strong impact on the over all performance since
the transition from the motherboard to the package is comparably large. In case of
the SMD-type packages of United Monolithic Semiconductors the motherboard
should be designed according to the information given in the following to achieve
good performance. Other configurations are also possible but can lead to different
results. If you need advise please contact United Monolithic Semiconductors for
further information.
SMD-type packages of UMS should allow design and fabrication of micro- and mm-
wave modules at low cost. Therefore, a suitable motherboard environment has been
chosen. All tests and verifications have been performed on Rogers RO4003. This
material exhibits a permittivity of 3.38 and has been used with a thickness of 200µm
[8 mils] and a 1/2oz or less copper cladding. The corresponding 50 Ohm
transmission line has a strip width of about 460µm [approx. 18 mils].
The contact areas on the motherboard for the package connections should be
designed according to the footprint given above. The proper via structure under the
ground pad is very important in order to achieve a good RF and lifetime performance.
All tests have been done by using a grid of plenty plated through vias with a diameter
of less than 200µm [8 mils] and a spacing of less than 400µm [16 mils] from the
centres of two adjacent vias. The via grid should cover the whole space under the
ground pad and the vias closest to the RF ports should be located near the edge of
the pad to allow a good RF ground connection. Since the vias are important for heat
transfer, a proper via filling should be guaranteed during the mounting procedure to
get a low thermal resistance between package and heat sink. For power devices the
use of heat slugs in the motherboard instead of a via grid is recommended.
For the mounting process the SMD-type package can be handled as a standard
surface mount component. The use of either solder or conductive epoxy is possible.
The solder thickness after reflow should be typical 50µm [2 mils] and the lateral
alignment between the package and the motherboard should be within 50µm [2 mils].
Caution should be taken to obtain a good and reliable contact over the whole pad
areas. Voids or other improper connections, in particular, between the ground pads of
motherboard and package will lead to a deterioration of the RF performance and the
heat dissipation. The latter effect can reduce drastically reliability and lifetime of the
product.
Ref. : DSCCHM1290REF2239 -27-Aug.-02
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Specifications subject to change without notice
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UMS [ UNITED MONOLITHIC SEMICONDUCTORS ]
