24-26GHz High Power Amplifier
CHA5093TCF
Application note
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. : DSCHA50932035 - 04-Feb.-02
4/6
Specifications subject to change without notice
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Tel.: +33 (0)1 69 33 03 08 - Fax : +33 (0)1 69 33 03 09
UMS [ UNITED MONOLITHIC SEMICONDUCTORS ]
