20-30GHz SHP Mixer

CHM1290REF

Ref. : DSCCHM1290REF2239 -27-Aug.-02

5/6

Specifications subject to change without notice

Route Départementale 128 , B.P.46 - 91401 ORSAY Cedex - FRANCE

Tel.: +33 (0)1 69 33 03 08 - Fax : +33 (0)1 69 33 03 09

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.