39 / 84
Figure 1: plastic encapsulated MMIC
devices.
Figure 3: semi-sealed and open component assemblies
Figure 2: hermetically sealed cavity packages.
the dielectric properties of the circuit,
resulting in shifts in RF performance.
For example, mixers and limiters are
generally unaffected by contact with
conformal coating, whereas VCOs and
diplexers are sensitive and unsuitable for
conformal coating unless contained in a
sealed case.
The Solution: Proprietary
Sealing Method
In an ideal world, we would simply adopt
hermetically sealed cavity packaging
for everything to withstand customers’
assembly processes, but there are
practical limits to this solution. Hermetic
packaging adds significant cost to the
component, and it is highly impractical
to make hermetically sealed packages for
larger structures. Therefore an alternative
technique to adapt open and semi-sealed
surface mount components for hi-rel
assembly without adding extraneous cost
or technical inconvenience to the process
is highly desirable.
In response to customer requirements
for open and semi-sealed components
in our catalog for systems undergoing
hi-rel assembly processes, Mini-Circuits
developed a proprietary sealing method
to protect these components during the
aqueous wash process and enable them
to operate reliably within the customer
conformal coat. A special pre-coating
is applied to certain areas of the Mini-
Circuits unit, which prevents direct
contact of the cleaning solution and the
customer’s conformal coat with the unit’s
sensitive circuitry. This pre-coating has
been qualified to withstand the conditions
of customer reflow, aqueous wash, and
conformal coating processes without
failures or shifts in RF performance.
The pre-coating seals the sensitive
areas of the unit such that during the
customer’s reflow process, there is no
wicking of solder or creation of solder
balls in the sealed structure, which would
otherwise cause reliability problems. This
economical technique can be used to
adapt open or semi-sealed surface-mount
components in Mini-Circuits’ catalog to
preserve reliability in hi-rel assembly
processes for minimal increase in cost.
Conclusion:
The trend toward aqueous wash and
conformal coating in hi-rel applications
means components that were once
universally used will be increasingly
unsuitable for integration into customer
assembly processes in their standard
form. Fortunately, Mini-Circuits has now
developed a cost-effective approach
to adapt non-sealed surface mount
components for outstanding reliability in
customer assembly processes involving
aqueous wash and conformal coating.
This gives customers the freedom to select
components without limitations based
on case style. Open and semi-sealed
parts may be adapted for customers
utilizing aqueous wash and conformal
coating without adding inordinate cost
or complexity to their board design or
assembly process.
Figure 4: Pre-coating
on air coil legs.
Figure 5: Pre-
coating on weld
spot
Figure 6: Pre-
coating on
inductor.
New-Tech Magazine Europe l 39