Tyco Electronics Corp.. 17
Data Sheet
July 2002 dc-dc Converters; 36 to 75 Vdc Input, 3.3 Vdc Output; 165 W to 198 W
FW250F1 and FW300F1 Power Modules:
Thermal Considerations (continued)
Heat Transfer with Heat Sinks (continued)
Then solve the following equation:
Use Figures 27 and 28 to determine air velocity for the
0.5 inch heat sink. The minimum airflow necessary for
the FW250F1 module depends on heat sink fin orienta-
tion and is shown below:
■ 2.0 m/s (400 ft./min.) (oriented along width)
■ 3.0 m/s (600 ft./min.) (oriented along length)
Custom Heat Sinks
A more detailed model can be used to determine the
required thermal resistance of a heat sink to provide
necessary cooling. The total module resistance can be
separated into a resistance from case-to-sink (θcs) and
sink-to-ambient (θsa) as shown in Figure 30.
8-1304 (C)
Figure 30. Resistance from Case-to-Sink and Sink-
to-Ambient
For a managed interface using thermal grease or foils,
a value of θcs = 0.1 °C/W to 0.3 °C/W is typical. The
solution for heat sink resistance is:
This equation assumes that all dissipated power must
be shed by the heat sink. Depending on the user-
defined application environment, a more accurate
model, including heat transfer from the sides and bot-
tom of the module, can be used. This equation pro-
vides a conservative estimate for such instances.
Solder, Cleaning, and Drying
Considerations
Post solder cleaning is usually the final circuit-board
assembly process prior to electrical testing. The result
of inadequate circuit-board cleaning and drying can
affect both the reliability of a power module and the
testability of the finished circuit-board assembly. For
guidance on appropriate soldering, cleaning, and dry-
ing procedures, refer to the
Board-Mounted Power
Modules Soldering and Cleaning
Application Note
(AP97-021EPS).
EMC Considerations
For assistance with designing for EMC compliance,
please refer to the FLTR100V10 data sheet
(DS98-152EPS).
Layout Considerations
Copper paths must not be routed beneath the power
module standoffs. For additional layout guidelines, refer
to the FLTR100V10 data sheet (DS98-152EPS).
θca
T
C TA–()
P
D
------------------------
=
θca
85 40–()
42
------------------------
=
θca 1.07 °C/W=
PD
TC TS TA
θcs θsa
→
θsa
T
C TA–()
P
D
-------------------------
θcs–=
