Printed circuit board material R
th
(j-a) P Diss
1.FR4 using the recommended pad-layout 50 °C/W 1.5 W
2.FR4 with heatsink on board (6cm
2
) 35 °C/W 2.0 W
3.FR4 with copper-filled through holes and external heatsink applied
12 °C/W 5.8 W
4. IMS floating in air (40 cm
2
) 8 °C/W 8.8 W
5. IMS with external heatsink applied 3.5 °C/W 20 W
TABLE 1
A new technology available today is IMS - an Insu-
lated Metallic Substrate. This offers greatly en-
hanced thermal characteristics for surface
mount components. IMS is a substrate consisting
of three different layers, (I) the base material which
is available as an aluminium or a copper plate, (II)
a thermal conductive dielectrical layer and (III) a
copper foil, which can be etched as a circuit layer.
Using this material a thermal resistance of 8°C/W
with 40 cm
2
of board floating in air is achievable
(see fig. 4). If even higher power is to be dissipated
an external heatsink could be applied which leads
to an R
th
(j-a) of 3.5°C/W (see Fig. 5), assuming
that R
th
(heatsink-air) is equal to R
th
(junction-
heatsink). This is commonly applied in practice,
leading to reasonable heatsink dimensions. Often
power devices are defined by considering the
maximum junction temperature of the device. In
practice , however, this is far from being exploited.
A summary of various power management capa-
bilities is made in table 1 based on a reasonable
delta T of 70°C junction to air.
The PowerSO-10 concept also represents an
attractive alternative to C.O.B. techniques.
PowerSO-10 offers devices fully tested at low
and high temperature. Mounting is simple - only
conventional SMT is required - enabling the users
to get rid of bond wire problems and the problem to
control the high temperature soft soldering as well.
An optimized thermal management is guaranteed
through PowerSO-10 as the power chips must in
any case be mounted on heat spreaders before
being mounted onto the substrate.
Fig. 4 :
Mounting on metal backed board
Fig. 5 :
Mounting on metal backed board with an
external heatsink applied
FR4 board
Copper foil
Aluminium
heatsink
Copper foil
Insulation
Aluminium
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use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted by
implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject to
change without notice. This publication supersedes and replaces all information previously supplied.
STMicroelectronics products are not authorized for use as critical components in life support devices or systems without express written ap-
proval of STMicroelectronics.
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