Printed circuit board material

P Diss

1.FR4 using the recommended pad-layout

50

°C/W

1.5 W

2.FR4 with heatsink on board (6cm

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

8.8 W

5. IMS with external heatsink applied

3.5

°C/W

20 W

TABLE 1

A new technologyavailable 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

(see fig. 4). If even higher power is to be dissipated

an external heatsink could be applied which leads

°C/W (see Fig. 5), assuming

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

Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences of

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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© 1998 STMicroelectronics - Printed in Italy - All rights reserved.

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