Surface mount packages

AN533

18/22

Figure 18.

Mounting techniques for power SMDs

As the FR4 board is commonly used in surface mounting techniques, there are several ways

of overcoming its low thermal performance:

●

use of large heat spreader areas (heat sink) at the copper layer of the PCB

●

use of copper-filled through holes in addition to an external heatsink for an even better

thermal management

However, due to its power dissipation limitation, using the FR4 board with these techniques

is advisable only for currents up to 8 A max.

A technology available today is Insulated Metallic Substrate (IMS). This offers greatly

enhanced thermal characteristics for surface mount components. IMS is a substrate

consisting of three different layers:

●

base material which is available as an aluminum or a copper plate

●

thermal conductive dielectric layer

●

copper foil, which can be etched as a circuit layer.

Even if a higher power is to be dissipated, an external heatsink can be applied leading to an

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 fully

exploited.

The designer should carefully consider which is appropriate mounting method (see Table 4)

to be used according to the dissipated power. The type of board will influence the thermal

techniques for DPAK and D²PAK.

Copper

foil

Insulation

Aluminium / copper

FR4 board

Copper

foil

Footprints

Copper

foil

FR4 board

Heatsink

Copper-filled

through-holes

Copper

foil

Insulation

Aluminium / copper

Heatsink

1

3

2

4