Fig 2 : Mounting on epoxy FR4 head dissipation by extending the area of the copper layer

Fig 3 : Mounting on epoxy FR4 by using copper-filled through holes for heat transfer

FR4 board

Copper foil

FR4 board

Copper foil

heat transfer

heatsink

SUBSTRATES AND MOUNTING INFORMATION

The use of epoxy FR4 boards is quite common for

surface mounting techniques, however, their poor

thermal conduction compromises the

otherwise

outstandingthermal performanceof the PowerSO-

10. Some methods to overcome this limitation are

discussed below.

One possibility to improve the thermal conduction

is the use of large heat spreader areas at the cop-

per layer of the PC board. This leads to a reduction

of thermal resistance to 35

board heatsink (see fig. 2).

Use of copper-filled through holes on conventional

FR4 techniques will increase the metallization and

decrease thermal resistance accordingly. Using

a configurationwith 16 holes under the spreader of

the package with a pitch of 1.8 mm and a diameter

of 0.7 mm, the thermal resistance (junction -

heatsink) can be reduced to 12

°C/W (see fig. 3).

Beside the thermal advantage, this solution allows

multi-layer boards to be used. However, a draw-

back of this traditional material prevent its use in

very high power, high current circuits. For instance,

it is not advisable to surface mount devices with

currents greater than 10 A on FR4 boards. A

Power Mosfet or Schottky diode in a surface mount

power package can handle up to around 50 A if

better substrates are used.

®

CLP200M

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