AN668 datasheet(16/19 Pages) STMICROELECTRONICS

16 / 19 page

AN668 APPLICATION NOTE

16/19

by the copper slug becomes very evident (Figure 25).

Due to the thermal capacitance of the slug, the tran-

sient thermal impedance of PowerSO-20/36 after 1

sec pulse duration is 4 times lower.

A summary of the thermal performance of PowerSO-

20/36 considering the different mounting approaches

is given in Table 3, assuming that the maximum rated

temperature of the device is 150°C and that the

∆Tj

is 50°C.

Table 3. Thermal performance (

∆Tj: 50°C)

Figure 24. Thermal impedance of different

packages

Figure 25.

SOLDERING INFORMATION

The soldering process causes considerable thermal

stress to a semiconductor component. This has to be

minimized to ensure a reliable and extended lifetime

of the device.

PowerSO-20/36 are certified as MSL3 according to

Jedec STD 020A

As eflow techniques are the most common in surface

mounting, typical heating profiles are given in Figure

26, with a preheating at 130 - 150°C for 80 -100 sec-

onds, either for mounting on FR4 epoxy substrate or

mounting on metal-backed boards (IMS). Peak tem-

perature should be at least 30°C higher than the

melting point of the solder chosen.

Figure 26.

PowerSO-20/36 packages

mounted on

Rth(j-a)

Pdiss

FR4 using the rec-

comended pad lay-out

50°C/W

1.0W

FR4 with heat sink on

board (6 cm2)

35°C/W

1.4 W

FR4 with heatsink (6

cm2) and ground

20°C/W

2.5W

FR4 with 16 via holes

and ground layer

15°C/W

3.3W

FR4 with 16 via holes

and external heatsink

12°C/W

4.2W

IMS floating in air

(40cm2)

7°C/W

IMS with external heat-

sink applied

2.5°C/W

20W

120

160

200

240

280

320

360

Time (sec)

100

150

200

245˚C

D94AN017

T (˚C)

250

215˚C

EPOXY FR4

BOARD

METAL-BACKED

BOARD

Preheating

Cooling

Soldering

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