AN533

Surface mount packages

19/22

2.4

Reflow soldering information

The surface mount assembly is a 4-step process.

1.

solder paste printing

2.

component placement on the board

3.

reflow soldering

4.

cleaning (optional)

The soldering process causes considerable thermal stress to a semiconductor component.

This has to be minimized to assure a reliable and extended lifetime of the device. SOT-23,

SOT-223, SO-8 and DPAK packages can be exposed to a maximum temperature of 260 °C

Overheating during the reflow soldering process may damage the device, therefore any

solder temperature profile should be within these limits. Reflow techniques are most

common in surface mounting. Typical heating profiles for leadfree solder (ST ECOPACK) are

given in Figure 19 for small packages (SOT-23, SOT-223, DPAK), either for mounting on a

FR4 or on metal-backed boards (IMS). Please refer to the IPC/JEDEC J-STD-020C

standard for further information about “small” and “large” component definitions.

Note:

Soldering profile defined in IPC/JEDEC J-STD-020C standard is used for reliability

assessment and typically describes warmest profiles used for component mounting, not the

necessary temperatures to achieve good soldering.

Wave soldering is not advisable for DPAK and D²PAK because it is almost impossible to

contact the whole package slug during the process.

Table 4.

Mounting method

Rth (j-a)

DPAK

FR4

70 °C/W

50 °C/W

FR4 with 10 cm² heatsink on board

40 °C/W

35 °C/W

FR4 with copper filled holes and external heatsink

13 °C/W

12 °C/W

IMS (40 cm²) in free air

9 °C/W

8 °C/W

IMS with external heatsink

4.5 °C/W

3.5 °C/W