AN1703 - APPLICATION NOTE

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First of all we have to note that the maximum allowable power dissipation for the newest small packages

(PowerFLAT and PowerSO-8) is quite similar to that for DPAK but require approximately half the PC board

space. This advantage is more impressive if we note that the max die housed in PowerFLAT (6x5 version)

is about 30% greater than those in DPAK. Also SOT-223 has a high thermal performance, but the max die

housed is half that of those for DPAK and PowerSO-8.

Since several automotive applications require devices rated at 175 °C, up to now only the standard SMD

withstand the high stresses in under-hood applications.

12. SOLDERING PROFILE

The most commonly used techniques for mounting SMD packages to the PCB are infrared and vapor

phase reflow. These are preferred over wave soldering because this typically involves increased heating

rate, higher temperatures and increased flux exposure.

The infrared reflow technique involves thermal energy supplied via lamps radiating at given wavelengths.

Therefore, the amount of thermal energy absorbed varies with board size, component size, component

orientation, and materials used. The surface temperature of the board is not uniform and the board edges

tend to run 10°C to 20°C higher than the center.

The vapor phase reflow technique uses vapor from a boiling inert fluorocarbon liquid. The heat of

condensation provides a thermal constraint dependent on the liquid selected. With essentially no

temperature gradient across the surface of the board, component location design rules even for heating

is not significant compared to infrared reflow.

The theoretical solder reflow temperature profile used, and the temperatures and time duration are shown

in the next figure:

Figure 30: Soldering profile, recommended reflow oven profile

Temp.

°C

Time (sec)

** Package volume

* Tmax=235 +5 / -0

°C

** Tmax=220 +5 / -0

°C

max 20 sec