INFORMATION FOR USING THE SOT–223 SURFACE MOUNT PACKAGE
MINIMUM RECOMMENDED FOOTPRINT FOR SURFACE MOUNTED APPLICATIONS
Surface mount board layout is a critical portion of the total
design. The footprint for the semiconductor packages must
be the correct size to insure proper solder connection
interface between the board and the package. With the
correct pad geometry, the packages will self align when
subjected to a solder reflow process.
SOT–223 POWER DISSIPATION
The power dissipation of the SOT–223 is a function of
the pad size. This can vary from the minimum pad size for
soldering to the pad size given for maximum power dissipa-
tion. Power dissipation for a surface mount device is deter-
mined by TJ(max), the maximum rated junction temperature
of the die, RθJA, the thermal resistance from the device
junction to ambient; and the operating temperature, TA. Us-
ing the values provided on the data sheet for the SOT–223
package, PD can be calculated as follows.
TJ(max) – TA
The values for the equation are found in the maximum
ratings table on the data sheet. Substituting these values into
the equation for an ambient temperature TA of 25°C, one
can calculate the power dissipation of the device which in
this case is 1.5 watts.
150°C – 25°C
= 1.50 watts
The 83.3°C/W assumes the use of the recommended
footprint on a glass epoxy printed circuit board to achieve
a power dissipation of 1.5 watts. Another alternative would
be to use a ceramic substrate or an aluminum core board
such as Thermal Clad™. Using a board material such as
Thermal Clad, a higher power dissipation of 1.6 watts can
be achieved using the same footprint.
The melting temperature of solder is higher than the rated
temperature of the device. When the entire device is heated
to a high temperature, failure to complete soldering within
a short time could result in device failure. Therefore, the
following items should always be observed in order to
minimize the thermal stress to which the devices are
• Always preheat the device.
• The delta temperature between the preheat and
soldering should be 100°C or less.*
• When preheating and soldering, the temperature of the
leads and the case must not exceed the maximum
temperature ratings as shown on the data sheet. When
using infrared heating with the reflow soldering
method, the difference should be a maximum of 10°C.
• The soldering temperature and time should not exceed
260°C for more than 10 seconds.
• When shifting from preheating to soldering, the
maximum temperature gradient should be 5°C or less.
• After soldering has been completed, the device should
be allowed to cool naturally for at least three minutes.
Gradual cooling should be used as the use of forced
cooling will increase the temperature gradient and
result in latent failure due to mechanical stress.
• Mechanical stress or shock should not be applied dur-
* Soldering a device without preheating can cause exces-
sive thermal shock and stress which can result in damage
to the device.