INFORMATION FOR USING THE SOT–363 SURFACE MOUNT PACKAGE
MINIMUM RECOMMENDED FOOTPRINTS FOR SURFACE MOUNTED APPLICATIONS
Surface mount board layout is a critical portion of the total
interface between the board and the package. With the
design. The footprint for the semiconductor packages must
correct pad geometry, the packages will self align when
be the correct size to insure proper solder connection
subjected to a solder reflow process.
0.5 mm (min)
SOT–363 POWER DISSIPATION
The power dissipation of the SOT–363 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
dissipation. Power dissipation for a surface mount device is
determined by TJ(max), the maximum rated junction tempera-
ture of the die, RθJA, the thermal resistance from the device
junction to ambient; and the operating temperature, TA.
Using the values provided on the data sheet, 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 150 milliwatts.
150°C – 25°C
PD = 833°C/W = 150 milliwatts
The 833°C/W for the SOT–363 package assumes the use
of the recommended footprint on a glass epoxy printed circuit
board to achieve a power dissipation of 150 milliwatts. There
are other alternatives to achieving higher power dissipation
from the SOT–363 package. 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, an aluminum core board, the power dissipation can be
doubled 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 during
* Soldering a device without preheating can cause excessive
thermal shock and stress which can result in damage to the
Motorola Small–Signal Transistors, FETs and Diodes Device Data