MMSZ5221BT1 Series
http://onsemi.com
6
INFORMATION FOR USING THE SOD-123 SURFACE MOUNT PACKAGE
MINIMUM RECOMMENDED FOOTPRINTS FOR SURFACE MOUNT 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 ensure proper solder connection
interface between the board and the package.
The minimum recommended footprint for the SOD-123
is shown at the right.
The SOD-123 package can be used on existing surface
mount boards which have been designed for the leadless 34
package style. The footprint compatibility makes
conversion from leadless 34 to SOD-123 straightforward.
mm
inches
0.91
0.036
1.22
0.048
2.36
0.093
4.19
0.165
Figure 11. Minimum Recommended Footprint
SOD-123 POWER DISSIPATION
The power dissipation of the SOD-123 is a function of
the pad size. This can vary from the minimum pad size for
soldering to a pad size given for maximum power
dissipation. Power dissipation for a surface mount device is
determined by TJ(max), the maximum rated junction
temperature of the die, RJA, the thermal resistance from
the device junction to ambient; and the operating
temperature, TA. Using the values provided on the data
sheet for the SOD-123 package, PD can be calculated as
follows:
PD = TJ(max) - TA
RJA
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 0.37 watts.
PD = 150°C - 25°C
340°C/W = 0.37 watts
The 340°C/W for the SOD-123 package assumes using
recommended footprint shown on FR-4 glass epoxy printed
circuit board. Another alternative is to use a ceramic
substrate or an aluminum core board such as
Thermal Clad. By using an aluminum core board
material such as Thermal Clad, the power dissipation can
be doubled using the same footprint.
GENERAL SOLDERING PRECAUTIONS
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
subjected.
•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 shall be a maximum of 10°C.
•The soldering temperature and time shall not exceed
260°C for more than 10 seconds.
•When shifting from preheating to soldering, the
maximum temperature gradient shall 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 cooling
* Soldering a device without preheating can cause excessive
thermal shock and stress which can result in damage to the
device.