SMF5.0AT1 Series
http://onsemi.com
6
INFORMATION FOR USING THE SOD−123 FLAT LEAD 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.
RECOMMENDED FOOTPRINT FOR SOD−123FL
mm
inches
0.91
0.036
1.22
0.048
2.36
0.093
4.19
0.165
POWERMITE POWER DISSIPATION
The power dissipation of the SOD−123 Flat Lead is a
function of the mounting 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 T
J(max)
, the
maximum rated junction temperature of the die, R
θ
JA
, the
thermal resistance from the device junction to ambient, and
the operating temperature, T
A
. Using the values provided
on the data sheet for the SOD−123 Flat Lead package, P
D
can be calculated as follows:
P
D
=
T
J(max)
− T
A
R
θ
JA
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 T
A
of 25°C,
one can calculate the power dissipation of the device which
in this case is 385 milliwatts.
P
D
=
150°C − 25°C
= 385 milliwatts
325°C/W
The 325°C/W for the SOD−123 Flat Lead package
assumes the use of the recommended footprint on a glass
epoxy printed circuit board to achieve a power dissipation
of 385 milliwatts. There are other alternatives to achieving
higher power dissipation from the SOD−123 Flat Lead
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.
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.
