MMSD301T1 MMSD701T1

http://onsemi.com

4

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 225 milliwatts.

INFORMATION FOR USING THE SOD–123 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.

SOD–123 POWER DISSIPATION

PD =

TJ(max) – TA

R

θJA

PD =

150

°C – 25°C

556

°C/W

= 225 milliwatts

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 dissipa-

tion. Power dissipation for a surface mount device is deter-

mined by TJ(max), the maximum rated junction temperature

of the die, R

θJA, 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:

The 556

°C/W for the SOD–123 package assumes the use

of the recommended footprint on a glass epoxy printed

circuit board to achieve a power dissipation of 225 milli-

watts. There are other alternatives to achieving higher

power dissipation from the SOD–123 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. There-

fore, the following items should always be observed in

order to minimize the thermal stress to which the devices

are subjected.

soldering should be 100

°C or less.*

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.

260

°C for more than 10 seconds.

maximum temperature gradient shall be 5

°C or less.

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.

during cooling.

* Soldering a device without preheating can cause exces-

sive thermal shock and stress which can result in damage

to the device.

SOD–123

mm

inches

0.91

0.036

1.22

0.048

2.36

0.093

4.19

0.165