MMSF3205

4

Motorola TMOS Power MOSFET Transistor Device Data

INFORMATION FOR USING THE SO–8 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 ensure 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.

mm

inches

0.060

1.52

0.275

7.0

0.024

0.6

0.050

1.270

0.155

4.0

SO–8 POWER DISSIPATION

The power dissipation of the SO–8 is a function of the input

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

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 SO–8

package, PD can be calculated as follows:

PD =

TJ(max) – TA

R

θJA

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 1.6 Watts.

PD =

150

°C – 25°C

80

°C/W

= 1.6 Watts

The 80

°C/W for the SO–8 package assumes the

recommended footprint on a glass epoxy printed circuit board

to achieve a power dissipation of 1.6 Watts using the footprint

shown. Another alternative would be to use a ceramic

substrate or an aluminum core board such as Thermal Clad

™.

Using board material such as Thermal Clad, 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.

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.

temperature gradient shall be 5

°C or less.

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.

cooling.

* Soldering a device without preheating can cause excessive

thermal shock and stress which can result in damage to the

device.