PZTA92T1

2

Motorola Small–Signal Transistors, FETs and Diodes Device Data

INFORMATION FOR USING THE SOT–223 SURFACE MOUNT PACKAGE

POWER DISSIPATION

The power dissipation of the SOT–223 is a function of the

pad size. These 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, 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

SOT–223 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 1.5 watts.

PD =

150

°C – 25°C

83.3

°C/W

= 1.5 watts

The 83.3

°C/W for the SOT–223 package assumes the

recommended collector pad area of 965 sq. mils on a glass

epoxy printed circuit board to achieve a power dissipation of

1.5 watts. If space is at a premium, a more realistic

approach is to use the device at a PD of 833 mW using the

footprint shown. Using a board material such as Thermal

Clad, a power dissipation of 1.6 watts can be achieved using

the same footprint.

MOUNTING 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.

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 should be a maximum of 10

°C.

260

°C for more than 10 seconds.

maximum temperature gradient should 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.

cooling

* Soldering a device without preheating can cause excessive

thermal shock and stress which can result in damage to the

device.

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.

0.079

2.0

0.15

3.8

0.248

6.3

0.079

2.0

0.059

1.5

0.059

1.5

0.059

1.5

0.091

2.3

mm

inches

0.091

2.3

SOT–223