MMSZ5221BT1 Series

Motorola TVS/Zener Device Data

7-6

500 mW Leadless (SOD-123) Data Sheet

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,

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:

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 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.

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.