MMBD701LT1 View Datasheet(PDF) -

MBD701 MMBD701LT1

INFORMATION FOR USING THE SOT–23 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

0.037

0.95

interface between the board and the package. With the

correct pad geometry, the packages will self align when

subjected to a solder reflow process.

0.037

0.95

0.035

0.9

0.079

2.0

0.031

0.8

SOT–23

inches

mm

SOT–23 POWER DISSIPATION

The power dissipation of the SOT–23 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 tempera-

ture of the die, RθJA, the thermal resistance from the

device junction to ambient, and the operating tempera-

ture, TA. Using the values provided on the data sheet for

the SOT–23 package, PD can be calculated as follows:

PD =

TJ(max) – TA

RθJA

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.

PD =

150°C – 25°C

556°C/W

= 225 milliwatts

The 556°C/W for the SOT–23 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 SOT–23 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 exces-

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