6

Assembly Information

SOT-323 PCB Footprint

A recommended PCB pad layout for the miniature SOT-323

(SC-70) package is shown in Figure 12 (dimensions are in

inches). This layout provides ample allowance for package

placement by automated assembly equipment without

adding parasitics that could impair the performance.

SMT Assembly

Reliable assembly of surface mount components is a

complex process that involves many material, process, and

equipment factors, including: method of heating (e.g., IR

or vapor phase reflow, wave soldering, etc.) circuit board

material, conductor thickness and pattern, type of solder

alloy, and the thermal conductivity and thermal mass of

components. Components with a low mass, such as the

SOT-323/-23 package, will reach solder reflow tempera-

tures faster than those with a greater mass.

After ramping up from room temperature, the circuit board

with components attached to it (held in place with solder

paste) passes through one or more preheat zones. The

preheat zones increase the temperature of the board and

components to prevent thermal shock and begin evaporat-

ing solvents from the solder paste. The reflow zone briefly

elevates the temperature sufficiently to produce a reflow

of the solder.

The rates of change of temperature for the ramp-up and

cool-down zones are chosen to be low enough to not

cause deformation of the board or damage to components

due to thermal shock. The maximum temperature in the

reflow zone (T

MAX

) should not exceed 260°C.

These parameters are typical for a surface mount assembly

process for Avago diodes. As a general guideline, the circuit

board and components should be exposed only to the

minimum temperatures and times necessary to achieve a

uniform reflow of solder.

0.026

0.039

0.079

0.022

Dimensions in inches

0.039

1

0.039

1

0.079

2.0

0.031

0.8

Dimensions in

inches

mm

0.035

0.9

Figure 12. Recommended PCB Pad Layout

for Avago’s SC70 3L/SOT-323 Products.

Figure 13. Recommended PCB Pad Layout for Avago’s SOT-23 Products.

SOT-23 PCB Footprint