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
