6
Figure 8. Surface Mount Assembly Prole.
25
Time
Temperature
Tp
T
L
tp
t
L
t 25° C to Peak
Ramp-up
ts
Ts
min
Ramp-down
Preheat
Critical Zone
T
L
to Tp
Ts
max
Lead-Free Reow Prole Recommendation (IPC/JEDEC J-STD-020C)
Reow Parameter Lead-Free Assembly
Average ramp-up rate (Liquidus Temperature (T
S(max)
to Peak) 3°C/ second max
Preheat Temperature Min (T
S(min)
) 150°C
Temperature Max (T
S(max)
) 200°C
Time (min to max) (t
S
) 60-180 seconds
Ts(max) to TL Ramp-up Rate 3°C/second max
Time maintained above: Temperature (T
L
) 217°C
Time (t
L
) 60-150 seconds
Peak Temperature (T
P
) 260 +0/-5°C
Time within 5 °C of actual Peak temperature (t
P
) 20-40 seconds
Ramp-down Rate 6°C/second max
Time 25 °C to Peak Temperature 8 minutes max
Note 1: All temperatures refer to topside of the package, measured on the package body surface
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 reow, 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 package, will reach solder reow temperatures faster
than those with a greater mass.
Avago’s SOT diodes have been qualied to the time-
temperature prole shown in Figure 8. This prole is
representative of an IR reow type of surface mount as-
sembly process.
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 evaporating solvents from the solder paste. The
reow zone briey elevates the temperature suciently
to produce a reow 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 compo-
nents due to thermal shock. The maximum temperature
in the reow zone (T
MAX
) should not exceed 260°C.
These parameters are typical for a surface mount assem-
bly 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 reow of solder.
