14
Figure 35. Surface Mount Assembly Profile.
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 packages, will reach solder reflow
temperatures faster than those with a greater mass.
Avago’s diodes have been qualified to the time‑tem‑
perature profile shown in Figure 35. This profile is repre‑
sentative of an IR reflow type of surface mount assembly
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
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 Reflow Profile Recommendation (IPC/JEDEC J-STD-020C)
Reflow 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
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 reflow zone briefly elevates the temperature suffi‑
ciently 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 compo‑
nents 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.
