SMT Assembly
Reliable assembly of surface mount components is a com‑
plex 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 fast‑
er than those with a greater mass.
Avago’s diodes have been qualified to the time‑tempera‑
ture profile shown in Figure 28. This profile is representa‑
tive of an IR reflow type of surface mount assembly pro‑
cess.
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.
tp
Ramp-up
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 sufficiently to pro‑
duce 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 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 reflow of solder.
Tp
Critical Zone
T
L
to Tp
T
L
Temperature
Ts
max
t
L
Ts
min
Preheat
ts
Ramp-down
25
t 25
°
C to Peak
Time
Figure 28. Surface Mount Assembly Profile.
Lead-Free Reflow Profile Recommendation (IPC/JEDEC J-STD-020C)
Reflow Parameter
Average ramp‑up rate (Liquidus Temperature (T
S(max)
to Peak)
Preheat
Temperature Min (T
S(min)
)
Temperature Max (T
S(max)
)
Time (min to max) (t
S
)
Ts(max) to TL Ramp‑up Rate
Time maintained above:
Peak Temperature (T
P
)
Time within 5 °C of actual
Peak temperature (t
P
)
Ramp‑down Rate
Time 25 °C to Peak Temperature
Temperature (T
L
)
Time (t
L
)
Lead-Free Assembly
3°C/ second max
150°C
200°C
60‑180 seconds
3°C/second max
217°C
60‑150 seconds
260 +0/‑5°C
20‑40 seconds
6°C/second max
8 minutes max
Note 1: All temperatures refer to topside of the package, measured on the package body surface
11
AVAGO [ AVAGO TECHNOLOGIES LIMITED ]
