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.
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 (TMAX) should not exceed 260°C.
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.
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.
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
Critical Zone
T L to Tp
Tp
T L
Ramp-up
tL
Ts
max
Ts
min
Ramp-down
ts
Preheat
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
Lead-Free Assembly
3°C/ second max
150°C
Average ramp‑up rate (Liquidus Temperature (TS(max) to Peak)
Preheat
Temperature Min (TS(min))
Temperature Max (TS(max)
)
200°C
Time (min to max) (tS)
60‑180 seconds
3°C/second max
217°C
Ts(max) to TL Ramp‑up Rate
Time maintained above:
Temperature (TL)
Time (tL)
60‑150 seconds
260 +0/‑5°C
20‑40 seconds
Peak Temperature (TP)
Time within 5 °C of actual
Peak temperature (tP)
Ramp‑down Rate
6°C/second max
8 minutes max
Time 25 °C to Peak Temperature
Note 1: All temperatures refer to topside of the package, measured on the package body surface
11
AVAGO [ AVAGO TECHNOLOGIES LIMITED ]
