
11
Figure 5. Reflow Profile.
representative for additional
details.
Figure 5 is a straight line
representation of a nominal
temperature profile for a
convective IR reflow solder
process. The temperature profile
is divided into four process zones
with four ∆T/∆time temperature
change rates. The ∆T/∆time
temperature change rates are
detailed in Table 1. The
temperatures are measured at the
component to printed-circuit (pc)
board connections.
In process zone P1, the pc
board and HSDL-2300
castellation I/O pins are heated to
a temperature of 125˚C to
activate the flux in the solder
paste. The temperature ramp up
rate, R1, is limited to 3˚C per
second to allow for even heating
of both the pc board and
HSDL-2300 castellation I/O pins.
Process zone P2 should be of
sufficient time duration to dry the
solder paste. The temperature is
raised to a level just below the
liquidus point of the solder,
usually 170˚C (338˚F).
Process zone P3 is the solder
reflow zone. In zone P3, the
temperature is quickly raised
above the liquidus point of solder
to 230˚C (446˚F) for optimum
results. The dwell time above the
liquidus point of solder should be
between 15 and 90 seconds. It
usually takes about 15 seconds to
assure proper coalescing of the
solder balls into liquid solder and
the formation of good solder
connections. Beyond a dwell time
of 90 seconds, the intermetallic
growth within the solder
connections becomes excessive,
resulting in the formation of weak
and unreliable connections. The
temperature is then rapidly
reduced to a point below the
solidus temperature of the solder,
usually 170˚C (338˚F), to allow
the solder within the connections
to freeze solid.
Process zone P4 is the cool
down after solder freeze. The
cool down rate, R5, from the
liquidus point of the solder to
25˚C (77˚F) should not exceed
–3˚C (26.6˚F) per second
maximum. This limitation is
necessary to allow the pc board
0
t-TIME (SECONDS)
T – TEMPERATURE – (°C)
200
170
125
100
50
15 60 90 120 150 195
30 45 75 105 135 165 180 210
150
183
230
P1
HEAT UP P2
SOLDER PASTE DRY P3
SOLDER
REFLOW
P4
COOL DOWN
25
R1
R2
R3 R4
R5
90 sec.
MAX.
ABOVE
183°C
Table 1. Reflow Process Zones.
Process Zone Symbol ∆T∆T/∆Time
Heat Up P1, R1 25˚C to 125˚C 3˚C/s max.
Solder Paste Dry P2, R2 125˚C to 170˚C 0.5˚C/s max.
Solder Reflow P3, R3 170˚C to 230˚C (235˚C max.) 4.0˚C/s typ.
P4, R4 230˚C to 170˚C –4.0˚C/s typ.
Cool Down P4, R5 170˚C to 25˚C –3˚C/s max.