10
Process Zone Symbol 'T Maximum 'T/'time or Duration
Heat Up P1, R1 25°C to 150°C 3°C/s
Solder Paste Dry P2, R2 150°C to 200°C 100s to 180s
Solder Reow P3, R3
P3, R4
200°C to 260°C
260°C to 200°C
3°C/s
-6°C/s
Cool Down P4, R5 200°C to 25°C -6°C/s
Time Maintained Above Liquidus Point, 217°C > 217°C 60s to 120s
Peak Temperature 260°C –
Time within 5°C of Actual Peak Temperature > 255°C 20s to 40s
Time 25°C to Peak Temperature 25°C to 260°C 8minutes
Recommended Reow Prole
50 100 300150 200 250
t-TIME
(SECONDS)
25
80
120
150
180
200
230
255
0
T - TEMPERATURE (°C)
R1
R2
R3
R4
R5
217
MAX 260C
60 sec to 90 sec
Above 217 C
P1
HEAT
UP
P2
SOLDER PASTE DRY
P3
SOLDER
REFLOW
P4
COOL DOWN
The reow prole is a straight-line representation of
a nominal temperature prole for a convective reow
solder process. The temperature prole is divided into
four process zones, each with dierent 'T/'time tem-
perature change rates or duration. The 'T/'time rates or
duration are detailed in the above table. The temperatures
are measured at the component to printed circuit board
connections.
In process zone P1, the PC board and component pins are
heated to a temperature of 150°C to activate the ux 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 component pins.
Process zone P2 should be of sucient time duration (100
to 180 seconds) to dry the solder paste. The temperature
is raised to a level just below the liquidus point of the
solder.
Process zone P3 is the solder reow zone. In zone P3, the
temperature is quickly raised above the liquidus point of
solder to 260°C (500°F) for optimum results. The dwell time
above the liquidus point of solder should be between 60
and 120 seconds. This is to assure proper coalescing of the
solder paste into liquid solder and the formation of good
solder connections. Beyond the recommended dwell
time the intermetallic mm growth within the solder con-
nections 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 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 6°C per second maximum.
This limitation is necessary to allow the PC board and
component pins to change dimensions evenly, putting
minimal stresses on the component.
It is recommended to perform reow soldering no more
than twice.
