SEF 551.10, Руководство по эксплуатации

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Page 7.3
7.0 Soldering profile management and production
Profile management 551.19 \ 12.2015 \
Parameter adjustment
Parameters for
temperature profile
Preheating time
An soldering or curing profile adapted to the assembled PCB is
the prerequisite for an optimal soldering result.
A profile depends on several factors:

Temperatures of the single process phases

Dwell times

Assembly of the PCB
The manufacturers of the solder pastes provide very detailed
information about the temperature-time regime. The component
industry mostly gives information about the short-term or long
term temperature limits which a component can resist.
In the IPC JEDEC J-STD 020C you will find qualification criteria
for electronic components which should be used with soldering
processes.
For the quantifying of a soldering profile the following criteria will
be examined (see Figure 5-1 - classification reflow profil):
Increase gradient / maximum ramp-up dT/dt
Preheating time t
s
Peak temperature T
p
Time to peak t
p
Time above melting temperature
(liquidus)
t
L
Decrease gradient / maximum ramp-down -dT/dt
The following sections give information about the single profile
characteristics:
Preheating
Contrary to standard IPC/JEDEC J-STD-020C the preheating
time often is defined as time between an individual start tem
-
perature (e.g. 25°C, start of the process) and the achievement of
the melting temperature (liquidus) of the solder (e.g. for Sn63Pb
is T
L
= 183 °C). In standard JEDEC J-STD-020C the preheating
time t
s
is given as time from reaching Ts
min
and the achievement of
T
s
max
. This time must be optimised under the observance of the
following influences. Resins are the active part of the flux in the
solder paste. The melting points are in the range between 70°C
and 120°C which means in the range of the preheating tempera-
ture. It is reasonable to keep the preheating time short because
at higher temperatures the permanent accumulation of oxide on
the metal surfaces of the join partners will consume flux con