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Sometimes a change in belt speed is all that is needed for different PCB’s unless there is a radical
difference in assembly density. The existence of heavy ground planes or heat sinks in multi-layer PCB’s
may require refining of profiles.
Correct profiling depends on board configuration, throughput requirements and solder paste. Consult the
solder paste manufacturer's recommendations for ramp-up rates, activation temperature, cure time and
cure temperatures. Asymtek ovens have been used successfully with a wide variety of solder pastes
including the new generation of "no clean" pastes. See below for typical temperature profiles for eutectic
and lead free solder.
Ideally the maximum differential between the highest and lowest temperature on the circuit board should be
less than 20°C, the hottest spot should be less than 40°C above the solder melting temperature and the
lowest temperature should be greater than 15°C above the solder melting temperature.
In general, it is possible to set up one generic profile and vary the belt speed to obtain acceptable results
with different types of board assemblies. Boards that are predominately populated with small resistor or
capacitor chips may be run at a faster rate than boards densely populated with large PLC's. Belt speeds for
all boards must be determined experimentally. {Factory default belt speeds are 170X model 23.6 in/minute
(60 cm/minute), 180X model 31.5 in/minute (80 cm/minute) and 191X model 39.4 in/minute (100
cm/minute)}
Good starting points for setting temperatures (in
O
C) are as follows:
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