7. Reflow Removal Procedure.
This procedure follows all of the
steps detailed in the Eutectic Procedure above with
the exception of contacting the Vacuum Pick Up
Assembly before eutectic condition so as to remove
the component automatically when all leads reach the
condition, In the Reflow Removal Procedure the vacuum
is turned on, but the Vacuum Pick Up Assembly is not
connected until the component is completely
re-flowed.
It is critical in this procedure to
use the no-clean paste flux and ensure all the leads
contain flux before proceeding to remove the
component as described previously.
The reflow time can either be
calculated by close observation of the component
during reflow, so that when the front, (easily
visible), leads can be seen to be re-flowing, a time
of twenty seconds (20) is added by noting the timer
and waiting until the extra 20 seconds is completed,
at which time the entire component is at reflow
condition and the Vacuum Pick Up Assembly can be
lowered Or as can be seen by the foregoing Eutectic
Procedure, from learning the time from performing a
single Eutectic Removal and the Reflow Time entered
into a written procedure for future repair operations
on the same type of component on the same circuit
board.
Once Reflow has been reached,
depress the Vacuum Pick Up Assembly lightly and
gently down by hand, do not be heavy handed, a light
and slow moving pressure should be applied with the
forefinger, (avoid pressing the component into the
reflowed solder on the contact pads, which could
cause bridging), observe under the nozzle as the
vacuum cup almost reaches the component body, the
body will lift to the cup and you may slowly draw the
component up into the nozzle, don’t release, but
control the Vacuum Pick Up Assembly all the way back
to the rest position. Release the Foot Pedal and the
Reflow Time will be recorded.
It is not necessary to hot air
level the contact pads as the contact pads are
coplanar and free of spikes or bridging, next clean
as previously described and apply new no-clean paste
flux.
The Chipmaster, (Illustration # 8)
is a Low Temperature operation machine and will not
damage board, components or degrade solder, providing
Low Temperatures are used, this is recommended to be
less than 450F (232C). Effectively this increases the
"Window of opportunity" to rework a
component and if for any reason you don’t
succeed first time you may retry with confidence that
you will not cause damage. As with any skill related
activity, experience breeds success and practice will
make the user highly skilled and the Chipmaster will
respect the skills you have learned.
