6.
Reinstallation of Components
6.1 Hot
air level the pads. In most instances, sufficient solder will
remain on the pads to attach a new chip; but the surface may
be rough, uneven, or have solder "icicles", making
accurate placement of a new chip impossible. To hot air level,
Locate the circuit board (still in the Board Holder) under the
nozzle, with the component removed, depress the foot pedal to
begin the heating cycle. It is recommended to add a little more
flux to the contact area to ensure thorough wetting, don’t
worry about flux residue as a cleaning process 6.3 will remove
residues. The GREEN display will begin counting DOWN to zero.
The solder will melt and become smooth; the solder should cover
the pad(s) completely, with a slightly rounded "pillow"
shape.
6.2 Remove
the board and board holder assembly from beneath the Chipmaster
nozzle (depress cylinder, slide holder and board out). Let the
board cool to ambient temperature.
Using the
Cleaning Fluid Pad Prep Pen from the SMT Tool Kit, release sufficient
fluid by, depressing the valve at the tip to soak the area and
using the cleaning tip proceed to clean entire contact and surrounding
area, using an Antistatic wipe 8200-1500 to finally remove all
traces of contamination and old material.
6.4 If there
is insufficient solder to cover the contact pad(s), add solder
using wire solder or solder paste and a soldering iron. Apply
no-clean paste flux to aid wetting and clean afterwards with
Pad Prep Cleaner as 6.3.
Now that
the contact pads are coplanar and free of all residues and contaminates,
apply a thin line of no-clean paste flux (0.025") around
all contacts and with the double sided "clean and flux"
brush supplied in the SMT Tool Kit, use the softer and longer
flux brush end to brush the flux from outside the contacts to
the center, ensure all contacts are adequately fluxed, it’s
important that too much flux is not applied otherwise the component
will float off position during reflow.
Now, take
a new component, (the removed component may be reinstalled if
required, providing leads are coplanar), and holding the center
of the component between thumb and forefinger of the right hand
and with clear view of the entire left hand side and half view
of the top and bottom of the component, place the component,
aligning the Y axis (left side) and then gently aligning top
and bottom half sides.
A small
hand 2.3 dioptic magnifier 8200-1200 held in the left hand easily
provides all the vision needed to align. Once the component
is in place gently release the chip out and away to the right,
the flux will support the component. Probes supplied in the
SMT Tool Kit will aid fine alignment or the entire alignment
procedure dependent upon personal preference. Aligning one full
side and two halves should align all four sides but each lead
must be exactly centered over the contact pads. The no-clean
paste flux will hold the component in place during reflow (melting)
of the solder. This flux will dissipate, however, by the completion
of the heating cycle. The component corners may be tagged with
a soldering iron for extra support prior to reflow, if so desired.
6.7 Place
the board under the nozzle of the Chipmaster, being careful
to center the component under the nozzle as accurately as possible.
Press the
INDEX key on the Chipmaster controller ONCE, and verify the
eutectic (Removal) time, now add twenty (20) seconds to this
eutectic time to provide sufficient time to reflow the entire
component. Use the UP arrows as described previously and press
ENTER to save the change. Press the INDEX key FOUR times to
return to the "Operator View Display".
Depress
the foot pedal to begin the heating cycle, (Illustration # 7).
When the timer reaches zero, the reflow is complete, wait for
the solder, component and board to cool remove the Board Holder
and inspect your work.
(Illustration # 7)
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