Yaesu FT-840 Service Manual page 5

Replacing Chip Components
Chip components are installed at the factory
by a series of robots. The first one places a spot
of adhesive resin at the location where each
part is to be installed, and later robots handle
and place parts using vacuwn suction.
For single-sided boards, solder paste is ap­
plied and the board is then baked to harden the
resin and flow the solder. For double-sided
boards, no solder paste is applied, but the
board is baked (or exposed to ultra-violet light)
to cure the resin before dip soldering.
In
our laboratories and service shops, small
quantities of chip components are mounted
manually by applying a spot of resin, placing
them with tweezers, and then soldering by
very small dual streams of hot air (without
physical contact during soldering). We remove
parts by first removing solder using a vacuwn
suction iron, which applies a light, steady vac­
uum at the iron tip, and then breaking the
adhesive with tweezers.
The special vacuwn soldering/ desoldering
equipment is recommended if you expect to do
a lot of chip replacements. Otherwise, it is
usually possible to remove and replace chip
components with only a tapered, temperature­
controlled soldering iron, a set of tweezers and
braided copper solder wick. Soldering iron
temperature should be less than 280 °C (536
OF).
FT-840 Technical Supplement
Chip Component Information
Precautions for Chip Replacement
)( Do not disconnect a chip forcefully, or the
foil pattern may peel off the board.
)(Never re-use a chip component. Dispose of
all removed chip components immediately
to avoid mixing with new parts.
)( Limit soldering time to 3 seconds or less to
avoid damaging the component and board.
Removing Chip Components
D Remove the solder at each joint, one joint at
a time, using solder wick whetted with
non-acidic flux as shown below. Avoid ap­
plying pressure, and do not attempt to re­
move the tinning from the chip's electrode.
D Grasp the chip on both sides with tweezers,
and gently twist the tweezers back and
forth (to break the adhesive bond) while
alternately heating each electrode. Be care­
ful to avoid peeling the foil traces from the
board. Dispose of the chip when removed.
D After removing the chip, use the copper
braid and soldering iron to which away any
excess solder and smooth the land for in­
stallation of the replacement part.
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