HP LT3200, Руководство по обслуживанию

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HP High-Definition LCD TV Service Manual
5
Attachment of SMDs
1 Locate the SMD on the solder lands by means of
tweezers and solder the component on one side. Ensure
that the component is positioned correctly on the solder
lands (A).
2 Complete the soldering of the terminals of the
component (B).
CAUTIONS:
•
When soldering the SMD terminals, do not touch them
directly with the soldering iron. The soldering should be
done as quickly as possible; care must be taken to avoid
damage to the terminals of the SMDs themselves.
•
Keep the SMD’s body in contact with the printed board
when soldering.
•
The soldering iron to be used (approximately 30 W)
should preferably be equipped with a thermal control
(soldering temperature: 360º to 380º C).
•
Soldering should not be done outside the solder land.
•
Soldering flux (of rosin) may be used but should not be
acidic.
•
After soldering, let the SMD cool down gradually at
room temperature.
•
The quantity of solder must be proportional to the size
of the solder land. If the quantity is too great, the SMD
might crack or the solder lands might be torn loose from
the printed board.
Rework on Ball Grid Array (BGA) ICs
General information
Although (LF) BGA assembly yields are very high, there
may still be a requirement for component rework. By
rework , we mean the process of removing the component
from the PWB and replacing it with a new component. If an
(LF) BGA is removed from a PWB, the solder balls of the
component are deformed drastically so the removed (LF)
BGA has to be discarded.
Device removal
As is the case with any component that, it is essential when
removing an (LF) BGA, the board, tracks, solder lands, or
surrounding components are not damaged. To remove an
(LF) BGA, the board must be uniformly heated to a
temperature close to the reflow soldering temperature. A
uniform temperature reduces the chance of warping the
PWB. To do this, we recommend that the board is heated
until it is certain that all the joints are molten. Then
carefully pull the component off the board with a vacuum
nozzle. For the appropriate temperature profiles, see the IC
data sheet.
Area Preparation
When the component has been removed, the vacant IC area
must be cleaned before replacing the (LF) BGA.
Removing an IC often leaves varying amounts of solder on
the mounting lands. This excessive solder can be removed
with either a solder sucker or solder wick. The remaining
flux can be removed with a brush and cleaning agent. After
the board is properly cleaned and inspected, apply flux on
the solder lands and on the connection balls of the (LF)
BGA.
NOTE:
Do not apply solder paste, as this has shown to
result in problems during resoldering.
Device replacement
The last step in the repair process is to solder the new
component on the board. Ideally, the (LF) BGA should be
aligned under a microscope or magnifying glass. If this is
not possible, try to align the (LF) BGA with any board
markers. To reflow the solder, apply a temperature profile
according to the IC data sheet. To avoid damaging
neighboring components, it may be necessary to reduce
some temperatures and times.