Philips 202P70/00, Руководство по обслуживанию

Страница: 86 / 90

86
Go to cover page
IBM C190 Plum
0. Warning
All ICs and many other semi-conductors are susceptible to
electrostatic discharges (ESD). Careless handling during
repair can reduce life drastically. When repairing, make sure
that you are connected with the same potential as the mass
of the unit via a wrist wrap with resistance. Keep components
and tools also at the same potential !
1. Servicing of SMDs (Surface Mounted Devices)
1.1 General cautions on handling and storage
- Oxidation on the terminals of SMDs results in poor soldering.
Do not handle SMDs with bare hands.
- Avoid using storage places that are sensitive to oxidation
such as places with sulphur or chlorine gas, direct sunlight,
high temperatures or a high degree of humidity. The
capacitance or resistance value of the SMDs may be
affected by this.
- Rough handling of circuit boards containing SMDs may
cause damage to the components as well as the circuit
boards. Circuit boards containing SMDs should never be
bent or flexed. Different circuit board materials expand and
contract at different rates when heated or cooled and the
components and/or solder connections may be damaged
due to the stress. Never rub or scrape chip components as
this may cause the value of the component to change.
Similarly, do not slide the circuit board across any surface.
1.2 Removal of SMDs
- Heat the solder (for 2-3 seconds) at each terminal of the
chip. By means of litz wire and a slight horizontal force,
small components can be removed with the soldering iron.
They can also be removed with a solder sucker (see Fig.
1A)
- While holding the SMD with a pair of tweezers, take it off
gently using the soldering iron's heat applied to each
terminal (see Fig. 1 B).
- Remove the excess solder on the solder lands by means of
litz wire or a solder sucker (see Fig. 1C).
1.3 Caution on removal
- When handling the soldering.iron. use suitable pressure and
be careful.
- When removing the chip, do not use undue force with the
pair of tweezers.
- The soldering iron to be used (approx. 30 W) should
Fig. 1 DISMOUNTING
SOLDERING
IRON
E.g. WELLER
SOLDER TIP PT-H7
VACUUM PISTON
4822 395 10159
SOLDER WICK
4822 321 40042
E.g. A PAIR OF TWEEZERS
HEATING
SOLDERING
IRON
SOLDER WICK
C
B
A
SOLDERING
IRON
HEATING
Fig. 2 MONUTING
E.g. A PAIR OF TWEEZERS
SOLDER
0.5-0.8 mm
PRESURE
SOLDERING
IRON
SOLDERING TIME
< 3 sec/side
B
A
SOLDER
0.5-0.8 mm
PRESURE
SOLDERING
IRON
Fig. 3 Examples
RIGHT
SOLDERING
IRON
Preferably be equipped with a thermal control
(soldering temperature: 225 degree V to 250 degree C.
-The chip, once removed, must never be reused.
-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 (see Fig. 2A)
-Next complete the soldering of the terminals of the component.
(See Fig. 2B)
1.4 Attachment of SMDs
2. Caution when attaching SMDs
- When soldering the SMDs terminals, do not touch them
directly with the soldering iron. The soldering should be
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 (approx. 30W) should
preferably be equipped with a thermal control (soldering
temperature: 225 degree C to 250 degree 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 SMDs 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 (See Fig. 3).
Repair Tips