Philips 241B4LPCS/00 - Page 80

5HSDLU7LSV
0. Warnin
All ICs and man other semi -conductors are susceptible to
electrostatic dischares (ESD). Careless handlin durin repair can
reduce life drasticall . When repairin make sure that ou 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. Servicin of SMDs (Surface Mounted Devices)
1.1 General cautions on handlin and storae
- Oidation on the terminals of SMDs results in poor solderin.
Do not handle SMDs with bare hands.
- Avoid usin storae places that are sensitive to oidation such as
places with sulphur or chlorine as direct sunliht hih temperatures
or a hih deree of humidit. The capacitance or resistance value of
the SMDs ma be affected b this.
- Rouh handlin of circuit boards containin SMDs ma cause
damae to the components as well as the circuit boards. Circuit boards
containin SMDs should never be bent or fleed. Different circuit board
materials epand and contract at different rates when heated or cooled
and the components and/or solder connections ma be damaed due
to the stress. Never rub or scrape chip components as this ma cause
the value of the component to chane.
Similarl do not slide the circuit board across an surface.
1.2 Removal of SMDs
- Heat the solde r (for 2-3 seconds) at each terminal of the chip. B
means of lit wire and a sliht horiontal force small components can
be removed with the solderin iron.
The can also be removed with a solder sucker (see Fi. 1A)
While holdin the SMD with a pair of tweeers take it off entl usin
the solderin iron's heat applied to each terminal (see Fi. 1 B).
- Remove the ecess solder on the solder lands b means of lit wire or
a solder sucker (see Fi. 1C).
While holdin the SMD with a pair of tweeers take it off entl usin
the solderin iron's heat applied to each terminal (see Fi. 1 B).
- Remove the ecess solder on the solder lands b means of lit wire or
a solder sucker (see Fi. 1C).
1.3 Caution on removal
- When handlin the solderin.iron. use suitable pressur e and be
careful.
- When removin the chip do not use undue force with the pair of
tweeers.
- The solderin iron to be used (appro. 30 W) should preferabl be
euipped with a thermal control (solderin temperature 225 to 250 C).
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1.4 Attachment of SMDs
- Locate the SMD on the solder lands b means of tweeers and solder
the component on one side. Ensure that the component is positioned
correctl on the solder lands (see Fi.2A).
- Net complete the solderin of the terminals of the component (see
Fi. 2B).
2. Caution when attachin SMDs
- When solderin the SMD terminals do not touch them directl with
the solderin iron. The solderin should be done as uickl as possible
care must be taken to avoid damae to the terminals of the SMDs
themselves.
- Keep the SMD's bod in contact with the printed board when
solderin.
- The solderin iron to be used (appro. 30 W ) should preferabl be
euipped with a thermal control (solderin temperature 225 to 250 C).
- Solderin should not be done outside the solder land.
- Solderin flu (of rosin) ma be used but should not be acidic.
- After solderin let the SMD cool down raduall at room temperature.
- The uantit of solder must be proportional to the sie of the solder
land. If the uantit is too reat the SMD miht crack or the solder
lands miht be torn loose from the printed board (see Fi. 3).
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