Repair Tips
preferably be equipped with a thermal control (soldering temperature: 225 to 250 oC). - The chip, once removed, must never be reused. 1.4 Attachment of SMDs - 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 Fiq. 2B). Fig. 2 MOUNTING
e.g. A PAIR OF TWEEZERS
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) Fig. 1 DISMOUNTING
SOLDERING IRON e.g. WELLER SOLDER TIP PT -H7
VACUUM PISTON 4822 395 10159
A
SOLDER 0.5 - 0.8 mm SOLDERING IRON PRESURE
SOLDERING TIME < 3 sec/side PRESURE
SOLDERmm 0.5 - 0.8 SOLDERING IRON
B
2. Caution when attaching SMDs
- 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 (approx. 30 W ) should preferably be equipped with a thermal control (soldering temperature: 225 to 250 oC). - 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 (see Fig. 3). Fig. 3 Examples
A
SOLDERING IRON SOLDER WICK 4822 321 40042 e.g. A PAIR OF TWEEZERS HEATING HEATING
B
SOLDERING IRON SOLDER WICK
C
- 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
