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- Multilayer Ceramic Chip Capacitors
A. When performing rework on MLCCs, care must be taken to prevent damage to the targeted component, surrounding components, and the PCB in general. The complexity of mixed technology designs and reduced real estate add to the difficulty of rework. For this reason, a rework station must be chosen that will allow enough flexibility to handle most typical situations.
As a minimum, a hot air pencil and a pair of SMT soldering tweezers are needed. Airflow rate for the hot air pencil as well as temperature control for both are also needed. These items offer the flexibility needed to handle most general rework situations.
Hot Air Pensil
Though it is best to avoid if possible, sometimes all that is available are solder irons. In this case, two irons are preferred, one for each end of the chip. The two soldering irons should be used simultaneously to lift the chip off the board. By using two irons, the temperature gradient across the MLCC is lowered and therefore the risk of thermal shock is partially reduced. If this method is selected, make sure that both irons are temperature controlled and that the tips are properly tinned and clean. When using solder irons, be sure to slowly approach the solder joint and do not contact the termination until the solder has completely wet. Once the irons contact the termination of the chip, do not touch the ceramic body and also keep the contact time to a minimum. This may appear similar to using SMT tweezers but the temperature control is not as not as good. Though mentioned here, solder irons are not highly recommended.
When selecting tips for SMT tweezers and solder irons, look for flat tips equal to or just slightly wider than the width of the chip. For example, some companies design tips specifically for 0805 case size SMT chips. In general look for a 30 tip. Another thing to consider is the length of the tip. If the tip is too short, the base or shaft of the tweezers (or solder iron) could cause damage to surrounding components such as connectors.
Hot air pencils are considered indirect heat methods while SMT Tweezers and solder irons are considered direct heat.