- Kondensatoren >
- Keramik-Vielschichtkondensatoren (MLCC)
A. When reworking an assembled PCB, the amount of mixed technology on the board adds to the complexity of reworking. Often components are placed close together and different components have different thermal thresholds. In general, most SMT components can withstand peak temperature exposure of 220°C for 90 seconds. Though MLCCs have a higher threshold, surrounding components may be damaged as a result of the rework proess.
MLCCs can be damaged by excessive heat in several forms including, peak temperature, prolonged exposure to high temperature, and thermal shock. In general it is recommended to set a △T of 2°C/sec. with a maximum of 4°C/sec. for MLCCs.
Typical 63Sn/37Pb solder wets above 181°C. For vapor phase/reflow or manual soldering, a temperature of 225±5° with a △T≤ 190°C is recommended. For wave soldering, the recommended solder temperature is 260±5 °C with a △T≤ 150°C. One concern when applying heat to a chip capacitor is to ensure that the ends of both terminations are seeing the applied heat at the same time in order to prevent thermal cracking.
When hand soldering, it is also recommended to preheat the rework area to minimize thermal cracking of the MLCC or surrounding components. Single sided PCB's can be placed on a circuit board preheater or a hotplate set at 150°C. PCB's with components populated on both sides can be preheated by forced air. The air temperature should be between 150 to 175°C and the air nozzle should be about 0.25 to 0.50 inches from the solder joint. Though preferred, preheating is not required when using SMT tweezers as long as the iron temperatures are below 315°C and temperature deviation from one tip to the other is
|Method||Min. Temp.||Max. Temp.|
|Hot Air Pencil||315°C||400°C|