© 2001 by CRC Press LLC 6. Since there is no moving gas, there is no built up of static. 7. The method allows the use of the assembly robot’s gripper and vacuum suction heads, which can be considered a major economic savings compared to the use of nozzles, which are all equipped with vacuums. 8. Despite the requirements of spot size adjustment and lens changing, the IR method eliminates nozzle head design and manufacturing problems which are currently concerns for hot air/gas systems. 9. Because there is closed-loop temperature control, the reliability of reworked joints or PCBAs should be better. 10. Noncontact heating eliminates tool marks. The disadvantages of this method are that reflowing of nearby joints on closely packed PCBAs is possible, and reflow may occur at higher temperatures due to the use of short-wave IR. The solder fountain and VDI–SI couple-based reflow methods have been compared. The study revealed that: 1. Solder fountain-based TH component rework is more effective because solder joints using a solder fountain are reliable joints, and removal can be performed more safely due to the elimination of sweated joints. Furthermore, exclusion of sweated joints also eliminates the need for secondary heating, which might degrade the PCB and take extra time. 2. Even though the solder fountain method requires an X-Y-Z positioning table, the requirement of an X-Y positioning table for all SM rework leaves only the need to justify a Z positioning table. This can indeed be justified, because the VDI–SI method requires a board reorientation facility. 3. The use of a solder fountain and X-Y-Z positioning table eliminates the scattering of metal parts on the PCBAs during leg cutting (removal). 4. The simultaneous desoldering and resoldering of the joints of the defective component decreases the rework cycle time compared with sequential removal and resoldering of each leg. 5. No adhesive dispensing is necessary. This also eliminates adhesive curing and dispensing facilities. 6. A solder fountain is less expensive than VDI–SI tooling. If double-sided mixed technology PCBAs are reworked, the method also has some disadvantages. If any insulated wire jumper exists in the vicinity of or just below a defective TH component, it may melt and cause shorts. If any SM components, such as micro-tabs, bobbins, or micro switches, which are not resistant or suitable for wave soldering, are located in vicinity of or just below a defective TH component, these can be damaged during removal. Therefore, these components and jumper wires would need to be removed during the preparation of the PCBAs for rework. 6.7 Determination of Other Rework Requirements Once decisions are made on the reflow methods for TH and SM components, analysis and decision making based on rework requirements can be carried out to specify the other rework tooling necessary for automation, and other related problems could be solved. Rework Tools To achieve fully automated rework, the following needs to be considered [25]. Preparation of PCBAs for Rework The cleaning of PCBAs and removal of conformal coatings are not necessary because the cell is designed to rework assembly defects directly after manufacture when they are not covered by dust or other contamination and conformal coatings (PCBAs are coated after the final test of the finished goods) and are not subject to field defects. The other problem when preparing a PCBA for rework is that of removing obstructions (i.e., heat sinks, jumper wires, threaded fasteners, other components, etc.). The first three . facility. 3. The use of a solder fountain and X-Y-Z positioning table eliminates the scattering of metal parts on the PCBAs during leg cutting (removal). 4. The simultaneous desoldering and resoldering of. compared to the use of nozzles, which are all equipped with vacuums. 8. Despite the requirements of spot size adjustment and lens changing, the IR method eliminates nozzle head design and manufacturing. to the elimination of sweated joints. Furthermore, exclusion of sweated joints also eliminates the need for secondary heating, which might degrade the PCB and take extra time. 2. Even though the