tailieunhanh - The Design of Manufacturing Systems Part 19

Tham khảo tài liệu 'the design of manufacturing systems part 19', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 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