SMT007 Magazine

SMT007-Sept2020

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100 SMT007 MAGAZINE I SEPTEMBER 2020 the flat surface of the tip as this will aid in heat transfer. For placement, apply the proper liq- uid flux to the pads and hold the 0201 down with the tip of a tweezer and touch the hoof tip for 2–3 seconds to one side of the pad to allow the solder to reflow. Finish the attachment by doing the same operation on the other side. An even faster hand soldering method uses a micro tweezer hand piece. These tweezers can reflow both ends of the 0201 simultaneously for component removal or replacement. The tips themselves are fragile structures and are easily damaged, which means care needs to be taken by the soldering technician. Because of the small geometries involved, the skill and patience of the soldering technician need to be at an advanced level. The site preparation pro- cess post component removal, regardless of the tip used, requires great care by the rework technician as the very small pad surface area means that the propensity to damage or lift pads is high. While hand soldering is the fast- est method for the removal and replacement of the 0201, it requires a high degree of operator skill and dexterity. Hot Air Rework Another reflow method employed by solder- ing technicians for the rework of these small passive devices is by using a hot air source. Both controlled (closed-loop rework sys- tems) and uncontrolled hot air sources (hot air guns or handpieces) can be used to reflow 0201s. These hot air sources must be designed with low airflow capability so as not to dis- turb the solder joint or blow the component off the pad. A controlled heat source has lim- ited throughput compared to the hand solder- ing rework method as there are several process steps, which takes time. A split vision rework system, which assists the operator in aligning the part to the pads, reduces the degree of skill required to rework these small packages. The downside of using a hot air reflow source is that components neighboring the compo- nent of interest can also be reflowed during the soldering or desoldering process. To pre- vent the hot air source from disturbing these neighboring components, they need to be ther- mally masked from the heat source. This fur- ther extends the rework process time. When using a hot air rework system, the removal of the component is accomplished by using a hot air nozzle specifically designed to push out low airflow. For replacement of the 0201 com- ponent, a high-resolution camera, combined with precision X-Y adjustments of the rework system, means device placement can be more precise and repeatable vis-à-vis the hand sol- dering approach. Using an IR Reflow Source While the hand soldering of 0201 packages requires highly-skilled soldering technicians and the hot air rework sources can easily disturb the solder or placement location of the light- weight 0201s, the use of an IR reflow source is a good alternative approach to reworking these packages. Infrared rework systems do not use any airflow as part of the reflow cycle, thereby preventing the problems associated with the hot air rework sources. The IR heat source can quickly heat these small component body style types before their removal. Magnification, as part of the rework sys- tem—along with a micro vacuum nozzle— can then remove the component once a liqui- dus state has been reached. Through the use of an IR BGA rework system and the high skill and dexterity level required for rework of these 0201 packages, without the downside risk of the positive airflow from the hot air source, makes the IR reflow source ideal for these components. SMT007 References 1. IPC, "IPC-7351 Generic Requirements for Surface- Mount Design and Land Pattern Standard," Bannockburn, Illionis, 2015. 2. Paul Neathway, et al. "A Study of 0201's and Tomb- stoning in Lead-Free Systems," Proceedings of SMTAI, 2014. Bob Wettermann is the principal of BEST Inc., a contract rework and repair facility in Chicago. For more information, contact info@solder. net. To read past columns or contact Wettermann, click here.

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