The Ultimate Guide to SMT Rework

The continued advancement in PCB density and the increased miniaturization of SMT devices, as well as the complexity of component packages, has made SMT rework more challenging.

Advanced densities of PCBs have made the challenges in SMT (Surface Mount Technology) rework that much acute. As the distance between components gets ever tighter and components are being placed directly opposite the area requiring rework, the care required in order to make sure the neighboring areas are protected from too much heat, make this one of the biggest challenges in SMT rework. A proper understanding of how to shield neighboring devices from unwanted excessive heat as well as protecting nearby underfilled devices from “pushing out” the solder underneath packages makes SMT reworks even more challenging.

Increase component miniaturization also is making SMT repair even more challenging for rework technicians. These technicians must practice extreme patience as the distance to neighboring components, especially for handheld consumer electronics, approaches only a few mm in distance. Pitches of modern SMT components also is routinely 0.5mm pitch and below meaning that the rework technicians must be well-versed in drag soldering techniques using lead-free solder. Site dressing also becomes very challenging as pads, only 6 x 6mils in some cases are easily lifted or inadvertently removed thereby causing the SMT Rework job to turn into an SMT repair job. This may cause reliability challenges down the road for the assembly depending on the end user operating environment.

These challenges have been caused PCB assemblers to take on these challenges through increased training, the purchase of different tools for SMT rework or increased outsourcing. Some of the challenges related to SMT repair can be overcome through the use of advanced soldering skills and PCB rework training. This usually includes the outsourcing of some of the advanced training concepts and hand skills taught in the IPC 7721 class. This class instructs students on the various techniques for removing and replacing devices. Even more advanced SMT rework training may include developing the skills used in learning through a repetitive series of tasks training methodology skills such as using micro tweezers for removal and replacement of passive devices, the use of low flow hot air pencils in order to not disturb solder joints and shift around very small package components such as 5 x 5mm micro SOICs or how to remove undefiled devices without causing solder to “squirt out” of neighboring package locations or damage the solder masks or pads during the removal process.

In addition to further SMT rework training investment in advanced soldering tools is also required in tackling the advanced SMT rework challenges. Tools such as IR rework tools for uBGAs, low hand soldering pencils, as well as more precise and advanced BGA, rework placement capabilities are just some of the equipment upgrades needing to take place. Finally, for some of the most advanced work, assuming that the equipment or skills level for advanced SMT rework is not yet in place, many firms are considering the outsourcing of this rework assuming the type of board value justifies this outside handling. Solder shield soldering, 01005 removals, and replacement, as well as heat sensitive device placement, are just some of the types of components where it makes sense to consider using an outside resource. The experience to make the rework look professional while obtaining the highest yields make outsourcing SMT rework a viable option.



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