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March, 2014 Selective Soldering With Added Flexibility By Heike Schlessmann, SEHO Systems GmbH, Kreuzwertheim, Germany
cation to learn how to gain the maximum benefits from those systems. For a typical printed-circuit board (PCB), components to be selectively soldered are usually surrounded by parts that have been attached by more traditional soldering methods, such as reflow solder or even hand soldering. As a result, any selective soldering system must pro- vide the precision and control to properly attach the desired components without causing damage to any previously soldered components. Fortunately, the SelectLine of selective solder-
S
ing systems from SEHO Systems GmbH provide the soldering precision and repeatability needed
elective soldering systems provide a great deal of capability for electronic manufactur- ing facilities, but they also require some edu-
for controlled selective soldering without danger of damaging previously attached components or por- tions of PCBs. In addition, these selective soldering systems
offer a great deal of flexibility for working on dif- ferent types of PCB assemblies without having to completely reconfigure the system. Effective selective soldering systems should
The SelectLine (left) and SelectLine-C
(right) are selective soldering systems that can be reconfigured by means of add-on function modules.
provide the control of soldering materials needed to avoid any waste of those materials. In addition, such systems should help minimize production time, in order to also minimize associated produc- tion costs. The SelectLine soldering systems employ micro-drop jet fluxers capable of high pre- cision and repeatability along with minimum con- sumption of soldering materials. Well-defined flux applications can be controlled in extremely small areas by as many as three nozzle heads on each SelectLine XY axis portion. These selective sol- dering systems are constructed with a modular design, allowing selection of various preheat and soldering mod- ules to achieve a desired configura- tion. In fact, depending on production requirements, these selective solder- ing systems can be equipped with as much or as little capability as needed for a particular application or set of applications. With the micro-drop jet fluxers available for the SelectLine soldering systems, multiple similar fluxers can be used for high-through- put applications. When greater flexi- bility is needed, two different flux types can be used simultaneously with these multiple fluxers, running under software control. For any selective soldering sys-
tem, process control starts with flux deposition. In the SelectLine selective soldering systems, both the filling level in the flux container and the function of the drop jet nozzles are continuously monitored under computer and soft- ware control. The flux quantity control in these systems actually measures the quantity of each drop of flux/solder that is applied to a printed circuit board (PCB).
Flexible Preheating A selective soldering system
requires a reproducible and effective preheating process to activate the flux and achieve optimum wetting activity. For flexibility, the preheat area of each SelectLine selective soldering system can be configured individually and by length and type, with excellent energy efficiency. Effective transfer of heat to the bottom side of a target PCB is achieved by quartz heating elements that can be individually activated. If necessary, additional infrared (IR) heaters can be installed in one of the selective soldering systems to provide topside PCB heating. Both the bottom- side and top-side heating subsystems are controlled by means of the system software, for highly precise and repro- ducible soldering temperature profiles. For large-mass PCB assemblies,
where a greater amount of heating may be required, the preheat module on these selective soldering systems can be equipped with convection heating capability. Such capability ensures complete and effective heat transfer with homogeneous temperature distri- bution within the preheat zone even for large-mass PCB assemblies. One concern for selective solder-
ing systems during long soldering cycles is maintaining a PCB assembly at the same required temperature. For
See at APEX, Booth 1925 Continued on next page
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