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Advantages of IR Rework Systems
Infrared rework systems offer several advantages to the rework process. Due to the computer controlled heat and time sources the profiles stored in the rework system are highly repeatable and more precisely controlled compared to their hot air counterparts. Since the lens focuses the spot size, a few lenses replace the costs and maintenance associates with the multitude of different rework nozzles required in convection heating systems. Due the localized heating the problems associated with bringing the neighboring components into reflow or damaging neighboring components using an IR source rework system. The IR method comes into its own on applications where tooling heads and irons cannot reach. (Components near or in between plastic connector sockets typically cause access problems). In addition masking of nearby components, due to the focused nature of the heating source, is not required with IR rework systems. Focused IR rework systems also allow the operator to view all four sides of the component at all times during rework processing. This feature helps to avoid removing a component too soon, which can result in pad damage or bent leads. Lastly, small or lightweight components cannot be "blasted away" as no air is required in an IR system thereby insuring a higher reliability rework process. The aforementioned advantages of an IR-based rework system make it well-suited for many applications.
The IR Source
The focused IR is a non-contact, rework tool free and employing IR from both above and below as its source of heating. Medium wave IR is used underneath to preheat the PCB and reduce the amount of energy and time required for top heating. Short wave IR energy. derived from a UV-free tungsten Halogen spot lamp is collimated and managed through a lens system which allows the control of the heating area. It also produces the red color for operator targeting.
Simulating a Reflow Oven Profile
In a reflow oven a PCB is passed through many zones creating a temperature profile so that interconnection between components and the PCB can take place in a controlled fashion. Focused IR technology treats a component and the PCB to very similar thermal conditions and, as such, produces high quality solder joints. Thus, in practice, any component that can safely pass through an IR oven can be reworked using Focused IR.
Limitations of IR Rework
While this technology offers several advantages over convection heating approaches it has its drawbacks. For instance the total rework cycle time tends to be longer. While this may not be an issue for a few component replacements it will be a large issue if there are hundreds or thousands of boards being reworked. In addition, thicker boards will be too massive for the IR systems in terms of being able to reach a time-temperature profile in an acceptable amount of time. Bulbs for such systems are costly thereby increasing the operating costs of the rework systems. Since this technology is not widely used, the number of highly trained technicians being able to operate the system is low, resulting in poor transferability of profile information between the rework client and the rework provider. Outside of these shortcomings IR rework systems have their place in various applications.
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