Two Prevalent Rework Heating Methods--Which One is Best?


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IR systems measure temperature empirically at the PCB or component, whereas hot air systems measure hot air temperature near the hot air exit source. This makes for a more-exacting profile based on achieved component temperature. In addition, IR heat sources require little tooling for specific BGA sizes. Another advantage is the ability to easily take in-process temperature data of the IC for each reflow operation. However, the primary advantage to the IR heating is the ability to not disturb very small components as no turbulent air flow exists along with the heating source.

Fig3-Wettermann-Nov2017.jpg

Figure 3: Focused IR heating technology for PCB rework.

While the infrared heating source has some distinct benefits over the hot air systems, it too has some shortcomings as a reflow source for BGA rework. There are still some underpowered IR heaters on the market which means that the rework process cycle time is much longer than a properly-designed nozzle and hot air system. This means that for very large boards such as servers, backplanes and other high current-carrying PCBs, the IR heat source may not be sufficient. The user needs to be aware that IR systems using medium wavelength IR resulting in darker-colored components have a different absorption of heat energy than light-colored components. In some cases, this means that the user must employ an ESD-safe black tape to make sure the component heats up to the right heat energy levels. Process control can be difficult with infrared heating as the absorbency spectrum and therefore reproducibility from component to component and board to board results can be an issue.

Both hot air and IR heat sources have their place in PCB rework with specific choices of rework heat source dependent upon the application at hand.

This article was originally published in the November 2017 issue of SMT Magazine.

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