Another advantage of Indium Corporation's epoxy flux, such as the 756-72, compared to underfill and other competitive epoxy flux options is that our epoxy flux is reworkable. The rework procedure is similar to that of a normal PoP flux or TACflux. Indium's epoxy flux offerings will turn to a soft gel (not a liquid) when heated that makes it very easy to remove with the proper solvent.
Components can be removed by using localized heating (hot air gun, hot air pencil, rework station, hot plate) as you would in a typical BGA rework process. The remaining solder on the pads can then be removed with solder wick and a soldering iron set at 800ºF. Once the solder is removed, the substrate can be heated to 150ºC, and the epoxy flux can be wiped off with a clean/dry foam swab (examples of rework swabs can be seen in the picture to the right).
Once the bulk of the epoxy flux is removed, the remaining epoxy flux can be cleaned with a swab soaked in solvent (MEK tends to be the best option, but there are also some other commercially available cleaning solutions listed below). After the board has been cleaned, re-assemble the board with the new component using the same procedure as the initial build – typically by dipping the component into epoxy flux and reflowing.
Epoxy flux is intended to be left on the board after reflow, so cleaning the residue off does not make sense to do. However it will need to be cleaned from the dipping reservoir and other equipment that is used in the manufacturing process. This can easily be done, and there are a number of commercially available solvent cleaners on the market that will aid in this. Below, you will find a brief list of materials that are known to work well:
- Kyzen Cybersolv C8502
- Zestron HC
I hope this will help. I look forward to our next discussion on Epoxy Flux.
* This post is part of the Understanding Epoxy Flux: The Need and the Process series.