My last two posts (1) (2) have been about the different facets of spray fluxing and the systems that are used. In this post, we are moving on from spray fluxing and discussing the final type of fluxer in this mini-series: a brush fluxer. It is, arguably, the oldest form of fluxing and it is rarely used today.
In the early days of circuit board assembly, flux was applied using, basically, a paintbrush. The system that I will be talking about is slightly more sophisticated than that. You can catch a glimpse of this system from the schematic you see here.
I like to think of it as an automated paint roller. The cylindrical brush is half-submerged in a bath of flux and is rotating on its center axis. The board contacts the brush at the apex and moves opposite the brush's rotational direction at the point of tangency. The flux deposition can vary significantly. This unpredictability is one of the reasons that it is not being used today.
This system is a recirculating system with the same problems that are associated with other open systems, such as foaming or wave. Also, the brush has to be washed very thoroughly. Have you ever left a paintbrush or roller out after painting, only to come back hours later unable to use it? Brush fluxers follow similar logic. For today's modern SMT designed circuit boards, this system is archaic and unsuitable. However, it is used in special circumstances that need a low-cost application method for simple product assemblies, or when you are unable to use the more modern methods.
This will complete the fluxer section of my blog.
*This is the sixth and final section of Fluxers, a mini-series which is part of the larger series entitled Wave Soldering (A Segmented Synopsis). Next week we move on to the beginning of the next mini-series focused on preheaters.