Reworking

Reworking is required if electrical or visual tests failed.

Reworking of shorts between neighboured pins (the component stays in place)

Components with small separations between their pins (e.g. the Molex-connector of the 30-pin display connector on the Adapterboard) tend to exhibit shorts caused by a too large amount of soldering paste. Don't worry about this, it can be simply solved using desoldering litz-wire (desoldering braid) and Fluxer and a traditional soldering iron with small tip. If you are unsure, watch some soldering videos on youtube, for example one of these:

Desoldering Braid: https://www.youtube.com/watch?v=AcbezX8TrOU

Solder removal: https://www.youtube.com/watch?v=BrAJpz9Mdm4

Reworking of BGA (Ball Grid Array, solder pads at the bottom of the component)

Common to both methods is that the heat must be focussed as good as possible. Therefore some thin metal plates can be used to cover parts which should be protected from heat, e.g. plasic connectors in the neighbourhood. It is also recommended to pre-heat the boards from below for several minutes. Pre-heating reduces the thermal stress to all parts. Another important point is to use enough Fluxer, which is very useful if the soldering tin has been melted several times before. Fluxer makes the soldered surfaces shiny and glossy and provides good adhesion and flow of the soldering tin. At the end of the Reworking-process, the remaining Fluxer must be removed from the board. There are special cleaner detergents available with glass-brushes to remove the fluxer at the end. Be careful with the MS5611 pressure sensors, which are sensitive to excessive Fluxer exposition. The MS5611 datasheet recommends to use “No Clean” fluxer. The Lead-free soldering process is more challenging than the traditional soldering process using Sn-Pb soldering paste because of the higher temperature needed for lead-free. Have a look on some youtube-Videos how to solder in general and how to rework:

SMD-soldering: https://www.youtube.com/watch?v=1z0IiuQ35HU

Reworking with Hot Air and Desoldering Braid: https://www.youtube.com/watch?v=ZypXa9BDXHw

Creative tinkerers can achieve astonishing results in soldering quality, even in a hobby-environment. I know people who soldered SMD on an electric iron or in a sandwich-toaster! But do not forget to ask your wife for permission before…

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