We are a high mix/low volume shop (avg. lot size is about 60). Hand solder was a bottleneck, so we looked into selective machines. We purchased a Vitronics-Soltec mySelective and are very happy with it so far. Although it has a large footprint, everything is internal to it, including the preheat and x-y fluxer. When comparing machines, make sure that the machines you are comparing have the same options. As far as time savings go, we had one board go from 2 hours/board in hand solder to 30 minutes (including insertion, selective soldering, and inspection). We had another go from 1 hour/board to 15 minutes. The selective machines really save time on connectors/headers. Most are very flexible to help deal with the varied board types that you have. You will probably have to use pallets occasionally, due to clearance issues of certain parts. Quality is also a big advantage. The biggest issue, eventually, will be time on the machine to do programming. Programmin and trouble shooting take quite a bit of time, depending on the board. Take a look at nitrogen generators as well, as liquid tanks can get expensive.
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