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While looking for rotary switches to use as user inputs to a processor, I came across these three footprints:

through-hole footprint

surface-mount long

surface-mount short

I'm considering using a surface-mount part for board layout considerations, but am concerned about physical stability with repeated adjustment.

To me, the through-hole part seems vastly more able to withstand repeated torques, but what about the two surface-mount footprints? Which one is going to be stronger against a twisting motion?

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    \$\begingroup\$ Depending on just what you mean by repeated, switches like these (footprint irrelevant) may not be a good choice. Most switches of this style are designed to be adjusted maybe just once, at least very infrequently, and as such favor low cost over reliable operation in the presence of frequent adjustment. Check the datasheets for reliability figures. If not specified, assume they are bad. \$\endgroup\$ – Phil Frost Jan 30 '14 at 20:05
  • \$\begingroup\$ Check the datasheets for reliability figures. If not specified, assume they are bad. This is important for almost anything. \$\endgroup\$ – Passerby Jan 31 '14 at 0:37
  • \$\begingroup\$ @Passerby I totally agree. However, for this question I'm more concerned with the physical connection of the device to a circuit board rather than the mechanical operation of the device itself. \$\endgroup\$ – Adam Head Jan 31 '14 at 0:48
  • \$\begingroup\$ @AdamHead The spec if given, would be useless for uninstalled parts. The testing would be done soldered with the suggested landing pattern... IE Typical use conditions. \$\endgroup\$ – Passerby Jan 31 '14 at 2:01
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From a ME perspective, I think you've ordered them in decreasing ability to withstand a torque. The lever arm is shortest on the J-lead (bottom) package.

Those switches continuously rotate, so I don't think torque will be a major issue. I'd worry more about a ham-fisted customer somehow prying the part sideways.

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  • \$\begingroup\$ I had a similar thought. But was unsure if the smaller contact area of the third footprint would affect anything. \$\endgroup\$ – Adam Head Jan 30 '14 at 20:55
  • \$\begingroup\$ Is it actually less contact area? You did not show the actual footprint. They're weakest in tension, so if the user could get their screwdriver under it.. \$\endgroup\$ – Spehro Pefhany Jan 30 '14 at 21:00

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