Archive for December 19th, 2009

Arduino Pro: Securing the Serial Connecor

Epoxy backfill on Arduino Pro serial connector

Epoxy backfill on Arduino Pro serial connector

The surface-mount serial connector on an Arduino Pro board isn’t the most robust of devices; the FTDI USB interface and USB cable can apply far too much torque to those little pins. Even before the situation described yesterday, the pins were getting wobbly.

The connector shell is a big part of the problem, as it doesn’t mechanically lock the pins in place. Installing and removing the FTDI USB board pushes and pulls the pins against their pads, which means the adhesive bonding the pads must handle all that stress.

Eventually, the Reset and TX pin pads tore loose from the circuit board. At that point, they have no mechanical stability at all; you can bridge a solder blob from the pin to its trace, but the adhesive holding the copper pad in place has lost all strength.

The fix is straightforward, if ugly.

  • Repair the pin-to-pad/trace connections with something better than a solder blob. I used small snippets of component leads.
  • Apply denatured alcohol and scrub away all the solder flux around the pads.
  • Apply enough epoxy to the back of the connector to bond it, the pins, and the circuit board into one mechanically stable unit. I worked the epoxy between the pins and slightly under the connector shell with a small screwdriver and toothpick.

Even with this repair in place, the connector is not particularly robust. It’s much better than it was, so we’ll count it as a win.

This Arduino Pro has survived several projects, hence the hideous solder blobs here & there. I suppose I should just throw the poor thing away, but … that’s not my nature.


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