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I have a problem that I've been embarrassingly working on for months and unable to completely solve. I'm a hobbyist and I have a simple PCB with a male USB Type A connector soldered to it: some of my boards work ok and some only see the power LED light up when I jiggle the connector around (boards are from the same batch). At this point, I am nearly positive it's a mechanical and not a circuit problem, but I cannot figure out what I am doing wrong and am seeking suggestions. I've tried different female ends (i.e., different cables, USB hubs, etc). I've tried different kinds of male Type A connectors soldered to the board (surface mount, through-hole, etc), with the through-hole connectors being the least problematic, but still some of my through-hole-type-A boards exhibit the problem (some don't).

Could it be rosin solder flux residue on the Type A contacts that result from me trying to clean off rosin solder flux on the PCB using a rubbing alcohol bath? The boards look clean but I'm wondering if just enough residue is being left on the USB contacts within the connector to be causing me problems. It seems far fetched, but other than this, I can't think of what else it could be -- I'm about out of ideas.

EDIT: When the problem exhibits itself, I see 0V when I put a voltmeter between the 5V and GND pins on the Type A connector.

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  • \$\begingroup\$ Pins connecting to planes are harder to solder, because the bulk copper in the plane thermally loads the pad you are trying to heat. The high heat capacity of the plane, and the large effective trace width, are both important. You probably are getting cold solder joints on these connections (the connector pin is hot enough for the solder to flow, but the PCB pad isn't). \$\endgroup\$
    – Ben Voigt
    Feb 20, 2018 at 23:18
  • \$\begingroup\$ The point where connectors (especially overhanging ones) attach to boards can indeed be a notorious mechanical failure point. But cheap USB connectors can also be unreliable. The problem is probably not going to be flux residue. It's not out of the question that the board is flexing and disturbing a loose connection elsewhere - do you have any QFN or BGA ICs? Or even a TQFP? Inspect the solder joints under high magnification. See if you can find a mechanical action more consistent than wiggling which consistently causes the problem. \$\endgroup\$
    – Chris Stratton
    Feb 20, 2018 at 23:21
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    \$\begingroup\$ How do you know that is a short and not an open circuit in the feed to one of those nodes from the host or charger? Can you plug it in through one of those USB current meters? If it's a short leading to shutdown, presumably the meter itself would loose power, while if it's an open the current would drop to zero but the meter would remain on. \$\endgroup\$
    – Chris Stratton
    Feb 20, 2018 at 23:42
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    \$\begingroup\$ Could you post some pictures of how does it all look? \$\endgroup\$
    – Ale..chenski
    Feb 21, 2018 at 2:32
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    \$\begingroup\$ check the continuity through the connector of the 5V and GND lines \$\endgroup\$
    – jsotola
    Feb 21, 2018 at 2:47

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