Problem with USB connector on bladeRF part 1: The Failure

A few weeks ago my bladeRF almost died. No, I did not electrocute it, I did not step on it, I did not try to make it work too hard, it did not suffer any kind of physical or intellectual abuse. All I did was to try to gently connect a USB cable. One moment I was pushing the plug into the connector, the next moment the plug was sitting completely loose in the metal frame.

What happened here was a complete surprise for me. I always treated the connector with great care, never pulled the USB cable, never pushed it too hard. Turns out, that my mishap was caused by a very unfortunate coincidence of poor design of the USB 3.0 Micro-B connector and less-than-perfect mechanical performance of ROHS solder joints.

The plastic part that you see sticking from the back of the connector is the plastic insert with contacts. As you can see it in the pictures below, only one of the leads shows signs of mechanical stress. The rest of the pins were either not deformed at all, or bent very slightly.

View at the plastic insert.

Closeup of the bent lead. Adjacent contact shows no signs of mechanical abuse.

The solder joints on the board do not show much damage either. The connector leads separated from the board cleanly.

View at the solder joints.

Close-up view of the solder joints.

To explain what exactly happened here, I will need first to explain in few words how the USB3 Micro-B connector is built.
The picture below shows Amphenol's USB3.0 connector similar to the one mounted on bladeRF. The plastic insert is held in place by the two indents in the metal frame (circled in red), which recess into cavities molded in the plastic part. Assuming sufficient mechanical strength of the insert's material and tight mechanical tolerances, this mechanism should be sufficient to firmly bind the two parts together and prevent them from moving. The load caused by plugging and unplugging the cable is transferred on the metal frame, which is firmly attached to the PCB. The stress caused by residual movements of the insert due to slack is dissipated in the vertical section of the pin, and the load exerted on the solder joints under the pins is minimal.

The marked indents in the metal frame are supposed to hold the parts of the connector together.

Unfortunately, it was not the case with the connector mounted on my board. Either was the material too weak, or was it a mechanical failure, the plastic eventually gave in and the insert became loose. As a result, every time the USB cable was connected or disconnected, the solder joints had to bear almost full force from the USB plug being pushed in. The pins, one by one, were loosing mechanical contact with the PCB (keeping electrical contact, so the failure remained unnoticed for a long time) until only one pin remained attached. In the end, the single pin was not able to withstand the force of connecting USB cable and was forcefully detached from the board (hence the bending).

Damage to the plastic insert.

Stay tuned for the next post, where I will describe how to remove the broken connector and install a new one.

Update: Second part of the story describes my first, partially successful attempt to replace the connector.