MMA8452QR1 Z Axis Stuck

[pmichael]

We use the NXP MMA8452QR1 accelerometer.

We assembled 50 devices. In 10% of devices we see that the Z Axis is stuck:

• No change in the value read
• Self-test mode does not change it.
• Oblique tapping (z-axis direction) will sometimes provide a temporary fix
• Problem returns in some of the “fixed” cases

BTW - Replacement of this chip solves this problem.

Can anybody explain what’s wrong?

Elements, assembly process, anything else?

Please advise.

[TomasVaverka]

Hello Michael,

Could you please tell us more about your application? Are you using the MMA8452QR1 just for static orientation measurements or are you exposing it to mechanical shocks?

However, if the Z-axis output is reporting exactly 0x7FF or 0x800 (+/-full scale) whereas the unit is only exposed to Earth's gravity, the probability that the device is suffering Z-axis stiction is high. 

In fact, sticking can arise during manufacturing or in the use of the device. As you can see in the PCN14989 and PCN15484, there were made some design improvements to eliminate this failure. These improvements are valid for all MMA845xQ family devices.

Unfortunately, there is no easy way to restore sensor functionality besides applying again shocks to the unit. 

Customers that experience an issue similar to this can contact our quality team and customer service team. The NXP Quality team will enter the information into the NXP CQC system to route to the correct quality team and business line contacts for support.

Best regards,

Tomas

[TomasVaverka]

Hello Michael,

In order to keep your answer confidential, I need to delete it from this thread.

The failure is usually activated by shock (high acceleration) or vibration, it should not happen during soldering/assembly if all requirements given in the application note are met.

For any other information, please get in touch with our Quality department (via AVNET) that will be analyzing faulty parts. 

Best regards,

Tomas