imxrt microcontroller failure

[ancymuhammed]

We are using imxrt1176 in one of our project. We had assembled 22 boards. Initially all the boards are working. Now in short observed in 4 boards for 3.3V rail & in 2 boards for 1.8V rail. The impedance shown in these boards is 15-30 ohms. If we remove the microcontroller the short is removed. What may be the possible reasons for this.

[vicentegomez]

Can you check with X-ray if there is not a solder short between the BGA balls?

regards

Vicente G

[ancymuhammed]

We had taken the X-ray, No solder ball found. These boards are working for the last 4 months. After removing the microcontroller we had checked the short in removed IC itself. The short is observed in NVCC_SD1. This bank we are used for connecting the WIFI SDIO lines and are powered from 1.8V. 1.8V is generated form 5V using a switching regulator. The enable pin of the regulator is connected to 3.3V which is given to the DCDC of imxrt. At the enable pin we had provided RC for 1ms. Is there any power sequence for 1.8V. Since the 3.3V has rise time, 1.8V seems to be appearing before the complete rise of 3.3V

[vicentegomez]

Normally when an IC has an internal short it was caused by an electrical overstress, maybe you are requesting demanding more current than the spec, for the power up sequence please check the following recommendations

https://www.nxp.com/webapp/Download?colCode=MIMXRT1170HDUG&location=null

Regards

[ancymuhammed]

We had provided external power source to VDDA_1P8. One observation we had seen in the power sequence is VDDA_1P8 is appearing before the complete rise up pf DCDC_IN. Is this will be an issue. This same 1.8V external source is provided to NVCC_SD bank supplies. The image is given below. We had observed short in 6 boards. Out of these boards in 2 boards 1.8V & in 4 boards 3.3V is shorted. These boards are working for the last 4 months

[vicentegomez]

Please check the following document 

https://www.nxp.com/webapp/Download?colCode=MIMXRT1170HDUG&location=null

on it you will find our hardware recommendation for the imx rt 1170 please check if your design meets all of them

Also, you can check the current on the different  voltages 

[ancymuhammed]

In the power sequence recommended in datasheet in our boards the below sequence is not met. VDDA_1P8 we are providing from the external source and it appears before the complete rise up of DCDC_IN. Now we had corrected it on the boards. But I want to confirm whether this is the reason for our board failures

[vicentegomez]

Yes this can be the reason, any condition out of the spec can produce that the device do not work properly if you are not having the proper power-up sequence it can damage the device.

regards

[ancymuhammed]

The short we observed in the line NVCC_SD1. This is powered in 1.8V and used as SDIO interface for WIFI. Whether this particular bank gets shorted due to the improper power up sequence

[vicentegomez]

Would be possible that you to enter an internal ticket on the nxp web page in order to share your schematics

[ancymuhammed]

In all the boards we found that VDD_SOC_IN is shorted. The below list gives the details of shorts found in the removed microcontroller

Board 1

NVCC_SD1

VDD_SOC_IN

Board 2

NVCC_LPSR

NVCC_GPIO

VDD_SOC_IN

Board 3

NVCC_SD2

NVCC_GPIO

VDD_SOC_IN

What may be the possible reasons for this