No solder paste was applied on Thermal Pad for AGND. What would this do?

To quote the datasheet:

--- Quote Start ---

The large thermal pad underneath the component must be connected to the system ground...

--- Quote End ---

Note the use of the word 'must'. However, it doesn't discuss whether the device relies on this as an electrical connection to the PCB. It goes onto say 'This provides the path for heat dissipation from the converter'.

I would suggest that, providing the device isn't getting hot, it'll continue to regulate well. As it heats up it's performance will suffer and there is a risk of the part failing. Hence, the need to remove any heat generated by the device from it. Worst case it may fail in a way that takes the rest of the circuit with it...

You could bond a heatsink to the top of the package. This would help dissipate any heat generated by it.

Regards,

Alex

Alex, how about at start/boot up of our processor. This device produces 1.8 VDC that is used by our Graphics processor and our Flash memory chips. We have a significant number of "no Communication" failures that we struggle to troubleshoot since we cannot communicate over our JTAG and have no access to the BGA pins for probing testing.

We have also seen our display "flicker" at hot which implies a problem with the graphics circuitry, but has been tough to track down root cause failure.

We of course are fixing the stencil to apply paste for the next batch of boards, but we have hundreds to try and troubleshoot.

Any more thoughts would be appreciated.

Julian

--- Quote Start ---

To quote the datasheet:

Note the use of the word 'must'. However, it doesn't discuss whether the device relies on this as an electrical connection to the PCB. It goes onto say 'This provides the path for heat dissipation from the converter'.

I would suggest that, providing the device isn't getting hot, it'll continue to regulate well. As it heats up it's performance will suffer and there is a risk of the part failing. Hence, the need to remove any heat generated by the device from it. Worst case it may fail in a way that takes the rest of the circuit with it...

You could bond a heatsink to the top of the package. This would help dissipate any heat generated by it.

Regards,

Alex

--- Quote End ---

I can only suggest that you have some of your failures re-worked so that you know the device is down correctly. That way you can (pretty much) rule it out when it comes to troubleshooting failing boards.

Can you monitor the voltage from the device during the boot process? Hook it up to an oscilloscope. Make sure you try this with 'cold' (room temperature) boards so there is no residual heat involved - i.e. give it the best chance it will get. If you can detect a drop in the voltage during boot then you may be onto something. If not, and it is regulating correctly throughout, then even though the device is not down correctly it will be doing what's required of it.

Cheers,

Alex

Yes, I can attached a scope probe to another device to determine this potential start up issue. Hot will be a bit trickier, but we have a thermal chamber that I can soak the device at 80C and repeat the test. We will start down this troubleshooting road soon. I appreciate your input.

Respectfully,

Julian