aQFN stand-off

[cairong.chen]

Hi,

What is your recommended stand-off for your aQFN package to PCB?

Below image is from x-section after mounting nRF52840 to PCB, these are aQFN pads, could you advise if this looks like OK solder joints to you?

Thanks and regards,

Cairong

[Andreas]

Hi,

 

The pads seem to be a little off-center, indicating the SoC might be a little poorly aligned. There also seems to be an air bubble or something in the one to the right, but this might not be a problem.

 

Best regards,

Andreas

[cairong.chen]

Thanks for feedback.

Our assembly house commented that the pad off-centering is caused by self-alignment of aQFN center pad. Have you seen this type of off-center, and is there any reliability concern due to this?

And once again, What is your recommended stand-off for your aQFN package to PCB?

Best regards,

Cairong

[Andreas]

Hi,

 

Yes, that sounds plausible. I do not believe we have a lot of reliability sweeps on alignment, but I would also expect this to be the case in most other designs. You could probably want some more wetting on the left hand side of the pad, but we have not received any reports that this is to be a weakness or common reliability concern for nRF52840. If you expect a lot of mechanical stress you might want to test this, but you would then probably want to test this regardless. We do not specify a required stand-off, but this looks fine.

 

Best regards,

Andreas

[cairong.chen]

Hi,

Ok, I accept your feedback. Thank you.

Best regards,

Cairong