Pre-tin a QFN chip?

[IronMike]

Hello, we use the nRF52840 in the aQFN 73 package, 7 x 7 mm.  Seeing some production failures with the boards.  Examined several boards under robotic X-ray and there are several questionable solder joints around the nRF chip.  The assembly house is recommending that we 'pre-tin' the chips.  This is something a third party does.  Does anyone have experience with this procedure?  Any recommendations as to who can do it in US?

Thanks.

[ketiljo]

Hi MIchael

I have never come across the need for this before. I suggest that they check the solder profile and amount of solder paste on the pads first. Please take a look at this whitepaper: https://infocenter.nordicsemi.com/topic/nan_040/APP/nan_040/nan40_intro.html

Best regards,

Ketil Aas-Johansen