How to replace/resolder nRF52840 manually (QFN 73)

[d.s.]

Hi all!

Resoldering usual QFN packages with pins along the edges is not such a big problem... but how is this usually done with devices they have pins underneath the package? (Like nRF52840's QFN 73 package.) I need to replace/resolder some nRF52840. Could anyone give me some advice?

Many thanks in advance!

Best regards

[ketiljo]

Hot air or reflow oven. Same as BGA, CSP etc. 

[d.s.]

Sounds obvious but how to get solder paste on the pads? I can't use a solder paste stencil anymore because the pcb is already assembled.

[ketiljo]

You can use a stencil that's cut to size so it fits where the chip normally is. But that can be fiddly if the surrounding components are close. Probably better to apply paste to the chip directly, from the underside of the stencil, and place the chip carefully on the PCB and re-flow.