Issue for smt (smd) aQfn package

[_maibi]

chip: nrf52840 aQFN package

5~10% of the products were defective. by causing  analysis, There are short some pins bottom of chip.

I already read this guide after this issue.

but the smt company suggests changing the package.

should we change the package to solve this issue?

[RK]

Well there's a couple of possibilities here, either you have a design problem, perhaps didn't quite follow the footprint exactly, or the board manufacturer can't do solder mask to those tolerances and you're not getting some between the pads. How closely have you followed the design, not just the pads but the solder mask and paste templates? 

Or the assembly house is at fault here and they're not using the right kind of solder paste or not getting the board reflowed properly or some other assembly issue. 

It's certainly possible to design and manufacture boards which use aQFN but you need a good design, a good board house and a good assembler. 

So it's your choice really. If the design is a bit wrong, you can fix it, or find another board manufacturer or assembler who can deal with the tolerances needed. Or you can switch the chip out for one which is easier to mount.