We are struggling to source STM32L4Q5CG chips due to global semiconductor shortage. Normally I am using LQFP48 package which allows me to easily rework PCB if necessary. But sometimes UFQFPN chips become available, and those can be installed by our fabrication house.
While looking at datasheet I noticed that outside of UFQFPN48 footprint is 7.3 mm, which is exactly the same as inside of LQFP48 footprint. Since the pinout of the chips is identical, it is theoretically possible to combine both footprints and have an option to install either chip.
My question is - could this affect the chip alignment during reflow?
I suspect the majority of alignment force comes from surface tension on the exposed ground pad of UFQFPN. And I can mask the ground pad on the stencil for LQFP to avoid blob of solder under the chip.
My second question is about that ground pad stencil. A lot of packages with exposed pad recommend splitting the hole into smaller parts to reduce amount of paste by about 10-20%. The ST datasheet does not mention this. Would it be better than one big opening?