FEDEVEL
Platform forum

RR4711 , 01-03-2022, 05:35 AM

Happy New Year

I'm designing a 6 Layer PCB with an NXP LPC546x8 CPU and 128Mbit SDRAM (167MHz). Due to the very problematic part market situation I would like to have the option to populate either the BGA180 or TQFP208 version of the CPU (I have 20 pcs of the TQFP208 here for prototyping but likely the BGA180 is available later on, but who knows, better be prepared...)

I arranged the BGA "under" the LQFP package as the LQFP package is quite large (and has BTW the most horrible pinout one can possibly imagine, everything is spreaded around the pins on full circumference...).

I have of course the problem that I will have for sure stubs on the SDRAM lines if I optimize it either for the LQFP or for the BGA (Between 12-20mm estimated stub length).

Has anyone tried something like this? Suggestions?

Markus

robertferanec , 01-03-2022, 06:12 AM

In cases like this I use serial optional resistors to reroute tracks. However that may be difficult to do for a bus with many signals

RR4711 , 01-03-2022, 06:16 AM

I am actually happy if I manage to get all connections fan out half way okish and length matched but I think resiitors will make the routing impossible. It's my first 6 Layer board but I think it's the minimum to have at least 3 controlled planes for signal/PWR.