I've created a new prototype circuit board with 217-LFBGA (AT91SAM processor) and 54-VFBGA parts (SDRAM memory). Unfortunately, I've found that some of the through-hole vias were too close to the BGA pads, and during reflow, the solder balls melted down the via holes :(
This is clearly shown on x-ray images of the PCB.
For the next revision of this prototype, I need to move the vias further away from the holes. Alternately, I've been told that I could "tent" the vias so that the holes are filled, but this may raise the cost of the PCB.
The problem is not too bad; approximately 10 pads per BGA are affected, and most are electrically connected :D
The real showstopper is that one of the pads is completely unconnected. This pad corresponds to "D5" on my SDRAM memory bus. I've written test programs, and these programs show that there is indeed an issue with reading and writing to this data bit. Moreover, this pad shows up as completely unconnected on the x-ray images.
I'm working on the PCB for a research project, and I would prefer to salvage this PCB so at least I could create a working prototype.
Any suggestions? I would be extremely interested in hearing about recommendations as to whether there is a board rework/repair facility somewhere in Canada (or even elsewhere in the world) that could successfully repair this PCB. Is there anything that I could do myself? I would prefer getting this taken care of as quickly and efficiently as possible.
As an aside: Although the main microcontroller being used in this system is an ARM9, there are two other 8-bit AVR parts on this circuit board, so I haven't abandoned the AVR architecture at all :wink: