iMX233 PCB Design with BGA

[Neoseb30]

Hi,

I am actually reviewing AN3989 and Gerbers 77066 of EVK to design my own board.

I have some question, first, EVK layer order is different from AN, what's better ?

I can't found information about impedance requirement between IMX and DDR,

EVK say 50ohm for 3mils (very thin !) and have 5.5mils trace on L1, this give around

35ohm, it is correct (particularly for two DDR chip) ?

Finally, BGA pad are 0.355mm on EVK, less than 0.43mm+/-0.06 from datasheet,

is it really safe regarding stress on solder joint ?

Thanks for your answer.

SeB.

[danix]

Hello Sebastien,

few years ago I designed a custom board with imx233(BGA package), the board is working flawlessly to this day. So, this is what I used

-I prefer the layer order in the AN, but I used four layers "top route-GND-POWER/GROUND-bottom route" I had imx233(BGA), 2X 64MB micron DDRs in TSOP-66, GSM modem, audio amplifiers, FM reciever, accelerometer and GPS chips all on top-layer of a "2.1x3.2" dimentson.

- The impedance matching is not that critical if you keep the traces very short. I used trace/space of 5mil and I haven't actually controlled the impedance, but I kept the traces as short as possible (longest 33mm)

- as for the balls, I used a 0.35mm pads, to get easy routing with 5mil traces and four layers.

cheers!

Dan