Short cricuit on mechanical package XCMECH-FFG1153

[j.galy]

Hello,

We have bought a mechanical package in order to test the assembly process for a Virtex-7 board, and it seems that some power supplies are short-circuited : 1V core, 1V2, vttddr.

Does anyone know if there are some connections between balls inside a XCMECH-FFG1153 mechanical package. I thought it was a 'no die' package ? I don't find any electrical information about this package.

Thanks,

Jérôme

[umamahe]

The mechanical package are mainly used for mechanical evaluations, process setup, etc. 

Most of our mechanical packages are based on the JEDEC outline, and these parts are at times referred to as "dummy" parts since mechanical samples do not contain die. So there is no chance of short inside the mechanical package unless it is faulty or some problem in your test board.

[j.galy]

Kodali, thank you for your quick answer. There is no die inside an XMECH package, as I read on the UG112, but maybe the substrate is present as it is a flipchip technology ? Is there a possibility that for example all the GND balls are linked together, even if the die is not mounted ? My problem is that FFG1153 is not the good package, it corresponds to a Virtex 5 device. The PCB is designed for Virtex 7 device, which is a FFG1157 package (4 balls missing is not a problem for the process setup).

Thanks,

Jérôme

[gszakacs · Accepted solution]

That's most likely the case.  Xilinx would not make a substrate just for mechanical samples, but rather use one that exists for the given part.  It is normal for BGA substrates to have planes interconnecting power and ground balls in order to help filter high-frequency noise and reduce ground bounce.  Of course you could check this if you pull the mechanical sample off the board or if you have another one.