Arria II problem-short circuited between VCCA_PLL and GND

hello everyone:

i'v got a problem about Arria II EP2AGX45-C6

recently, i'v got 8 pcs EP2AGX45 board can't work, I test and find +2.5V is shorted to GND in all these boards, and the FPGA was the root cause.

FPGA's VCCA_PLL pins E6/Y6/F17/W17 was shorted-circuit to its GND pin B5

the impedance is only about 0.3ohm or 19ohm

The impedance between VCCA_PLL pin and its GND pin is at least 10Kohm in normal FPGA

I guess there should be some EOS porblems

Then I write a test code to make the board repeat working for 30 minutes then power down for 5 seconds, run this case 5 days and the oscillograph get nothing about overshoot or undershoot on +2.5V power domain during power on/ working/power off

I was confused about the cause of FPGA's PLL power pin shorted-circuit to GND

how could that happened?

By the way: 4 DDR2 chips connected to top and right bank of FPGA runs at 267MHz in half-rate mode, that's a violation, because EP2AGX45-C6 only can supports 200Mhz max clock rate with 4 ddr2 chips.

It this the cause?