Its 100% Not the Logic Board. I have repaired over a dozen iphones and iPads with Nand Flash errors at bootup. This is a Hardware related failure. You need to strat disconnecting each flex cable individually until you figure out which flex cable is defective. On the iPhones its usually the Proximity Sensor Light Flex Cable.....
http://www.etechparts.com/Proximity-Sensor-Light-Flex-Cable-Ribbon-for-iPhon-p/822-5406.htm
On the iPads its usually the interconnection Board flex cable...
http://www.etechparts.com/Interconnection-Board-for-iPad-3-p/822-8322.htm.
I have repaired this Nand Flash error over a dozen times with 100% Success..
Hope this helps you guys out....
www.StevesiPhoneRepairs.com