This is a known issue in Mid 2010 Macbook Pro of bad Nvidia Chip, hence i straightway ordered the graphics chip & replaced. The result is Cris-cross pattern on screen and shutdowns...
This was the first time, i had to replace graphics chip in macbook and a big failure at first attempt.
Reading across various forums, i learnt that the VRAM glue may create issue in solder joints of VRAM, especially if the VRAM is not protected from bottom heat. Secondly the profile must be tweaked to have lesser variation of temperature across BGA during reflow. Given the uneven distribution of board across the four sides of BGA, i had a reason to believe that the reflow profile may not be correct.
The BGA glue surrounding VRAM was removed and residue was cleaned with 99% IPA. Also the GPU was reflowed keeping thick Aluminum Tape over VRAM. Thermocuople location changed to center of edge of BGA and increased the bottom heat setting during last phase of reflow, also increased time at peak temp from 25 sec to 35 secs, which gave TAL (Time Above Liquidus) of around 60 secs.
Went ahead and reflown the GPU and we have success...No more GPU Panics.
The fan on GPU heatsink was noisy, and a bit slow, which also caused overheating, replaced fan as well and machine goes back to customer..
