Take off the logic board from the hard drive. Set it as level as possible on a good work surface with some washers wood blocks, ect... Use a heat gun on the hi setting, heat the board for about 30 seconds to a minute while constantly moving the air gun around. So as not to heat one spot too hot and burn something. Hold the heat gun higher up and reduce heat. You are cooling the board with out letting it cool too fast and get possible stress cracks. What you have just done is a reballing on the logic board. flip over and repeat. Works about 50% of the time.