Now that the processor is in place, turn your attention to the heat sink.

Apple uses a thermally conductive film that must be removed prior to reinstalling the heat sink.

Use a razor blade (or anyother flat object such as a credit card, etc.) to remove all of the old solidified thermal material from the heat sink.

Next use a small amount of rubbing alcohol to remove all traces of the old thermal material.

Allow the heat sink to dry before proceeding.