An old engineers trick is to use a soft pink eraser. Although the contact pads are gold plated for the best possible conductivity, even gold will tarnish, given time and humidity.
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soft pink eraser will gently clean the contacts to like new conditions with negligible abrasion. In addition to Intel CPUs, this also works on any male edge connectors such as PCIe cards, memory modules, NVMe drives, etcetera.
Wipe the contact surfaces with alcohol, then when dry, use the eraser. Just be sure to keep your work well clear of female connectors to protect any exposed slots such as on a motherboard. When finished, use a clean brush to remove eraser residue. Also, never touch any contacts with your fingers, as the oil from your skin will cause the contacts to tarnish and attract dust.
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