Why do gold and tin contacts make a difference? Isn't gold better?

• To quote Compaq: "IMPORTANT NOTE: SIMM connectors can be either gold or tin plated. Contact reliability can be affected if the different metal types are mixed, for example, placing a tin-plated SIMM into a gold-plated memory socket. This metal mixing can cause accelerated corrosion, which results in bad connections and can ultimately cause system failure."
• The dissimilar metals in contact with each other creates a perfect environment for accelerated corrosion. Corrosion creates electrical current and changes the capacitance value along the circuit.
• Many people insist mixing will have no effect, but the manner and quality of the gold or tin application can amplify what might have otherwise been a minute affect.
• Gold is a better conductor of electricity and is more resistant to corrosion. Gold is also easier to apply in a thin uniform layer.
• Tin is much less expensive, but is very difficult to apply in a thin uniform layer.
• Intel recommends NOT mixing dissimilar metals.
• According to Intel: Studies show that fretting occurs when tin comes in pressure contact with gold or any other metal. Tin debris will transfer to the gold surface and oxidize. Continued transfer will build up an oxide film layer. Tin surfaces always have a natural oxide. Despite this, electrical contact is easily made between two tin surfaces. Oxides on both soft surfaces will bend and break, ensuring contact. The resistance of the oxidation layer builds up over time when one surface is hard. Increasing the contact resistance will ultimately result in memory failures.
• Mixing gold and tin leads doesn't always cause an immediate problem. The problem usually occurs over time and can be abated by removing the memory module and cleaning the contacts.
• Our advice is not to mix gold and tin contacts.)

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