Switch lifetime

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Keyboard switches do not last forever.

Contact resistance

An ideal switch has infinite resistance when open, and no resistance when closed. In reality, the switch will always offer a certain amount of resistance even when new. Some manufacturers cite the contact resistance when new, and at the end of the switch's rated lifetime.

Switch/series	Type	Resistance (new)	Resistance (end of life)	Rated life at rated load
RAFI RS 76 M	Crosspoint	≤ 100 mΩ	≤ 3 Ω	≥ 10 million
RAFI RS 76 M (illuminated)	Bridge contact	≤ 200 mΩ	≤ 3 Ω	≥ 100 thousand
Clare-Pendar Series S820	Reed	≤ 200 mΩ	≤ 1 Ω	5 million
Clare-Pendar Series S880	Reed	≤ 300 mΩ	≤ 1 Ω	100 million
Futaba MD-4P	Metal leaf	≤ 100 mΩ	≤ 5 Ω	10 million

Contact bounce

The contact bounce time for a switch increases with use.

Switch/series	Type	Bounce time (new)	Bounce time (end of life)	Rated life at rated load
Futaba MD-4P	Metal leaf	≤ 2 ms	≤ 5 ms	10 million