Patent ID: 8182932

Claim:
An Sn-plated copper alloy strip comprising an Sn or Sn alloy plating film formed on the surface of a copper alloy strip by electroplating and reflowing treatment, wherein the average hydrogen concentration in the Sn-plated copper alloy strip is 0.1 to 2 mass ppm, and the fatigue limit is about 300 to about 500 MPa when measured by: taking a rectangular piece with 10 mm width such that the longitudinal direction of the piece is parallel with a rolling direction of the strip; applying alternating bending stresses repeatedly on the piece in a direction perpendicular to a thickness of the piece, and determining a number of vibrations repeated until the piece is snapped, the vibration waveform being 50 Hz sine wave, the stress σ applied to the piece being calculated by the equation: L=(3·t·E·f/(2·σ) 1/2 , where: L is the length of the vibrating section, t is the thickness of the piece, f is the amplitude of the vibration, and E is Young's modulus; calculating N for different values of σ to determine an SN curve; determining from the SN curve a value of σ at which N=10 million; and taking the value of σ at that point as the fatigue limit.