Effect of Surface Machine Roughness on Detectability of Sub-Millimeter Reflectors in Polycrystalline Materials Using Ultrasonic Immersion Testing

Detection of sub-millimeter defects in high purity polycrystalline materials used in manufacturing of sputtering targets is an important quality requirement imposed by Semiconductor Industry on target manufacturers. According to requirements the tiny defects with the size range of 0.25 mm to 1.0 mm should be detected, resolved, and reported. Typically, the fabricated plates and the cast ingots used in target manufacturing have tightly controlled grain texture and crystallography. Since texture is controlled, only two major variables which affect detectability of minute flaws during ultrasonic immersion testing remain to be addressed; surface roughness and equipment-related electronic noise. It was shown that electronic noise could be reduced by at least 5% if low noise pre-amplification during signal conditioning.

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