镀镍前或锡电镀间的阴极接触不良，放电火花将铜材熔成凹洞。
Before or tin plating nickel plating of bad contacts between the cathode, discharge sparks will melt into hollow copper hole.
镀镍前或锡电镀间的阴极接触不良，放电火花将铜材熔成凹洞。
Before or tin plating nickel plating of bad contacts between the cathode, discharge sparks will melt into hollow copper hole.
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