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The narrower the pitch of a PCB is, the easier electro-migration occurs. The duty cycle of the pulse currents, defined as the ratio between the maximum and the average pulse power, has a large influence on this. If the conditions for migration are determined at about 65°C, 95 % relative humidity, 50 V voltage (70 Hz, single electrode), 0.1 mm wire spacing, then the probability of electro-migration is around 30% at a duty cycle value of 0.5 or higher (Tsukui, Kushida, Nagatanigawa : Research Reports of the Company for Electronics and Information Technology, Vol. 90 , No. 9, 1990, p. 29). See also Electro-migration.