Evaluation of the effects of residual stress occurred and hydrogen co-deposited during tin electroplating on the suppression and growth of tin whisker

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Effects of the electroplating bath temperature on the growth of whisker from tin film electroplated from an acid tin sulfate bath were investigated. Brass was used as the plating substrate, since brass always accelerated the growth of tin-whisker compared with the other metals. Tin electroplating was performed at seven kinds of bath temperature such as 0℃, 5℃, 10℃, 15℃ 20℃, 25℃ and 50℃. The internal stress always changed from tension at the beginning of electrolysis to compression with successive electroplating of tin. The compressive stress in as-deposited tin film decreased with increasing in bath temperature. The residual stress in tin film deposited at 50℃ was almost zero. The higher the bath temperature was, the larger the granular size of deposited tin became and the current efficiency for tin deposition increased. The growth of tin-whisker was enhanced in temperature orders of O℃>5℃>10℃>15℃>20℃>25℃>50℃.The Influences of tin-zinc alloy formation on tin whisker growth out of the e … More lectroplated tin was also investigated. The substrate of specimen was aluminum sheet with one-side chemically plated zinc and the reverse side insulated electrically by a plastic resin on it. Tin was electroplated on the zinc film. The aluminum sheet with the plated tin deposits was put in the incubator controlled thermostatically at 50℃ for the purpose of accelerating tin whisker growth. After some tin whisker grew, the specimen with tin whisker was covered by nickel electroformed from a nickel sulfamate bath. The plastic resin was stripped off for exposing the other-side aluminum, which was immersed and corroded in 1.0 moldm^<-3> NaOH solution at 25℃ and the corrosion potential was measured.Only the corrosion potentials concerning the zinc and tin electrode were detected for the specimen before tin whisker occurred. On the other hand, the specimen with some tin whisker always showed the corrosion potentials concerning tin-zinc alloy except the corrosion potential of tin and zinc, respectively. Such results suggested that zinc diffused into the plated tin to form tin-zinc alloy, which resulted in tin whisker growth. Less