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Tin alloy plating

Conventionally, Sn-10%Pb solder plating, melting at a low point of 183°C, would be used, but because lead-containing solder plating has become unusable according to an RoHS Directive, reflow tin plating, Sn-Cu alloy plating, Sn-Bi alloy plating, and Sn-Ag alloy plating are playing more active parts as lead-free solder plating.
Type of plating Features Characteristic value
Sn-Pb alloy plating - Sn-10Pb alloy plating
Solderability (excellent), whisker suppression (excellent)
Melting point 212°C
Sn-Cu alloy platingGreen mark - Sn-3Cu alloy plating
Solderability (good), whisker suppression (fair)
Melting point 229°C
Sn-Bi alloy platingGreen mark - Sn-2Bi alloy plating
Solderability (good), whisker suppression (good)

- There are many examples of plating for legs of lead frames.
Melting point 221°C
Sn-Ag alloy platingGreen mark - Sn-3.5Ag alloy plating
Solderability (good), whisker suppression (good)
Melting point 221°C
Reflow Sn platingGreen mark - Solderability (good), whisker suppression (excellent)

- While the alloy compositions of various types of alloy plating greatly change depending on plating conditions, single plating like reflow tin plating is highly reliable precision plating having no composition variations. Recently, reflow specification of semigloss tin plating has been increasing more than alloy plating.
Melting point 232°C
Adoption examples
Tin alloy plating
Reflow tin plating
Being free of whiskers and having good solder wettability are indispensable to solder plating. The abovementioned tin-based alloy plating, having both advantages and disadvantages, is used according to product type.