めっき技術

Solderability

Electronic devices do not function until electronic parts and elements are bonded and assembled, when solderability is a key factor. In other words, together with being whisker-free, prior plating with good solder wettability is a requisite condition for facilitation of soldering. Here, the solderability of recent lead-free solder plating is introduced in contrast to conventional tin-lead solder plating.
Type of plating Characteristic value Uses
Tin-lead alloy plating - Sn-10Pb alloy plating
Solderability (excellent), whisker suppression (excellent)
Electronic parts, semiconductor parts, and electrical machine parts
Tin-copper alloy platingGreen mark - Sn-3Cu alloy plating
Solderability (good), whisker suppression (good)
Tin-bismuth alloy platingGreen mark - Sn-2Bi alloy plating
Solderability (good), whisker suppression (good)

- Frequently used for legs of lead frames
Tin-silver alloy platingGreen mark - Sn-3.5Ag alloy plating
Solderability (good), whisker suppression (good)
Reflow tin plating Green 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 specifications of semigloss tin plating have increased more than alloy plating.
採用事例
Solderability
Reflow tin plating
- Solderability is classified into three types: “fusible plating” the films of which fuse at a soldering work temperature (around 230°C), “soluble plating” the films of which do not melt but fuse in molten solder, and “non-fusible/non-soluble plating” the films of which do not dissolve in molten solder.

(1) Fusible plating: Tin alloy plating, tin plating
(2) Soluble plating: Gold plating, silver plating, copper plating
(3) Non-fusible/non-soluble: Nickel plating

- Soldering is to bond at 450°C or lower temperatures, which is also known as soft solder.
Brazing is to bond at temperatures higher than 450°C, which is also known as hard solder.