Chemical gold surfaces

The surface chem. Ni/Au = Electroless Nickel(-Phosphorus)/Immersion Gold = ENIG = Sudgold = Flash-Gold is well suited for both aluminum wire bonding and multiple soldering and is therefore the ideal surface for combining both joining techniques. It consists of a 4-6 µm thick nickel layer which, for process-related reasons, usually contains 6-8 % phosphorus. For tarnish protection, the nickel layer is coated with 70 nm – 120 nm gold. The storage time is more than 12 months.

The gold layer dissolves completely in the tin during soldering. The actual solder connection is then made with an intermetallic Ni/Sn phase between the solder and the nickel layer.

Press-fit technology is not primarily possible because of the brittle nature of the nickel. Some connector manufacturers offer press-fit pins with special press-fit zones, which are also said to be suitable for chem. Ni/Au.

Gold surfaces on flexible conductor plates must not extend over longer distances (e.g. over the entire surface or on conductors), since the brittle nickel can break during handling and this can lead to conductor interruptions. Furthermore, the transition area from a gold-plated pad to the covered conductor is a mechanical weak point that readily serves as a predetermined breaking point during handling.