MICRO MACHINING | ARTICLE
NICKEL ELECTROFORMING of Microscopic Structures
words | Dr Jan-Henrik Müller
<< Figure 1: Depiction of the electroforming process. >>
W
hen, in 1780, the Italian doctor Luigi Galvani discovered how electric current works, he would have had little idea of the electroplating opportunities that
would arise from this discovery. Not so long afterwards, nickel was successfully separated from salt solutions and the great potential of galvanically isolated nickel layers was recognised. From the middle of the 19th century, a great many patents were taken out on this coating process. Modern nickel baths have been in existence since the beginning of the 20th century.
By 1838, it was discovered that apart from the basic nickel plating, the surface was also reproduced extremely accurately. This was how electroforming came into being and it found an increasing number of uses in the replication of complex and micro structured surfaces.
The galvanic process The electroforming process is depicted in figure 1. The principle of each electroforming process is the same: the workpiece from which a mould will be made is known as the mandrel or master
(1). If the surface is non-metallic, it is covered with a conductive coating (2). The workpiece, which can potentially be very large, is deposited in an electrolytic bath containing a nickel salt solution (nickel electrolyte) and connected electrically. The current flow results in the nickel anode dissolving, with the pure nickel being deposited on the mandrel (cathode) (3).
Anode reaction: Cathode reaction: Ni2+ (in solution) + 2 e- 4 Ni (solid, pure). Ni (solid) 4 Ni2+ (in solution) + 2 e-
The current source thus serves as an electron pump. Electrons are depicted as e-. The layer of nickel on the mandrel can reach a thickness of several millimetres. Once the process is complete, it is removed from the mandrel (4). The resulting electroform is a replica of the mandrel, retaining its shape and structure. Raised areas on the mandrel result in indentations in the electroform. In comparison to other materials, this nickel electroform is a sturdy and durable tool. Note that there are also copper electroforms, but these lack some of the advantages of nickel ones.
18 | commercial micro manufacturing international Vol 6 No.5
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