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LIGA and Micromolding 4-71

FIGURE 4.52 LIGA spinneret nozzles. (a) Spinneret plate; (b) profiled spinneret nozzles; (c) spinning synthetic
fiber. (Courtesy of IMM, Germany.)

development steps [d] and die electroforming [e]. The die [f] is made by electroforming of aNiCo alloy on
2
the Al substrate from a Ni/Co sulfamate bath at current densities between 1 and 5A/dm .The addition of
increasing amounts of cobalt sulfamate increases the hardness of the deposit to about 420 Vickers. At a con-
centration higher than 20g/L Co sulfamate, the hardness saturates. With increasing hardness also comes
increased residual stress, which must be carefully controlled. Polypropylene (PP) was used to duplicate the
NiCo microstructures by injection molding through a stainless steel tool as shown in Figure 4.53b.After the
LIGA die is removed,the result is a field of polymer microstructures standing up from the stainless steel tool.
The stainless steel substrate is subsequently used for plating the spinneret structures. Polyester fibers typi-
cally melt at 260°C and are extruded at speeds of over 3000m/min. During this fiber extrusion, the spin-
neret suffers high-temperature excursions of up to 280°C, and high-temperature wear resistance becomes
a problem when using a NiCo. To improve the high-temperature hardness of Ni spinnerets, Shew et al.
plated a Ni/SiC composite [Shew et al., 1999]. With the addition of SiC nanopowder to the sulfamate plat-
ing electrolyte, stable composite hardness of 500 Hv (Vickers hardness) at temperatures as high as 500°C
was demonstrated. The authors suggest that these new types of spinnerets will enable the production of
a new generation of fibers with ultrafine sizes and new functionalities at a low cost.

Example 3. LIGA Fiber-Chip Coupling
LIGA elements for coupling monomode fibers with integrated optical chips have been developed.
These prealignment arrays may utilize fixed nickel guiding structures in combination with leaf springs
to ensure a precise alignment of the optical fibers relative to the optical chip with an accuracy in the

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