Micromolds for micromolding

Mimotec SA is a Swiss moldmaker and parts fabricator. Although Mimotec just started production in November 1998, well over 50 million parts were molded in its tools in only six months. Impossible? Hardly—not when you consider the size of the parts molded in Mimotec’s molds.

You see, Mimotec specializes in extremely precise micromoldmaking. It also rapidly prototypes extremely complex micro parts in metal. In both cases, Mimotec uses a proprietary, patented 2.5-D manufacturing process similar to one commonly used in the microsystems industry called LIGA. This technology combines lithography and galvanizing, or as the latter is more commonly known in the U.S., electroplating.

With the LIGA technique (see p.80), high-priced, high-resolution X-ray lasers are used to make parts like silicon wafers for computer chips. However, Mimotec’s LIGA process uses a much less expensive ultraviolet light source.

Micromold Replication
To some, Mimotec’s process may resemble a fusion of rapid prototyping and CD mold manufacturing systems. In it, a glass/chromium mask is created from a CAD file. The mask is used to build a master from SU-8, a commonly used photosensitive epoxy from MicroChem Corp.

Layer by layer, the epoxy exposed through the mask is hardened by the UV light source. Curing follows. Structures up to 1.5 mm high can be created. Such structures are considered to be extremely high in microelectronics. There are no lateral size limitations in Mimotec’s masters.

The finished master is electroplated with 2 to 3 mm of nickel or a nickel alloy. The master is destroyed and the resulting mold cavity is lapped down to finished thickness at Mimotec with tabletop lapping systems. Multicavity micromolds can be created in a single process. Mimotec’s micromolds also can be used as inserts in larger tooling.

Micro Parts Fabrication

Mimotec can produce a number of molds in a single run, and it can easily stock spares for quick deliveries, should a customer’s production schedules warrant. Typically, five to six weeks from the receipt of a CAD file is required for turnaround.

Hubert Lorenz, 33, a graduate of the Swiss Federal Institute of Technology, invented the UV-LIGA process for making micromolds and micro parts. Lorenz has initially targeted his micromoldmaking capacity at the Swiss watch industry for micromolding watch movements; how-ever, next-generation medical bio-sensors is planned as a future area of activity. Lorenz is also considering licensing Mimotec’s micromold-making process.