After nearly 30 years of R&D, nano molding may be too small to see, but it’s real. Nano details that are so small they can’t even be seen under a microscope are being injection molded. They’re read by electron microscopes or by defraction using a laser pointer. Molded nano features include invisible logos on parts to prevent counterfeiting, functional surfaces like radar deflection, and hologram-like iridescence.
The original technology was developed in the 1980s by what is now the Karlsruhe Institute of Technology in Germany to make nozzles for uranium enrichment for atomic energy. Called LIGA, short for lithography, electroplating and molding in German, it uses concentrated X-rays to cure successive layers of PMMA to make highly precise, straight-sided parts, which are then electroplated with nickel alloys or gold.
But X-ray LIGA has drawbacks for nano molding. Vertical walls are hard to demold, so it would only work for shallow nano surfaces. The technology also requires a costly, colossal X-ray concentrating machine called a synchrotron. KIT’s is the size of a very large warehouse. An even larger one in Switzerland is the size of a small stadium. Only two companies use X-ray LIGA commercially – Microworks GmbH in Eggenstein-Leopoldshafen, Germany, a spinoff from KIT in 2007, and HT MicroAnalytical Inc., Albuquerque, NM . Neither has made an injection mold insert.
Nano-featured injection mold inserts are beginning to be made by UV-cured LIGA, which is less expensive than X-ray, and by nano imprint lithography. Both lithography technologies have been used for over a decade to emboss nano features on film, but only recently tried for injection molding. Mimotec SA in Sion, Switzerland , was founded in 1998 to develop UV LIGA for micron-scale molding technology, as the name says. Instead Mimotec’s market turned out to be direct production of electroplated watch parts. Mimotec only made its first commercial nano mold insert with UV LIGA three years ago for a French office supply company. The insert, mounted on an ejector pin, puts an invisible logo on parts for authentication.
Mimotec’s patented UV-LIGA technology (EP 2855737) exposes up to three layers of polymer to make a nano feature. First a flat silicon substrate is coated with an epoxy-based photo-sensitive polymer called “SU8.” Then the reverse of the part is exposed to UV laser light using a mask. After UV exposure it takes a week for each layer to harden unless a curing agent is used. Once the layers harden, uncured polymer is washed away, and the cavity is sent out for electroplating with nickel, nickel phosphorous or gold. Electroplating is up to 0.8 mm thick, much thicker than conventional electroplating, which is only microns thick.
Now, we used this technology in our bezel-less smartphone Elephone S3.