By: Joseph A. Grande

Researchers at Lehigh University's P.C. Rossin College of Engineering and Applied Science in Bethlehem, Pa., are on a mission to redefine the world of micro-molding. They are pushing the size range of injection molded parts down from micron size ([10.sup.-5] in.) to nanometer scale ([10.sup.-8] in.). Take for example, an injection molded post that is tinier than the HIV virus, about 100 nanometers (nm). That's small. Lehigh researchers are exploring the unimaginable world of "nanomolding," where parts-or molded features on parts-are measurable only with an electron microscope.

Lehigh researchers, led by John Coulter, professor and associate dean of the P.C. Rossin College, have experimented extensively with nano-scale molding on small injection machines like the 15-ton model 12 A from Boy Machines Inc., Exton, Pa. Lehigh molds nano-scale features onto 0.5-in. squares of plastic 0.5-mm thick and weighing about 0.1 g. The parts are usually made of Topas cyclic olefin copolymer (COC) from Topas Advanced Polymers Inc., Florence, Ky. The resin provides good optical properties, mechanical stability, and ability to be imaged with scanning electroscopes.

Lead project researcher Aleksander Angelov says the molds are made of silicon using standard micro-machining techniques including electron-beam lithography and deep reactive ion etching. A plasma polymerization process deposits a 5- to 10-nm-thick release coating on the mold surface. The silicon mold is then embedded in epoxy and placed in a steel fixture for support during molding.

The injection machine, equipped with a 12-mm-diam. screw, typically injects only 3 cc of material, about one-third of the maximum shot size. A mold temperature of 135 C, close to the glass-transition temperature (Tg) of COC, ensures good flow and mold replication, says Angelov. Parts are demolded manually with tweezers.

Lehigh molded a Boy logo with letters 50 microns long, about half the size of a human hair. Another logo has letters that are 15 microns long, or a little larger than a human blood cell. More recent work has resulted in accurate molding of posts down to 50 nm size.

These nano components show promise as a high-density storage medium for magnetic and optical data. In the biomedical industry, nano-scale surfaces are well suited for starting cell growth. A South Korean research project focused on data storage has molded nano features on the scale achieved at Lehigh, says Coulter.

Robert Koch, president of Boy Machines, says nanomolding holds tremendous potential: "Because our machines are so well suited to the molding of miniaturized parts, we expect them to be vital to advances going forward."