Fabrication of High Hardness Micro Mold Using Double Layer Nickel Electroforming

The LIGA is a total process for fabricating the metal mold of microstructure using deep X-ray lithography, electroforming a micro metal mold, and precise molding. This advantage is that it could reliably fabricate high-accuracy microscopic parts at a high speed and lower cost by using a micro mold to transfer a high aspect ratio pattern. Nickel electroforming is used as a fabrication technology of micro metal mold including LIGA process. However, neither the strength nor peelability of electroformed nickel is enough. A higher hardness is required for extending mold service life and improving the releasability of injection-molded parts. There are several methods to improve strength of metal mold alloying, and using additive composition agent of electroplating bath, for example. We obtained the surface hardness of 601 Hv at room temperature and 580 Hv even at 250degC using the sodium-allylsulfonate-containing high-concentration nickel sulfamate bath. But, an organic additive added to nickel plating bath has a stress decreasing effect. In this research, with an aim of increasing the hardness and relieving the internal stress of nickel micro mold, we have fabricated a 4 mm thick mold in two stages. One is a thin hard nickel layer deposited over the electroformed mold surface using an organic-additive-containing nickel plating bath. Another one is conventional nickel electroforming bath for producing warp free surface, thereby completing a double layer nickel micro mold.