Performance of nickel and bulk metallic glass as tool inserts for the microinjection molding of polymeric microfluidic devices

Electroformed nickel and bulk metallic glasses (BMGs) can be designed to incorporate features with length scales ranging from millimeters to nanometers. This, combined with their good mechanical properties relative to other materials, makes them competitive candidates for manufacturing multi-scale molds to produce high volumes of polymeric microfluidics components and other micro/nano devices. Despite this attractiveness, BMGs are newly developed engineering materials and their capabilities as a mold material have not been evaluated. This paper compares the performance of nickel tools made by an electroforming process and BMG tools made by a thermoplastic forming process, specifically with regard to typical microfluidics patterns and features. Ni shows excellent capabilities for good feature replication. BMG thermoplastic forming is highly dependent on the choice of alloy composition, which restricts the achievable feature size and aspect ratio. Compared to Ni, BMG has hardness values that are close to those of stainless steel and shows the superior mechanical strength that is required for mass production applications. However, oxidation in BMG tool manufacturing process affects the tool surface finish significantly and reduces the tool's corrosion resistance. Future development of BMG tools include preventing the formation of oxidation layers or developing BMGs with an anti-oxidation composition, and further reducing their overall cost and widening its processing window parameters. Despite these challenges, however, BMGs are shown to combine excellent mechanical properties and capabilities for multi-scale forming; this makes them significantly more attractive than relatively soft Ni tools.