Micro injection molding for mass production using LIGA mold inserts

Micro molding is one of key technologies for mass production of polymer micro parts and structures with high aspect ratios. The authors developed a commercially available micro injection molding technology for high aspect ratio microstructures (HARMs) with LIGA-made mold inserts and pressurized CO₂ gasses. The test inserts made of nickel with the smallest surface details of 5 μm with structural height of 15 μm were fabricated by using LIGA technology. High surface quality in terms of low surface roughness of the mold inserts allowed using for injection molding. Compared to standard inserts no draft, which is required to provide a proper demolding, was formed in the inserts. To meet higher economic efficiency and cost reduction, a fully electrical injection molding machine of higher accuracy has been applied with dissolving CO₂ gasses into molten resin. The gasses acts as plasticizer and improves the flowability of the resin. Simultaneously, pressurizing the cavity with the gasses allows high replication to be obtained. Micro injection molding, using polycarbonate as polymer resins, with the aspect ratio of two was achieved in the area of 28 × 55 mm² at the cycle time of 40 s with CO₂ gasses, in contrast to the case of the aspect ratio of 0.1 without the gasses.