Injection molding technology offers the most competitive potential to meet the growing demand for cost-effective
manufacturing of components with micro and nanoscale features due to its far greater production rates than the other
techniques. Since conventional mold tooling materials and techniques are not suitable for sub-micron scale molding,
mature silicon processing technology were evaluated as tooling for these features. Simple pattern geometries of trench
lines were employed to simplify the analysis and all parts were molded using optical grade high-flow polycarbonate.
Replication quality was evaluated in terms of depth ratio (height of molded feature/depth of corresponding tooling
feature) and root-mean-square roughness. Although perfect replication has not been achieved with the given system,
several factors including surface adhesion and feature aspect ratio were found to be critical for replication of
nanoscalefeatures. Of four factors possibly affecting replication, adhesion of the polymer to silicon surface during
ejection was found to be critical and is influenced by processing temperatures, cooling times, tooling mounting systems,
and tooling surface roughness. Trapped of air in tooling trenches, damage to the silicon tooling during molding, and
shrinkage of polymer during cooling may also have contributed to less-than-perfect replication. All factors seem
synergistic and the effects are greater for small feature geometries.
Injection molding technology is one of the most promising candidates for the economically viable manufacturing of nanoscale parts, but the composition and surface properties of tooling materials become more critical as the size of the molded features decreases. In the study, the effect of novel tooling with micro and nanoscale features was investigated by employing this tooling as inserts for micro injection molding of polycarbonate. Parts molded from etched silicon wafers with pattern depths of 300 nm and widths of 200 to 980 nm showed a significant decrease in replication quality with the size the features, probably because polymer adhered to the tooling surface. Silicon tooling from a different source and titanium-coated gallium arsenide tooling produced higher quality replication. The replication quality from the silicon tooling, however, was constant over 3000 molding cycles and coated gallium arsenide inserts survived the molding pressures; (the uncoated gallium arsenide fractured). These findings suggest that modifications to the insert surfaces will allow for viable tooling for injection molding of plastic parts with nanoscale features.