Effect of Tooling Surface Roughness in Micro-Injection Molding

Quality of tooling surface has been considered as one of the important factors defining the injection molded part quality. Therefore, surface polishing has been an important and relatively expensive step in conventional mold making process. Although the poor surface quality impacts the product quality when molding macroscale parts, it becomes more significant with sub-micrometer features. Previous micro injection molding research result has indicated that rough tooling surface may cause polymer adhesion on the tooling surface. To evaluate the effect of roughness, optical grade polycarbonate was molded using silicon inserts with artificially generated surface roughness (root-mean-square roughness: 3∼143 nm) by dry etching. The silicon and molded parts surface were characterized using atomic force and scanning electron microscopy. Filling and ejection of the parts as well as residual polymer on the tooling correlated surface roughness of the tooling.