POSTCURE SHRINKAGE OF PHOTO-SENSITIVE MATERIAL USED IN LASER LITHOGRAPHY PROCESS

Shrinkage causes distortion and warpage due to the internal stresses b uilt up during fabrication, and greatly influences the dimensional acc uracy of a part. This paper presents an experimental study on the rela tionships between the key parameters of the laser lithography (LL) (or commonly known as Stereolithography) process and the resulting post-c uring shrinkage due to thermal and ultraviolet (UV) exposure. The UV-s ensitive material used in the experiment is an acrylic-based resin, na mely SCR-310. The post-curing process causes partially-cured and uncur ed resin to be further polymerised and is necessary for the improvemen t of the final mechanical properties of the parts. In principle, a lar ger laser power or a smaller layer pitch will result in a smaller amou nt of partially-cured or uncured resin, with less shrinkage after post -curing. A better understanding of the behaviour and characterisation of the shrinkage process during thermal and UV treatments will help to reduce the post-cure distortion, and will lead to more accurate rapid prototypes produced by the LL process. The origin of shrinkage from p hoto-polymerisation is closely examined through the measurements along both the scanning and transversal directions.