As mentioned, negative resists are photopolymers that become insoluble upon exposure to radiation. They have found a variety of commercial applications, especially in the area of designing and printing small chips for electronics. A characteristic found in most negative tone resists is the presence of multifunctional branches on the polymers used. Radiation of the polymers in the presence of an initiator results in the formation of a chemically resistant network polymer. A common functional group used in negative resists is epoxy functional groups. An example of a widely used polymer of this class is SU-8. SU-8 was one of the first polymers used in this field, and found applications in wire board printing. In the presence of a cationic photoinitiator photopolymer, SU-8 forms networks with other polymers in solution. Basic scheme shown below.
SU-8 is an example of an intramolecular photopolymerization forming a matrix of cross-linked material. Negative resists can also be made using co-polymerization. In the event that two different monomers, or oligomers, are in solution with multiple functionalities, it is possible for the two to polymerize and form a less soluble polymer.
Manufacturers also use light curing systems in OEM assembly applications such as specialty electronics or medical device applications.