Better Adhesion with UV Irradiation in Vacuum
Plastic surfaces must be pretreated to enable adhesion of metal plating. Experiments have shown that UV irradiation in vacuum enhances bonding.
Irradiation of a plastic surface with ultraviolet light in vacuum (VUV) can enhance adhesion of metals. This is the conclusion reached by researchers at the Fraunhofer Institute for Applied Polymer Research in Potsdam. The experiments were conducted with a variety of plastics.
It was determined that when treating ABS with VUV radiation, different reactions occur in the plastic surface depending on the process gas. Different adhesion characteristics are obtained as a result. The surface becomes noticeably rougher with extended and more intense irradiation. The adhesion of nickel/copper layers was about 8 N/cm in regions that were close to the radiation source during irradiation. In contrast, in regions farther away from the source, adhesion varied between 4 and 5 N/cm. Investigations of ABS/PC blends showed that surface roughening is less than on ABS. Adhesion to ABS/PC blends is lower as well. Polyimide (PI) test specimens were also subjected to VUV irradiation. Following this, the PI surface was copper-plated via either sputtering or a combination of electroless plating and electrolytic plating. In a peel test, the sputtered material attained adhesion values of 5.5 N/mm, while the wet-plated material reached 12 N/mm. Another series of tests investigated COC that was initially irradiated and then underwent electroless nickel plating followed by electrolytic plating with palladium. The multilayer system passed the adhesion test using tape undamaged.
Similarly good results were achieved with sintered, porous objects made from PE. After irradiation, PEI was applied as a molecular primer, and the test specimens were then plated with copper or nickel. Both metal platings passed the adhesion test using tape.