Thick film coating materials and fast conformal coating processes - a contradiction?

Abstract

Conformal coatings are of strongly growing importance to the manufacturers of electronics. Users have realised that the reliability and life span of electronic products can be considerably improved and increased by applying these speciality coatings. However, the processing can be troublesome and a number of these products have strong limitations with respect to their application under severe climatic conditions, especially in thick film applications. This paper discusses the following questions: What are the main product "families" available in the field of conformal coatings, what are their advantages and disadvantages, where are their limitations? What are the fields of application for thick film coatings? To what degree can conventional conformal coatings be used for thick film applications ranging from approx. 200 to 2000 /spl mu/m, what are the alternatives, how are these products processed and what equipment is needed? What experiences have been gathered with newly formulated thick film conformal coatings combining UV cure functionality (enabling instant handling and offering immediate protection) and a subsequent cure with ambient moisture to achieve maximum insulation and protective properties? How do these systems work, what are their capabilities and properties regarding chemical and mechanical resistance as well as their dielectrical performance and how do they behave underneath components compared to conventional conformal coatings (e.g. encapsulation of residual solvents and the "shadowing phenomenon" with UV-curable products as well as capillary effects)? How are these "dual cure" or "twin cure" conformal coatings processed As a comparison, problem-oriented solutions with new solvent-free silicone coatings applied as thick film coatings are introduced and discussed additionally. The technologically special position of silicones is briefly presented and elucidated.