Development of selective conformal coating process based on advanced packaging for harsh environments

Conformai coating has been traditionally used to protect Printed Circuit Board Assemblies (PCBA) in harsh environments. The benefit of conformal coating is usually enhanced resistance to mechanical and thermal stresses. Various coating techniques exist, including brushing, dipping and spraying. Today, automation makes selective coating possible. The biggest improvements include: no masking time before coating, chemicals confinement and delivery of a replicable and repeatable process. When using an automated platform, a balance between two major problems must be considered: minimum pattern size and specified thickness range. At the same time, current improvements in selective coating must deal with new schemes: heterogeneous integration and high-density integration. Among drop-on-demand solutions, inkjet is used extensively for printing applications while jetting based on mechanical collision is used in advanced packaging. Based on inkjet knowhow, a theoretical approach has been introduced and then compared with actual experimental results. Both areas are discussed and combined in this paper.