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100 The PCB Magazine • March 2014 by Michael Carano omg electronic chemicals llc Oxide vs. Oxide Alternative Chemistry for High-Performance Resin Systems, Part 2 c o l u m n trouble iN your taNk Introduction In last month's column, I presented an over- view of conventional oxide chemistry and the critical success factors of the process. In this col- umn, we begin our review of the oxide alterna- tive process that is often referred to as an organo- metallic coating process. The reason for this al- ternative name will be explained in this column. With continued emphasis on long-term reliability and vastly improved electrical per- formance, manufacturers of high layer-count multilayer printed wiring boards are beginning to abandon the reduced oxide bonding pro- cess in favor of alternative methods. One such method, presented here as an organo-metallic adhesion promotion system, increases the bond strength of the resin to the copper by modify- ing the topography of the copper surface and simultaneously depositing an organic layer that acts as an adhesion promoter. The surface area or topography of the copper is enhanced by the selective micro-etching along the grain bound- aries of the copper. (This mechanism will be discussed further below.) This is in contrast to the oxide-based chemical processes in that the oxide processes are designed to "grow a crystal structure" on the copper surface. The concern with oxide processes (even the formulations de- signed to give a denser shorter crystal structure) is that the higher pressures and temperatures of lamination required for higher performance laminate materials will fracture the oxide crys- tal structure reducing the bond strength. With that said, let's discuss oxide alternative or orga- no-metallic chemistry and how it all works. Oxide Alternative Chemistry and the Theory of Bonding Before presenting the particulars of alterna- tive oxide chemistry, it would be a good idea to present multilayer bonding theory. There are two main factors involved in enhancing the bonding strength of copper to the prepreg for multilayer lamination of circuit boards. They are 1) the type and degree of roughness impart- ed to the copper surface and 2) the type and thickness of any coating that is applied to the copper surface [1] .

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