From Mechanical to Chemical Adhesion

Abstract

In the development of electronic systems, the miniaturization of electronic devices is strongly driven by the market and technology demands within the portable electronics sector. This size reduction affects all subsystems and components. Such reduction is observed in circuitry as the conductor lines and space dimensions are now aiming at dimensions significantly below ten microns. This continuing trend in miniaturization leads to challenges as printed circuits (typically copper) must adhere to a new generation of dielectric substrates, typically highly filled organic resins, for performance and reliability reasons. Good adhesion of chemically deposited copper to the dielectric surface is currently achieved through mechanical means. The dielectric surface is typically chemically roughened or desmeared. Copper deposited onto the roughened surface will have good adhesion as surface features act as anchoring points. As the dimensions of the circuitry are reduced, a highly roughened surface becomes increasingly undesirable, as it will ultimately create poor line definition or even shorts in the circuit. On the other hand insufficient roughness will result in poor adhesion. It is evident that other means of adhesion (for example, chemical) will become necessary for smaller line widths. This paper will review the current process for treating the dielectric surface for the subsequent deposition of electroless copper and will compare it to new treatments. The data presented will show that improved copper-to-dielectric adhesion with minimal roughening can be achieved with the new treatments. The origin of the improvement in adhesion is attributed to chemical bonding.