Surface characterization of the copper–epoxy adhesion interface from production printed circuit boards

In the construction of multilayered printed circuit boards, the interface adhesion between copper foils and glass cloth reinforced FR4 epoxy is critical to the life performance of the product. This paper describes the surface characterization of the copper and epoxy interfaces obtained from production run printed circuit boards and control samples produced on production equipment. The interface surfaces, obtained by mechanically separating the copper foil from the copper–epoxy laminate, were characterized by x‐ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), scanning electron microscopy, and energy dispersive spectroscopy. The results indicate that for copper foils, with the adhesion promoting ‘‘brown oxide’’ surface produced by oxidation with sodium chlorite, the separation occurs primarily within the epoxy matrix. This epoxy layer is very thin and on the order of the sampling depth of XPS and AES (approximately 50–75 Å). Analysis of the changes in the copper 2p_3/2,1/2 photoelectron line shape indicates the copper is substantially reduced to the 1+ state after lamination relative to the initial fully oxidized 2+ state of the foil surface prior to lamination. Higher than expected nitrogen levels are also detected on the interface.