Au-Less, Ni-Less & Roughness-Less PCB Cu Surface Treatment Using All-in-One Al2O3 Passivation

Cu conductors in PCB require surface treatments for interconnect bonding on exposed pads and adhesion promoter on embedded lines. Conventional surface finishes are composed of Au and Ni, and Cu adhesion is increased by interlocking mechanisms of roughened Cu surfaces. Au is costly, and high-frequency packages require Ni-less and roughness-less for enhancing signal and power integrity. In this work, we present our inventions of aluminum oxide (Al 2 O 3 ) passivation for PCB Cu pads and lines, which satisfy the requirements of passivation, adhesion, bondability, reliability. Ultrathin Al 2 O 3 passivation layers (∼10nm) of non-conducting ceramic material of Al 2 O 3 were coated on PCB Cu pads and lines for replacing conventional Au/Ni surface finishes and Cu roughness. This paper presents coupon, PCB and product-level experiment data, in terms of passivation, adhesion, bondability and reliability.