7.1 Introduction

Due to the fast growth in demands for mobile computing and telecommunication, the technologies of microelectronics packaging require high density, fine pitch, high performance, high reliability, and low cost. In particular, it is becoming more and more difficult for the conventional PCBs with mechanically drilled vias and PTHs to meet the packaging density requirements and to justify their manufacturing cost. To overcome these challenges, new PCB manufacturing schemes for high-density and high-performance multilayer PCBs have been developed recently. These new HDI technologies are categorized as SBU or build-up multilayer (BUM) processes for making laminate-based substrates or PCBs containing microvias formed by laser drilling, photoimaging, or plasma etching. Conductive paste or ink materials may be used to fill the microvias and through-holes to make reliable vertical or z-interconnects.1 The surface metallization may be accomplished either by chemical deposition or by laminating copper foil onto the dielectric surface. A few examples of this category of high-density PCBs include Matsushita s any-layer inner via hole (ALIVH),2 DuPont s CB100,1 and Ormet s OrmeLink.3

The SBU technology with conductive paste/ink-filled microvias can achieve a connection pad density of up to 100 pads/cm ², while the conventional PTHs can reach only 20 pads/cm ². The general fabrication processes for conductive paste/ink-filled BUMs consist of: (1) formation of microvias in individual prepreg layers by laser drilling or photo- imaging, (2) filling via holes with conductive paste/ink materials, (3) lamination of copper foil onto the prepreg with filled microvias, (4) circuitization of copper foil...