TABLE OF CONTENTS Based on a full life-cycle analysis,1 , 2 it is unclear whether lead-free solders are actually more environmentally friendly. If materials and component availability, reliability uncertainty, increased processing difficulties, and end-of-life (EOL) issues are accounted for, lead-free solders may not be a better choice. Ultimately, the best solutions may be completely new attachment technologies that do not use solder (i.e., solderless, as discussed in Chap. 4). For example,1 46 flip chips with Cu stud bumps, Au stud bumps, Au bumps, Cu bumps, Ni-Au bumps, Cu wires, or Au wires on printed circuit board (PCB)/substrate with isotropic conductive adhesive (ICA), anisotropic conductive paste (ACP), anisotropic conductive film (ACF), or nonconductive adhesive (NCA). In this chapter, various of these technologies are discussed briefly. The novel development of these materials will be discussed in Chaps. 17 through 20.
In this section, direct chip attach (DCA) with solderless flip chip on board (FCOB) with ACF will be considered.4 The chip is bumped with three different metallugies (Ni-Au, Au, and Cu), as discussed in Chap. 4, Secs. 4.3 through 4.5, respectively. The Cu pads on the FR-4 epoxy PCB are with electroless Ni-immersion Au and are organic-coated. Hitachi s ACF is used for this study. The design, materials, and assembly process flow are shown in Fig. 5.1. In the following sections, some of the major steps will be discussed. Also, some thermal cycling...
