ABSTRACT
Lead-free solder alloys are being investigated from both assembly and reliability perspectives. The lead-free solder bumps require more flux when using a dip flux application process and a nitrogen reflow atmosphere. The liquid-to-liquid thermal cycle reliability of the tin-silver-copper (Sn-AgCu, SAC) eutectic bumps is slightly less than that of Sn-Pb bumps. Rapid innovation in packaging is evident from the introduction of new package formats, including area array packages (flip-chip ball grid array (BGA) and flip-chip chip-scale packages (CSP)); leadless packages, direct chip attach, wafer-level packaging (WLP), wirebond die stacking, flip chip-wirebond hybrid, PoP, PiP and other forms of 3-D integration and others. In addition, there are new packaging requirements emerging such as Cu/low-k materials, and interconnects to address the need for flexibility and expanding heat and speed requirements.
