Sea of leads ultra high-density compliant wafer-level packaging technology

Sea of leads (SoL) is a novel ultra high-density compliant wafer-level packaging technology. SoL extends wafer-level batch processing of multilayer on-chip interconnect networks to include x-y-z compliant chip input/output (I/O) interconnects with a density exceeding 10⁴ leads per cm². A package with 12×10³ compliant leads distributed across a cm² has been demonstrated. The compliance enables wafer-level testing as well as eliminates the need for underfill between chips and substrates with a CTE (coefficient of thermal expansion) mismatch thereby enhancing reliability, electrical performance, manufacturing throughput, and cost. Two methods of fabricating nonadherent or ´slippery´ leads are demonstrated. The fabrication of slippery leads is desirable because adhesion between the lead and the package polymer layer is eliminated thereby freeing the leads to stretch and contract during thermal cycling. Compared to adherent leads, preliminary results show that slippery leads enhance the overall in-plane compliance. Moreover, the feasible z-axis compliance attained from polymer films with and without embedded air-gaps is compared.