Thermo-Mechanical performance of large body and small ball pitch Flip chip packages using higher layer count substrates with ENEPIG solder pad finish

Flip chip packages used in data centers, network base stations and industrial applications are getting bigger with complex silicon dies and passive components inside the packaging. These packages use higher layer count build up substrates with smaller solder ball pitches to maximize I/O counts in a given package real estate.Build up organic substrates play a critical role in the semiconductor package supply chain with fluctuating demand and supply. Substrate finish on the BGA pads should not hinder high volume manufacturing capacities and at the same time must meet thermo-mechanical stresses in operating conditions in the field.For the study discussed in this paper, daisy chain package components with BGA pad finish of ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) were mounted on printed circuit boards. Units were then put through temperature cycle tests to evaluate the thermo-mechanical performance of the solder joints between the package and PCB.This paper discusses the experimental legs, details of PCB used, package placement on the PCB, thermal mechanical stresses, characteristics life of solder joints using Weibull models, failure signatures and intermetallic compound conditions using ENEPIG solder finish. Results show robust solder joint reliability with ENEPIG surface finishes.