A reliability and failure mode analysis of no flow underfillmaterials for low cost flip chip assembly

摘要

Development of new material systems will increase flip chip marketgrowth provided they reduce manufacturing time and enhance reliability.Among these new materials are no flow underfills. Properly formulated,these underfills can significantly decrease manufacturing cost byeliminating the fluxing process, the underfill flow process, and theunderfill cure process. This work evaluates the reliability of no-flowunderfill materials and performs a critical failure mode analysis offlip chip structures using no flow underfills. Six test vehicles andfour reliability tests were used to evaluate and analyze the reliabilityperformance of several commercial no-flow underfill materials. Differenttest vehicles were used to evaluate the effect of varying chip size,interconnect density, pad surface finish metallization, and soldermaskopening design. Accelerated reliability tests performed includedliquid/liquid thermal shock (LLTS), air/air thermal cycling (AATC),moisture sensitivity preconditioning, and temperature humidity aging(TH). Materials tested in this work demonstrated the ability to survive1000 cycles in LLTS and AATC without failure, 1000 hours of TH and levelthree preconditioning. A number of unique failure modes are identifiedincluding bulk underfill cracking, fillet cracking, solder interconnectfatigue cracking and underfill interfacial delamination