Reworkable no-flow underfilling for both tin-lead and lead-free reflows for CSP assembled under air

Abstract

Two novel no-flow underfill materials, NF220 for SnPb and NF260 for Pb-free, were developed and evaluated for CSP reliability enhancement applications. Results indicate these materials exhibit outstanding performance on yield and reliability, with both temperature cycling and drop test performance being one order of magnitude greater than current industry practices. In particular, those novel materials exhibit very wide processing windows, as reflected by their great tolerance toward variation in volume and pattern of underfill dispensed, humidity, reflow window, thermal aging, and a variety of surface finishes, accordingly can be easily utilized for double-sided reflow under air for a wide variety of surface finishes. Most noteworthily, these no-flow underfills are easily reworkable, thus further promise reduction of manufacturing cost