Development of flip chip attach technology using Ag paste bumpwhich formed on printed wiring board electrodes

摘要

We have developed original flip chip attach (FCA) technology usinganisotropic conductive film (ACF), which can perform electricalconnection and encapsulation simultaneously. The advantages are that allbumps on the substrate are formed simultaneously and that ordinary barechips without bumps on electrodes can be used. This paper presents theresults of the FCA process for a 150 μm pad pitch sample chip and ofthe reliability tests. Ag paste bumps were formed by Ag paste transferand curing on the electrode pads of a PWB by screen-printing methods,and printing conditions were evaluated for good bump formation for thisFCA process. Three kinds of ACFs with different physical properties wereused for the experiment, and the FCA conditions were evaluated for eachACF. Moreover, the effect of the surface treatment on Ag paste bumps wasalso evaluated with regard to FCA connection resistance. Assuming thatpassive component assembly is done by soldering, reliability tests ofthe FCA samples were carried out after two additional heat treatments atreflow temperature. High-temperature and high-humidity storage tests(THS) and temperature cycling tests (TCT) were performed as reliabilitytests. The connection resistance between electrodes on bare chip and PWBwas measured by a four-probe method. Although connection resistanceincreased after THS and TCT, it was saturated at under 500 μΩper bump in the sample with surface treated Ag bumps