The influence of NiSn intermetallics on the performance of flip chip contacts using a low cost electroless nickel bumping approach

A low cost approach to obtain bumped dice using electroless nickel under bump metallization and different solder bumping techniques was realized in this work. This paper demonstrated the use of electroless Ni(P)-Au UBM for flip chip interconnections with solder applied by either stencil printing, solder ball placement, or mechanical solder bumping for an automotive application. In order to characterize the performance and reliability of such flip chip interconnections, the influence of the growth of NiSn intermetallics during thermal aging at 150 degrees C on their electrical performance was evaluated in this work. In this respect, two near-eutectic lead-tin alloys with different dopants were used. The results obtained are compared with those of conventional Ti:W-Cu UBM with electroplated eutectic solder bumps. Destructive mechanical test results are presented and compared for both under bump metallizations. This study indicated the suitability of electroless Ni(P)-Au UBM for flip chips even for harsh environments, stimulating the prototyping of a four chip MCM-L for automotive use, which is presented as a case study.