One potential method for improving the reliability of solder joints that are operated at elevated temperatures is to use a low melting point solder that is liquid during the operation. Mechanical integrity is retained by use of a polymer underfill or glob top. This paper reviews the advantages and disadvantages of several solder / barrier metallization systems which have been used in liquid solder joint systems. The solders include In-Sn solder, and Sn-Bi based solders with additions of 1-2wt.% of Al, Cr, Si, Zn, Ag, Au, Ru, Ti, Pt, Nb, and Cu. The  barrier  layers  include  Nb,  Ni-P, Ni-P-W, and Cu.  The ultimate lifetime of  such solder / barrier  layer systems at temperatures  up to 260C is described, and failure mechanisms of assemblies utilizing liquid solder joints described.

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