Alternative bumping processes for DRAM-CSP

The usual assembly of CSP on printed circuit boards requires a relatively high volume of solder paste in a very small pitch. That's why a multiple step process is used with bumping of the interposer using pre-formed solder balls, with screen printing of solder paste on the substrate and with an reflow soldering step. In this paper three variants of bumping of CSP are discussed and some results of optimising the bumping and the assembly process of CSP are presented.