Lead-free semiconductor packaging

Pending lead-free legislation and OEM customer demand force semiconductor companies to changeover to lead-free packages. Packages must have a lead-free terminal plating and, for modules, first level interconnect of e.g. flip chips and passives has to be lead-free. The current and lead-free packages have to be qualified for current (lead-free packages only) and lead-free assembly processes. The main hurdles are the qualification for the moisture sensitivity level (MSL) and the choice of the lead-free plating type. Due to the higher reflow temperature for lead-free assembly, a drop of the MSL of one or two levels is observed for some IC package types and encapsulated modules. With adapted encapsulation materials, the MSL is improved. Matt Sn is the preferred lead-free plating type because of the good compatibility with the current plating, easy processability, good solderability, low cost and low environmental impact. Whiskering during package storage, however, is a point of attention. At the moment no proper accelerated whisker test is available.