Finite element analysis for Solder Ball Connect (SBC) structural design optimization

Abstract

Solder Ball Connect (SBC) is a second-level surface mount electronics packaging technology in which ceramic modules containing one or more chips are joined to a circuit card (FR-4) by means of an array of nonhomogeneous solder columns. These columns consist of a high-temperature-melting 90%Pb/lO%Sn solder sphere attached to the module and card with eutectic solder fillets. The solder structures accommodate the bulk of the strain (which is due to the thermal-expansion mismatch between FR-4 and the 9211 ceramic of the modules) generated during power cycling. If the solder structures are not properly designed, the thermal strain can be a source of premature fatigue failure. In this work, finite element analysis is used to characterize the plastic strains that develop in the SBC interconnection during thermal cycling. Since plastic strain is a dominant parameter that influences low-cycle fatigue, it is used as a basis of comparison for various structural alternatives. Designed experiment techniques are used to systematically evaluate the thermal strain sensitivity to structural variables. Results are used to identify an optimally reliable structure that is robust in terms of assembly-process variables.