Analysis of Tombstoning Phenomenon During Reflow

Abstract

A dynamic model is established to investigate tombstoning phenomenon of passive SMT components during reflow. This model consists of three dynamic equations for the motion of the component and four nonlinear algebraic equations for area conservation, constant curvatures for solder fillets, and solder height-length relations. The formulation neglects the gravity effect in the solder. It is shown that formation of tombstoning depends on a combination of parameters such as component geometry, pad sizes, gap size between pads, molten solder volume and properties, and contact angles. For some values of these parameters encountered in practice, tombstoning can take place. For a given component, this model may be used to improve solder pad and stencil designs to avoid tombstoning.